Citation
Load Response of Flexible Pipe Subjected to Sustained Loading - Instrumentation

Material Information

Title:
Load Response of Flexible Pipe Subjected to Sustained Loading - Instrumentation
Creator:
Taylor, Matt
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
Boxes ( jstor )
Carts ( jstor )
Data acquisition ( jstor )
Instrumentation ( jstor )
Lasers ( jstor )
Loggers ( jstor )
Potentiometers ( jstor )
Sensors ( jstor )
Soils ( jstor )
Structural deflection ( jstor )
Lasers
Materials--Dynamic testing
Materials--Dynamic testing--Instruments
Genre:
Undergraduate Honors Thesis

Notes

Abstract:
In spring of 2009, the FDOT decided to test the load response of flexible pipe subjected to sustained loading. Several pieces of instrumentation were needed to measure vertical and horizontal deflection along the pipes. This equipment included earth pressure cells, a laser displacement sensor and a number of string potentiometers. The pressure cells were dispersed throughout the box to measure vertical and horizontal stresses in the soil. A laser sensor measured the distance from the laser to the inside wall of the pipe which was used to calculate deflection of the pipe. String potentiometers were used to determine the location of the deflection measurements as well as measure soil compression due to the sustained load. Results were analyzed simultaneously to relate deflection to simulated surcharge in the box. ( en )
General Note:
Awarded Bachelor of Science in Civil Engineering; Graduated May 3, 2011 summa cum laude. Major: Civil Engineering
General Note:
Advisor: Dr. David Bloomquist
General Note:
College/School: College of Engineering
General Note:
Legacy honors title: Only abstract available from former Honors Program sponsored database.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright Matt Taylor. 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.

Full Text

PAGE 1

1 Load Response of Flexible Pipe Subjected to Sustained Loading Instrumentation Matt Taylor Spring 2011 Summa Cum Laude Bachelor of Science in Civil Engineering

PAGE 2

2 Abstract I n spring of 2009 the FDOT decided to test the load response of flexible pi pe subjected to sustained loading. A soil box was delivered to ab in August of 2009 to undergo said testing Several pieces of instrumentation were needed to measure vertical and horizontal deflection along the pipes T his equipment include d earth pressure cells, a laser displacement sensor and a number of string potentiometers The pressure cells we re dispersed throughout the box to measure ver tical and horizontal stresses in the soil. A laser sensor measured the dista nce from the laser to t he inside wall of the pipe which was used to calculate deflection of the pipe String potentiometers we re used to determine the location of the deflection measurements as well as measure soil compression due to the sustained load. R e s ults we re analyzed simultaneously to relate deflection to simulated surcharge in the box

PAGE 3

3 Table of contents Abstract ........................................................................................................................... 2 Intro duction. ............................................................................... .................................... 4 Instrumentation ............................................................................................................... 6 Pressure Cells ........................................................... ................................ .......... 6 Laser Displacement Sensor ..................................... ............................... . ...........8 String Potentiometer s ... ............ ............................... ......... ...................... ............10 Data Acquisition................................................................................ ..............................13 Conclusion........................................ ..............................................................................1 5 References.................................................................................. ......................... ..........16

PAGE 4

4 Introduction Soil box M eetings were held in the months of March and May of 2009 to discuss the possibility of undergoing research to evaluate the deformation characteristics of flexible pipe under sustained loads. It was suggested that metal, HDPE and PVC pipes should be tested because al though t here is plenty of information on their mechanical and material properties, there is limited amount of data on full scale pipes ( 3 foot diameter by 10 length sections) loaded under field conditions. The FDOT agreed that testing full length pipes subjected t o the same backfill and load applications as in the field would be useful in determining proper installation as well as causes of poor pipe installation The CREEP phenomenon that occurs as a result of long term exposure to high levels of stress would also be observed. The soil box was constructed before the project began It measur es 20 feet by 10 feet by 8 feet and is made of steel reinforced with I beams to prevent un wanted bending It is located in the Coastal Lab just southeast of campus

PAGE 5

5 The focus o f this report is the instrumentation used in the project. To measure vertical and horizontal deflection along the pipes, several pieces of instrumentation are required Pressure cells are needed to measure vertical and horizontal stresses in the soil at di fferent locations and elevations throughout the box. A laser displacement sensor is needed to measure the displacement of the walls along the pipe. String potentiometers are required to measure the position of the displacements.

