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- Permanent Link:
- https://ufdc.ufl.edu/UFE0024991/00001
## Material Information- Title:
- Erection Stresses In Reinforced Concrete Tilt-Up Wall Panels
- Creator:
- Abi-Nader, Guy
- Place of Publication:
- [Gainesville, Fla.]
- Publisher:
- University of Florida
- Publication Date:
- 2009
- Language:
- english
- Physical Description:
- 1 online resource (176 p.)
## Thesis/Dissertation Information- Degree:
- Doctorate ( Ph.D.)
- Degree Grantor:
- University of Florida
- Degree Disciplines:
- Design, Construction, and Planning Doctorate
Design, Construction, and Planning - Committee Chair:
- Muszynski, Larry C.
- Committee Co-Chair:
- Issa, R. Raymond
- Committee Members:
- Minchin, Robert E.
Elefteriadou, Ageliki L. - Graduation Date:
- 8/8/2009
## Subjects- Subjects / Keywords:
- Cements ( jstor )
Compressive strength ( jstor ) Concretes ( jstor ) Cylinders ( jstor ) Flexural strength ( jstor ) Loggers ( jstor ) Maturity tests ( jstor ) Physical maturity ( jstor ) Software ( jstor ) Tensile strength ( jstor ) Design, Construction, and Planning -- Dissertations, Academic -- UF compression, concrete, flexural, flexure, maturity, strain, strength, stress, tensile, tilt, up - Genre:
- Electronic Thesis or Dissertation
born-digital ( sobekcm ) Design, Construction, and Planning Doctorate thesis, Ph.D.
## Notes- Abstract:
- In tilt-up construction, prior to lifting a panel, it is required that compressive and flexural testing should be performed on samples retained in the field to validate that the panel has attained the required strength. In reality, usually, only compressive tests are performed and flexural strengths are calculated using one of the many available correlation formulas. In this study, the maturity method, a non-destructive method of determining the strength of concrete at early age, was evaluated. The use of the maturity method was found to be an effective tool to predict the compressive and flexural strengths of in-place concrete at time of lifting. Furthermore, correlation curves and formulas were developed relating the compressive, flexural and splitting tensile strength of concrete. These curves were generated for three different mix-designs used currently in the tilt-up concrete industry. The correlation curves showed that each mix design has its own correlation formulas. The use of pre-existing formulas might under or over-estimate the strength of concrete. Moreover, a small scale tilt-up panel was instrumented with surface mount strain gages in order to determine the stresses of the panel during lifting. The panel dimensions were also sent to four different tilt-up design companies. The anticipated stresses were predicted using their in-house software. Preliminary hand calculations based on statistical analysis were also performed in order to find the stresses. The data collected from the instrumented panel, software predictions and preliminary static calculations were compared. The results showed a variation in stresses calculated by different tilt-up design companies using their software as well as some differences between the measured stress values obtained from the instrumented panel and the calculated values. ( en )
- General Note:
- In the series University of Florida Digital Collections.
- General Note:
- Includes vita.
- Bibliography:
- Includes bibliographical references.
- Source of Description:
- Description based on online resource; title from PDF title page.
- Source of Description:
- This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
- Thesis:
- Thesis (Ph.D.)--University of Florida, 2009.
- Local:
- Adviser: Muszynski, Larry C.
- Local:
- Co-adviser: Issa, R. Raymond.
- Statement of Responsibility:
- by Guy Abi-Nader.
## Record Information- Source Institution:
- University of Florida
- Holding Location:
- University of Florida
- Rights Management:
- Copyright Abi-Nader, Guy. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
- Resource Identifier:
- 489208603 ( OCLC )
- Classification:
- LD1780 2009 ( lcc )
## UFDC Membership |

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PAGE 1 1 ERECTION STRESSES IN REINFORCED CONCRETE TILT -UP WALL PANELS By GUY GEORGES ABI NADER A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2009 PAGE 2 2 2009 Guy Georges Abi Nader PAGE 3 3 To my family who encouraged my continued education and made this research possible PAGE 4 4 ACKNOWLEDGMENTS I would like to exp ress my sincere gratitude to my committee chairman Dr. Larry Muszynski, my co chair Dr. R. Raymond Issa, Dr. Edward Minchin and Dr. Lilly Elefteriadou for their support and encouragement. Dr. Muszynski provided feedback and guidance. Dr. Issa provided visi on and feedback. Dr. Minchin and Dr Elefteriadou provided interest and patience. I would like to thank the Rinker Hall Laboratory Technician, Mr. Donald Allex who assisted me and helped me in preparing the samples and testing them. We made a good team. I am grateful to my father Georges and mother May for their encouragement, support and unconditional love. I thank my brother Walid who has a Ph.D. in law, as well as my pharmacist brother Ralph and my little sister Lea, who recently received a Master in L aw (L L M ) from the University of Florida, for their constant encouragement and support. I am grateful to all the companies that contributed to this research: Steinbick er & Associates (Joe Steinbicker and Nick Fischer) BNG Construction (Tommy Albritton) Cemex Ready Mix S.A.B. (Chris Anderson) Ajax Construction (James Marini) Dayton Superior Corporation (Jeffrey Von Handorf) Engius (Dale Gillham) Meadow Burke (Lance Osborne) Florida Rock Industries (Gene Engle) Florida Rigging and Crane (John Lafon) Inducta Engineering (Emil Jankulovski) Gerdau AmeriSteel (Paul Hardaker) and Vishay (Darryl Peterson) I am thankful for their donations. Finally, I would like to thank my friends for their total support and understanding. This research is one of my be st achievements and I could not have accomplished my goals without the support and encouragement of the above mentioned people and companies PAGE 5 5 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................................... 4 LIST OF TABLES ................................................................................................................................ 9 LIST OF FIGURES ............................................................................................................................ 12 ABSTRACT ........................................................................................................................................ 16 CHAPTER 1 INTRODUCTION ....................................................................................................................... 18 1.1 Research Overview ............................................................................................................... 18 1.2 Goals and Objectives ............................................................................................................ 20 2 LITERATURE REVIEW ........................................................................................................... 21 2.1 History of Tilt -Up ................................................................................................................. 21 2.2 Benefits of Tilt -Up ................................................................................................................ 22 2.3 Mix Design ............................................................................................................................ 23 2.4 Strengths of Tilt -Up Panels .................................................................................................. 24 2.5 Maturity Testing .................................................................................................................... 26 2.6 Stresses in Tilt -Up Wall Panels ............................................................................................ 28 2.7 Current Studies ...................................................................................................................... 29 3 ANALYSIS OF SURVEY RESULTS ...................................................................................... 30 3.1 Introduction ........................................................................................................................... 30 3.2 Survey Results ....................................................................................................................... 30 3.3 Survey Results ....................................................................................................................... 32 3.3.1 Demographic Questions .......................................................................................... 32 3.3.2 Tilt up Construction Questions ............................................................................... 34 4 TEST METHODS ....................................................................................................................... 42 4.1 Introduction ........................................................................................................................... 42 4.2 Concrete Mix Designs .......................................................................................................... 42 4.2.1 Mix Proportion of Concrete .................................................................................... 42 4.2.2 Materials Used in Concrete Mixes .......................................................................... 44 4.2.2.1 Cement ..................................................................................................... 44 4.2.2.2 Air Entrained Agent ................................................................................ 44 4.2.2.3 Water Reducer ......................................................................................... 44 4.2.2.4 C oarse Aggregates .................................................................................. 47 PAGE 6 6 4.2.2.5 Fine aggregate ......................................................................................... 47 4.2.2.6 Fly ash ...................................................................................................... 48 4.2.2.7 Slag ............................................................................................................ 49 4.3 Preparation of Concrete Specimen ....................................................................................... 51 4.4 Tests on Fresh Concrete ....................................................................................................... 52 4.4.1 Slump of Hydraulic Cement Concrete .................................................................... 52 4.4.2 Air content of Freshly Mixed Concrete by Pressure Method ............................... 53 4.4.3 Unit Weight .............................................................................................................. 54 4.4.4 Temperature Test ..................................................................................................... 54 4.5 Tests on Hardened Concrete ................................................................................................. 54 4.5.1 Compression Testing ............................................................................................... 54 4.5.2 Third Point Flexure Test .......................................................................................... 55 4.5.3 Splitting Tensile Test ............................................................................................... 56 4.6 Maturity Method ................................................................................................................... 58 4.6.1 Introduction .............................................................................................................. 58 4.6.2 Estimating the Streng th of Concrete using Maturity Testing ................................ 58 4.6.2.1 Nurse Saul method (Temperature Time) ................................................ 58 4.6.2.2 Arrhenius Method (Equivalent ag e at specific Temperature) ............... 59 4.6.3 Maturity Testing Process ......................................................................................... 59 4.6.4 Maturity Measurement Device ................................................................................ 61 4.6.5 Corrected Temperature Time Factor ...................................................................... 62 4.6.6 Determination of Datum Temperature (T0) ............................................................ 62 4.6.7 Correlation curves .................................................................................................... 64 5 MATURITY AND CONCRETE TESTING RESULTS ......................................................... 66 5.1 Datum Temperature .............................................................................................................. 66 5.2 Maturity Correlation Curves ................................................................................................ 67 5.3 Evaluation of Maturity Curves ............................................................................................. 72 5.3.1 UF Hough Hall Pan el .............................................................................................. 73 5.3.2 Perry Construction Yard Panel .............................................................................. 76 5.4 Concrete Correlation Formulas ............................................................................................ 79 5.4.1 Relationship Between Compressive and Flexural Strength .................................. 79 5.4.2 Relationship Between Splitting Tensile Strength and Compressive Strength ..... 83 5.4.3 Relationship Between Splitting Tensile Strength and Flexural Strength ............. 85 5.5 Estimating the Flexural and Splitting Tensile Strength using Existing Co rrelation Formulas ............................................................................................................................ 90 6 TILT UP PANEL INSTRUMENTATION ............................................................................... 94 6.1 Introduction ........................................................................................................................... 94 6.2 Panel Design .......................................................................................................................... 94 6.3 Preliminary Static Calculations ............................................................................................ 95 6.3.1 Sign Convention and Assumption .......................................................................... 96 6.3.2 Critical Angle of Inclination ................................................................................... 96 6.3.3 Moments Calculations in the Y Y Direction ......................................................... 98 PAGE 7 7 6.3.4 Stresses Calculations in the Y Y Direction .......................................................... 100 6.3.5 Wide Lift Analysis ................................................................................................. 101 6.3.6 Stresses Calculations in the X -X direction at 7ft ................................................. 104 6.4 Finding Stresses Using 1.5 Suction Factor ........................................................................ 105 6.5 Checking For Safety ........................................................................................................... 105 6.6 Panels Construction ........................................................................................................... 107 6.6.1 Casting The Slab .................................................................................................... 107 6.6.2 Formwork Steel reinforcement ............................................................................. 108 6.6.3 Lifters ...................................................................................................................... 110 6.6.4 Bond Breaker ......................................................................................................... 111 6.6.5 Casting the Panel .................................................................................................... 112 6.7 Strain Gages Installation ..................................................................................................... 114 6.7.1 Strain Gage Reader and Recorder ......................................................................... 114 6.7.2 Installation of Surface Mount Strain Gages ......................................................... 115 6.7.3 Strain Gages Location ........................................................................................... 117 6.8 Lifting the Panel .................................................................................................................. 118 7 STRESS ANALYSIS O F A TILT -UP PANEL DURING LIFTING ................................... 122 7.1 Introduction ......................................................................................................................... 122 7.2 Critical Angle of Inclination .............................................................................................. 123 7.3 Field Data Collection .......................................................................................................... 123 7.4 Comparing the Stresses ...................................................................................................... 124 7.3 From Strains to Stresses ..................................................................................................... 125 7.4 Modulus of Elasticity .......................................................................................................... 125 7.5 Stresses Comparison ........................................................................................................... 127 7.6 Summary of Results ............................................................................................................ 132 8 CONCLUSION AND RECOMMANDATIONS ................................................................... 134 8.1 Conclusion ........................................................................................................................... 134 8.2 Recommendations ............................................................................................................... 135 8.2.1 Maturity Method .................................................................................................... 135 8.2.1.1 For the industry ...................................................................................... 135 8.2.1.2 For future studies .................................................................................... 135 8.2.2 Panel Instrumentation ............................................................................................ 136 8.2.2.1 For the industry ...................................................................................... 136 8.2.2.2 For future studies .................................................................................... 136 APPENDIX A QUESTIONNAIRE ................................................................................................................... 137 B TEMPERATURE AND MATURITY DATA RECORDED BY MATURITY LOGGERS ................................................................................................................................. 139 C STRESSES AT ZERO DEGREES INCLINATION USING 1.5 SUCT ION FACTOR ..... 153 PAGE 8 8 D SOFTWARE RESULTS ........................................................................................................... 160 LIST OF REFERENCES ................................................................................................................. 173 BIO GRAPHICAL SKETCH ........................................................................................................... 176 PAGE 9 9 LIST OF TABLES Table page 3 1 Final sample size needed for various population sizes and characteristics, at three levels of precision (Dillman and Salant 1994) ..................................................................... 31 4 1 Mix Design for the Plain Concrete (Mix1) ......................................................................... 42 4 2 Mix Design for 80% C ement and 80% Fly Ash (Mix 2)* ................................................... 43 4 3 Mix Design for 50% Cement and 50% Slag* ....................................................................... 43 4 4 Chemical properties of cement provided from Cemex ........................................................ 45 4 5 Physical properties of cement provided from Cemex .......................................................... 46 4 6 Physical properties of the Cemex coarse aggregate ............................................................. 47 4 7 Physical properties of the Florida Rock Industries coarse aggregate ................................. 47 4 8 Physical properties of the Cemex fine aggregate ................................................................. 48 4 9 Physical properties of the Florida Rock Industries fine aggregate ..................................... 48 4 10 Chemical properties of fly ash ............................................................................................... 49 4 11 Physical properties of fly ash ................................................................................................ 49 4 12 Chemical properties of slag ................................................................................................... 49 4 13 Ph ysical properties of slag ..................................................................................................... 50 4 14 Concrete specimen for each mix design ............................................................................... 51 4 15 Properties of fresh concrete mix ............................................................................................ 54 4 16 Maturity Loggers specifications ............................................................................................ 61 4 17 IntelliRock IITM Reader specifications .................................................................................. 62 5 1 Data for determining the datum temperature of Mix 1*................................................... 66 5 2 Calculated regression coefficients for Equation 4 7 ............................................................ 67 5 3 Maturity and strength data for the correlation curves for Mix 1* ....................................... 