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Shear Strength of Anchor Steel with Stand-off Base Plate

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Title:
Shear Strength of Anchor Steel with Stand-off Base Plate
Creator:
Golzbein, Jason
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
Adhesives ( jstor )
Base courses ( jstor )
Concretes ( jstor )
Diameters ( jstor )
Hydraulics ( jstor )
Nuts ( jstor )
Photographic plates ( jstor )
Shear strength ( jstor )
Steels ( jstor )
Structural deflection ( jstor )
Civil engineering
Shear (Mechanics)
Genre:
Undergraduate Honors Thesis

Notes

Abstract:
The current design of embedded anchors in shear is based on connections where the base plate is mounted flush with the concrete surface. However, cantilever signal/sign structures use a connection where the base plate has a stand-off distance above the concrete. The purpose of the research performed in this report is to establish a relationship between the steel shear strength and the base plate stand-off distance. A double anchor connection was tested. The steel anchors tested were 5/8-inch diameter ASTM A193 Grade B7 threaded rods. The anchors had an ultimate tension stress of 143 KSI and a 23% axial elongation. The anchors were installed with a 5-inch embedment depth, 6-inch spacing, and a large enough edge distance to avoid concrete breakout failure. The anchors were tested at stand-off distances of 1.4, 2.0, 3.0, and 4.0 times the diameter of the anchors. The results of these tests showed an insignificant variation between the steel shear strength of the anchors with flush-mounted base plates and those with base plate stand-off distances of 1.4 and 2.0 diameters. The shear strength of the anchors with stand-off distances greater than 2.0 diameters decreased as the stand-off distance increased. ( en )
General Note:
Awarded Bachelor of Science in Civil Engineering; Graduated May 4, 2010 magna cum laude. Major: Civil Engineering
General Note:
Advisor: Ronald Cook
General Note:
College of Engineering

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University of Florida
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University of Florida
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Copyright Jason Golzbein. 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.

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Shear Strength of Anchor Steel with Stand off Base Plate By: Jason Scott Golzbein Spring 2010 Magna Cum Laude Bachelor of Science in Civil Engineering Faculty Advisor: Dr. Ronald Cook Tests Performed: August 2009

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Shear Strength of Anchor Steel with Stand off Base Plate 1 ACKNOWLEDGEMENTS I thank Dr. Cook for giving me the opportunity to perform research and for all the support he has provided during my undergraduate career. I also thank Dr. Prevatt and Dr. Gibson for being part of my Honors Thesis Committee. Additionally, I must show my gr atitude towards Chuck Broward and Philipp Grosser for teaching me everything I have learned about working in a structures laboratory up to this point, and to Jessica Rigdon for assisting me with my tests. Lastly, I thank Todd Davis for helping me edit my r eport.

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Shear Strength of Anchor Steel with Stand off Base Plate 2 List of Figures Figure 1 Stand off Base Plate Assembly with Grout Pad Figure 2 Flush mounted and Stand off Base Plates Figure 3 Sample graph of Equation 1 Figure 4 Ratio of Shear Deflecti on to Flexural Deflection with I ncreasing Stand off Figure 5 Pictures and Drawings of the Test Frame Figure 6 Lateral Support Figure 7 Tie Down Figure 8 Tension Test Graph Figure 9 Tension Test Setup Figure 10 Drill Figure 11 Side View of Base Plate Figure 12 Top View of Base Plate Figure 13 Top View of Hinge Figure 14a Stand off Distance= 1.4 Diameters Figure 14b Stand off Distance= 2.0 Diameters Figure 14c Stand off Distance= 3.0 Diameters Figure 14d Stand off Distance= 4.0 Diameters Figure 15 Hydraulic Pump Figure 16 Hydraulic Actuator and Load Cell Figure 17 LVDT Figure 18 Load vs. Displacement Graph for a Stand off Distance of 1.4 Diameters Figure 19 Load vs. Displacement Graph for a Stand off Distance of 2.0 Diameters Figure 20 Load vs. Displacement Graph for a Stand off Distance of 3.0 Diameters Figure 21 Load vs. Displacement Graph for a Stand off Distance of 4.0 Diameters Figure 22 Normalized Ultimate Shear Loads Figure 23 Failed Steel of Test 1.4D 2 Figure 24 Failed Steel of Test 2D 3