PAGE 6

6 Instrumentation Earth Pres sure Cells The pressure cells being used a re Geokon 4800 series earth pressure cells These cells use vibrating wire pressure transducers and therefore have the advantages of long term stability, reliable performance with long cables and insensitivity to moisture intrusion These proved to be ideal for measuring the vertical and horizontal stresses with in the soil box. The figure below is one of the many cells used throughout the box Figure 1 : Earth pressure c ell Because these pressure cells were use d in a previous research project t he y had to be gathered from Reed lab, cleaned and then tested using a vibrating wire readout box to determine wh ich cells were still functional The working cells were then sent off to Ge o kon to be calibrated if necessar y In order for the earth pressure cells to reach the data logger outside of the soil box, extra wire had to be ordered form Geokon and spliced to the ends of the existing wire. Waterproofing compound sealed the splicing area to prevent water from damagin g the

PAGE 7

7 pressure cells during testing. T o allow wire s to travel from the cells inside the box to the instrumentation room outside the box, one of the unused portholes had to be altered Holes on the porthole cover were machined such eaded i n and wires pulled through. Figure 2 : Routing of the pressure cell cables (outside soil box) Figure 3 : Routing of pressure cell cables (inside soil box)

PAGE 8

8 As mentioned above a data logger i s currently used to compile all data collected from the pressure cells This allows the outputs of the cells to be organized and converted to pressure readings before being sent to the Multi Logger program. Figure 4 : Data L ogger Laser Displacement System A laser displacement sensor i s used to calculate def lection of the pipe The system uses a laser beam to measure the distance from the laser to an object ; the inside of a pipe in our case The laser was previously used for the purpose of displacement measurement in another FDOT/UF project. Because that proj ect had ended and the laser was unused at the FDOT State Materials Office we were allowed the laser for our use. The laser being used, as shown in figure 5 is a Micro Epsilon Laser Displacement Sensor with a resolution of 50 micrometers and a measuring range of 200mm to 950mm. Though the mounting system that was designed took this range into account there were still instances when the bottom of the pipe was too close to the laser and caused the laser to relay invalid measurements

PAGE 9

9 Figure 5 : Laser di splacement s ensor and cables T he laser is set up such that it is attached to a cart that moves along a beam fixed to the soil box walls at each end of the pipe. The cart is connected to a spool o f wire and a crank. The cart is then cranked along the pipe using a hand crank located on the side of the box There are two beams, two carts and two hand cranks total (one for each pipe) but only a single laser sensor. See the figures below Figure 6: Cart on which laser mounts

PAGE 10

10 Figure 7 : Hand crank that mob ilizes cart Measurements from the laser sensor are relayed to the TracerDAQ program on one of the computers in the instrumentation room. This data can then be se nt to MATLAB and finally exported to Excel for analysis. A ctual data acquisition procedure wil l be discussed later in its own section of the report. String Potentiometer s To measure position of the cart and laser along the pipe, a string potentiometer is connected to the cart (see figures 6 and 8 for clarification) Attached to the cart is a wire that spools inside a string potentiometer. As the cart moves along the track, readings from the string potentiometer are sent to the TracerDAQ computer program along with the displacement data from the laser sensor. Similar to the laser measurements, data from the TracerDAQ can be transferred to MATLAB and exported to Excel for analysis.

PAGE 11

11 Figure 8 : String potentiometer on side of soil box There is one string potentiometer for each pipe (two in all). The two instruments differ such that t he north tring pot entiometer outputs data in amps whereas the south pipe outputs data in volt s As a result, a device was made to convert current to voltage in the north pipe Two m ore string potentiometers are located on top of the soil box to measure vertical st rain of the soil A buried horizontal steel plate is connected to a wire which is connected to a string potentiometer. Measuring the vertical strain of the soil at the pipe elevations will tell us how much the soil has compressed See figure 9.

PAGE 12

12 Fig 9 : S tring potentiometer on top of soil box

PAGE 13

13 Data Acquisition To obtain readings from the pressure cells, data is recorded by the data logger and sent to the multi logger program on the computer in the instrumentation room. There it can be transferred to an E xc el file and analyzed Figure 1 0 : Multi Logger program Attaining readings from the laser and string potentiometer s is not as automated as it is for pressure cell readings During pipe testing the simulated surcharge is either increasing or decreasing by a certain amount daily depending on the phase of testing being performed : loading or unloading r espectively To see the effect of this change, deflection readings a re recorded e very day (excluding weekends and holidays) at app roximately the same time Daily measurement is generally a two person job and begins with assembling the laser to the cart and attaching the cables, as shown in figure 1 1 below. One person will connect the cables from inside the instrument ation room to the appropriate device whil e the other person connects the cables to the laser from the outside After everything is

PAGE 14

14 connected and tested to make certain all is in order, the actual recording can begin. One person operates the laptop in the instrumentation room while the other crank s the laser along the pipe from one side to the other and back at a slow constant rate. Figure 1 1 : Laser and string potentiometer equipment T his is done four times per pipe; once for each laser orienta tion: top, bottom, and two sides Between each ori entation the laser has to be readjusted on the cart. The entire acquisition process takes less than an hour if everything goes without complication Finally, w hen all data is gathered calculations can be performed to determine relationships such as : ver tical deflection vs. length of pipe at varying pressures horizontal deflection vs. length of pipe at varying pressures, etc.

PAGE 15

15 Conclusion As of now, the described instrumentation setup will be used for all future tests for the duration of the project

PAGE 16

16 Ref erences FDOT/UF Soil b ox progress reports # 1 6 Ken Pasken 2010 2011, University of Florida 4800 Series Earth P ressure C ell S pecifications Geokon, Inc., 2010, www.geokon.com Pictures taken by Ken Pasken 2010 2011, University of Florida