68 5 4 Maturity and strength data for the correlation curves for Mix 2* ....................................... 69 PAGE 10 10 5 5 Maturity and strength data for the correlation curves for Mix 3* ....................................... 71 5 6 Maturity and strength data for verification purposes of the UF Hough Hall panel ........... 73 5 7 Maturity and strength data for verification purposes of the Perry Yard panel ................... 76 5 8 Critical t values respected to the confidence level ........................................................... 87 5 9 Comparison between splitting and flexural strength ............................................................ 88 5 10 Ratios of Splitting tensile over Flexural strength for Mix 1 ............................................ 88 5 11 Descriptive analysis for the ratios of Mix 1 ..................................................................... 89 5 12 Ratios of splitting tensile over flexural strength for Mix 2 ............................................. 89 5 13 Descriptive analysis for the ratios of Mix 2 ..................................................................... 89 5 14 Ratios of Splitting tensile over Flexural strength for Mix 3 ............................................ 90 5 15 Descriptive analysis for the ratios of Mix 3 ..................................................................... 90 5 16 Comparison between existing formulas and experimental results at da y 7 ........................ 91 5 17 Comparison between existing formulas and experimental results at day 28 ...................... 92 6 1 Physical and Chemical properties of t he bond breaker ...................................................... 112 7 1 Strain data collection ............................................................................................................ 123 7 2 Stresses at Zero Degrees Inclination in the Y Y Direction ............................................... 127 7 3 Stresses at zero degrees inclination in the X -X direction .................................................. 128 7 4 Stresses at fifteen (15) degrees inclination in the Y Y direction ...................................... 129 7 5 Stresses at thirty (30) degrees inclination in the Y Y direction ........................................ 129 7 6 Stresses at forty (40) degrees inclination in the Y -Y direction ......................................... 129 7 7 Stresses at forty five (45) degrees inclination in the Y Y direction .................................. 130 7 8 Stresses at fifty (50) degree s inclination in the Y Y direction .......................................... 130 7 9 Stresses at sixty (60) degrees inclination in the Y -Y direction ......................................... 130 7 10 Stresses at seventy (70) degrees inclination in the Y -Y direction ..................................... 130 7 11 Stresses at seventy five (75) degrees inclination in the Y Y direction ............................. 130 PAGE 11 11 7 12 Stresses at eighty (80) degrees inclination in the Y Y direction ....................................... 131 PAGE 12 12 LIST OF FIGURES Figure page 2 1 Maturity concept .................................................................................................................... 26 3 1 Companies annual volume ................................................................................................... 33 3 2 Overall business experience .................................................................................................. 33 3 3 Compan ies active region/location ........................................................................................ 3 4 3 4 Normal time of lifting the panel ............................................................................................ 35 3 5 Finding the flexural strength .................................................................................................. 36 3 6 ASTM C 78 Third -Point Loading ........................................................................................ 36 3 7 ASTM C 293 Center Point Loading .................................................................................... 36 3 8 Fi nding the tensile s trength .................................................................................................... 39 3 9 Samples storage ...................................................................................................................... 39 3 10 Samples and panels curing condition .................................................................................... 40 3 11 The use of maturity method in tilt up construction .............................................................. 40 3 12 Willingness to adopt the maturity method ............................................................................ 41 4 1 Gradation of Cemex coarse aggregate .................................................................................. 47 4 2 Gradation of Cemex fine aggregate ...................................................................................... 48 4 3 Beam and cylinder specimens ............................................................................................... 52 4 4 Slump test ............................................................................................................................... 53 4 5 Compression Test for cylinders ............................................................................................. 55 4 6 Third point flexural test ......................................................................................................... 56 4 7 Splitting tensile test ................................................................................................................ 57 4 8 Maturity Testing Process ....................................................................................................... 60 4 9 Compression test for mortar cubes ........................................................................................ 64 5 1 Compressive strength development of mortar cubes ........................................................... 66 PAGE 13 13 5 2 Determination of T(0) for Mix 1 ............................................................................................ 67 5 3 Correlation curve between Compressive strength and the temperature time maturity index for Mix 1 ...................................................................................................................... 68 5 4 Correlation curve between Flexural strength and the temperature time maturity index for Mix 1 ................................................................................................................................. 69 5 5 Correlation curve between splitting tensile strength and the temperature time maturity index for Mix 1 ....................................................................................................... 69 5 6 Correlation curve between Compressive strength and the temperature time maturity index for Mix 2 ...................................................................................................................... 70 5 7 Correlation curve between Flexural strength and the temperature time maturity index for Mix 2 ................................................................................................................................. 70 5 8 Correlation curve between splitting tensile strength and the temperature time maturity index for Mix 2 ........................................................................................................ 70 5 9 Correlation curve between compressive strength and the temperature time maturity index for Mix 3 ...................................................................................................................... 71 5 10 Correlation curve between flexural strength and the temperature time maturity index for Mix 3 ................................................................................................................................. 71 5 11 Correlation curve between splitting tensile strength and the temperature time mat urity index for Mix3 .................................................................................................... 72 5 12 Comparison between the maturity correlation curve and compressive strength verification data (UF Hough Hall Panel) .............................................................................. 73 5 13 Comparison between the maturity correlation curve and flexural strength verification data (UF Hough Hall) ............................................................................................................ 74 5 14 Embedded maturity loggers ................................................................................................... 75 5 15 Lifting the panel at UF Hough Hall ...................................................................................... 75 5 16 Comparison between the maturity correlation curve and compressive strength verification data (Perri Ya rd Panel) ...................................................................................... 77 5 17 Comparison between the maturity correlation curve and flexural strength verification data (Parry yard Panel) ........................................................................................................... 77 5 18 Samples s tored near the panel ............................................................................................... 78 5 19 Reading the maturity index.................................................................................................... 78 PAGE 14 14 5 20 Correlation curve between flexural strength and compressive strength for Mix1 ........ 80 5 21 Correlation curve between flexural strength and compressive strength for Mix2 ........ 81 5 2 2 Correlation curve between flexural strength and compressive strength for Mix 3 ........ 81 5 23 Correlation curve between splitting tensile and compressive Strength for Mix1 ......... 83 5 24 Correlation curve between splitting tensile and compressive Strength for Mix2 ......... 84 5 25 Correlation curve between splitting tensile and com pressive Strength for Mix 3 ......... 84 5 26 Correlation curve between splitting tensile and flexural Strength for Mix 1 ................. 85 5 27 Corr elation curve between splitting tensile and flexural Strength for Mix 2 ................. 86 5 28 Correlation curve between splitting tensile and flexural Strength for Mix 3 ................. 86 6 2 Load, Shear, and Moment Diagrams for a simply supported beam .................................... 96 6 3 Angle of inclination during lifting ........................................................................................ 97 6 4 Wall section divisions in order to determine stresses in the Y Y direction ....................... 98 6 5 Load, shear and moment diagram of the panel at zero degrees inclination(Y -Y Direction) ................................................................................................................................ 99 6 6 Moments acting on the panel in the Y Y direction ............................................................ 100 6 7 Wall section divisions in order to determine stresses in the X -X direction ..................... 101 6 8 Load diagram for the wide lift a nalysis after imposing equal reactions ........................... 102 6 9 Shear diagram for the wide lift a nalysis after imposing equal reactions .......................... 103 6 10 Moment diagram for the wide lift Analysis after imposing equal reactions .................... 103 6 11 Moment diagram along the X -X direction at the insert location ....................................... 104 6 12 Four (4) feet tributary band ................................................................................................. 105 6 13 Casting the sla b .................................................................................................................... 108 6 14 Panel formed by 2 by 4 studs. ............................................................................................. 108 6 15 Design of reinforcement in panel ....................................................................................... 109 6 16 Steel Reinforcement elevation ............................................................................................. 109 6 17 Reinforced panel .................................................................................................................. 110 PAGE 15 15 6 18 Inserts reinforced .................................................................................................................. 111 6 19 Casting the panel .................................................................................................................. 113 6 20 Starting up the maturity loggers embedded inside the panel ............................................ 113 6 21 P3 Reader and Recorder ...................................................................................................... 115 6 22 Surface mount strain gages installation .............................................................................. 116 6 23 Bricks laid on top of gages to assure enough pressure for bonding .................................. 117 6 24 Strain gages location ............................................................................................................ 118 6 25 Panel set up before lifting .................................................................................................... 119 6 26 Recording the Reader Screen for 30 sec. before tilting. (In this picture, it is shown that the reader was recording since 17 sec) ........................................................................ 120 6 27 Digital reader at 60 degrees inclination ............................................................................. 120 6 28 Video recording the digital level readings .......................................................................... 121 6 29 Panel lifted at 90 de grees inclination .................................................................................. 121 7 1 Annotations of the strain gages installed on top surface of the panel ............................... 122 7 2 Stress distribution of t he panel ............................................................................................ 125 7 3 Test set up for determining the modulus of elasticity ........................................................ 126 7 4 Stresses in the Y Y direction at zero degrees inclination .................................................. 133 PAGE 16 16 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy ERECTION STRESSES IN REINFORCED CONCRETE WALL PANELS DURING TILT -UP CONSTRUCTION By Guy Georges Abi Nader August 2009 Chair: Larry Muszynski Cochair: R. Raymond Issa Major: Design, Construction and Planning In tilt u p construction, prior to lifting a panel, it is required th at compressive and flexural testing should be performed on samples retained in the field to validate that the panel has attained the required strength. In reality, usually only compressive tests are performed and flexur al strengths are calculated using on e of the m any available correlation formulas In t his study the maturity method, a nondestructive method of determining the strength of concrete at early age, was evaluated. The use of the maturity method was found to be an effective tool to predict the compressive and flexural strengths of in-place concrete at time of lifting. Further more, correlation curves and formulas were developed relating the compressive, flexural and splitting tensile strength of concrete. These curves were generated for three different mix -designs used currently in the tilt up concrete industry. The correlation curves showed that each mix design has its own correlation formulas. The use of pre existing formulas might under or over -estimate the strength of concrete. Moreover, a small scale tilt up panel was instrumented with surface mount strain gages in order to determine the stresses of the panel dur ing lifting. T he panel dimensions were also sent to PAGE 17 17 four different tilt up design companies. The anticipated stresses were predict ed using the ir in house software Preliminary ha nd calculations based on statistical analysis were also performed in order to find the stresses. The data collected from the instrumented panel, software predictions and preliminary static calculations were c ompared. The results showed a variation in stresses calculated by different tilt up design companies using their software as well as some differences between the measured stress values obtained from the instrumented panel and the calculated values PAGE 18 18 CHAP TER 1 INTRODUCTION 1.1 Research Overview Tilt-Up construction is one of the fastest growing areas of the US construction industry. According to the Tilt -Up Concrete Association, at least 10,000 buildings enclosing more than 650 million square feet are cons tructed annually. This is due in part, to the economics of tilt u p, which combine reasonable cost with low maintenance, durability, speed of construction, and minimal capital investment. In tilt u p construction, before lifting a panel, the building codes require that compressive and flexural testing should be performed on samples retained in the field to make sure that the panel has attained the required strengths But in reality, most of the time, only compressive tests are performed and flexur al strengt hs are calculated using one of the many available correlation formulas existed. Most of the se formulas are based on plain concrete. But most concrete used today is not plain; it is a more complex combination that include s both mineral admixtures as cem ent substitutes, and chemical admixtures. A survey was sent to different tilt u p construction companies. The companies were asked about their own methods for determining the different types of strength of concrete before tilting. They were also asked thei r opinions about the matu rity method as discussed in this study This study determined the different correlation formulas between flexural, compressive and splitting tensile strength for three sp ecific mix designs used in the tiltup c onstruction industry. The goal of this approach was to determine how accurate the current approach of determining the flexur al strength of panels using correlation formulas is. In this study the matu rity method described in ASTM C 1074 (2004) was performed. From the proposed maturity method, empirical relationships between compressive and flexural PAGE 19 19 strength with maturity index w ere determined. Using this method it will only be necessary to read the maturity index of a panel (using maturity devices embedded in concrete) in order to determine its strengths and its suitability for erection The purpose of the maturity method is to demonstrate a non -complex method for monitoring concrete strengths in real time using concrete maturity technology. Concrete maturity enables real time in -place strength measurements that are more accurate and more cost -effective than field -cast specimens. Rather than having to wait for field -cast specimens to reach the required strength, the panel can be lifted at the earliest possible moment because t he in -place flexural and compressive strength can be obtained instantaneously. In addition, this study had determined the actual stresses in -situ of a tilt up wall panel during erection. Surface mount strain gages were installed at expected high stress l ocations to determine the actual bending stresses in the concrete panel during the lifting sequence. The panel was constructed using one of the mix design s studied. M aturity device s w ere also embedded in the panel. Cylinder and beam samples were tested for flexural and compressive strength in order to check the accuracy of the empirical relationship between maturity index and strength s These samples were cas ted from the same concrete mix that was used for the panel Finally, several software analysis mode ls were generated in order to find the stresses in the constructed panel. The design of the panel was sent to several tilt up design companies. The companies were asked to run their own software programs and to determine the stress es of the panel during er ection A comparison between the companies software results and the ones determined in this study was also conducted. PAGE 20 20 1.2 Goals and Objectives The s cope of the project was to provide sufficient scientific information on the strengths and stresses of ti ltup wall panels before and during erection. The objectives of this research were mainly : 1 Conduct a survey among different tilt up construction companies. The purpose of the survey is to gather recent information about the types of testing performed nowad ays in tilt up industry. 2 Estimate the strength of concrete using maturity t esting. This was done by determining empirical relations between flexural strength and maturity index, and compressive strength and maturity index. These relation ships may make it u nnecessary to perform mechanical tests (compression, flexure) o n tilt up walls before erection. Only maturity index will be required to find the corresponding strength from these empirical relations. 3 Determine correlation formulas between the flexural com pressive and splitting tensile strength of concrete used for tilt up wall panels using three different mix designs. This will determine if a single universal formula can be used by contractors in order to determine the flexural strength of the panel. 4 Determine the stresses in a tiltu p wall panel during the lifting sequences as the panel rotates from zero t o ninety degrees using software currently used in t ilt up industry. 5 Determine the actual strains and stresses in -situ of a tilt up wall panel during ere ction. 