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Shear Strength of Anchor Steel with Stand off Base Plate 3 Figure 25 Failed Steel of Test 3D 2 Figure 26 Failed Steel of Test 4D 3 Figure 27 Ultimate Shear Strength Test Results Compared to Design Equation Figure 28 Ancho rage in Concrete Conctruction Equation vs. Test Results List of Tables Table 1 Test Matrix Table 2 Ultimate Shear Loads

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Shear Strength of Anchor Steel with Stand off Base Plate 4 Table of Contents List of Figures List of Tables ......................... 5 2.0 Background 2.1 Anchorage in Concrete Construction ......................... ..........6 ......................... .7 3.0 Testing 3.1 Setup 3.1.1Test Setup.. ...................................................................................................... ........................10 3.1.3 Anchors............................................................ .............................................. ........................12 3.1.4 Embedment Depth.......................................................... ......................... ..............................14 3.1.5 Anchor Installation ........................................................ ........................... ..............................14 3.1.6 Base Plate........................................................................ ......................... .......................... ....16 3.1.7 Nuts and Washers............................................................ ........................ ..............................17 3.1.8 Hinge............................................................................... .................. ....... ..............................17 3.2 Procedure 3.2.1 Stand off Distances......................................................... ..................................... ..................18 3.2.2 Hydraulic Actuator and Pump...................... .................. ......................... ..............................19 3.2.3 Data Acquisition............................................................. ......................... ..............................20 4.0 Results 4.1 Load Displacement Graphs........................................................ ......................... ..............................22 4.2 Ultimate Shear Loads................................................................. ............... .......... ..............................24 5.0 Conclusion 5.1 Design Equations........................................................................ .................................................. ....27 5.2 Test Results Compared to Background Research....................... ........................ ..............................28

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Shear Strength of Anchor Steel with Stand off Base Plate 5 1.0 Introduction The steel shear strength used for design of embedded anchors is curr ently based on connections where the base plate is mounted flush with the concrete surface. Although, this is often the case, it is not the type of connection used for cantilever sign/signal structures. These structures use a stand off base plate assembly as shown in Figure 1. This type of connection may or may not contain a grout pad. The purpose of this research is to quantify the steel shear strength of anchors installed with stand off base plates. Tests were performed with double anchor connections comp aring flush mounted base plates and stand off base plates as shown in Figure 2. The stand off distance was varied to establish a relationship between steel shear strength and base plate stand off distance. Figure 2 Flush mounted and Stand off Base Plates Figure 1 Stand off Base Plate Assembly with Grout Pad

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Shear Strength of Anchor Steel with Stand off Base Plate 6 2.0 Background This section is based on research performed prior to this project. The information included describes possible explanations for the results acquired during the testing procedure. Section 2.1 discusses Anchorage in Concrete Construction (2006) Section 2.2 discusses the influence of a shear deflection to flexural deflection ratio on the ultimate shear load. 2.1 Anchorage in Concrete Construction Equation Currently, ACI 318 Appendix D (2008) does not inc lude design standards for the ultimate steel shear strength for a n anchor with a stand off base plate. However, research has been done on the subject. In Anchorage in Concrete Construction (2006) the shear failure load for a stand off installation is expressed as : = (Equation 1) where: = 1.0 when rotation of the base plate and/or anchor is not restrained = 2.0 when the anchor is restrained from rotation at the ba se plate = distance between the concrete surface and the applied shear load plus 0.5 d (diameter of anchor) = plastic bending moment at failure, which if there is no tensile stress applied simultaneously to the shear stress, is taken to be : = 1 7 where: = elastic section modulus for the threaded part calculated based on the net tensile area = specified steel yield strength The coefficient 1.7 comes from the geometry of a circular anchor. More generally, i t can be written that = For a circular anchor, = 3 6 and = 3 32 T herefore, by simple arithmetic, for the case of a circ ular anchor = 1 7

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Shear Strength of Anchor Steel with Stand off Base Plate 7 Figure 3 shows a s ample graph of Equation 1 for a 5/8 inch diameter anchor, steel yield stress of 135 ksi and the anchors are restrained from rotation at the base plate. The shear strength using a flush mounted base plate was c alculated as: 0 = 0 6 Figure 3 Sample graph of Equation 1 As shown in Figure 3, Equation 1 infers that increasing stand off distance will initially significantly decre ase the shear capacity but does not greatly affect shear capacity above a stand off distance of 2 anchor diameters 2.2 Compare Shear and Flexural Deflections An anchor loaded in shear with a stand off base plate will act similarly to a cantilever beam with a tip load The anchor will be subjected to both shear and flexural def lections. Shear deflection for a solid round member with a concentrated load at the free end is (Young, 2002) : = 31 30 where: V = vertical shear, L = stand off distance, 0 20 40 60 80 100 120 0 1 2 3 4 Ultimate Shear Load (% of V 0 ) Stand off Distance (diameters)

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Shear Strength of Anchor Steel with Stand off Base Plate 8 A = cross sectional area, and G = modulus of rigidity. Letting A 2 and = 2 ( 1 + ) = 0.24, shear deflection can be simplified to: = 2 666 2 Flexural deflection for a member fixed at one end and guided on the other end where the load is applied is (Young, 2002) : = 3 12 where: E = modulus of elasticity, I = moment of inertia, and all other terms have been previously defined. Letting = 4 4 for a circular member, flexural deflection can be simplified to: = 3 3 4 The ratio of the shear deflection to the flexural deflection is : = 8 2 2 Expressing r and L in terms of anchor diameter, d where number of anchor diameters in the stand off distance, t he ratio of shea r to flexural deflection reduces to : = 2 2 This analysis shows that as the stand off distance is increased, the deflection of the anchor is more dominantly affected by the resulting m oment, and not just the shear load alone. Figure 4 shows a graph of the ratio of shear to flexural deflection as the stand off distance increases. As the figure displays, at shorter stand off distances the shear load is the controlling factor in deflection At the stand off distance of 1.41 the deflection ratio is equal to 1 .0 and at stand off distances greater than 1.41 deflection becomes more dominantly caused by flexure.

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Shear Strength of Anchor Steel with Stand off Base Plate 9 Figure 4 Ratio of Shear Deflection to Flexural Deflection with increasing Stand off 0 0.5 1 1.5 2 0 1 2 3 4 Ratio of Shear Deflection to Flexural Deflection Stand Off Distance, (diameters)

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Shear Strength of Anchor Steel with Stand off Base Plate 10 3.0 Testing This chapter presents the testi ng program. This chapter has been divided into two sections. Section 3.1 discusses the testing setup, and Section 3.2 discusses the testing procedure. 3.1 Setup This section of the report covers the test setup. This section includes a schematic of the test area, information about the anch ors used, the anchor installation procedure, and information on the base plate, nuts, washers and hinge used in the testing program. 3.1.1 Test Setup Fig ure 5 shows pictures and drawings of the test frame. The left side of the figure shows pictures of the test frame without the instruments or concrete slab present. The testing frame is connected to a strong wall and strong floor with strength capacities of 50 and 200 kips, respectively. The right side of the figure shows a drawing of the test area. The top drawing is a plan view and the bottom drawing is the side view. The shear load was applied to the right. The instrumentation and other objects labeled wi ll be discussed further in this chapter. Figure 5 Pictures and Drawings of the Test Frame

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Shear Strength of Anchor Steel with Stand off Base Plate 11 Figure 6 is a photograph of the lateral support used on the face of the concrete slab to restrict the slab from sliding or rotating horizontally while the shear f orce was applied to the anchors. Figure 7 is a photograph of the tie down used to keep the back end of the concrete slab from deflecting up while the shear load is applied to the anchors. The tie down is attached to the strong floor. Figure 6 Lateral Su pport Figure 7 Tie Down

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Shear Strength of Anchor Steel with Stand off Base Plate 12 3.1.2 Test Matrix Table 1 presents the test matrix for the test program performed in this report. The stand off distances used and the number of trials for each stand off distance are listed. The test matrix also displays the indi vidual test names designated for each test performed. The tests performed with zero stand University of Florida in 2009. Further explanatio n of the stand off distances chosen is discussed in Section 3.2.1. Table 1 Test Matrix Stand off Distance (diameters) Trail 1 Trial 2 Trial 3 Comments 0 0d 1 0d 2 0d 3 Performed by P. Grosser (2009) 1.4d 1.4d 1 1.4d 2 1.4d 3 2.0d 2.0d 1 2.0d 2 2.0d 3 3.0d 3.0d 1 3.0d 2 3.0d 3 4.0d 4.0d 1 4.0d 2 4.0d 3 3.1.3 Anchors Shear testing was performed on 5/8 inch diameter steel anchors. The anchors were ASTM A193 Grade B7 threaded rods. This grade of steel is commonly used to manufacture threaded rods. The American Society for T esting and Materials (ASTM) designates a minimum ultimate tensile stress of 125 ksi for anchors made of B7 steel and with a diameter less than 2.5 inches. From tension tests performed in the laboratory, the steel used for testing had an average ultimate tension stress of 143 ksi. Additionally, the minimum designated percent elongation during these tension tests is 16%. Tension tests performed to evaluate the ductility of the steel measured an elongation of 23% ( 0.495 inches over a gage length of 2.125 inches ), indicating the steel anchors used are more ductile than the average minimum steel at this grade. This above average ductility allows the steel anchors to be deflected farther and withstand a higher shear load than steel ancho rs with the minimum ductility requirement. Figure 8 shows the load vs. elongat ion graph of the tension test conducted and Figure 9 shows a picture of the test setup of this tension test. The threaded rods used for testing were ordered and purchased from F lorida Fasteners and Tool Co, 2826 NE Waldo Rd, Gainesville, FL.