6 Evaluate the efficiency of different software used by different tilt up construction design companies. The objective of this study is to compare the results generated by the companies software to the actual stresses obtained from the instrumented panel PAGE 21 21 CHAPTER 2 LITERATURE REVIEW 2.1 History of Tilt -Up Casting a slab on the ground then tilting it up into position is not a new idea. It was probably 2000 years ago that some Roman builders discovered that tiltingup a slab after casting it is much easier than placing concrete between the forms vertically and then removing the forms (Brooks 1997). According to ACI 551 (1992) Tiltup construction is a construction technique of casting concrete elements in a horizontal position at the jobsite and then tilting and lifting the panels to their final position in a structure. The big change in the concrete industry happened with the use of reinforced concrete in the early 1900s.This is when Robert Aiken in 1909 described an innovative method of casting w a ll panels on tilting platform (T ilting Tables) and then lifting them vertically into place by means of specially designed mechanical jacks (Aiken 1909). This tilt table method was used on the Jewett Lumber Company in Des Moines, Iowa, between 1906 and 1912, and on several a rmy facilities, factory buildings, and churches. The tilt table method was also used on the Zion Methodist Church in suburban Chicago. The church construction incorporated decorative pre cast elements that were embedded in the tilt up panels. In the late 1940s the mobile truck crane b ecame available which made the t ilt up construction industry more popular. With access to mobility and lif ting capacity of truck cranes, t ilt up construction started to spread quickly, from Southern Calif ornia, across the Sunbelt states. Today, tilt up buildings can be found in nearly every state (Brooks 1997). Tiltup construction was first used for simple structures mostly warehouses and distribution centers. Today, this is still the governing type of ti ltup buildings. In addition, PAGE 22 22 schools, churches, multistory office buildings, industrial and manufacturing projects are also built using t ilt up construction. The most recent applications for tilt up structures are small buildings and residential structure s ( ACI 551 2005). Tiltup projects represent only about 10% of the total U.S. non residential buildings. So a large potential of growth is a waiting this industry. 2.2 Benefits of Tilt-Up Tiltup construction continues to grow due to its benefits. This ty pe of construction eliminate s the use of a large number of expensive formwork and scaffolding. It is a fast construction; the panels can be lifted after 5 to 7 days of being cast. In fact, tilt up construction has grown at an annual volume of more than a quarter billion square feet of walls. Market growth means that the number of Architect/Engineers and C ontractors using this method are increasing, requiring increase d attention to safety, which is another longrecognized benefit of tilt up (Baty 2006). Acc ording to the Tilt -Up Concrete Association (2005) tilt up proved to be more cost effective than other competing construction methods for similar types of buildings. For instance, the South California const ruction market is dominated by tilt up construction instead of m asonry buildings. Tilt up is known for its speed in construction. In f our to five weeks from the time of placing the slab, a building shell can be built. Tilt up projects are durable; building s casted in the late 1940s show little sign of age and some are being attractively remodeled. One of the major benefit s of tilt up is its low maintenance cost. It is only required that a tiltup wall will have a new coat of paint every six to eight year s Due to its fire resistance and d urability, a tilt up building has low insurance rate. All the features listed above in addition to the architectural attractiveness of tilt u p construction encourage the investment in constructing tilt up buildings PAGE 23 23 Safety is a major concern in this industry and determining when t ilt u p concrete panels can be safely lifted in place is of great importance. Many parameters should be considered before lifting the panels. According to ACI 551 (2005) "Tilt-Up Concrete Construction Guide," concrete used for tilt up panels should provide adequate strength for the in -place condition and for panel erection requirements. It is necessary to make sure that the shear strength of the concrete must be satisfied and that the tensile strength, or modulus of rupture, requirements are met to c ontrol cracking during rotation as the panel is lifted into place. 2.3 Mix Design In order to get the required strengths, it is very important to make sure that the following steps are taken into consideration. The mix design for a tilt up wall panel is not the same as a regular mix for other concrete jobs. It is more complicated. For tilt up construction, not only the 28 day compressive strength should be met but early age flexural strength also. There is no single mix design for tilt up construction. In a recent survey of tilt up contractors conducted by the Tilt -Up Concrete Association (TCA), most of the contractors surveyed stated that the right mix design is a balance between admixtures, aggregate gradation, and cement content. It was concluded that different project s will need different mix design s due to the time constrain on lifting the panels (Baty 2006). Brooks (1997) gave some guidelines for the mix design. He stated that the specified compressive strength at time of lift is usually 2,500 psi which is recommended by the lifting insert manufacturers. The slump should also not exceed 4 to 5 inches. According to ACI 551 (2005) the concrete specification for tilt up panels are: 28day compressive strength = 3000 to 5000 psi 28day flexural streng th = 650 psi Maximum size aggregate = 0.75 to 1.5 inches Entrained air = 1% to 3% PAGE 24 24 The question remains as to how to make sure that the concrete has reached its required strengths at the time of tilting. 2.4 Strengths of Tilt-Up Panels The common methods f or determining appropriate concrete strengths are the compressive strength and flexural s trength (modulus of rupture). Just because the required compressive strength is met does not necessarily mean that the required modulus of rupture has been attained or that the panels can be lifted without cracking. Only by performing both tests, can one assure that the design parameters of the concrete have been met. The Tilt -Up Concrete Association requires that test specimens for the compression and flexural streng th tests should remain in the field with the panels and have to be given the same curing treatment. The primary concern for this test is whether or not the concrete has sufficient strength for the lift, not the ultimate strength of the concrete under ideal curing conditions. Testing, however, should be done in a laboratory. M ost of the contractors today are just performing the compressive strength test. The flexur al strength or bending strength of concrete produced in the field is most often determined indi rectly by breaking compressive strength cylinders and determining the flexural strength using one of several available correlation formulas. In reinforced concrete design, the standard formula to convert compressive strength to flexural strength is MR = 7 .5 (ACI 435) Nawy (2008) noted that the flexural strength varies from 7.5 to 12 Other correlation formulas developed by researches have varied between fr = 8 et al 1968). Researchers have also deve loped formulas relating splitting tensile strength to flexural strength and claim to obtain a more accurate correlation. The major problem associating any formulas based on cylinder stren gth and relating them to flexural strength is the number of variables associated with concrete PAGE 25 25 strength and testing concrete strength. A major concern is the fact that most concrete used today is not plain, that is consisting of just Portland cement, water, coarse and fine aggregates, but rather more complex combinations that include both mineral admixtures as cement substitutes, and chemical admixtures. Most of the formulas developed have been based on plain concrete, moist cured for 28 days, and tested at that time. Today, most concrete contain blended cements, consist ing of fly ash and/or blast furnace slag, and chemical admixtures. Other variables include: type and amount of cement; type, size and distribution of both coarse and fine aggregates; water cement ratio; and curing conditions These are just some of the factors that affect compressive strength, and in doing so would also affect any correlation formula developed relating compressive strength to flexural strength. Another potential problem with testing for flexural strength is the ASTM method used. ASTM C 293 (2002 ) is a center point test that is most commonly used in the field. It overestimates the flexural or bending strength of the concrete by 15 to 25 percent because it includes both shear and bending stresses. ASTM C 78 (2002) is a test method referred to as third point loading which results in a more conservative value and does not include the shear component of the stress. The literature showed that the current method of determining the flexural strength of tilt up concrete before lifting using correlat ion formulas is not an accurate one. Nowadays, in concrete pavement construction, engineers are performing a method called Maturity Method (ASTM C 1074 2004) which enables them to estimate concrete strength at early ages in order to determine the appropriate time to open a pavement to traffic. This method is also used for form stripping, removal of s horing and re -shoring, post tensioning, loading PAGE 26 26 structures, saw cutting and harvesting pre -cast members. So why not use this particular method to estimate t he strength of tilt up panels before erecting them. 2.5 Maturity Testing From a technique known as maturity t esting for concrete, according to ASTM C1074 (2004) the gain of the in -situ strength of concrete can be estimated. The concept of maturity was fi rst developed in the late 1940s to early 1950s, but it was not until 1987 that the American Society for Testing and Materials (ASTM) published its first standard practice for maturity (Malhotra 1994).This concept is rarely used today for tilt up wall pan els. It is widely used for pavement and other concrete applications. The basic assumption in the maturity method is that two concrete samples with the same maturity will have the same strength even though they might be exposed to different curing conditions (CPTP 2005). Figure 2 1. Maturity c oncept ( Nelson 2003, CPTP 2005) ASTM C 1074 (2004) illustrates how to determine the compressive and flexur al strength using the m atur ity m ethod. The maturity is expressed either in terms of temperature -time (Nurse Saul method) or in terms of equivalent age at a specific temperature (Arrhenius method). Both methods are described in ASTM C1074. To = Datum Te mperature ( C) M = Maturity ( C hrs) TTF = Temperature Time Factor ( C hrs) PAGE 27 27 In the late 1940s to early 1950s, it was proposed that the product of time and temperature could be used to account for the combined effects of time and temperature on strength development for different elevated temperature curing methods (Carino and Lew 2001). These concepts led to the Nurse -Saul equation. The Nurse Saul method is based entirely on empirical observations. It is based on the assumption that the initial rate of strength gain (during the acceleratory period that follows setting) is a linear function of temperature (Carino and Malhotra 1991). The benefits of the Nurse Saul method is that it is easy to explain and use, and is relatively conservative because it generally underestimates the in -place strength of concrete. In the late 1970s, it was realized that the linear approximation of the Nurse -Saul equation might not be valid when curing temperatures vary over a w ide range. The Arrhenius equation is used to describe the effect of temperature on the rate of a chemical reaction. It allows the computation of the equivalent age of concrete. The Arrhenius method overcame one of the main limitations of the Nurse Saul met hod because it allowed for a non -linear relationship between the initial rate of strength development and curing temperature. It is a better representation of time -tempera ture function than the Nurse Saul equation when a wide variation in concrete tempera ture is expect ed (Carino and Lew 2001). The use of the Arrhenius equation eliminated the discrepancies between strength -maturity relationships developed with different initial curing temperatures, that is, it eliminated the discrepancy at early maturity. Comparative studies showed that this new maturity function is superior to the Nurse -Saul equation On the other hand, the Arrhenius equation is not able to account for the effects of early age temperature on the later age strength (Carino and Malhotra 1991 ). PAGE 28 28 Recently, the industry has developed devices that include maturity instruments which automatically compute and display either the temperature -time factor or the equivalent age. These devices will be embedded in concrete samples to measure the matur ity index. If the Arrhenius method was to be adopted, temperature loggers would be preferred. These temperatures readings can then be plugged into the Arrhenius equation in order to determine the equivalent age. The Arrhenius method is preferably used when large variation s of temperature occur as mentioned previously. In case s of small variation s of temperature, it is recommended to use the Nurse -Saul equation. Both methods follow the same procedure s in developing the relationship curves The difference is that the Nurse -Saul equation will be expressed in Temp time and the equivalent age will be expressed in days at a specific temperature. T he Nurse -Saul methodology is more widely used by State highway agencies due to its simplicity. 2.6 Stresses in Tilt -U p Wall Panels No references were found whereby tilt up concrete panels have actually been instrumented and bending stresses measured in the field. On the other hand, many companies are using their own software programs to calculate the stresses in a panel during the lifting sequences as the panel rotates from zero to ninety degrees. Recently an article in Concrete International, Automating Lifting and Bracing Analysis, by Stojanoski and Jankulovski, introduced a software program called PanelsPlus, that ca lculates the stress envelopes for lifting and rotating panels Data from the paper indicate that the bending stresses are in excess of 400 psi can be develo ped during this process. Other tilt up design software, s ome of them include fifnite element features and others do not are used in the tilt up industry. T hese include but not limited to Tiltmax, PAC WALLsoftware, Enercalc Engineeri ng Software, RAM Advanse V.9. PAGE 29 29 2.7 Current Studies Compressive strength tests according to ASTM C39 (2005) and flexural stren gth tests according to ASTM C 78 (2002) were performed. An empirical relationship between compressive strength and maturity index as well as flexural strength and maturity index were determined. In this study, an addition empirical relation between splitti ng tensile strength and maturity was also determined. Calibration curves were developed based on no changes in mix design. Different mix design s will have different calibration curves. This is why this study will perform maturity testing on three differen t mix designs. From each mix design correlation curves will be determined in order to find the corresponding correlation factors between flexural, compressive and splitting tensile strength. From the empirical relations, it will be only necessary to read the maturity index in order to find out the compressive, flexural and splitting tensile strengths of concrete. The Maturity method will estimate the strength of concrete before tilting the panels, but what are the actual stresses of these walls during lif ting? In this study, an instrumented tilt up wall panel was constructed in order to determine the actual stresses of the panel during lifting. The data collected from this study were compared to several tilt up design software results. PAGE 30 30 CHAPTER 3 ANALYSIS OF SURVEY RESULTS 3.1 Introduction The Maturity Method Usage in Tilt -Up Construction Survey ( Appendix A) was intended to find out current practices by tilt u p construction companies in order to estimate the strength of the wall panel during or just befor e lifting. The survey questionnaire was meant to study the types of strength that contractors are looking for and the different testing methods performed. 3.2 Survey Results In to order to assure the appropriate sample size for a survey, three major steps should be achieved: identify the target population, put together a population list and select the sample size (Dillman and Salant 1994). The sample size will be the number of surveys to be disseminated. In this research the targeted population is any cons truction company that deals with tilt up construction. The Tilt -Up Concrete Association is a dedicated group of contractors, professionals, and manufacturers with the interest of improving the quality and acceptance of Tilt -Up construction. The mission o f the Tilt -Up Concrete Association is to expand and improve the use of Tilt -Up as the preferred construction method by providing education and resources that enhance quality and performance. What better population list can be chosen other that the companie s which are members of the Tilt -Up Concrete Association? The chosen list is the list of all construction companies that are members of this a ssociation. It consists of 196 construction f irms that have had many years of experience tilt up construction An e mail was sent to these 196 companies. The questionnaire was mailed to only the companies that were interested in filling out the questionnaire. The responses in this survey are based on a 28 % return rate, 54 respondents out of 196 targeted construction c ompanies. PAGE 31 31 In order to find out the acceptable response rate of these surveys, it is required to know the acceptable or desired sampling error. Table 3 1 provides a clear idea about the process. Table 3 1. Final sample size needed for various population si zes and characteristics, at three levels of precision (Dillman and Salant 1994) Population Size Sample size for the 95percent confidence level Sampling Error 3% 5% 10% 50/50 split 80/20 split 50/50 split 80/20 spl it 50/50 split 80/20 split 100 92 87 80 71 49 38 250 203 183 152 124 70 49 500 341 289 217 165 81 55 750 441 358 254 185 85 57 1,000 516 406 278 198 88 58 2,500 748 537 333 224 93 60 5,000 880 601 357 234 94 61 10,000 964 639 370 240 95 61 25,000 1,023 665 378 234 96 61 50,000 1,045 674 381 245 96 61 100,000 1,056 678 383 245 96 61 1,000,000 1,066 682 384 246 96 61 100,000,000 1,067 683 384 246 96 61 A 50/50 split means population is relatively varied. An 80/20 split means it is less varied, most people have a certain characteristic, a few do not. Unless the split is known ahead of time, it is best to be conservative and use 50/50. In this study, all the respondents are employed in a construction company that deals with tilt up. An 80/20 spli t will be fair enough for this research. According to Table 3 1, using a 95% confidence level with a sampling error of 10%, the sample size is estimated to be 49 for a 250 population size, while for population size of 500, the sample size is estimated to be 55. PAGE 32 32 In this study, the population size is 196 and the sample size ended up being 54. This means that the Sample size of this Questionnaire is based on a 95% confidence Interval with a maximum sampling error of 10%. 3.3 Survey Results It is very impo rtant to understand that in this questionnaire, the participants were allowed to select all answers that apply to a question. 3.3.1 Demographic Questions The first part of the survey was concerning demographic questions. Information about company number of employees, revenue, and geographical location were asked in order to find out whether the smaller or larger firms were using tilt up as a construction technique. The survey results (see Figure 3 1) indicated that a large group of the companies that dea l with tilt up are small size companies. Sixty percent (60%) of the tilt up companies had an annual income of less than $50 million. This shows that tilt up construction does not demand high cost resources in order to perform it. Most of the tilt up contra ctors who responded were mid to small -size companies. As shown in Figure 3 2 the companies that participated in this survey had considerable construction experience. Sixty seven percent (67%) had over 20 years of experience. All the other ones had more t ha n 11 years of experience. The extensive experience of most of the respondents gave more credibility to this survey. As shown in Figure 3 3, based on the responses, tilt up construction is a nationwide construction technique. Most of this type of construc tion is happening in the West( 27%) and in the Southeast (30%). The use of tilt up is growing rapidly and its share of the construction market is expanding. PAGE 33 33 Figure 3 1. Companies annual volume Figure 3 2. Overall business experience PAGE 34 34 Figure 3 3. Companies active region/location 3.3.2 Tilt -up Construction Questions As mentioned previously, the purpose of this survey was to inventory the different methods in use in the tiltup construction industry in order to find the required strength of concrete before/during tilting. The responses to the survey question concerning the norma l time elapsed before lifting a panel after casting are shown in Figure 3 4. More than ninety percent (90%) of the panels were being lifted before reaching day 14 after c asting. Around fifty percent (50%) of the panels were lifted between day 5 a nd day 10 after casting. Thus, panels were being tilted before reaching their required 28-day strength. This is why this study focused on finding the strength of the panel just bef ore tilting This led to the survey questions that targeted the test methods performed in order to find the strength of concrete at early ages. PAGE 35 35 Figure 3 4. Normal t ime of lifting the panel The contractors were asked about their interest in finding th e compressive strength of the panel before tilting. All the participants (100%) indicated that compression tests on cylinders were performed in order to find the concrete compressive strength before tilting. This is usually a typical test for any type of c oncrete construction. ASTM C39 (2005) Standard Test Method for Compressive Strength of Cylindrical Specimen is the most common guide used nowadays. Another question was targeted at finding whether cont ractors were interested in the flexural s trength of th e panel. This question was asked beca use building codes require the computation of the flexural strength of the panel in addition to its compressive strength. If the panel were to fail during tilting, it would fail in flexure not in compression. As shown i n Figure 3 5 sixty one (61 %) of the participants were performing the Center -point Loading test, while only seventeen percent (17%) were performing the t hird point f lexure test. The flexural strength is expressed as Modulus of rupture (psi) and is determined by standards test methods ASTM C 78 (2002) for third -point l oading ( Figure 3 6 ) or ASTM C 293 (2002) c enter -p oint l oading (Figure 3 7). PAGE 36 36 Figure 3 5. Finding the flexural s trength Figure 3 6. ASTM C 78 Third -Point Loading Figure 3 7. ASTM C 29 3 Center Point Loading PAGE 37 37 The Center -point loading test overestimates the flexural or bending strength of the concrete by 15 to 25 percent because it includes both shear and bending stresses. The entire load is applied at the center span. There are substan tial shear forces as well as unknown stress concentrations at the point of load application, which act along the line on which the specimen generally fails .The maximum stress is present only at the center of the beam. The Third -point loading test results in a more conservative value and does not include the shear component of the stress. The specimen, in the middle third of the span, is subjected to a pure moment, with zero shear. Half the load is applied at each third of the span length. Maximum stress i s present over the center 1/3 portion of the beam (NRMCA 2000). In other words, Center point loading yields higher strength than third -point loading. The Center -point loading is not as good as the Third -point loading test method and is not a substitute for it (Darwin et al. 2003) Eleven percent (11%) of the participants replied that there is no need to estimate the flexural strength. They only look into the compressive strength. But as mentioned previously, knowing the compressive strength is not enough. O n the other hand, eleven percent (11%) of the contractor were estimating the flexural strength by using correlation formulas to convert compressive strength to flexural strength. In reinforced concrete design, the standard formula to convert compressive st rength to flexural strength is fr = 7.5 (ACI 435). Nawy (2008) noted that the flexural strength varies from 7.5 to 12 Other correlation formulas developed by researches have varied between fr = 8 c) and fr = 10 et al 1968). Resea rchers have also developed formulas relating splitting tensile strength from flexural strength and claim to obtain a more accurate correlation. The major problem associating any formulas based on cylinder strength and relating them to flexural strength is the number of variables associated with concrete strength and testing for concrete strength. A major concern is PAGE 38 38 the fact that most concrete used today is not plain, that is consisting of just Portland cement, water, coarse and fine aggregates, but rather more complex combinations that include both mineral admixtures as cement substitutes, and chemical admixtures. Most of the formulas developed have been based on plain concrete, moist cured for 28 days, and tested at that time. Today, most concrete mixes contain blended cements, consisting of fly ash and/or blast furnace slag, and chemical admixtures. Other variables include: type and amount of cement; type, size and distribution of both coarse and fine aggregates; water cement ratio; and curing conditio ns. These are just some of the factors that affect compressive strength, and in doing so would also affect any correlation formula developed relating compressive strength to flexural strength. Another question was asked in order to find the contractors co ncerns about the finding of the tensile strength of the panel. As shown in Figure 3 8, sixty -one percent (61%) of the respondents indicated that there is no need to find the tensile strength. Thirty nine percent (39%) would perform the splitting tensile te st if needed. In this research, the splitting tensile test was performed in order to find out whether there are better correlation formulas between Tensile and Flexural strength rather than between Flexural and Compressive strength. A major issue in conc rete construction is the curing of the samples taken in the field. As shown in Figure 3 9, sixty -seven percent (67%) answered that they stored the samples in a laboratory and thirty three percent (33%) kept them on site near the panel. Figure 3 10 shows th at s ixty one percent (61%) of the respondents indicated that the samples had different curing conditions than the panels, while thirty-nine percent indicated the same conditions. PAGE 39 39 Figure 3 8. Finding the tensile s trength Figure 3 9. Samples storage The samples were taken in the field during the pouring of the panel. After 24 hours, most of the contractors moved the samples in t o their laboratories. Consequently that the samples kept in a laboratory curing in a water bath will definitely have different curing conditions than the panel itself. Hence the strength of the samples tested will definitely be different than that of the pan el. This is why the use of the maturity m ethod will be discussed in Chapter 4. As shown in Figure 3 11 seventy two percen t (72%) of the participants indicated that they have never used Maturity Method in tilt up construction. Seventy seven percent (77%) of PAGE 40 40 those who never used the Maturity Method before were willing to adopt it if it is more accurate and cost effective. F igure 3 10. Samples and p anels curing condition Fi gure 3 11. The use of maturity method in t ilt up construction PAGE 41 41 Figure 3 12. Willingness to adopt the maturity m ethod The m aturity testing m ethod will be discussed in Chapter 4 because it offers to th e tilt up construction industry a more accurate and cost effective method to estimate the strength of a tilt up panel. Concrete maturity testing can result in fewer beam specimens required on a project, particularly the number of field-casted beams. This i s because a single maturity sensor embedded in a tilt up panel can provide a n unlimited number of in -place c ompressive/ f lexural and tensile strength measurements at a given location. As such, multiple sets of beams to support the lifting decisions are no longer required. PAGE 42 42 CHAPTER 4 TEST METHODS 4.1 Introduction Three ready -mix concrete designs already used in the tilt up construction industry were tested and evaluated in this research. This chapter provides information about the ingredients and the mi x proportions of the concrete mixes. Various tests on fresh and hardened concrete were performed. The maturity method was adopted in order to find the actual strength of concre te in compression and flexure. A d etailed procedure for the maturity method is a lso included. 4.2 Concrete Mix Designs 4.2.1 Mix Proportion of Concrete The first concrete mix design (Mix 1) studied in this research was a typic al mix design used for tilt up wall c onstruction. The same mix design was used to cast the UF Hough Hall til t up panels at the University of Florida. This design used plain concrete. The s econd mix design (Mix2) contained 20% of Fly Ash and 80% Portland c ement. The third mix design (Mix 3) contained 50% Slag and 50% Portland c ement. Tables 4 1, 4 2 and 4 3 show the mix designs details for the studied concrete. Table 4 1. Mix Design for the Plain Concrete (Mix1) Material TYPE Quantity Cement C 150 II 565 Lbs Water -250 Lbs Fine Aggregate C 33 Sand 1275 Lbs Aggregate C 33 #57 Stone 1700 Lbs Admixture C 260 AIR Entrained Agent 0.23 oz/ 100# cement Admixture C494 water Reducer (Plain) 5.35 oz/ 100# cement W/C Ratio 0.45 Slump (in) 4 1" Air Content (%) 3.5 1.5% Plastic Unit Weight (lb s/cf) 140.4 1.5 PAGE 43 43 Table 4 2. Mix Design for 80% Cement and 80% Fly Ash (Mix2)* Amount Specific Absolute Material Description Qty Gravity Volume Cement Cement Type I/II ASTM C150 481 lbs 3.15 2.45 Fly Ash Fly Ash Class F ASTM C 618 120 lbs 2.25 0.85 Co arse Aggr egate #57 (1") ASTM C 33 1725 lbs 2.45 11.28 Fine Aggr egate DOT Sand ASTM C33 1237 lbs 2.63 7.54 Admix 1 W.R. Grace WRDA 60 type A/D ASTM C494 19.2/28.9 oz Total Water Potable 32.5 gal Total water (includes any admixture water present) 2 70.7 lbs 1 4.34 Total Cementitious Material Per ASTM C595 601 lbs Design Percent Air (En t rapped Air) 2.00% 0.54 Slump range (from Mixer Discharge) 3 to 5 inches Air Content (from Mixer Discharge) 2% ( 1.5%) Absolute Volume Plastic Densit y ("Unit Weight") 142 lb/ft 27.00 ft W/C ratio 0.45 total Weight 3834 lb/yd Materials per Cubic Yard Table 4 3. Mix Design for 50% Cement and 50% Slag* Amount Specific Absolute Material Description Qty Gravity Volume Cemen t Cement Type I/II ASTM C150 235 lbs 3.15 1.20 GGBF Slag Type 120 ASTM C989 235 lbs 2 1.88 Coarse Aggr egate #57 (1") ASTM C 33 1700 lbs 2.45 11.12 Fine Aggr egate DOT Sand ASTM C33 1303 lbs 2.63 7.94 Admix 1 W.R. Grace WRDA 60 type A/D ASTM C494 oz Total Water Potable 30 gal Total water (includes any admixture water present) 250 lbs 1 4.01 Total Cementitious Material Per ASTM C595 470 lbs Design Percent Air (En t rapped Air) 3.00% 0.81 Slump range (from Mixer Discharge) 4 1 inches A ir Content (from Mixer Discharge) 3% Absolute Volume Plastic Density ("Unit Weight") 137.9 1.5 lb/ft 27.00 ft W/C ratio 0.53 Total Weight 3723 lb/yd *Materials per Cubic Yard PAGE 44 44 4.2.2 Materials U sed in Concrete Mixes Concrete mixes used in this research were provided by Cemex Ready Mix and Florida Rock Industries. Mix 1 was used twice in this research. Mix 1 Concrete was provided from Florida Rock Industries through Ajax Construction while they were pouring their tilt up panels for the H ough Hall project at the University of Florida. Mix 1 was also used to cast the instrumented panel, the c oncrete was provided by Cemex. Both Mix 2 and Mix3 were provided by Cemex. 4.2.2.1 Cement The cement was provided by the Cemex Brooksville Cement Pl ant. The Chemical and Physical properties analyzed by the Cemex Brooksville South Pant are shown in Tables 4 4 and 4 5 4.2.2.2 Air Entrained Agent The air entraining agent used by Cemex was the Darex AEA manufactured by Grace Construction Products. It me ets the specifications for Chemical Admixtures for Concrete, ASTM C260 and AASHTO M154. The air entraining agent used by Florida Rock Industries is AEA 92 S from Euclid Concrete Admixtures. It meets the requirements of the following specifications: Corps of Enginners Specification CRD C 13, ASTM C260, AASHTO M154 and ANSI/NSF STD61. 4.2.2.3 Water Reducer The water reducer used by Cemex was WRDA 60 manufactured by Grace Construction Products. It meets the specifications for Chemical Admixtures for Concrete ASTM C494 (Type A and D ) and AASHTO M154 (Type A and D). The water reducer used by Florida Rock Industries was EUCON WR from Euclid Concrete Admixtures. It meets the requirements of ASTM C494 (Type A and D), AASHTO M194 and ANSI/NSF 61. PAGE 45 45 Table 4 4. Ch emical properties of cement provided from Cemex Standard Chemical Requirements (ASTM C114) Spec ASTM C 150 ASTM C 150 AASHTO M 85 AASHTO M 86 Test Results Type I Low Alkali Type II Low Alkali Type I Low Alkali Type II Low Alkali Silicone Dioxide (S iO 2 ) % Minimum 20 20.6 Aluminum Oxide (Al 2 O 3 ) % Maximum 6 4.9 Ferric Oxide (Fe 2 O 3 ) % Maximum 6 6 3.8 Calcium Oxide (CaO) % 65.1 Magnesium Oxide (MgO) % Maximum 6 6 6 6 0.6 Sulfur Trioxide (SO 3 ) % Maximum 3 3 3 3 2.8 Loss of Ig nition (LOI) % Maximum 3 3 3 3 2 Insoluble Residue (IR) % Maximum 0.75 0.75 0.75 0.75 0.55 Alkalies (Na 2 O equivalent) % Maximum 0.6 0.6 0.6 0.6 0.35 Carbon Dioxide in cement (CO 2 ) % 0.57 Limestone % in cement (ASTM C150 A1) Maximum 5 5 5 5 1.4 C a CO3 in limestone % (2.274 x % CO 2 LS) Minimum 70 70 70 70 89 Tricalcium Silicate (C 3 S) % Maximum 60 Dicalcium Silicate (C 2 S) % 14 Tricalcium Aluminate (C 3 A) % Maximum 8 8 7 Tetracalcium Aluminoferrite (C 4 AF) % 12 (C 3 S + 4.75 C 3 A) Maximum 100 100 91 C 4 AF + 2C 3 A) or (C 4 AF + C 2 F) % Maximum 25 PAGE 46 46 Table 4 5. Physical properties of cement provided from Cemex Specs ASTM C 150 ASTM C 150 ASTM C 1157 AASHTO M 85 AASHTO M 86 Test Results Type I Low Alkali Type II Low Alkali GU Type I Low alkali Type II Low Alkali (ASTM C204) Blaine Fineness, cm2/g Minimum 2800 2800 2800 2800 3743 (ASTM C204) Blaine Fineness, cm2/g Maximum 4200 4200 3743 (ASTM C430) 325 Mesh % 96.4 (ASTM C191) Time of set ting (Vicat) Initial Set, minutes Minimum 45 45 45 45 45 87 Final set, minutes Maximum 375 375 420 375 375 190 (ASTM C185) Air content of mortar % Maximum 12 12 12 12 7 (ASTM C 151) Autoclave Expa nsion % Maximum 0.8 0.8 0.8 0.8 0.8 0.05 (ASTM C 187) Normal Consistency % 25.3 (ASTM C1038) Expa nsion in water % Maximum 0.02 0.02 0.02 0.02 0.02 0.011 (ASTM C186) 7 day heat of hydration cal/g Max if specified 70 76 (ASTM C109) Compressive Strength, psi 1 Day 2229 3 Days Minimum 1740 1450 1450 1740 1450 3957 7 days Minimum 2760 2470 2465 2760 2470 5033 28 days Minimum 6717 PAGE 47 47 4.2.2.4 Coars e Aggregates The coarse aggregate used in these mixes was #57 limestone The physical properties of th e coarse aggregates provided for this research are shown in Tables 4 6 and 47. The gradation of the coarse aggregates provided by Cemex is shown in Figure 4 1. Table 4 6 Physical properties of the Cemex coarse aggregate Fineness Modulus 7.03 ASTM C 127 Specific Gravity (SSD) 2.45 ASTM C127 Absorption 5.80% Table 4 7 Physical properties of the Florida Rock Industries coarse aggregate D ry Specific Gravity 2.4 D ry Rodded Unit Weight 90 PCF Absorption 5.30% Figure 4 1. Gradation of Cemex coars e aggregate 4.2.2.5 Fine aggregate The physical properties of fine aggrega tes provided for this research are shown in Tables 4 8 and 4 9. The gradation of the fine aggregates provided by Cemex is shown in Figure 4 2. PAGE 48 48 Table 4 8. Physical properties of the Cemex fine aggregate Fineness Modulus 2.33 ASTM C 128 Specific Gravity (SSD) 2.63 ASTM C128 Absorption 0.3% Table 4 9. Physical properties of the Florida Rock Industries fine aggregate Fineness Modulus 2.18 Dry Unit Weight 100 PCF Absorption 0.5 % Figure 4 2 Gradation of Cemex fine aggregate 4.2.2.6 Fly ash The Chemical and Physical properties of fly ash analyzed by Boral Material Technologies and provided by Cemex are shown in Tables 4 10 and 4 11. PAGE 49 49 Table 4 10. Chemical properties of fly ash Tests Results ASTM C 618 Calss F/C AASHTO M 295 Class F/C Chemical Tests Silicone Dioxide (SiO 2 ) % 57.87 Aluminum Oxide (Al 2 O 3 ) % 26.79 Iron Oxide ( Fe 2 O 3 ) % 4.45 Sum of SiO 2 Al 2 O 3 Fe 2 O 3 % 89.11 70.0/50.0 min 70.0/50.0 min Calcium Oxide (CaO) % 2.44 Magnesium Oxide (MgO) % 0.94 Sulfur Trioxide (SO 3 ) % 0.28 5.0 max 5.0 max Sodium Oxide (Na 2 O) % 0.54 Potassium (K 2 O) % 2.41 Total Alkalies (as Na 2 O ) % 2.13 Table 4 11. Physical properties of fly ash Tests Resul ts ASTM C 618 Calss F/C AASHTO M 295 Class F/C Physical Tests Moisture Content, % 0.07 3.0 max 3.0 max Loss of Ignition, % 2.32 6.0 max 5.0 max Amount Retained on No. 325 Seive, % 24.69 34 max 35 max Specific Gravity 2.18 Autoclave Soundne ss, % 0.02 0.8 max 0.8 max SAI, with Portland Cement at 7 days, % of Control 82.9 75 min* 75 min* SAI, with Portland Cement at 28 days, % of Control 93.7 75 min* 75 min* Water Required, % of Control 97.9 105 max 106 max Meeting the 7 day or 28 day S trength Activity Index will indicate specification compliance 4.2.2.7 Slag The ground granulated blast furnace slag used in this research was provided from Florida Rock Industries. The chemical and physical properties of slag are shown in Table s 4 12 and 4 13. Table 4 12. Chemical properties of slag Slag Chemical Analysis Maximum Limit Sulfide Sulfur (S) 1.04% 2.50% Sulfur Trioxide (SO 3 ) 2.60% 4.00% PAGE 50 50 Tables 4 13. Physical properties of slag Slag Physical Analysis Composition Lim it ASTM C 989 Fineness Retained on 325 sieve ( ASTM C430) 2.60% Maximum 20% Blaine, m 2 /kg (ASTM C204) 501 Specific Gravity (ATSM C188) 2.95 Air Content (ASTM C185) 3.90% Maximum 12% ASTM C989 Test Results Limit ASTM C 989 Compressive Strength (psi) ASTM C 109 Grade 120 50 50 slag and reference Portland cement) 7 days : 4600 28 Days : 7090 Slag Activity Index, % 7 days: 95 Minimum 95% 28 Days: 117 Minimum 115% Reference Cement per ASTM C989 Fineness Blaine (m 2 /kg) ASTM C 204) 371 Compressive Strength (psi) ASTM C 109 7 days : 4820 28 Days : 6076 Min 5000 Total Alkalis: 0.73% 0.60 0.90 % Compound Composition C3S 46.4% C2S 24.4% C3A 9.2% C4AF 8.3% PAGE 51 5 1 4.3 Preparation of Concrete Specimen All concrete used in this research was mixed in a ready mix. For each concrete mix, thirty cylinders (6 inches x 12 inches) and fifteen beams (6 inches x 6 inches x 21 inches) were cast Tab le 4 14 shows a list of concrete samples obtained to test for each mix in this research. Table 4 14. Concrete specimen for each mix design Test Specimen Size Number of samples Time of testing (days) Standards Compressive 6 by 12 Cylinder 15 1,3,7,14 an d 28 ASTM C39 Flexure 6 by 6 by 21 Beam 15 1,3,7,14 and 28 ASTM C78 Splitting tensile 6 by 12 Cylinder 15 1,3,7,14 and 28 ASTM C 496 Specimens were prepared according to ASTM C 192 (2007) Fresh concrete tests were performed as soon as the tr uck unloaded the concrete. For the cylinders, three layers of approximately equal volume were used to fill the molds. Each layer was rodded 25 times with the rounded end of a rod. For the beams, two layers of approximately equal volume were used to fill th e mold. The number of roddings per layer for beams was one for each 2 in of top surface area of the specimen. After consolidation, the top surface was finished with a trowel. The maturity loggers were embedded inside two cylinders and t wo beams of each mi x. T he embed ed loggers were connected to the reader prior to start up. At that instance, the loggers started recording the temperature and maturity of the specimens. The samples were kept in there molds for a full day. After twenty four hours, the sample s were moved to a curing tank at the Rinker Hall Laboratory at the University of Florida. All specimens were moist cured in a curing tank at 70 F according to ASTM C 511 (2005) PAGE 52 52 Figure 4 3. Beam and cylinder specimens. A) Samples stored on -site for the first 24 hours. B) Samples Stored in curing Tank af ter 24 hours of casting 4.4 Tests on Fresh Concrete ASTM standard tests were performed on the fresh concrete of each concrete mix used in this study. The properties of the fresh concrete for each of the three concrete m ixes are shown in Table 4 15. 4.4.1 Slump of Hydraulic Cement Concrete Slump test was performed for ea ch mix design according to ASTM C 143 (2005) The purpose of this test is to check the workability of concrete. The procedures of the slump test are as follows: The cone was positioned on the base plate with the smaller aperture uppermost. Freshly concrete was poured into the cone to approximately one third of its depth (4 -inches). The concrete was tamped using 25 strokes of steel rod. Further concrete was added to fill the cone to approximately two third depth (ie: othe r 4 inches of concrete). Again, the c oncrete was tamped using 25 stroked of the rod. More concrete was added till t he cone was filled to the top and tamped using a final 25 strokes with the steel rod. Some concrete was added to bring it leveled PAGE 53 53 with the top of the cone. The cone was carefully lifted upwards and placed upside -down next to the concrete. After a minute or so, the unrestrained concrete was settled downwards or slump due to gravity. The steel rod was used to span the inverted cone and the slump was measured to the nearest inch The results are shown in Table 4 15. Figure 4 4 Slump t est 4.4.2 Air content of Freshly Mixed C oncrete b y Pressure M ethod This test method covered the determination of the air content of freshly mixed concrete made with dense aggregate according to ASTM C 231(2004) A suitably designed air meter employing the principle of Boyles law was used to determine the air conte nt of the plastic concrete. An air m eter consists of a measuring bowl (capacity of 0.2ft) and cover assembly with pressure gauge. Th e t ools needed to perform this test are: Tamping Rod (5/8 diameter) Scale ( 0.01lb accuracy) Mallet rubber, weighing approximately 1.25 lb Strike off Bar The p rocedures stated in ASTM C231 (2204) were followed in order to determine the Air content of eac h mix. The results are shown in Table 4 15. PAGE 54 54 4.4.3 Unit Weight For quality control purposes, the density of concrete should be measured. The unit weight of concrete varies with the amount and density of the aggregate, the amount of entrapped or en trained air, the water and cement content In this research, the unit weight of concrete was determined according to ASTM C138 (2001) The results are shown in Table 4 15. 