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Shear Strength of Anchor Steel with Stand off Base Plate 13 Figure 8 Tension Test Graph Figure 9 Tension Test Setup 0 5 10 15 20 25 30 35 0 0.2 0.4 0.6 Tension (kips) Elongation (in)

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Shear Strength of Anchor Steel with Stand off Base Plate 14 3.1.4 Embedment Depth and Edge Distance An a nchor embedment dept h of 5 inches was chosen for all shear tests to avoid anchor pryout during testing The purpose of this test program was to investigate the shear strength of the steel; hence, the desired failure mode is steel rupture. In shear testing performed by Philipp Grosser at the University of Florida in 200 9, steel rupture occurred with an embedment depth of 5 inches when the edge distance was large enough to resist concrete breakout failure. Grosser also performed tests with anchors installed with an embedment depth of 8 inches and found no significant chan ge in the shear strength of the steel. Therefore, an embedment depth of 5 inches was determined to be adequate to produce the desired failure mode. In order to avoid concrete edge breakout, e quation D 24 from ACI 318 Appendix D.6.2.2 (2008) was used to de termine an adequate edge distance. The edge distance chosen was 10 inches. 3.1.5 Anchor Install ation The anchors were post installed in the concrete. An ICC AC308 approved adhesive anchor product was used; procedures to prope rly ensure optimal concrete anchor connection were followed The first step was drilling the holes into the surface of the concrete. A drill rig was used to ensure that the holes were drilled perpendicular to the concrete surface and at the correct embedment depth. The drill rig is shown in F igure 10 Lines drawn on the concrete surface perpendicular to the concrete edge helped to ensure that the anchors were correctly aligned and that during testing the lateral supports beared flat against the concrete edge. A template was used to accurately l ocate the holes with the proper 6 inch spacing. A 5/8 inch diameter drill bit was used to make shallow preliminary holes to aid in drilling the final hol es. A 3/4 inch

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Shear Strength of Anchor Steel with Stand off Base Plate 15 Figure 10 Drill After the holes were drilled vacuum and compressed air were used to remo ve dust and small particles that accumulated in the hole during the drilling. A steel wire brush was also used to clean the sides of the hole and dislodge any dust. The vacuum and compressed air were again used to clean the hole. If the hole is not properl y cleaned the adhesive will not bond well to the concrete. Once the holes were cleaned, the adhesive was injected into the hole. The adhesive filled approximately three quarters of the embedment depth prior to inserting the anchor When injecting the adh esive it is important to start at the bottom of the hole and slowly retract to limit the amount of voids in the hole. Voids can cause inadequate concrete anchor connections and a spitting of the adhesive out of the hole when inserting the anchor. Proper ey ewear and gloves wer e worn to avoid contact of the adhesive with the skin or eyes. Immediately after injecting the adhesive, the threaded rod (cut to the appropriate length) was inserted in the hole. Once both anchors were inserted in the holes, the base plate and inserts used for testing were installed to ensure that the anchors remained vertical and at the proper spacing while the adhesive cured Several g roups of tests were installed o ne after another in order to reduce the number of adhesive injection nozzle s needed ; if the adhesive was allowed to rest in the nozzle it would harden within minutes requiring the nozzle to be replaced.

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Shear Strength of Anchor Steel with Stand off Base Plate 16 3.1.6 Base Plate A base plate was used to apply the shear load to the anchors. A 7/8 inch diameter 9 TPI threaded attached to the end of the base plate at a depth of 1.6 inches was used to apply the load via the actuator The base plate was 14.5 inches long, 4 inches wide, and 1.18 inches thick. This small thickness was used to reduce the effect of further load eccentricity. The base plate was made of case hardened steel and could apply loa ds up to 50 kips. Five holes at were drilled in the base plate. The plate was manufactured by Precision To ols and Engineering, 2706 NE 20 th Way, Gainesville, FL. Various i nserts were used in the holes to allow for multiple anchor diameters and to decrease the stress in the base plate at sections without anchors Figure 11 and Figure 12 are photographs of the base plate used with anchors installed and only the leveling nuts in place. The red wires were connected to strain gages attached to the base plate during previous testing. They were not used in this test program and were later removed. Figure 11 Side V iew of Base Plate

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Shear Strength of Anchor Steel with Stand off Base Plate 17 Figure 12 Top View of Base Plate 3.1.7 Nuts and Washers Steel nuts were placed above and below the base plate. The leveling nuts below the base plate supported the base plate so that the specified stand off distance could be ensured between the concrete surface and the base plate. The nuts above the base plate helped keep the base plate level during testing The nuts were tightened to 100 in lb using a torque wrench Washers were used in between the base plate and the nuts. The nuts were Heavy Hex 5/8 inch diameter ASTM A194 Grade 7 steel. The washers were Black Oxide Jumbo Flat Washers. 3.1.8 Hinge A U joint was used to connect the threaded rod attached to the base plate and the thread ed rod being pulled by the actuator. This joint acted as a hinge to release the moment in the loading rod. With a base plate stand off distance the base plated tended to rotate during loading This bending stress could cause significant damage to the base plate at the threaded rod connection The U join t released this moment and the bas e plate did not rotate and remained completely horizont al during testing Figure 13 is a photograph of the hinge connected to the base plate and the threaded rod used to apply the shear load.

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Shear Strength of Anchor Steel with Stand off Base Plate 18 Figure 1 3 Top View of Hinge 3.2 Procedure This section discusses the testing procedure for the shear strength of anchors with a base plate stand off distance. This section will cover the stand off distances chosen and the instruments used to apply and measure the loads and displacements. 3.2.1 Stand off Distances Base plate stand off distances were chosen to compare the effect of increase load eccentricity to anchor shear strength. Stand off distance was measured from the surface of the concrete to the bottom of the base plate. Stand off d istances of 1.4, 2.0, 3.0, and 4.0 times the diameter of the anchor were chosen. With an anchor diameter of 5/8 in ch, these distances are 0.875 inches, 1.25 inches, 1.875 inches, and 2.50 inches, respectively. The minimum stand off distance of 1.4 diameter s (0.875 inches ) was chosen because it was the sho rtest distance possible that provide d enough space for the leveling nuts and washers in between the base plate and concrete. When setting the base plate at the correct stand off di stance it was important to en sure that the base plate was level and the stand off distance was uniform all around the base plate. Also, the actuator and pulling thread rod had to be aligned to ensure that the load was applied horizontal ly Figure 1 4 show s photographs of the chosen base plate stand off distances. Hinge

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Shear Strength of Anchor Steel with Stand off Base Plate 19 Figure 1 4 a Stand off Distance= 1.4 Diameters Figure 1 4 b Stand off Distance= 2.0 Diameters Figure 1 4 c Stand off Distance= 3.0 Diameters Figure 1 4 d Stand off Distance= 4.0 Diameters 3.2.2 Hydraulic Actuator and Pump A hydraulic actuator and pump were used to apply the shear load to the anchors. The actuator was an Enerpac Oil O Cylinder. The hydraulic pump was an Enerpac P802 with a maximum pressure of 10,000 PSI. Per ASTM E488, the load must be applied at a continual rate to produce failure at 21 minute Figure 1 5 and Figure 1 6 show a photograph of the hydraulic pump and actuator, respectively.