4.4.4 Temperature Test In order to find out the temperature of fresh concrete, ASTM C1064 (2005) procedures were followed The results are shown in Table 4 15. Table 4 15. Properties of fresh concrete mix Mix 1 Concrete Samples Mix 1 Panel Mix 2 Concrete Samples Mix 3 Concrete Samples Slump (inches) 4.5" 6.5" 2.75" 3" Air Entrained (% ) 3 1.3 1.9 2.9 Temperature ( F) 87 95 92 92 Unit weight (pcf) 142 149 142 138 4.5 Tests on Hardened Concrete 4.5.1 Compression Testing A c ompression test was performed for each mix design at ages 1, 3, 7, 14 and 28 days in accordance with ASTM C 39 (2005) The compressive strengt h of each specimen was calculated by dividing the maximum load carried by the specimen during the test by the average cross -sectional area. (4 1) P = Maximum Load carried by the sp ecimen (Lbs) r = Radius of the specimen (in) r = 3 inches in this research PAGE 55 55 Two specimens were tested at each time interval and the average strength was computed. At each test age, the average maturity index was also recorded. The average compression strength was plotted as a function of the average value of the maturity index. The resulting curve is the compressive strength-maturity relationship to be used for estimating the compression strength of concrete cured under different temperature conditions. F igure 4 5. Compression Test f or cylinders. A) During testing. B) After testing 4.5.2 Third Point Flexure Test The Third Point Flexure tests were performed at ages 1, 3, 7, 14 and 28 days according to ASTM C 78 (2002) In this study, all the fracture initiated in the tension surface occurred within the middle third of the span length, the Modulus of rupture was calculated as follows: R= PL/ bd (4 2) where R = modulus of rupture (psi) P = Maximum applied load indicated by the testing mach ine (l bf) L = Span length (in); 18 inches b = average width of specimen (in); b= 6 inches d = average depth of specimen (in); d = 6 inches PAGE 56 56 Two specimens were tested at each age and the average strength was computed. At each test age, the average maturit y index was also recorded. The average flexural strength was plotted as a function of the average value of the maturity index. The resulting curve is the Flexural strength -maturity relationship to be used for estimating the flexural strength of concrete c ured under different temperature conditions. Figure 4 6. Third point flexure test. A) During t esting. B ) After t esting 4.5.3 Splitting Tensile Test ASTM C1074 (2004) mentioned the relationship be tween compressive strength and m aturity and the relationshi p between flexural strength and maturity. In this research, the relationship between the splitting tensile strength and m aturity was also determined The same procedure was followed for the flexural and compressive strength tests in order to develop the sp litting tensile strength -maturity relationship. Cylinder specimens were prepared according to ASTM C 192 (2007) Each cylinder is 6 by 12 inches. Fifteen cylinders were poured using the same mix design. The splitting tensile tests were performed at ages 1, 3, 7, 14 and 28 days in accordance with ASTM C 496 (2004) The splitting tensile strength of each specimen was calculated as follows: PAGE 57 57 T = 2P/ (4 3) where T = splitting tensile strength (psi) P = maximum applied load indicated by the testing machine (lbf) l = length of the specimen (in); l= 12inches d = diameter of the specimen; d= 6 inches Two specimens were tested at each age and the average strength was computed. At each test age, the average maturity index for each of the two specimens was also recorded. The average tensile strength was plotted as a function of the average value of the maturity index. The resulting curve is the splitting tensile strength -maturity relationship to be used for estimating the splitting tensile strength of concrete cured under other temperature conditions. Figure 4 7 Splitting tensile test. A) During testing. B) After testi ng PAGE 58 58 4.6 Maturity Method 4.6.1 Introduction In Tilt -Up construction, the knowledge of early strength gain in concrete is critical for deciding when the panel had reached sufficient strength to be lifted and to avoid the risk of failure during tilting. A s mentioned earlier in the literature review, the current practices of estimating in place concrete strength by testing large numbers of beams and cylinders in the field have been found to be difficult. A proven method to reduce the use of beam and cylinde r samples in the field is the Maturity Method. This method is a completely non-destructive technique for estimating concrete strength in the field. The objective of the work presented in this research is to provide information regarding the accuracy and f easibility of the maturity method for the measurement of the concrete strength of tiltup panels. Information is provided regarding the use of the maturity method for measurement of compressive, flexural and splitting tensile strengths. 4.6.2 Estimating th e Strength of Concrete using Maturity Testing This test was used to estimate the in -place strength of concrete to determine the appropriate time to lift a tilt up panel. There are two alternative equations for computing the Maturity index of concrete. One of them is expressed in terms of temperature time (Nurse -Saul method) and the other in terms of equivalent age at a specific temperature (Arrhenius method). 4.6.2.1 Nurse -Saul method (Temperature -Time) The Nu rse Saul Equation is: M = (4 4) where M = maturity (time -temperature factor) at age t T (o) = datum temperature PAGE 59 59 4.6.2 .2 Arrhenius Method (Equivalent age at specific Temperature) The Arrhenius equation is: t(e) = (Q)[1/(273+Ta)(4 5) where t(e)=equivalent age at reference curing temperature Q= activation energy divided by the gas constant (K); (Q= E/R) E=activation energy, J/mol R=universal gas constant, 8.3144 J/(mol K) Tr=reference temperature, C Though both functions can predict the strength of in-place concrete equall y well, the Nurse Saul equation was preferred for this study due to its simplicity. 4.6.3 Maturity Testing Process The maturity testing process shown in (Figure 4 9) consists of two steps: developing the maturity calibration curve and measuring the maturit y of the in -place concrete. From this information, the strength of the in-place concrete can be monitored and assessed (CPTP 2005). The following steps were followed: Step 1: Develop maturity calibration curve by: Determining the datum temperature (T0). Measuring the maturity index: temperature time factor ( TTF ) Determining the concrete strength by perform mechanical testing on beam and cylinder specimens. Establishing relationship between strength values and the maturity index Step 2: Estimate the in-place strength of concrete by: Measuring the maturity of in-place concrete Determining t he concrete strength from maturity calibr ation curves developed in the previous step. PAGE 60 60 Figure 4 8 Maturity Testing Process In this study, the Maturity Method was p erformed for three differe nt mix designs used in the tilt up construction i ndustry. Plain Concrete (Mix 1) Concrete with Fly Ash (Mix 2) Concrete with Slag (Mix 3) The purpose of choosing three different designs is to show that each design may have diffe rent calibration curves. Correlation curves were developed that related the temperature history to strength for the specific concrete mixture that was studied. The correlation curve consists of a maturity index plotted against strength. The maturity index is a value that increases with age according to a maturity function. From the empirical relations, it will be only necessary to read the maturity index in order to find out the compressive, flexural and splitting tensile strengths of concrete. PAGE 61 61 4.6.4 Matur ity Measurement Device IntelliRock TM loggers from ENGIUS were used in this study. Based on ASTM C 1074 (2004) Standard Practice for Estimating Concrete Strength by the Maturity Method IntelliRock TM maturity loggers analyze the time and temperature p rofile of inplace concrete to calculate the in place strength of concrete in real time, with the push of a button. IntelliRock TM maturity loggers log temperature and maturity each hour for 28 days and calculate maturity using the Nurse Saul (time -tempera ture factor) as well as the Arrhenius (equivalent age) calculation methods. The maturity loggers that used the Arrhenius equation to compute the equivalent age are based on a constant value of activation energy. The activation energy cannot be changed. F or simplicity, this study did not to use these loggers because each mix design will have a different activation energy value. If the Arrhenius method was to be adopted temperature loggers would be preferred These temperatures will be plugged into the Arr henius equation in order to determine the equivalent age. T he Nurse Saul methodology is more widely used by State highway agencies because of its simplicity. In this Research maturity loggers that used the Nurse -Saul equation were adopted. The specificati ons of the IntelliRock maturity loggers and IntelliRock IITM reader are shown respectively in Tables 4 16 and 417. Table 4 16. Maturity Loggers s pecifications Operating Temperature: 5 C to 85 C Storage Time & Temperature: 0 to 35 C for 2 years. Max T emperature measurement Range 18 to 99 C (unwarranted outside of "operating temperature" range) Temperature Accuracy +/ 1 C, 5 to 85 C Temperature Resolution 1 C Time accuracy 1 minute per month Temperature measurement rate 1 minute (resolution for min/max) Maturity integration period 1 minute PAGE 62 62 Table 4 17. IntelliRock II TM Reader s pecifications Time accuracy 1 minute per month Logger data storage 999 logger downloads PC Interface USB 4.6.5 Corrected Temperature -Time F actor The use of the N urse Saul equation required the determination of datum temperature The maturity testing was performed before computing the real datum temperature. The datum temperature was set to zero degrees Celsius in the Reader. The value of temperature -time factor di splayed by the reader should then be corrected for the new datum temperature as follows according to ASTM C1074: Mc= Md (To Td) t (4 6) where Mc= the corrected temperature time factor, degree -days or degree -hours Md= the temperature time factor displayed in step 1 To= the appropriate datum temperature C Td= the assumed datum temperature T= the elapsed time from when the test started to when a reading was taken, days or hr. 4.6.6 Determination of Datum Temperature (T0) The Datum Temperature represents a temperature below which no active hydration of cement is considered to take place that contributes towards strength development The datum temperature for a given concrete depends on: Type of Cement Type and Dosage of Admixtures Temperature of Concrete at the Time of Hardening T he determination of the datum temperature via mortar cubes was performed according to ASTM C1074. F or Type I cement without admixtures and a curing temperature range from 0C to 40C, the recommended datum temperature is 0C (35F). PAGE 63 63 On the other hand, according to a study from the U. S. Department of Transportation (2005) the datum temperature using Nurse-Saul equation varies from 10C to 12 C (11 F to 14 F) in concrete pavement. According to Michael Fox, the president of Engius Constructive Intelligence: With most non -exotic mix designs using T ype I and II cements, the majority of projects assume a 0 C datum. In this study, t he instrumented panel was cast with Mix 1. Only Mix 1 was used to evaluate the datum temperature. For Mix 2 and Mix3, a datum temperature of 32 F (0 C) was assumed. Three sets of 2 inches mortar cubes were to be prepared. Each set consisted of 18 cubes. Each set was cured at different temperature s In this research, the se three temperatures used were: 40F = the minimum temperature expected for in -place concrete 68F = A median temperature between the high and low values 92F = the maximum temperature expected for in place concrete For each set of cubes, the compression strength of three cubes was determined according to ASTM C109 (2008) During casting the cylinder and beam samples for Mix1, a fresh concrete was sieved throug h the #4 sieve The concrete passing sieve #4 was used to cast 2in by 2in cubes in order to determine the datum temperature. According to the standards, it was required to plot strength gain versus time and fit the data with the following function: S= Su [ k (t to)]/[1+k(t to)] (4 7) where S = average cube compressive strength at age t (a variable), t = test age (a variable), Su = limiting strength (a regression coefficient), to = age when strength development begins (a regression coefficient), PAGE 64 64 K = the rate constant (a regression coefficient). The SPSS Software program was used to calculate the best -fit values of Su, to and k of Equation 4 7. The k -values versus the curing temperatures were plotted in Chapter 5 The intercept of the best -fitting straight line with the temperature axis is the datum temperature T(0), used in the Nurse Saul method (Equation 4 4). F igure 4 9 Compression test for mortar cubes A) Before testing. B) After t esting 4.6.7 Correlation curves The co rrelation curve equation can be based on any function that accurately describes the data. This study used the logarithmic f unction developed by Plowman ( 1956). The form of the logarithmic function is as follows: S= A +B Ln (TTF ) (4 8) where S = estimated strength of the concrete at a given maturity (a variable), A and B = regression constants, TTF = Temperature time factor known as maturity index (a variable). PAGE 65 65 Using MS Excel, the data were generated in order to determine the regression constants and the correlation equations. MS Excel is also capable of generating logarithmic equation s PAGE 66 66 CHAPTER 5 MATURITY AND CONCRETE TESTING RESULTS 5 .1 Datum Temperature Table 5 1 lists the data generated for det ermining the datum temperatu re, T(0), of the first concrete mix design Mix 1 using the method specified in ASTM C 1074. Equation 47 was fitted to the data for each temperature as shown in Figure 5 1. The corresponding regression coefficients are given in Table 5 2. The rate consta nt, K, was plotted for the three test temperatures as shown in Figure 5 2, and the linear equations shown in the figure were fitted to the data points. Equation 4 7 was used to determine T(0). Table 5 1. Data for determining the datum temperature of Mix 1* Curing Temperature ( F) Age (d ays) Average Strength (psi) Curing Temperature ( F) Age (Days) Average Strength (psi) Curing Temperature ( F) Age (Days) Average Strength (psi) 40 1 805 68 0.5 850 92 0.4 955 2 1,438 1 2,230 0.8 2,555 4 2,510 2 3,390 1.6 3,220 8 4 310 4 3 800 3.2 4230 16 4,660 8 5,030 6.4 5,170 32 5,905 16 6,140 12.8 5,320 *Numbers are rounded to the nearest integer. F igure 5 1. Compressive strength development of mortar cubes PAGE 67 67 Table 5 2 Calculated regression coefficients for Equ ation 4 7 Mix Design Curing Temperature ( F) Su (psi) K (1/days) T (0) (days) Mix 1 40 6858.263 0.172 0.315 68 6752.818 0.425 0.044 92 5764.011 1.033 0.18 Figure 5 2. Determination of T(0) for Mix 1 Figure 5 2 shows that Mix 1 had an actual datum temperature of 33 F (0.5 C). It is fair enough to use a datum temperature of zero. 5 .2 Maturity Correlation Curves Table 5 3, 5 4, 5 5 show the maturity, compressive, flexural and splitting tensile strength data used for the correlation curves for all mixes studied in this research. The temperature -time factors were recorded for each of the maturity meter at the time of the cylinder and beam tests. Only two cylinder s and two beams tests were required at each specified time. The average values for the maturity indices, the compressive, flexural and splitting tensile strength were calculated and plotted in Figure 5 3 to 5 10 Appendix B shows the temperature and maturity data recorded by the maturity loggers in this study. Correlation curves were generated based on Equation 4 8. PAGE 68 68 Table 5 3. Maturi ty and strength data for the correlation curves for Mix 1* Cylinder Specimen Beam Specimen Time (Days) Average Temperature Time Factor (C hour) Average Compressive Strength (psi) Average Tensile Strength (psi) Average Temperature Time Facto r (C hour) Average Flexural Strength (psi) 1 792 2279 208 847 412 3 1806 3468 277 1834 541 7 3737 4391 342 3770 598 14 7096 5179 365 7154 638 28 13647 5969 405 13697 688 *All Numbers are rounded to the nearest integer Figure 5 3. Correlat ion curve between Compressive strength and the temperature time maturity index for Mix 1 PAGE 69 69 Figure 5 4. Correlation curve between Flexural strength and the temperature time maturity index for Mix 1 Figure 5 5 Correlation curve between splitting tensil e strength and the temperature -time maturity index for Mix 1 Table 5 4. Maturity and strength data for the correlation curves for Mix 2* Cylinder Specimen Beam Specimen Time (Days) Average Temperature Time Factor (C hour) Average Compressiv e Strength (psi) Average Tensile Strength (psi) Average Temperature Time Factor (C hour) Average Flexural Strength (psi) 1 652 2238 249 745 438 3 1711 3189 318 1746 612 7 3780 4622 353 3727 710 14 7553 5230 377 7404 755 28 14684 5938 410 14467 7 91 *All Numbers are rounded to the nearest integer PAGE 70 70 Figure 5 6 Correlation curve between Compressive strength and the temperature time maturity index for Mix 2 Figure 5 7 Correlation curve between Flexural strength and the temperature time maturit y index for Mix 2 Figure 5 8 Correlation curve between splitting tensile strength and the temperatur e -time maturity index for Mix 2 PAGE 71 71 Table 5 5. Maturity and strength data for the correlation curves for Mix3* Cylinder Specimen Beam Specimen Time (D ays) Average Temperature Time Factor (C hour) Average Compressive Strength (psi) Average Tensile Strength (psi) Average Temperature Time Factor (C hour) Average Flexural Strength (psi) 1 811 943 106 810 168 3 1916 1664 190 1922 347 7 4051 2332 282 406 1 472 14 7553 2963 292 7569 541 28 14610 3344 316 14661 621 *All Numbers are rounded to the nearest integer Figure 5 9. Correlation curve between compressive strength and the temperature time maturity inde x for Mix 3 Figure 5 10. Correlation cu rve between flexural strength and the temperatur e time maturity index for Mix 3 PAGE 72 72 Figure 5 11. Correlation curve between splitting tensile strength and the temperatur e -time maturity index for Mix 3 5 .3 Evaluation of Maturity Curves The final step of the maturity method is to evaluate the adequacy of the correlation formulas. This evaluation was performed on two different tilt up panels poured with Mix 1 as described in Chapter 4. The first panel was one of the tilt up panels used to build the UF Hough H all. The second panel was the small scale pane l casted and lifted at the Perry Construction yard. Figure 5 3 was used to estimate the compressive strength, Figure 5 4 to estimate the flexural strength and Figure 55 to estimate the splitting tensile streng th. The correlation formulas obtained from these figure are: S = 1289.9 ln(TTF) 6 265.5 (for compression) (5 1) MR= 94.466 ln(TTF) 197.16 (for flexure) (5 2) ST = 68.738 ln(TTF) 241.34 (for splitting tensile) (5 3) w here S= Compr essive strength in psi MR= Modulus of Rupture or Flexural strength in psi TTF= Temperature time factor known as Maturity Index in C hours ST= Splitting tensile strength in psi The evaluation was only performed for the flexural and compressive strength correlation formulas. PAGE 73 73 5 .3.1 UF Hough Hall Panel Before casting one of the tilt up panel s of the UF Hough hall, two maturity loggers were embedded. The pan el studied was poured with Mix 1 studied in Chapter 4. While casting the panel, two beam s and two c ylinder samples were poured and left near the panel in order to have the same curing conditions. At the day of tilt, 6 days after the concrete was poured, and just before lifting the panel, compression and flexure tests according to ASTM standards were per formed on the samples left in the field. Maturity was also recorded from the embedded loggers. A comparison between the strengths estimated from the calibration curves and the samples testing is shown in Table 5 6 and Figures 5 12 and 5 1 3 : Table 5 6. Mat urity and strength data for verification purposes of the UF Hough Hall panel DAY 6 Maturity Index ( C hrs) Compressive strength using equation (psi) Flexural Strength using Equation (psi) Beam Flexural Strength Test (psi) Cylinder Compressive Strength Test (psi) 4,126 4,473.00 589.28 591 4,538 4,378 4,549.47 594.88 604 4,591 Figure 5 12. Comp arison between the maturity correlation curve and compressi ve strength verification data ( UF Hough Hall Panel) PAGE 74 74 Figure 5 13. Comparison between the maturity correlation curve and flexural strength verification data (U F Hough Hall) From Table 5 6 on the d ay of tilt, the maturity method estimated an average compressive strength of 4,511psi The compressive tests performed on the cylinders left near the panel resulted of an average value of 4 565 psi. The average flexural strength estimated by the correlatio n formulas was 592 psi. The flexure tests performed on the beams left near the panel resulted in an average value of 598 psi. The strengths values ended up to be very close. This evaluation has proved that maturity method is a good mean of estimating the i n -place strength of concrete. PAGE 75 75 Figure 5 14. Embedded maturity loggers. A) Before pouring concrete. B) Reading maturity index Figure 5 15. Lifting the panel at UF Hough Hall PAGE 76 76 5 .3.2 Perry Construction Yard Panel In order to find out how accurate thes e curves are, the t ilt up panel discribed in Chapter 6 was poured using Mix 1 design. Two Maturity loggers were embedded inside the panel while pouring. Beam and cylinder samples were casted with same concrete mixture used to pour the panel. These samples were left near the panel in order to cure in the same environment as the wall (Figure 5 18). The verifications of the curves were performed at days 3, 7 and 10 after pouring. At each of these three days, c ompressive testing for cylinders and flexure testi ng for beams were performed. At the same time, the temperature time factor was read using the maturity reader (Figure 5 19). The temperature time factor was integrated in E quations 5 1 and 5 2. A comparison between the strength estimated by the curves and the actual testing results was performed in Table 5 7 and Figures 5 16 and 5 1 7 Table 5 7 Maturity and strength data for ve rification purposes of the Perry Yard panel Maturity Index ( C-hrs) Compressive strength using equation (psi) Flexural Strength using Equation (psi) Beam Flexural Strength Test (psi) Cylinder Compressive Strength Test (psi) Day 3 1,960 3,512.84 518.96 548 3,707 1,976 3,523.33 519.73 554 3,737 Day 7 4,2 91 4,523.58 592.98 625 4,738 4,240 4,508.16 591.85 631 4,697 Day 10 6,811 5,119.54 636.62 633 5,077 6,891 5,134.60 637.73 645 4,989 PAGE 77 77 Figure 5 16. Comparison between the maturity correlation curve and compressi ve strength verification data ( Perr y Yard Panel) Figure 5 17. Comparison between the maturity correlation curve and flexural strength verification data (Pe rry yard Panel) PAGE 78 78 Figures 5 16 and 5 1 7 show that the verification data are slightly underestimating the compressive and flexural streng th at D ays 3 and 7. On the other hand, the flexural stre ngth is very well predicted at D ay 10. The compressive strength was slightly overestimated. However, the calibration c urves were determined using Mix 1 provided by Florida Rock Industries and the p ane l was pouring using also Mix1 but provided by Cemex ready mix. This difference in sources of materials mig ht be the cause of this slight variance in values. Figure 5 18. Samples s tored near the panel. A) Beam samples. B) Cylinder s amples Figure 5 19. Reading the maturity index PAGE 79 79 5 .4 Concrete Correlation Formulas Correlation formulas between different types of strength for concrete were established for the three mix designs studied. In the following section, each formula will be compared to an existing e quation that is currently used in concrete construction. 