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Shear Strength of Anchor Steel with Stand off Base Plate 20 Figure 1 5 Hydraulic Pump Figure 1 6 Hydraulic Actuator and Load Cell 3.2.3 Data Acquisition A Precision Pancake Tension/Compression Load Cell Model: SRP4 was placed behind the act uator to measure the applied load The maximum load for this load cell is 50 kips which is sufficient for measuring the loads being applied to the anchors. F igure 1 6 shows the load cell placed behind the actuator and held in place with a nut and washer. An LVDT was used to measure the deflection of the base plate. The LVDT was secured with hot glue to the surface of the concrete. The LVDT was connected to the base plate with a string and a magnet. The Hydraulic Actuator Load Cell

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Shear Strength of Anchor Steel with Stand off Base Plate 21 LVDT used was a Model 604, with distance of 4.0 inches. The output from the LVDT and load cell was processed by a National Instruments Lab View 8.5 program The instrumentation was calibrated to accurately measure the shear force and horizontal deflection. Figure 1 7 shows a photograph of the LVDT used during testing. Figure 1 7 LVDT

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Shear Strength of Anchor Steel with Stand off Base Plate 22 4.0 Results This chapter presents the results of the testing program This chapter includes load vs. displacement graphs for all tests at each stand off distance. At the end of this chapter is a table of the ultimate loads obtained for each test. 4.1 Load Displacement Graphs Figures 1 8 2 1 are Load vs. Displacement graph s for each series of tests The load is the shear force in kips applied to the base plate. The displacement is the horizontal deflection of the base plate. Figure 1 8 Load vs. Displacement Graph for a Stand off Distance of 1.4 Diameters 0 5 10 15 20 25 30 0 0.5 1 1.5 2 Shear Load (kips) Displacement (in) Test 1.4D 1 Test 1.4D 2 Test 1.4D 3

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Shear Strength of Anchor Steel with Stand off Base Plate 23 Figure 19 Load vs. Displacement Graph for a Stand off Distance of 2.0 Diameters Figure 2 0 Load vs. Displacement Graph for a Stand off Distance of 3.0 Diameters 0 5 10 15 20 25 30 0 0.5 1 1.5 2 Shear Load (kips) Displacement (in) Test 2D 1 Test 2D 2 Test 2D 3 0 5 10 15 20 25 30 0 0.5 1 1.5 2 Shear Load (kips) Displacement (in) Test 3D 1 Test 3D 2 Test 3D 3

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Shear Strength of Anchor Steel with Stand off Base Plate 24 Figure 2 1 Load vs. Displacement Graph for a Stand off Distance of 4.0 Diam eters 4.2 Ultimate Shear Loads Table 2 shows the ultimate loads reached for each test and the average for each stand off distance. The normalized value is the average ultimate load divided by the average ultimate load for a flush mounted base plate at a di stance of zero stand off diameters. The results of the tests with a stand off distance of zero diameters were taken from a research project performed by Philipp Grosser at the University of Florida in 2009. Table 2 Ultimate Shear Loads Stand off (diameters) Repetition 1 (kips) Repetition 2 (kips) Repetition 3 (kips) Average (kips) Normalized 0 27.0 26.5 26 5 26. 7 1.00 1.4 26.2 25.2 29.3 26.9 1.01 2.0 27. 3 25. 1 25. 2 25.8 0.97 3.0 15.5 13. 3 12.7 13. 9 0.52 4.0 10.1 9.19 10.2 9.84 0.37 0 5 10 15 20 25 30 0 0.5 1 1.5 2 Shear Load (kips) Displacement (in) Test 4D 1 Test 4D 2 Test 4D 3

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Shear Strength of Anchor Steel with Stand off Base Plate 25 Figure 22 is a graph of the normalized ultimate shear loads. The graph shows an insignificant variation in the ultimate shear load with a stand off distance of 2.0 diameters or less, but a reduction to nearly half the original strength with a stand off dis tance of 3.0 diameters or more. Figure 2 2 Normalized Ultimate Shear Loads Figures 23 26 show the failed anchors of one test from each stand off distance. The first number in the test name corresponds to the stand off distance in diameters and the last nu mber corresponds to the test repetition. As these figures show, in some tests both anchors ruptured, while during other tests only one anchor ruptured, typically the back anchor. The arrows indicate the direction of the load. 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0 1 2 3 4 5 Normalized Shear Load (V/Vo) Standoff Distances (diameters)

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Shear Strength of Anchor Steel with Stand off Base Plate 26 Figure 2 3 Failed Steel of Test 1.4D 2 Figure 2 4 Failed Steel of Test 2D 3 Figure 2 5 Failed Steel of Test 3D 2 Figure 2 6 Failed Steel of Test 4D 3

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Shear Strength of Anchor Steel with Stand off Base Plate 27 5.0 Conclusion This chapter presents the conclusi ons drawn from the testing program Part 1 of this chapter presents recommended design equations for anchors with stand off distances. Part 2 compares the results found in this report to the information discussed in the background chapter. 5.1 Design Equations The tests performed at stand off distances of 1.4 and 2.0 diameter s resulted in ultimate shear strengths that were insignificantly different from t he ultimate shear strength with the base plate flush to the concrete. From these results, design sp ecifications can be constructed to allow for the ultim ate shear strength of concrete e mbedded anchors with the same material properties as the ones tested in this report and with base plate stand off distances equal to or less than 2.0 times the anchor dia meter to be equal to the ultimate shear strength of anchors with zero stand off distance. For stand off distance < 2.0d, = 0 The tests performed at stand off distances o f 3.0 and 4.0 diameter s resulted in ultimate shear strengt hs significantly less than th e ultimate shear strengths with t he base plate flush to the concrete This reduction in shear strength is a product of an increasing bending moment that occurs at the surface of the concret e slab. The steel anchor must endure f lexural deflection caused by this moment, as well as the shear deflection caused by the horizontal shear f orce. A conservative design equation for the ultim ate shear strength of concrete e mbedded anchors with a stand off distance greater than 2.0 times the diameter is: For stand off distance > 2.0d, = 0 4 5 2 number of anchor diameter s in the stand off distance. Figure 27 compares the ultimate shear strength test results to the proposed design equation s. From this graph, it can be shown that the design equations are fairly accurate and become more conservative at larger stand off distances.

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Shear Strength of Anchor Steel with Stand off Base Plate 28 Figure 2 7 Ultimate Shear Strength Test Results Compared to Design Equation 5.2 Test Results Compared to Background Research The test results show different findings than those discussed in the background section of the report The Anchorage in Concrete Construction (2006) concludes that the ultimate shear streng th significantly decreases at small stand off distance s and then varies less as the stand off distance is further increased. The results from this test program show that a decrease in shear strength will not occur at a stand off distance of less than 2.0 t imes anchor diameter Figure 28 clearly shows that Equation 1 from Anchorage in Concrete Conctruction (2006) is very compare its shear strength to the s tand off distance. However, at small stand off distances, the bending moment is not the controlling force; the shear load will control, as shown in the test results. The resulting bending moment caused by the eccentricity of the load is insignificant in th e shear strength analysis at short stand off distances. 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0 1 2 3 4 5 6 Ultimate Shear Load (V/V 0 ) Stand off (diameters = 5/8") Test 1 Test 2 Test 3 Average Equation d Equation d T

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Shear Strength of Anchor Steel with Stand off Base Plate 29 Figure 28 Anchorage in Concrete Conctruction Equation vs. Test Results The comparision of deflections caused by shear and moment as stand off distance changes was analyzed in Section 2.2. The ratio of shear deflection to flexural deflection is: = 2 2 This ratio shows that at short stand than the flexural deflection. The flexural deflecti on will equal the At stand off distances below this value, the shear strength could be analyzed as if the base plate was flush e the ultimate load at this stand off distance was insignificantly different than when the base plate is flush mounted. At stand 1 2 because it could be shown that the shear streng th was related to the ratio of shear deflection to flexural deflection. 0 0.2 0.4 0.6 0.8 1 1.2 0 1 2 3 4 Ultimate Shear Strength (V/Vo) Stand off Distance (diamaters) Equation 1 Test Results

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Shear Strength of Anchor Steel with Stand off Base Plate 30 6.0 References ACI Committee 318. Building Code Requirements for Structural Concrete (ACI318 08) and Commentary (ACI318 08). American Concrete Institute, Farmington Hills, MI, 2008. ASTM E488 96 (2003), Standard Test Methods for Strength of Anchors in Concrete and Masonry Elements. American Society for Testing and Materials, West Conshohocken, PA. Eligehausen, R., Mallee, R., & Silva, J.F. Anchorage in Concrete Construction 107 109. Ernst and Sohn, Berlin, 2006. Grosser, Philipp R. Load Bearing Behavior of Anchor Groups Arranged Perpendicular to the Edge and Loaded by Shear Towards the Free Edge Structures Report 2000 1 (August 2009), University of Florid a, Department of Civil and Coastal Engineering. Young, W.C. & Budynas, R.G Roark's Formulas for Stress and Strain (7th Edition). McGraw Hill, 2002.