5 .4.1 Relationship Between Compressive and Flexural S trength In this section, the relationship between compressive and flexural strength was conducted for the three mix designs studied. In order to e valuate the results, it is suggested to compare the obtained equations with currently used ones in estimating the flexural from the compressive strength. Most of the formulas correlating compressive to flexural strength are of the form: MR= A x fc B (5 4 ) where MR= Modulus of Rupture or Flexural Strength in psi fc = Compressive strength of concrete in psi A = Coefficient B = Coefficient ACI Committee 435 suggested that a reasonable estimate to the flexural strength varies from 7.5 to 12 MR= 7.5 x fc1/2 (5 5 ) MR= 12 x fc1/2 (5 6 ) On the other hand, ACI C ommittee 330, Guide for Design and Construction of Concrete Parking Lots uses another formula to estimate flexural strength: MR= 2.3 x fc 2/3 (5 7 ) Furthermore, a study by the Florida State Road Department and Portla nd Cement Association reported the following rela tionship: MR= 1.66 x fc 0.71 (5 8 ) PAGE 80 80 Equation 5 8 was updated when using #57 limestones from South Florida. The suggested formula is in the form of: MR= 1.572 x fc 0.71 (5 9 ) The relationship between compressive strength and the flexural strength was developed for each Mix design and plotted in Figure s 5 20 to 5 22. Regression equations were developed to present the be st fit relationship between compressive and flexural strength. Figure 5 20. Correlation curve between flexural strength and compressive strength for Mix 1 PAGE 81 81 Figure 5 21. Correlation curve between flexural strength and compressive strength for Mix 2 Figure 5 22. Correlation curve between flexural strength and compressive strength for Mix 3 PAGE 82 82 Figures 5 20 to 5 2 2 show the relationsh ips between compressive and flexural strength s for the three different mix designs studied Each mix design had its own correlation formula as shown below: For Mix 1: MR= 7.3654 x fc 0.5231 (5 10) For Mix 2: MR= 5.0264 x fc 0.5857 (5 11) For Mix 3: MR = 0.1588 x fc 1.0253 (5 12) In the following analysis, a comparison between these studied cor relation formulas and existing ones is performed. Equation 5 5 underestimated the flexural strength for mixes 1 and 2. On the other hand, it overestimated the flexural strength of Mix 3 for day 1, then underestimated it starting day 3 and up. For all thr ee mix designs, Equation 5 6 overestimated the flexural strength. For Mix 1, Equations 5 7 5 8 and 5 9 had good estimates for flexural strength at days 1 and 3. These equations overestimated it afterwards. For Mix 2, Equations 5 7 5 8 and 5 9 underestim ated the flexural strength except at day 28. At that day, Equation 6 5 had a very close estimate. For Mix 3, Equations 5 7 5 8 and 5 9 underestimated the flexural strength at day 1 and overestimated it at day 7 and above. At day 3, these equations made g ood predictions. As it is seen from the above comparisons, each mix design had its own correlation formula relating compressive to flexural strength. It is interesting to note that using a specific existing formula can overestimate or underestimate the fle xural strength of the same mix design depending on the required day of finding the strength. PAGE 83 83 5 .4.2 Relationship B etween Splitting T ensile Strength and Compressive Strength Most of the formulas correlating compressive to flexural strength are of the form: fs t= A x fc B (5 1 3 ) where fs t = Splitting tensile strength in psi fc = Compressive strength of concrete in psi A = Coefficient B = Coefficient Nilson (1991) noted that the split -cylinder strength is around 6 to 8 fs t = 6 x fc 1/2 (5 14) fs t = 8 x fc 1/2 (5 15) The relationship between compressive strength and the splitting tensile strength was developed and plotted in Figures 5 23 to 5 25. Figure 5 23. Correlation curve between splitting tensile and compressive Strength for Mix 1 PAGE 84 84 Figure 5 24. Correlation curve between splitting tensile and compressive Strength for Mix 2 Figure 5 2 5 Correlation curve between splitting tensile and compressive Strength for Mix 3 PAGE 85 85 As shown in Figur es 5 23 to 5 25, the actual splitting tensile strength of both mixes were low compared to the formulas suggested by Nilson (1991) for normal concrete. These low values might be explained by the use of # 57 limestone. The limestone used had a specific gravi ty of 2.45 compared to other coarse aggregates like gravel that have a specific gravity of 2.6 or more. The correlation formulas relating compressive to splitting tensile strength obtained from this study are the following: For Mix 1: fs t= 0.9535 x fc 0. 697 (5 16) For Mix 2 : fs t= 6.518 x fc 0.4756 (5 17) For Mix 3: fs t= 0.274 x fc 0.8775 (5 18) This research had shown once again, that existing correlation formulas to estimate splitting tensile from compressive strength a re not applicable for all mix designs. Each mix design has its own correlation formula. 5 .4.3 Relationship Between Splitting T ensile Strength and Flexural Strength The relationship between flexural strength and the splitting tensile strength was developed and plotted in Figu res 5 26 to 5 28. Figure 5 26. Correlation curve between splitting tensile and flexural s trength for Mix 1 PAGE 86 86 Figure 5 2 7 Correlation curve between splitting tensile and flexural s trength for Mix 2 Figure 5 2 8 Correlation curve between splitting tensile and flexural s trength for Mix 3 PAGE 87 87 Regression equations 5 19 to 5 21 were developed to present the best fit relationship between flexural strength and splitting tensile strength. For Mix 1: MR= 7.7783 x fs t 0.7472 (5 1 9) For Mix 2: MR= 0.5018 x fs t 1.2309 (5 20) For Mix 3: MR= 0.8013 x fs t 1.1488 (5 21) Popovics (1998) listed the strength and related properties of concrete as shown in Table 5 9 in order to present the ratio of splitti ng tensile streng th over flexural strength. There is not single ratio or even interval that can be used in order to correlate splitting tensile to flexural strength. In this study, the ratios were conducted in Tables 5 10, 5 12 and 5 14. A descriptive ana lysis was perform ed of the ratios ( Tables 5 11, 5 13 and 5 15). A confidence level of 95% was chosen for this research. The confidence interval is calculated using E quation 6 19: CI = Xave tcr [ SD/ (5 22) where : CI = 95% confidence interval Xave= averag e or mean value tcr= Critical tvalue = 1.96 from Table 5 8 SD= Standard deviation n= sample size (5) Table 5 8 Critical t values respected to the confidence level Confidence Interval Critical "t" Value 90% 0.1 1.65 95% 0.05 1.96 99% 0.01 2.58 99.50% 0.005 2.81 99.90% 0.001 3.29 PAGE 88 88 Table 5 9 Comparison between splitting and flexural strength Source: ( Popovics 1998) Table 5 10. Ratios of Splitting tensile over Flexural strength for Mix 1 Time (Days) Splitting Tensile (psi) Flexure ( ps i) Splitting Tensile/ Flexure 1 208 412 0.505 3 277 541 0.512 7 342 598 0.572 14 365 638 0.572 28 405 688 0.589 PAGE 89 89 Table 5 11. Descriptive analysis for the ratios of Mix 1 Mean 0.550 Standard Error 0.017 Median 0.572 Standard Deviation 0.039 S ample Variance 0.001 T he confidence interval for Mix 1 is calculated using E quation 5 22: CI= 0.5 5 1.96 [0.039/ 5] The 95% confidence interval is equal to [0. 52; 0.58]. When using Mix 1, there is 95% confidence that the ratio of the splitting tensile strength over the flexural strength lies between 0.52 and 0.58. Table 5 12. Ratios of s plitting tensil e over flexural strength for Mix 2 Time (Days) Splitting Tensile (psi) Flexure ( psi) Splitting Tensile/ Flexure 1 249 438 0.568 3 318 612 0.520 7 3 53 710 0.497 14 377 755 0.499 28 410 791 0.518 Table 5 13. Descriptive analysis for the ratios of Mix 2 Mean 0.552 Standard Error 0.016 Median 0.544 Standard Deviation 0.036 Sample Variance 0.001 The confidence interval for Mix 2 is calculated using E quation 5 22: CI= 0.522 1.96 [0.036/ 5] The 95% confidence interval is equal to [0.49; 0.55]. When using Mix 2, there is 95% confidence that the ratio of the splitting tensile strength over the flexural strength lies between 0.49 and 0.55. PAGE 90 90 Table 5 14. Ratios of Splitting tensile over Flexural strength for Mix 3 Time (Days) Splitting Tensile (psi) Flexure ( psi) Splitting Tensile/ Flexure 1 106 168 0.631 3 190 347 0.548 7 282 472 0.597 14 292 561 0.520 28 316 621 0.509 Table 5 15. Des criptive ana lysis for the ratios of Mix 3 Mean 0.561 Standard Error 0.023 Median 0.548 Standard Deviation 0.0519 Sample Variance 0.003 The confidence interval for Mix 3 is calculated using E quation 5 22: CI= 0.561 1.96 [0.0519/ 5] The 95% confidence interval is equal to [0.52; 0.61]. When using Mix 3, there is 95% confidence that the ratio of the splitting tensile strength over the flexural strength lies between 0.52 and 0.61. The results have shown once again that each mix de sign has its own relationship between splitting tensile and flexural strength. 5 .5 Estimating the Flexural and Splitting Tensile Strength using Existing Correlation Formulas In tilt up construction, to estimate the flexural strength of a concrete panel at the day of lifting is just as important as determining the compressive strength. The target of this section is to determine the flexural strength and splitting tensile strength of concrete using existing correlation formulas based on compressive strength. The results were PAGE 91 91 compared to the experimental data. This comparison is performed for the three mix designs studied in this research. A summary of the results at day 7 and day 28 are listed in Tables 516 and 517. Day 7 is chosen to be an early age date. Day 28 is chosen because most of the formulas were based on the 28 -day compressive strength. Table 5 16. Comparison between existing formulas and experimental results at day 7 Equation Mix 1 7day compressive strength 4,391 psi Mix 2 7day compressive st rength 4,622 psi Mix 3 7day compressive strength 2,332 psi Flexural Strength (psi) Splitting Tensile Strength (psi) Flexural Strength (psi) Splitting Tensile Strength (psi) Flexural Strength (psi) Splitting Tensile Strength (psi) Equation 5 5 7.5 x fc0.5 497 510 362 Equation 5 6 12 x fc0.5 795 815 579 Equation 5 7 2.3 x fc2/3 617 638 404 Equation 5 8 1.66 x fc0.71 640 664 409 Equation 5 9 1.572 x fc 0.71 606 629 387 RANGE 497 795 510 815 362 579 Experimental Results 598 710 472 Equation 5 14 6 x fc 0.5 398 407 289 Equation 5 15 8 x fc 0.5 530 543 386 RANGE 398530 407543 289386 Experimental Results 340 353 282 Table 5 16 shows that the experimen tal results for flexural strength of Mix -1 matched Equation 5 9 of the Florida State Road Department and Portland Cement Association As far as for Mix 2, only Equation 5 6 overestimated the flexural strength and the rest underestimated it. PAGE 92 92 On the other hand, all the formulas underestimated the flexural strength of Mix3 except Equation 5 6 from the ACI codes that overestimated it. The estimation of the splitting tensile strength resulted in both formulas overestimating the splitting tensile strength of concrete. As mentioned earlier, this may be due to the low specific gravity of #57 limestone used in the mixes. Table 5 17. Comparison between existing formulas and experimental results at day 28 Equation Mix 1 28day compressive strength 5 969 psi Mix 2 28day compressive strength 5 938 psi Mix 3 28day compressive strength 3 344 psi Flexural Strength (psi) Splitting Tensile Strength (psi) Flexural Strength (psi) Splitting Tensile Strength (psi) Flexural Strength (psi) Splitting Tensile Strength (psi) E quation 5 5 7.5 x fc0.5 579 578 433 Equation 5 6 12 x fc0.5 927 925 694 Equation 5 7 2.3 x fc2/3 757 754 514 Equation 5 8 1.66 x fc0.71 796 793 527 Equation 5 9 1.572 x fc 0.71 754 751 500 RANGE 579 927 578 9 25 433 694 Experimental Results 688 791 621 Equation 5 14 6 x fc 0.5 463 462 346 Equation 5 15 8 x fc 0.5 618 616 462 RANGE 463618 46261 346462 Experimental Results 405 410 316 Table 5 17 shows that the experimental results for flexural strength of Mix -2 matched Equation 5 8 of the Florida State Road Department and Portland Cement Association As for Mix 1, only Equation 5 5 underestimated the flexural strength and the rest overestimated it. PAGE 93 93 On the other hand, all the formulas underestimated the flexural strength of Mix 3 except Equation 5 6 which over estimated it. The estimation of tensile strength resulted in both formulas overestimated the splitting tensile strength of concrete. As mentioned earlier, this might be due to the low specific gravity of #57 limestone used in the mixes. It appears that the existing correlation formulas to determine flexural and splitting tensile strength based on the compressive strength are not valid for all mix d esigns at all times. Each mix design has its own correlation formulas that need to be determined by testing sample cylinders and beams. PAGE 94 94 CHAPTER 6 TILT UP PANEL INSTRUMENTA TION 6.1 Introduction What differentiates t ilt up wall design from a regular s h ear wall design is that the panels must be designed not only for the in-place service loads but also for the stresses that occur during lifting. Sometim es the lifting stresses require additional reinforcement beyond that required for the in -place service l oads (TCA 2005). No references were found whereby tilt up concrete panels have actually been instrumented and bending stresses measured in the field during tilting. On the other hand, many companies are using their own software to calculate the stresses in a panel during the lifting sequences as the panel rotates from zero to ninety degrees A major goal of this study is to determine the actual stresses in a tilt up wall panel during lifting from zero to ninety degrees. In order to achieve this target, a tilt up wall panel was designed, built, instrumented and lifted in a way that suited the laboratory available at the University of Florida. This chapter will provide detailed information about this process. 6.2 Panel Design Designing a tilt up wall panel w as not a major goal in this study, the purpose of this research was to analyze the actual stresses that occurred in a wall panel during lifting. Steinbiker & Associates Inc, a structural design firm, offered their staff and experience in order to design t he Panel (Figure 6 1). It was decided to use the facilities of the University of Florida in order to perform all the tests needed. In house facilities are less time consumi ng and cost effective. The Perry Construction Yard of the Rinker School of Buildin g Construction was chosen to be the place of casting and tilting the desired t ilt up panel. This facility has a two (2) tons capacity lifting crane. PAGE 95 95 The hook of the crane could reach a maximum of thirteen (13) feet height above the finished floor. The cap acity of the crane and its height were the major constrains in designing the panel. The weight of the panel and its height were limited due to these constrains. This is why the test panel used had a smaller scale than a typical panel built for a n actual pr oject. Figure 6 1. Panels Dinemsions as designed by Steinbiker & Associates Inc Thickness= 3.5 Inches 28day compressive strength = 4000psi Compressive strength at day of lifting = 2500psi. Reinforcement : #4 bars Two (2) Lifting inserts at 7 ft fro m the bottom A 4ft by 4ft opening 6.3 Preliminary Static Calculations Some of the preliminary static calculations were performed in order to determine at which angle of inclination the maximum stresses occurred. The locations of the maximum stresses were also determined. These preliminary static calculations helped in determining the locations where PAGE 96 96 to install the surface mount strain gages used in this research. These calculations were based on statics analysis. 6.3 .1 Sign C onvention and Assumption In the preliminary static calculations, a positive moment indicates a moment occurring on the bottom part of the panel. A negative moment indicates a moment occurring on the top part of the panel. The bottom part of the panel is the one facing the floor. The top part of the panel is the exposed one. In this section, the following calculations did not take into consideration any, suction, dynamic and/or load factors. The calculations were done using pure statics. Other preliminary static calculations shown in Appendix C took into consideration a suction factor of 1.5. 6.3.2 Critical Angle of Inclination It is important to estimate at which angle of inclination the maximum bending moments occurred. For simplicity, the panel was assumed to be a simply supported bea m with a uniformed applied dead load. This assumption is acceptable for a 1 wide x 2 high r igging system. Figure 6 2. Load, Shear, and Moment Diagrams for a simply supported beam PAGE 97 97 As shown in Figure 6 2, the maximum moment at zero degree inclination is computed from the following formula: M(max)= (WL)/8 (6 1) w here: W = weight of the panel (PLF) L = height of the panel 3) Figure 6 3. Angle of inclination during lifting From Equation 6 1, t he maximum moment calculated at a given angle of inclination is determined as : M = 8 The maximum m From the above calculation, the maximum stresses should occur at zero degrees of inclination. All the following calculations were performed at 0o inclination as it is considered the critical case. PAGE 98 98 6.3.3 Moments Calculations in the Y -Y Direction In order to find t he distributed weight of the wall, the panel was divided into thre e s ections as shown in Figure 6 4. This weight division was used in order to determine the stresses in the Y Y direction. Figure 6 4. Wall section divisions in order to determine stresses in the Y Y direction The Unit Weight of concrete used in these calculations is 150 lbs/ft W1 = Weight of section 1 W2= Weight of section 2 W3= Weight of section 3 NB: These calculations have not taken into consideration any suction, dynamic or load fac tors. W1 = 10ft x 3.5in x 1 ft/in x 150 pcf = 437.5 lb/ft 12 W2 = 6ft x 3.5in x 1 ft/in x 150 pcf = 262.5 lb/ft 12 W3 = 10ft x 3.5in x 1 ft/in x 150 pcf = 437.5 lb/ft 12 PAGE 99 99 The load, shear and moment diagrams of the panel at zero degree inclination are shown in Figure 6 5. Figure 6 5. Load, shear and moment diagram of the panel at zero degrees inclination(Y Y Direction) Reaction at A is the floor reaction. Reaction at B is considered equal to both inserts tension. The floor reaction at zero degrees inclination is 1006.3 lbs (Figure 6 5). Both lifters reactions are 2231.2 Lbs. Each insert had a tension of 2231.2/2 =1115.6 Lbs From the moment diagram it is shown that the maximum moment of 1,403.6 ft lbs will occur at 3.17 ft from the floor at the bottom a of the panel (Figure 6 5 and 6 -6). A moment of 875 ft lbs is also shown at 7ft from the floor at the top part of the panel. PAGE 100 100 Figure 6 6. Moments acting on the panel in the Y Y direction 6.3.4 St resses Calculations in the Y-Y D irection At 3.17 ft from the floor on the bottom part of the panel, the stresses were determined using Equation 6 2 Sb = M/ Sx (6 2) where: Sb = Bending Stress (psi) M= Bending Moment (in -lb) Sx= Section Modulu s(in) The section modulus is determined using equation (63) Sx= (bd)/6 (6 3) where: Sx= Section Modulus (in) b= width of the section studied (in) d= Thickness of the panel (in) Sx= (10f t 4 ft) x 12 (in/ft) x (3.5in) = 147 in 6 Sb = M/ Sx= 1,403.6 lb-ft x 12(in/ft) = 114.58 psi 147 in PAGE 101 101 The stresses at the bottom part of the panel, 3.17ft from the floor was estimated to be 114.58 psi. At 7 ft from the floor on the top part of the panel, the stresses were determined using Equation 6 2. Sx= bd = (10ft ) x 12 (in/ft) x (3.5in) = 245 in 6 6 Sb = M/ Sx= 875 lb-ft x 12(in/ft) = 42.86 psi 245 in The stresses at the top part of the panel 7ft from the floor were estimated to be 114.58 psi. 6.3.5 Wide Lift Analysis The wide lift analysis was performed in order to determine the stresses in the X -X direction across the inserts. In order to find the distributed weight of the wall, the panel was divided into three Sections as shown in Figure 6 7. This weight division was used in order to determine the stresses in the X -X direction. Figure 6 7. Wall section divisions in order to determine stresses in the X -X direction PAGE 102 102 The Unit Weight of concrete used in these calculations is 150 lb/in. W1 = Weight of section 1 W2= Weight of section 2 W3= Weight of section 3 NB: These calculations have not taken into consideration any suction, dynamic or l oad factors. From the Shear diagram in Figure 6 5, the base reaction is equal to 1006.3 lbs and the zero shear occurred at 3.17 ft from the floor. W1 = (9ft 3.17) x 3.5in x 1 ft/in x 150 pcf = 255.2 lb/ft 12 W2 = 4ft x 3.5in x 1 ft/in x 150 pcf = 175 lb/ft 12 W3 = (9ft 3.17ft) x 3.5in x 1 ft/in x 150 pcf = 255.2 lb/ft 12 From the analysis of finding the floor reaction and lifting te nsions, Figure 6 -5 showed that it is required to impose a reaction of 1,115.6 Lbs at each insert. Reaction at A and reaction at B should be equal (Figure 6 8). These reactions represent the tension of each lifting cable. These tensions should be equal to avoid any rotation of the panel during tilting. Figure 6 8 .Load diagram for the wide lift a nalysis after imposing equal reactions PAGE 103 103 Figure 6 9. Shear diagram for the wide lift a nalysis after imposing equal reactions Figure 6 10. Moment diagram for t he wide lift a nalysis after imposing equal reactions As shown in Figure 6 10, the moment diagram did not close at zero on the right side. In order to do that, a moment shift of 192.4 ft -lbs should be added to the right insert. The right insert would have a corrected moment of: 433.3192.4 = 625.7 ft lbs The moment at the left insert will remain: 404.86 ft lbs The central moment will remain: 484.98 lbs -ft The final Moment diagram considered is shown in Figure 6 11. PAGE 104 104 Figure 6 11.Moment diagram along th e X -X direction at the insert location 6.3.6 Stresses Calculations in the X -X direction at 7ft To convert moments to stresses, a 4 ft tributary width was used as shown in Figure 6 12. The stress at the right insert was calculated using Equation 6 3. Sb = M/ Sx= 625 .7 lb-ft x 12(in/ft) = 76.62 psi 4ft x 12(in/ft) x 3.5/ 6 The stress at the left insert was calculated using Equation 6 3 Sb = M/ Sx= 404.86 lb-ft x 12(in/ft) = 49.57 psi 4ft x 12(in/ft) x 3.5/ 6 The stress at 4.54ft from the edge was calculated using Equation 6 3 Sb = M/ Sx= 484.96 lb-ft x 12(in/ft) = 59.38 psi 4ft x 12(in/ft) x 3.5/ 6 PAGE 105 105 Figure 6 12. Four (4) feet tributary band 6.4 Finding Stresses Using 1.5 Suction Factor Following the same procedure described in Section 6.3, the stresses of the panel were determined using a suction factor of 1.5 at zero degrees inclination. The detailed calculations are provided in Appendix C. The comparison of the results is discus sed in Chapter 7. 6.5 Checking For Safety During the tilt up concrete construction process, when concrete panels are lifted off the casting slab or panel stacks, suction loads can occur. These add direct loading to the crane and lifting gear. In some situ ations the suction loads can cause lifting gear failure, structural crane damage or crane instability in the case of mobile cranes. Suction loads can also damage concrete panels. These loads should be considered as part of the dead load that the designer s hould take in PAGE 106 106 consideration. They occur at separation (lift off) from the casting bed. They may vary according to the finish of the panel and the type of form or casting bed. For concrete cast onto a steel bed, a 20% increase should be applied to the dead load. When casting concrete onto concrete casting beds, a 40% increase should be applied to the dead load. Where the casting bed has a profiled or textured surface the suction load may exceed 100% of the dead load. It is also important to take into cons ideration a dynamic factor due to the lifting. The size of the dynamic loading is mainly determined by the choice of the lifting equipment. The speed of lifting has also an influence. The Australian Standard AS 3850 (2003) requires that lifting inserts be designed, manufactured and installed such that the Working Load Limit (factor of safety) is at least 2.5 against failure. A minimum dynamic and impact factor of 20% of the dead load of the panel must also be incorporated into the design. If using a suctio n factor of 1.4 and a dynamic factor of 1.2, the safety factor considered should be greater than 1.4 x1.2= 1.68 at zero degree of inclination. It was important to make sure that the design panel could be lifted by the crane available in the Perri Construct ion Yard. The crane is an ER020L Hurrington Electric Chain Hoist. It has a 2 Tons lifting capacity. The lifting speed is 14ft/sec. The first constrain was that the height of the panel cannot exceed the height of the hook of the crane. Height of panel = 9f t < Height of the hook = 13ft (OK) The second constrain is not to exceed the two tons capacity of the crane. The weight of the Panel should not exceed the capacity of the crane. Panel Weight= [Gross Volume of the Panel Volume of the Opening] x Unit W eight of Concrete. PAGE 107 107 [9ft x 10ft X 3.5in /(12 in/ft) 4ft x 4ft X 3.5in /(12 in/ft) ] x 0.15 Kips/ft = 3.24Kips. Panel Weight = 3.24kips < Crane Capacity = 4 kips (OK) In order to be on the safe side the suction factor was taken into consideration. At z ero degrees the vertical reaction is around 1007 lbs (Figure 6 5). This will lead that the actual weight on the cables at zero degrees is: 3237lbs 1007 lbs = 2230 lbs. The factor of safety at zero degrees = Crane Capacity / Weight supported by cables = 4 000lbs/2, 230lbs = 1.794 > 1.68 (OK) In addition the full panel weight is considered at 90 degrees where there is no suction: Factor of safety at 90 degrees = Crane Capacity / Weight supported by cables =4 000lbs/3, 237lbs = 1.24 > 1.2 (OK). After check ing the safety of the design, the construction of the panel was the following step. The procedure of casting the slab, formwork and steel installation, and casting the panel are described in details in the following sections. 6.6 Panels Construction 6.6.1 Casting T he Slab The p anel was casted inside the Perry Construction yard of the University of Florida. The plan was to pour the panel on the slab floor. It was observed that the floor was not leveled. As a solution, an 11 ft by 11ft by 3.5 inches thick n ew slab was casted above the original laboratory floor slab. Plastic sheet s were used in order to prevent the concrete to be in touch with the original floor. BNG C onstruction provided the labors. 3.5 inches wood studs were used as formwork. PAGE 108 108 Figure 6 13 .Casting the slab. A) Pouring concrete. B) Leveling the slab 6.6.2 Formwork Steel reinforcement Two weeks of pouring the mud slab, the formwork was installed. The formwork used for this panel was 2 by 4 wood studs. These studs had 3.5 inches width whi ch matched exactly the thickness of the panel. Figure 6 14. Panel formed by 2 by 4 studs PAGE 109 109 The reinforcement used for this panel was the one suggested by Steinbicker & Associates who had designed the whole panel and its reinforcements. Figure 6 15. Des ign of reinforcement in panel Figure 6 16. Steel Reinforcement elevation One inch chair were used to support steel reinforcement at level 2. The steel reinforcement was provided by Gerdau Ameristeel from Jacksonville, Florida. The steel bars used are only s traight ones: PAGE 110 110 3 #4 x 0 ft 8in 3 #4 x 1 ft 8in 6 #4 x 3 ft 8in 4 #4 x 4 ft 0in 8 #4 x 8 ft 8in 8 #4 x 9 ft 8in 8 #4 x 1ft 6in (for inserts) Figure 6 17. Reinforced panel 6.6.3 Lifters The inserts us ed in this project were RL 24 p late anchor s provided by Meadow Burke. This plate is desi gned with a plate welded to the bottom to provide high pullout strength with a low profile. This design makes the anchor ideal for face and back lifts of thin-wall units and stripping, handling and erection applications. The inserts were reinforced by four (4) 18 long #4 rebar as shown in Figure 6 18 according to the manufacturer application manual. More than concrete cover was provided below the anchor. These plates were designed for a 2 ton Panel. PAGE 111 111 Figure 6 18. Inserts reinforced 6.6.4 Bond Breaker Three (3) days prior to pouring the slab, bond breaker agent was sprayed on the slab. The reinforcements were removed in order to spray the agent and then reinstalled afterwards. The Bond breaker used is J 6 WD from Dayton superior. BNG Construction pro vided the agent. Two coat of Sure -Lift were applied before casting the panel. The agent needed 2 hours to dry. The specifications of the b ond breaker are illustrated in Table 6 1. The functions of the bond breaker are: To enable a clean, complete separati on of the panel from the casting surface. To minimize the dynamic loading caused by suction at time of separation. To function as a curing compound for the casting surface. PAGE 112 112 Table 6 1. Physical and Chemical properties of the bond breaker Physical and Che mical properties General information Form Liquid Color Red Odor Slight Change in condition Melting point Undetermined Boiling Point 212 F Flash point 484 F Auto Igniting Product is not self igniting Danger of explosion Does not present an explosion hazard Vapor pressure at 68 F 17 mm Hg Density at 68 F 0.992g/cm Miscibility with water Not miscible or diffic ult to mix Solvent content Organic solvents 0.50% Water 90.40% Volatile Organic Compounds 88g/l 6.6.5 Casting the Panel The concrete used to cast this panel was provided by Cemex Ready Mix. The Mix used was the Mix 1 studied in Chapter 3. Cylinder and Beam specimen were also poured in order to validate the Maturity Method. Two maturity loggers were embedded inside the panel; one at 3.2ft from the bottom and the other at 7 ft. The location of the loggers was chosen to be where maximum stre sses were estimated to occur. PAGE 113 113 Figure 6 19. Casting the panel Figure 6 20. Starting up the maturity loggers embedded inside the panel PAGE 114 114 6 .7 Strain Gages Installation In tilt up construction, the panel is lifted from zero to ninety degrees. This process required the use of gages that have the capability of determining dynamic strains not static strains. Strain gages from Vishay Micro -measurements were selected to be installed on this panel. 6 .7.1 Strain Gage Reader and Recorder Two P3 strain indicators and recorders were used in order to determine the strain at different location of the panel during lifting. Each reader had 4 -four input channels. Four gages were connected to each Reader. Data, recorded at a rate of 1 reading per channel per second, was stored on a removable flash card and was transferred by USB to a laptop. The P3 Reader and Recorder specifications are : Four input channels Direct reading LCD display On board data storage Intuitive, menu driven operations Portable, lightweight and rugge d Quarter, half and full bridge circuit (Quarter bridge circuit used in this study). Automatic zero -balancing and calibration Basic Range: 31,000 microstrain (1 microstrain resolution) Accuracy: 0.1% of reading 3 counts. (at Gage Factor = 2.11) Gage F actor Settings: Range 0.500 to 9.900. Operational Environment: o Temperature 0 to + 50C o Humidity up to 90% RH PAGE 115 115 Figure 6 21. P3 Reader and Recorder 6 .7.2 Installation of Surface Mount Strain G ages With a stiff -bristled brush, the area where the gages sho uld be inst alled was scrubbed (Figure 6 22 A). Then the area was cleaned with isopropyl alcohol (Figure 6 22 B). Mean while the gages were prepared on a cleaned plastic straight surface by taping them from the top (Figure 6 22 C). Layout lines were marked in order to highlight the location of the center of the gages. Application of a 100%-solids adhesive to the gaging area will provide a suitable gage -bonding surface. M Bond AE 10 was used for this purpose. The M -Bond was also applied to the bottom surfa ce of the gages in order to assure a high bondage (Figure 6 22 D and E). After bonding the gages to the concrete, silicone rubbers were put above the gage (Figure 6 22 F). Then around 5psi of pressure was applied on the top of the gages (Figure 6 23). Aft er six hours, the tape was removed from the top part of the gages. M -Bond AE 10 was then applied to the top surface of the gages in order to keep it clean and safe from the environment. PAGE 116 116 Figure 6 22. Surface mount strain gages installation. A) Scrubbing. B) Cleaning. C) Preparing the gages D) Epoxy the gages. E) Gages Installed. F) Rubber band between the gages and the bricks PAGE 117 117 Figure 6 23. Bricks laid on top of gages to assure enough pressure for bonding 6 .7.3 Strain Gages Location The gages were inst alled were the maximum moments were expected. Figure 6 24 shows the layout location of the gages. Six Gages were installed along the Y axis and Two Gages along the x axis. The critical sections of this panel during lifting were the sections near the insert s and at 3.7 ft from the bottom of the wall. PAGE 118 118 Figure 6 24. Strain gages location 6 .8 Lifting the Panel In tilt up construction, the panels were usually lifted between 7 to 14 days after casting. In this study, it was intended to lift the panel at day 10 Strengths of the panel at day of tilt were discussed in details in Chapter 7. Before pouring the panel a steel plate was embedded at the edge of the panel. A digital level was attached to that plate in order to determine the angle of inclination. The bas e of the level was magnetic so it could stick to the steel plate. PAGE 119 119 Both stain gage readers were synchronized. Before starting the lifting, the readers were turned on. The time showing on the readers was video recorded for the first 30 seconds. The video cam era was turned on since then till the end of the tilting process. Then the camera was moved to record the digital leveling from zero to ninety degrees inclination. This way it will be very easy to recognize at what time the level reached a certain degree o f inclination. Then, using the data recorded in the readers, the strain at that time will be checked. This is how the strains were determined at each angle of inclination. The process of lifting is illustrated from Figure 6 25 to Figure 6 29. Figure 6 25. Panel set up before lifting PAGE 120 120 Figure 6 26. Recording the Reader Screen for 30 sec. before tilting. (In this picture, it is shown that the reader was recording since 17 sec) Figure 6 27. Digital reader at 60 degrees inclination PAGE 121 121 Figure 6 28.Video reco rding the digital level readings Figure 6 29. Panel lifted at 90 degrees inclination PAGE 122 122 CHAPTER 7 STRESS ANALYSIS OF A TILT -UP PANEL DURING LIF T ING 7.1 Introduction In this study, a wall panel has been instrumented with surface mount strain gages where ac tual strains were computed on site during the lifting process from zero to ninety degrees inclination. Results extracted form the field were compared to several tilt up design software used by designers nowadays. As mentioned previously, the design of the panel was performed by Steinbicker & Associates Inc. This design was sent to four different tilt up design companies. The panel was generated into each of the companys software. The purpose of the software analysis was to determine the stresses of the pan el during lifting from zero to ninety degrees. The software results were compared to both preliminary static calculations performed in this study as well as to real field data collection. Figure 7 1 shows the annotations for the surface mount strain gages used during the lifting process. Figure 7 1. Annotations of the strain gages installed on top surface of the panel PAGE 123 123 7.2 Critical Angle of Inclination The four Software results showed that the maximum stresses occurred at an angle of zero degrees. The pr eliminary static calculations in Chapter 6 led also to the same outcome. This is why the preliminary static calculations were only performed at this angle. Just two of the companies had determined the stresses at different angle of inclination. The other t wo only found stresses at zero degrees inclination. One company used a finite element modeling software. All software results are shown in Appendix D 7.3 Field Data Collection Table 7 1 shows the strains collected during the l ifting of the panel at the P erry Construction Yard. The strain gages were installed on the top face of the panel. A positive strain recorded by the reader indicates that the panel is in tension at the loca tion of the gage A negative strain recorded by the reader indicates that the p anel is in compression at the location of the gage. Table 7 1. Strain data collection Angle Strain (in/in) Strain (in/in) Strain (in/in) Zero degrees A1 0.00004 A3 0.000014 A2 0.00002 A4 4.1 x 10 5 B4 0.000012 B3 1.6 x 10 5 B2 4.3 x 10 5 B1 0.000024 15 degrees A1 3.7 x 10 5 A3 0.000011 A2 0.00002 A4 3.9 x 10 5 B4 0.000008 B3 1.4 x 10 5 B2 4.2 x 10 5 B1 0.000023 30 degrees A1 3.2 x 10 5 A3 0.000012 A2 0.000022 A4 3.4 x 10 5 B4 0.000008 B3 9 x 10 6 B2 3.6 x 10 5 B1 0.000024 45 degrees A1 2.8 x 10 5 A3 0.000012 A2 0.000018 A4 0.00003 B4 0.000008 B3 0.00001 B2 3.2 x 10 5 B1 0.000022 PAGE 124 124 Table 7 1. C ontinued Angle Strain (in/in) Strain (in/in) Strain (in/in) 60 degrees A1 2.3 x 10 5 A3 0.000012 A2 0.000013 A4 2.5 x 10 5 B4 0.000007 B3 1.1 x 10 5 B2 2.6 x 10 5 B1 0.000018 75 degrees A1 1.4 x 10 5 A3 0.00001 A2 0.000004 A4 1.9 x 10 5 B4 0.000005 B3 1.2 x 10 5 B2 1.8 x 10 5 B1 0.000012 89 degrees A1 4 x 10 6 A3 0.000003 A2 0.000001 A4 6 x 10 6 B4 0.000001 B3 4 x 10 6 B2 5 x 10 6 B1 0.0 00004 Table 7 1 1 shows that the maximum strains occurred at zero angle of inclination which was determined by all Software and Preliminary static calculations done in this study. The strains started to decrease when the angle of inclination was increased The maximum strains were recorded by gages A1, A4 and B2 which are located at 3.2 ft above the floor in the Y Y direction. 7.4 Comparing the Stresses In this study analysis, the tiltup panel is considered as simply supported beam. In concrete stress an alysis, the stress at the top surface of the panel is equal but opposite sign to the stress at the bottom side of the panel if the panel was not reinforced as shown in Figure 7 2. In this study, the reinforcements are located at the neutral axis of the pan el. The stress at the top surface of the panel is still estimated to be equal to the stress at the bottom surface of the panel but opposite sign. With this assumption, a comparison between field data collection, software results and preliminary static calculations was conducted. PAGE 125 125 Figure 7 2. Stress distribution of the panel 7.3 From Strains to Stresses In order to find the stresses in the panel, Equation 7 1 was applied Sb= (7 1 ) where: Sb = Bending Stress (psi) E= Modulus of Elasticity (psi) 7.4 Modulus of Elasticity The modulus of elasticity was determined according to ASTM C 469 standard. The chord modulus of el asticity of concrete cylinders was determined when a compressive load is applied on a concrete cylinder in longitudinal direction. Figure 7 3 shows the equipment used to perform the test. A linear variable differential transformer (LVDT) was used to measure the deformation of the concrete cylinder during the compression test. The modulus of elasticity was determined according to E quation 7 2 : E= (S2-S1)/( 21) (7 2 ) where E= chord modulus of elasticity, psi S2= stress corresponding to 40% of ultimate load, psi S1= stress corresponding to a longitudinal strain 1 2= longitudinal strain produced by stress S2 PAGE 126 126 At the day of tilting, the comp ressive strength of the cylinders was determined to be 5,100psi according to ASTM C39 standard. The 40% of ultimate compressive strength of concrete specimen at day of lifting was S2 = 5100 x 0.4= 2,040 psi. 1 was taken to be 5.625 x 105. The stress S2 that corresponded to 1 was determined to be 200 psi. The modulus of elasticity was determined according to Equation 7 2 : E= (2,040 psi 200 psi)/ (5.25 x 104 5.625 x 105) E= 3.84 x 106 psi The modulus of elasticity of concrete at day of tilting w as determined to be 3.84 x 106 psi. Figure 7 3. T est set up for determining the m odulus of elasticity PAGE 127 127 7.5 Stresses Comparison In order to understand the location of the stresses, point A in Figure 7 1 is considered the center of the X Y axis. X (A) = 0 ft; Y ( A) = 0 ft In the following analysis, the tresses were followed by the letter B implementing stresses occurring at the bottom surface of the panel and by the letter T top surface of the panel. All the field data results are collected from the top surface; this is why they are all followed by T. Table 7 2. Stresses at Zero Degrees Inclination in the Y Y Direction Stress (psi) x (ft) y ft) Stress (psi) x (ft) y (ft) Stress (psi) x (ft) y (ft) Static Calculations (Suction Free) 115B X 3.17 1 15B X 3.17 115B X 3.17 Static Calculations (With Suction) 172B X 3.17 172B X 3.17 172B X 3.17 Software 1 115B X 3.17 115B X 3.17 115B X 3.17 Software 2 112B X 3.1 112B X 3.1 112B X 3.1 Software 3 111B X 3.17 111B X 3.17 111B X 3.17 Software 4 170B 1.78 3.17 X X X 180B 9 3.17 Field results 154T 1 3.17 157T 3 3.17 165T 9 3.17 Static Calculations (Suction Free) 43T X 7 43T X 7 Static Calculations (With Suction) 64T X 7 64T X 7 Software 1 42T X 7 42T X 7 Software 2 45T X 6.96 45T X 6.96 Softwar e 3 45T X 7 45T X 7 Software 4 150T 1.78 7 160T 7.78 7 Field results 54T 3 7 46T 9 7 From T able 7 2, the stresses at zero degrees inclination are shown. At 3.17 ft, software 1,2 and 3 and preliminary static calculations without a suction factor obtain ed similar stresses (112 psi 115 psi) It seems that S oftware s 1, 2 and 3 were not taking into consideration any suction factor. On the other hand, Software 4 had high stresses (170 psi 180 psi) at this elevation. The preliminary static calculation wi th a 1.5 suction factor got a stress of 172 psi at 3.17 ft. The data collected show a stress variation between 154 psi and 165 psi. Not to forget that the stresses obtained from the software at this elevation are the one applied on the bottom surface of t he PAGE 128 128 P anel. The strains recorded by the reader are for the top surface of the panel. It is shown that Software s 1, 2 and 3 were underestimating the stresses in the panel at 3.17 ft. Software 4 was to close. The preliminary static calculations with a suctio n factor were also close in predicting the stresses at 3.17 ft. As it is shown, Software s 1, 2, 3 and the preliminary static calculations assumed that the stresses across the panel a t 3.17ft were the same. The field data collected showed that they are clos e but not the same. Moving to analyze the stresses in the Y Y direction at or near the inserts, it is observed that Software 4 overestimated the stresses at the inserts. But not to forget that the strain gages were not measuring the stresses exactly at t he inserts. The gages were shifted a foot to the right. This is why the stresses at the gages should be less than the stresses determined at the inserts. Software s 1, 2, 3 and preliminary static calculation s without suction factor underestimated the stress es at the left inserts. Using a suction factor of 1.5 shows a stress of 64 psi at the insert compared to 54 psi a foot to the right. Moving to the right insert stress analysis, Software 2 and 3 estimated a very close value of stresses at the one recorded ( 46 psi). Software 4 overestimated the stress. Table 7 3 shows the stresses in the x -x direction near the inserts. The strain gages were located 6 inches below the inserts. The expected recorded value of the reader should be less than the stresses at the l ocation of the inserts. Table 7 3 Stresses at zero degrees i nclination in the X -X d irection Stress x (ft) y ( ft) Stress (psi) x (ft) y (ft) Stress x (ft) y (ft) (psi) (psi) Static Calculations (Suction Free) 50T 1.78 7 59B 4.5 7 77T 7.78 7 Sta tic Calculations (With Suction) 74T 1.78 7 84B 4.5 7 115T 7.78 7 Software 1 49T 1.78 7 53B 4.5 7 76T 7.78 7 Software 2 X X X X X X X X X Software 3 49T 1.78 7 46B 4.41 7 71T 7.78 7 Software 4 160T 1.78 7 X X X 180T 7.78 7 Field results 77T 1.78 6. 5 61 T 4.78 6.5 92T 7.78 6.5 PAGE 129 129 Table 7 3 shows that Software 4 overestimated the stresses by 100%. Software 1, 2 and 3 underestimated the stresses. Preliminary static results with suction factor of 1.5 were the closest. The stresses at the left insert were u nderestimated by all. For the stresses at the right insert, the preliminary static calculation obtained reasonable stresses (115 psi) which are and should be little higher then the recorded ones (92 psi). Only Software s 1 and 2 provided the stresses at dif ferent angle of inclination. Those stresses were compared to each other and to the field measurements. Tables 7 4 through 7 12 illustrate the stresses occurring at different locations from 15 to 80 degrees angle of inclination. Table 7 4. Stresses at fifte en (15) degrees inclination in the Y Y d irection Stress (psi) x (ft) y ft) Stress (psi) x (ft) y (ft) Stress (psi) x (ft) y (ft) Software 1 111B X 3.17 111B X 3.17 111B X 3.17 Field results 142T 1 3.17 150T 3 3.17 161T 9 3.17 Software 1 41T X 7 41T X 7 Field results 42T 3 7 31T 9 7 Table 7 5. Stresses at thirty (30) degrees inclination in the Y Y d irection Stress (psi) x (ft) y ft) Stress (psi) x (ft) y (ft) Stress (psi) x (ft) y (ft) Software 1 100B X 3.17 100B X 3.17 100B X 3.17 Software 2 100B X 2.76 100B X 2.76 100B X 2.76 Field results 123T 1 3.17 131T 3 3.17 138T 9 3.17 Software 1 36T X 7 36T X 7 Software 2 52T X 6.96 52T X 6.96 Field results 46T 3 7 31T 9 7 Table 7 6. Stresses at forty (40) degrees inclination in the Y Y d irect ion Stress (psi) x (ft) y ft) Software 1 88B X 3.17 Software 2 91B X 2.48 Software 1 33T X 7 Software 2 57T X 6.96 PAGE 130 130 Table 7 7. Stresses at forty five (45) degrees inclination in the Y Y d irection Stress (psi) x (ft) y ft) Stress (psi) x (ft) y (f t) Stress (psi) x (ft) y (ft) Field results 108T 1 3.17 115T 3 3.17 123T 9 3.17 Field results 46T 3 7 30T 9 7 Table 7 8. Stresses at fifty (50) degrees inclination in the Y Y d irection Stress (psi) x (ft) y ft) Software 1 74B X 3.17 Software 2 79 B X 2.10 Software 1 27T X 7 Software 2 63T X 6.96 Table 7 9. Stresses at sixty (60) degrees inclination in the Y Y d irection Stress (psi) x (ft) y ft) Stress (psi) x (ft) y (ft) Stress (psi) x (ft) y (ft) Software 1 57B X 3.17 57B X 3.17 57B X 3.17 Software 2 65B X 1.6 65B X 1.6 65B X 1.6 Field results 88T 1 3.17 96T 3 3.17 100T 9 3.17 Software 1 21T X 7 21T X 7 Software 2 71T X 6.96 71T X 6.96 Field results 46T 3 7 27T 9 7 Table 7 10. Stresses at seventy (70) degrees inclinat ion in the Y -Y d irection Stress (psi) x (ft) y ft) Software 2 49B X 1.0 Software 2 79T X 6.96 Table 7 11. Stresses at seventy five (75) degrees inclination in the Y Y d irection Stress (psi) x (ft) y ft) Stress (psi) x (ft) y (ft) Stress (psi) x (f t) y (ft) Software 1 29B X 3.17 29B X 3.17 29B X 3.17 Field results 54T 1 3.17 73T 3 3.17 69T 9 3.17 Software 1 11T X 7 11T X 7 Field results 38T 3 7 19T 9 7 PAGE 131 131 Table 7 12. Stresses at eighty (80) degrees inclination in the Y Y d irection St ress (psi) x (ft) y ft) Software 2 45B X 1.0 Software 2 87T X 6.96 It is remarkable that S oftware s 1 and 2 that provided the stresses from zero to ninety degrees were most of the time underestimating the stresses. For instance at thirty degrees incl ination, stresses obtain ed in the field at 3.17 ft were 20 to 40 % higher than the predicted ones from the software. At 7 ft Software 2 was overestimating and Software 1 was underestimating near the left insert and overestimating near the right one. A big difference was seen between Software s 1 and 2 whi le determining the stresses at 7 ft in the y -y direction.Software 1 estimated that the stresses were decreasing from zero to ninety degrees. Software 2 assumed that the stresses were increasing. The data collected showed that stresses at 7 ft were slowly decreasing while lifting. High stresses at zero degrees were expected if suction is considered. This is why the stresses obtained by software 1, 2 and 3 were underestimating the stresses. Software 4, whic h has a finite element feature, estimated well the stresses at 3.17 ft at zero degrees inclination. Not to forget, that the strains recorded by the gages determine the stresses at the top of the panel and the stre sses obtained from the software are the one occurring at the bottom part of the panel at 3.17ft. On the other hand, any mislocation of the reinforcement during the construction will affect the stresses. The top stresses will not be equal to the bottom stresses anymore and that will influence all t he results. Concerning the stresses near the inserts, the gages were installed one foot away form the inserts at 7 ft for the y -y direction and 6 inches below the insert for the x-x direction. The strains PAGE 132 132 recorded by the gages at those location are not nec essary the stresses at the inserts. Therefore, the comparison of the stresses at that location is difficult. Data collected in the field during tilting from 15 to 90 degrees, shows that the results are 20% to 40 % more than determined by Software 1 and 2 at different angle of inclination at 3.17ft. The 20 % increase is justified by the dynamic factor that is usually estimated to be 1.2 according to Australian Standards. Another factor that might influence the data collection is the position the slings. Dur ing the lifting, the slings were not all the time in a vertical position. This might put more pressure to the panel and cause higher bending moment. 7.6 Summary of Results The target of this section is to summarize the most critical case scenario at the t ime of lifting where the maximum stresses occurred. The designer is usually interested in the worst case scenario in order to design a tilt up panel. The maximum stresses occurred at zero degrees inclination in the Y Y direction. This is why this summary is performed at this angle of inclination. Figure 7 4 shows all the different stresses obtained in this study at 3.17ft and at 7ft in the Y Y direction at zero degrees inclination. The average values of the stresses showed in Table 7 2 were implemented in this Figure 7 4 in order to simplify the comparison between the stresses obtained from different sources. From Figure 7 4, it is shown that the stresses estimated by Software 4 and the Static calculations considering a 1.5 suction factor were very close to the experimental data at 3.17ft. On the other hand, the other software estimations were close to the Static Calculation without suction factor. At 7 ft, Software 4 estimated the stresses at the inserts. The data collected from the experiment estimated the stresses a foot away from the inserts. The other software PAGE 133 133 estimations considered constant stresses at 7 ft from edge to edge. This is why the results of Software 4 cannot be directly compared to the data collected. The other software results estimated the stresses to be approximately 11% less than the actual stresses determined by the instrumented panel. Figure 7 4. Stresses in the Y Y direction at zero degrees inclination Stresses at 3.17 ft Stresses at 7 ft PAGE 134 134 CHAPTER 8 CONCL U SION AND RECOMMANDAT IONS 8.1 Conclusion The survey illustrat es the current practice of determining the strength of concrete before lifting a tilt up wall panel. It is required by building code s to determine the compressive and the flexural strength s of the wall panel before lifting the tilt up panel Today, some of the contractors only determine the compressive strength and use a correlation formula to predict the flexural strength. Flexural strength testing is normally conducted by the center -point flexural strength method instead of the third-point flexural test in order to determine the flexural strength of concrete. Previous researcher s have shown that the center -point loading test overestimates the flexural or bending strength of the concrete by 15 to 25 percent because it includes both shear and bending stresse s In this study, the maturity method, a nondestructive method of determining the strength of concrete at early age, was evaluated. The use of the maturity method was found to be an effective tool to predict the compressive and flexural strengths of the in -place concrete at time of lifting. Furthermore, correlation curves and formulas were developed relating the compressive, flexural and splitting tensile strength of concrete. These curves were generated for three different mix -designs, incorporating pla in, fly ash and slag cement, used currently in the tilt up concrete industry. The correlation curves showed that each mix design has its own correlation formulas. The results showed that the use of pre -existing formulas under or over -estimated the strength of concrete at different ages. Moreover, a small scale tilt up panel was instrumented with surface mounted strain gages in order to determine the stresses of the panel during lifting. Simultaneously the panel PAGE 135 135 dimensions were sent to four different tilt up design companies. The anticipated stresses were predicted using their in -house software. Preliminary hand calculations based on statics analysis were also performed in order to find the stresses. The data collected from the instrumented panel, software predictions and preliminary calculations were compared. The results showed a variation in stresses calculated by different tiltup design companies using their software as well as some differences to the measured stress values obtained from the instrument ed panel. 8.2 Recommendations This study targeted two major areas in tilt up construction: finding the strength of the concrete using the maturity method and determining the actual stresses of a tilt up panel during lifting. The following recommendations constitute some suggestions and recommendations for tilt up construction companies and for future research needs. 8.2.1 Maturity Method 8.2.1.1 For the industry The use of the maturity method as specified in ASTM C 1074 is recommended for determining the in -place compressive and flexural strength of reinforced concrete wall panels at any time of tilt. If the maturity method is not used, it is recommended to determine the compressive strength and third -point flexural strength of cylinders and beam specimens respectively. This is best accomplished by testing cylinders and beams cast from the same concrete mixture used to cast the wall panels, cured in place adjacent to the wall panels, and tested at time of tilt. 8.2.1.2 For future studies Evaluate the effect of using one or more mineral admixtures on the determination of the datum temperature Perform a similar effort using maturity loggers programmed for the Arrhenius method to determine the in place strength of the reinforced concrete wall panels and compa re the results to the Nurse -Saul Method. Evaluate the maturity method to determine the in-place strength using the Nurse Saul and Arrhenius equations for structural lightweight concrete tilt up wall panels. PAGE 136 136 8.2.2 Panel Instrumentation 8.2.2.1 For the indu stry It is suggested that tilt up designers evaluate the data obtained in this study to evaluate their proprietary in house software for predicting concrete stresses during the tilt up operation. 8.2.2.2 For future studies It is recommended that the liftin g inserts are also instrumented with strain gauges as well as the reinforced concrete in the area of maximum bending moments. It is recommended that a full size panel is instrumented in a similar fashion as described in this work. If the concrete wall pan el thickness requires two layers of steel, it is further recommended that the reinforcing steel be fitted with instrumented rebar strain meters, welded into the rebar cage, to determine the actual strain in -situ of a tilt up wall panel during erection. PAGE 137 137 APPENDIX A QUESTIONNAIRE PART 1: DEMOGRAPHIC QUESTIONS 1. What are your job functions? (Please circle all that apply) a Executive (CEO, Owner, VP, etc) bOperations Management (Project Manager, Project Engineer, etc) c Field Operations (Superintendent, Foreman, etc) dSkilled Labor (Operator, Carpenter, Steel Worker, Welder, etc) e Other (Please describe) ________________________________________________________ 2. Length of service in current company: a Less than 5 years c 11 to 20 years b5 to 10 years dOver 20 years 3. Overall Business Experience: a Less than 5 years c 11 to 20 years b5 to 10 years dOver 20 years 4. Companys annual volume: a Less than $50 million c $10 0 to $499 million b$50 to $99 million d$500 million & Over 5. Number of employees : a Less than 50 c 100 to 499 e 1000 and over b50 to 99 d500 to 999 6. Companys Active Region/Location: (Please circle all that apply) a No rtheast c Midwest bSoutheast dSouthwest e West PART 2 TILT UP CONSTRUCTION QUESTIONS 1. What types of concrete strength properties does your company measure before lifting a tilt up panel? (Please Mark an X in all boxes that apply) Day of lifting 7 day required strength 14 day required strength 28 day required strength Compressive strength Tensile strength Flexural (Bending) Strength Other, Please specify: __________________ 2.What is the norm al time for lifting a panel? (Please circle all that apply) a. Less than 5 days b. 5 to 7 days c. 7 to 10 days d. 10 to 14 days e. Other, Please specify: ________________________________________________________ PAGE 138 138 3If interested in finding the compressive strength of the panel before lifting, your company will perform: (Please circle all that apply) a. Compression test for cube specimens b. Compression test for cylinder specimens c. Maturity Method to find the compressive strength d. Use correlation formul as: Please specify: ______________________________________________ e. Use the information provided by the concrete mix design provider. f. No need to find the compression strength 4If interested in finding the tensile strength of a tiltup panel before lifting, your company will perform: (Please circle all that apply) a. Perform the splitting Tensile Test for cylinder specimen b. Use correlation formulas: Please specify: ______________________________________________ c. Use the Maturity Method to find t he tensile strength d. Use information provided by the concrete mix design provider. e. No need to find the tensile strength 5If i nterested in finding the Flexural ( Bending) strength of the panel before lifting, your company will perform: (Please Circl e all that apply) a. Perform the Third point (four point) Flexure Test for beam specimens b. Perform the Three point flexure test for beam specimens c. Perform the Maturity Method to find the flexure strength d. Use correlation formulas: Please specify: __ _____________________________________________ e. Use the information provided by the concrete mix design provider. f. Other, Please specify: ______________________________________________________________ g No need to find the Flexure strength 6The speci mens to be tested in order to find the required strength of the concrete are stored: (Please circle all that apply) a. In a laboratory b. On site near the panels c. Other: __________________________________________________________________________ 7Do the specimens that are tested have the same curing conditions as the corresponding panels to be lifted? a. No b. Yes, How? _______________________________________________________________________ c. No need for testing specim ens to find the required strengths 8Have you ever used maturity testing data for estimating concrete strength? a. Yes b. No 9If yes to question #8, have you or your company performed or had a testing company perform maturity testing for concret e in order to find: (Circle all that apply) a. Compressive Strength b. Tensile Strength c. Flexure (Bending) Strength d. Other, Please specify: _____________________________________________________________ e. Never used this method 10 If no to questi on #8, would your company be willing to use the results of the Maturity Testing Method in lieu of those from compressive/flexure strength testing? a. Yes b. No, why?_______________________________________________________________________ c. Already using the Maturity Method PAGE 139 139 APPENDIX B TEMPERATURE AND MATURITY DATA RECORDED BY MATURITY LOGGERS Figure B 1. Temperature Vs Time for the first beam sample of Mix 1 Figure B 2. Maturity Vs Time for the first beam sample of Mix 1 PAGE 140 140 Figure B 3. Temperature Vs Time for the second beam sample of Mix 1 Figure B 4. Maturity Vs Time for the second beam sample of Mix 1 PAGE 141 141 Figure B 5. Temperature Vs Tim e for the first cylinder sample of Mix 1 Figure B 6. Maturity Vs Time for the first cylinder sample of Mix 1 PAGE 142 142 Figure B 7. Temperature Vs Time for the second cylinder sample of Mix 1 Figure B 8. Maturity Vs Time for the second cylinder sample of Mix 1 PAGE 143 143 Figure B 9. Temperature Vs Time for the first beam sample of Mix 2 Figure B 10. Maturity Vs Time for the first beam sample of Mix 2 PAGE 144 144 Figure B 11. Temperature Vs Time for the second beam sample of Mix 2 Figure B 12. Maturity Vs Time for the second beam sample of Mix 2 PAGE 145 145 Figure B 13. Temperature Vs Time for the second cylinder sample of Mix 2 Figure B 14. Maturity Vs Time for the second cylinder sample of Mix 2 PAGE 146 146 Figure B 15. Temperature Vs Time for the first beam sample of Mix 3 Figure B 17. Ma turity Vs Time for the first beam sample of Mix 3 PAGE 147 147 Figure B 18. Temperature Vs Time for the second beam sample of Mix 3 Figure B 19. Maturity Vs Time for the second beam sample of Mix 3 PAGE 148 148 Figure B 20. Temperature Vs Time for the first cylinder sample of Mix 3 Figure B 21. Maturity Vs Time for the first cylinder sample of Mix 3 PAGE 149 149 Figure B 22. Temperature Vs Time for the first logger embedded in the UF Hough Hall Panel Figure B 23. Maturity Vs Time for the first logger embedded in the UF Hough Hall Pa nel PAGE 150 150 Figure B 24. Temperature Vs Time for the second logger embedded in the UF Hough Hall Panel Figure B 25. Maturity Vs Time for the second logger embedded in the UF Hough Hall Panel PAGE 151 151 Figure B 26. Temperature Vs Time for the first logger embedded in the small scale panel Figure B 27. Maturity Vs Time for the first logger embedded in the small scale panel PAGE 152 152 Figure B 28. Temperature Vs Time for the second logger embedded in the small scale panel Figure B 29. Maturity Vs Time for the second logger embedded in the small scale panel PAGE 153 153 APPENDIX C STRESSES AT ZERO DEG REES INCLINATION USING 1.5 SUCTION FACTOR Floor and lifters reactions (Y -Y) Direction The critical case is at zero degree inclination. In order to find the distributed weight of the wa ll, the panel was divided into three Sections as shown in Figure C 1. The Unit Weight of concrete used in these calculations is 150 pcf. W1 = Weight of section 1 W2= Weight of section 2 W3= Weight of section 3 W1 = 10ft x 3.5in x 1 ft/in x 150 pcf = 437. 5 lb/ft 12 W2 = 6ft x 3.5in x 1 ft/in x 150 pcf = 262.5 lb/ft 12 W3 = 10ft x 3.5in x 1 ft/in x 150 pcf = 437.5 lb/ft 12 Updated loads after addin g: Suction factor of 1.5 W1= 437.5 lb/ft x 1.5 x 1= 656.25 lb/ft W2= 262.5 lb/ft x 1.5 x 1= 393.75 lb/ft W3= 437.5 lb/ft x 1.5 x 1= 656.25 lb/ft Figure C 1. Sections of the Panel PAGE 154 154 The Free -body, Shear and moment diagrams of the panel at zero de gree inclination is shown in figure C 2. Reaction at A is the floor reaction. Reaction at B is the inserts tension. Figure C 2. Load, Shear and moment diagrams of the panel at zero degrees inclination PAGE 155 155 Figure C 3. Moments acting on the panel in the Y Y direction The floor reaction at zero degrees inclination is 1,811.25 lbs (Figure C 2). Both lifters reactions are 3346 Lbs. Each insert had a tension of 3346/2 =1673 Lbs From the moment diagram it is shown that the maximum moment of 2,105.5 ft lbs will o ccur at 3.17 ft from the floor bottom of the panel. From Moments to strains (yy) At 3.27 ft from bottom Sx= bd = (10ft 4 ft) x 12 (in/ft) x (3.5in) = 147 in 6 6 2,105.5 lb-ft x 12(in/ft) = 171.88 psi 147 in At 7 ft from bottom PAGE 156 156 Sx= bd = (10ft ) x 12 (in/ft) x (3.5in) = 245 in 6 6 1312.5 lb-ft x 12(in/ft) = 64.29 psi 245 in Wide Lift Analysis ( X -X Direction) This is performed in order to find the strain in the X -X direction across the inserts Base reaction= 1509.4 lbs Zero shear at y= 1509.4 lbs (1ft x 10 ft x 3.5in x (1/12) ft/in x 150 pcf x 1.5 )= 2.1667ft 6 ft x 3.5in x (1/12) ft/in x 150 pcf x 1.5 The zero shear occurred at 2.1667 ft above the opening, which means 3.1667ft from the bottom of the panel as shown also in figure 2. In order to find the distributed weight of the wall that will be carried by the lifters, the panel was divided into three Sections as shown in Figure C 4. Figure C 4. Sections to find load distribution at inserts in X -X directions The Unit Weight of concrete used in these calculations is 150 pcf. W1 = Weight of section 1 W2= Weight of section 2 W3= Weight of section 3 W1 = (9ft 3.1667ft) x 3.5in x 1 ft/in x 150 pcf x (1.5) = 382.81 lb/ft 12 PAGE 157 157 W2 = 4ft x 3.5in x 1 ft/in x 150 pcf x (1.5) = 262.5 lb/ft 12 W3 = (9ft 3.1667ft) x 3.5in x 1 ft/in x 150 pcf x (1.5) = 382.81 lb/ft 12 From the analysis of finding the floor reaction and lifting tensions, figure C -2 showed that it is required to impose a reaction of 1811.25 Lbs at each insert. Reaction at A and reaction at B should be equal (Figure C 5). These reactions represent the tension of each lifting cable. These tens ions should be equal to avoid any rotation of the panel during tilting. Figure C 5 .Load Diagram for the wide lift Analysis after imposing equal reactions Figure C 6. Shear Diagram for the wide lift Analysis after imposing equal reactions Figure C 7. Moment Diagram for the wide lift Analysis after imposing equal reactions PAGE 158 158 As shown in the moment diagram (figure C 7), the moment diagram did not close at zero on the right side. In order to do that, a moment shift of 17.5 ft -lbs should be added to t he right insert. The right insert would have a corrected moment of: 920.8317.5 = 938.33ft -lbs The moment at the left insert will remain: 607.3 ft -lbs The central moment will remain: 687 lbs -ft The final Moment diagram considered as shown in Figure C 8. Figure C 8.Moment diagram along the X -X direction at the insert location To convert moments to stresses, a 4 ft tributary width was used (Figure C -9): 938 lb-ft x 12(in/ft) = 114psi for the right insert 4ft x 12(in/ft) x 3.5/ 6 607.3 lb-ft x 12(in/ft) = 74.36 psi for the left insert 4ft x 12(in/ft) x 3.5/ 6 687 lb-ft x 12(in/ft) = 84.12 psi at 4.5 ft from left edge PAGE 159 159 4ft x 12(in/ft) x 3.5/ 6 Figure C 9. Four feet tributary Band PAGE 160 160 APPENDIX D SOFTWARE RESULTS SOFTWARE 1 PAGE 161 161 PAGE 162 162 PAGE 163 163 PAGE 164 164 Horizontal Analysis PAGE 165 165 SOFTWARE 2 PAGE 166 166 PAGE 167 167 PAGE 168 168 SOFTWARE 3 PAGE 169 169 PAGE 170 170 SOFTWARE 4 The results displayed below are for an angle of inclination of 0 degrees which reflects the most critical case. Suction Factor: 1.5 Dynamic Factor: 1.2 Load Factor: 1.0 Figure D 1 Lifting Forces PAGE 171 171 Figure D 2 S tresses in the X -X at zero degrees inclination Figure D 3 S tresses in the Y Y direction at zero degrees inclination PAGE 172 172 Figure D 4 .Moments in the X -X at zero degrees inc lination Figure D 5 Moments in the Y -Y direction at zero degrees inclination PAGE 173 173 LIST OF REFERENCES ACI 330. (1982). Concrete parking lots and site paving, American Concrete Institue, P.O. Box 9094, Farminton Hills, Mich. ACI 435. (1963). 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M aturity testing for concrete pavement a pplications U.S. Department of Transportation, Federal Highway Administration Tilt-Up Concrete Association, (2005) Tilt up construction and engineering manual : a comprehensive reference manual for Tilt up contractors and engineers 6th Edition, Tilt Up Concrete Association, Mount Vernon, Iowa. Tilt-Up Concrete Association Site [Internet]. Mt. Vernon, IOWA.TCA Member Directory; [cited 2009 March 16]. Available from: http://www.tilt up.com /TCAMemberDir/tca/ PAGE 176 176 BIOGRAPHICAL SKETCH Guy Georges Abi Nader was born in Abdelli, Lebanon. He was the third son and third child born to Georges Abi Nader and May Salloum. He received his high school diploma from Zahrat El Ihsan School in Lebanon in 1999. He received his Bachelor of Engineering from the Lebanese American University in 2004. In August 2004, he moved to Gainesville, Florida, as a gradua te student in the M.E. Rinker, Sr., School of Building Construction at the Unive rsity of Florida. Prior to his m aster s degree graduation, Guy was accepted in the PhD program of the Design Construction and Planning College under the School of Building Cons truction. He received his Master of Science in Building Construction in May 2006. During his PhD studies, Guy showed interest in Transportation Engineering. He joine d the program and received his m aster s degree in Civil Engineering in December 2008. Guy r eceived his Ph.D. in Design, Construction and Planning from the University of Florida in the summer of 2009. |