final paper reu summer2010

7/28/2019 Final Paper Reu Summer2010

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PROJECT REPORT

NON-DESTRUCTIVE TESTING OF A BOX GIRDER BRIDGE

Submitted To

The 2010 Summer NSF REU Program in Engineering TomorrowPart of

NSF Type 1 STEP Grant

Sponsored By

The National Science Foundation

Grant ID No.: DUE-0756921

College of Engineering and Applied Science

University of Cincinnati

Cincinnati, Ohio

Prepared By:

Robert Golsby, Chemical Engineering, University of Cincinnati

Eliseo Iglesias, Mechanical Engineering, Trinity University

Kenechukwu Okoye, Biomedical Engineering, University of Cincinnati

Report Reviewed By:

_______(signature)______

Richard A. Miller, PhD, PE, FPCI

Professor

Department of Civil Engineering

University of Cincinnati

June 21-August 13, 2010


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AbstractThe scope of this project involved the examination, testing, and analysis of an adjacent

box girder bridge. The purpose of this project was initially to find a relationship between visual

damage of pre-stressed concrete box girders within the bridge and the actual performance of the

bridge. This relationship is important because any kind of correlation would serve for the benefitof officials in charge of rating the quality of these types of bridges. Due to time constraints, only

baseline tests were completed. The REU students in these baseline tests took data and video of

the experiment, which involved placing trucks on the test bridge (which was a bridge in Fayette

County). From these tests, the students (using models created in Visual Analysis) were able toapproximate the concrete strength and moment of inertia of the adjacent box girders. Also it was

found that the bridge is at least partially continuous; further testing is needed to confirm. These

baseline tests allowed for the examination of the bridge under loads; this sets up as a control for

future destructive tests.


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Acknowledgements

Research Contr ibutors

Research Experience for Undergraduates Site in Structural Engineering: Development of

Enhanced Materials and Structural Assemblages Used in Seismic Performance EvaluationStudies No. DUE-0756921 NSF REU Grant

University of Cincinnati Staff

Dr. Carlo Montemagno-Project Director

Dr. Anant R. Kukreti- Project Coordinator

Dr. Richard Miller-Faculty Mentor

Ms. Marlo Thigpen-Grant Coordinator

Phil Grosvenor- IT Coordinator

Ms. Mary Ann Schaefer- Senior Business Administrator

Dawit Alemayehu - Graduate Assistant

Tyler Stillings- Graduate Assistant

Sanooj Edalath Graduate Assistant Helper

Elie Hantouche- Graduate Assistant Helper Dr. Eric Steinburg- Associate Professor of Civil Engineering David R. Breheim, Research

Associate

Dr. Sam Khoury Research Engineer

Ohio University Graduate Studentso Jon Huffman, Clint Setty, Kyle Grupenhoff, Brendan Kelly and Santiago Camino

ODOT (Ohio Department of Transportation)

Steven G. Luebbe. P.E., P.S., Fayette County Engineer

REU Seminar Presentors

Andrea Burrows

Dr. Ron Millard

Kim Simmons

Dr. Raj Manglik Amber Erickson

Ted Baldwin

Jim Casper

Dr. Makram Sidan

Dr. Dorothy Air

Geoffery Pinski

Dr. Tim Keener


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Table of ContentsAbstract.......................................................................................................................................................................... 2

Acknowledgements ....................................................................................................................................................... 31. INTRODUCTION ............................................................................................................................................... 6

2. GOAL AND PROJECT OBJETIVES ............................................................................................................... 7

3. RESEARCH TASKS ........................................................................................................................................... 8

3.1. Literature Review....................................................................................................................................... 8

3.1.1. Types of Loads on Bridges .................................................................................................................... 8

3.1.2. Truck Loading ....................................................................................................................................... 8

3.1.3. Precast Concrete .................................................................................................................................... 8

3.1.4. Adjacent Box Girder Bridges ............................................................................................................... 9

3.1.5. Deformation and Deterioration ............................................................................................................ 9

3.2. Rudimentary Analysis of Bridge............................................................................................................... 9

3.2.1. Bridge Information ................................................................................................................................ 9

3.2.2. Determination of Calculated and Derived Values............................................................................. 11

3.2.3. Assumed and Approximated Values .................................................................................................. 11

3.2.4. AASHTO Specifications ...................................................................................................................... 12

3.3. Simulation of loading ............................................................................................................................... 13

3.3.1. Purpose of Simulating ......................................................................................................................... 13

3.3.2. Simulation Setup .................................................................................................................................. 14

3.3.3. Simulation Results ............................................................................................................................... 15

4. MEASURING INSTRUMENTS ...................................................................................................................... 17

4.1. Strain Gauges ........................................................................................................................................... 17

4.2. String Potentiometer ................................................................................................................................ 17

5. BENCHMARK TEST ....................................................................................................................................... 18

5.1. Initial Preparation.................................................................................................................................... 18

5.2. Placement of Instruments ........................................................................................................................ 19

5.3. Collection of Data..................................................................................................................................... 20

5.4. Results ....................................................................................................................................................... 21

6. ANALYSIS OF RESULTS ............................................................................................................................... 22

6.1. Finding the AASHTO specified Moment Distribution Factor ............................................................. 12

6.2. Tuning the Data to Find Experimental Physical Characteristics. ....................................................... 22

6.3. Tests for Continuity ................................................................................................................................. 23

7. CONCLUSION AND APPLICATION ............................................................................................................ 26

8. RECOMMENDATIONS .................................................................................................................................. 26

9. FUTURE WORK............................................................................................................................................... 27

APPENDIX I: NOMENCLATURE AND GLOSSARY OF TERMS ................................................................... 32


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Glossary ...................................................................................................................................................................... 32

Nomenclature ............................................................................................................................................................. 32

APPENDIX II: RESEARCH TIMELINE ............................................................................................................... 32

APPENDIX II: RESEARCH TIMELINE ............................................................................................................... 33

APPENDIX III: SAMPLE CALCULATIONS ....................................................................................................... 34

Table of F igures

Figure 1: Arial View of the Bridge

Figure 2: Cross-Sectional View of the Adjacent Box Girders with the lateral tie

Figure 3: Cross-Section of a Box Girder

Figure 4: Fayette County Bridge (Test Bridge)

Figure 5: Sketch of Bridge Supports

Figure 6: Simulation of Bridge Behavior under load

Figure 7: Visual AnalysisModel

Figure 8: Moment, Shear, and Displacement reactions from simulation

Figure 9: Instrumentation Position

Figure 10: Truck Position 1

Figure 11: Truck Position 2

Figure 12: Bridge DeflectionTest 3 Load

Figure 13: Bridge DeflectionsTest 4 Load

Figure 14: Dynamic Test

Figure 15: Test 4 LoadTuned Continuous Model (top) vs. Tuned Discontinuous Model (Bottom)

Figure 16: Test 3 LoadTuned Continuous Model vs. Tuned Discontinuous Model (Bottom)

Tables

Table 1: Bridge Facts and Figures

Table 2: Property Values of the Girders

Table 3: Simulation Results

Table 4: Strain Gauge Properties

Table 5: Wire Potentiometer Sensitivities

Table 6: Truck Dimensions and Weights

Table 7: Moment of Inertia

Table 8: Concrete Strength

Table 9: Comparison of the Tuned Continuous and Discontinuous Models


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1. INTRODUCTIONWhen bridges are designed, engineers must follow a set of constraints set by the

American Association of State Highway and Transportation Officials (AASHTO). These

guidelines are set primarily for safety reasons. They involve strict criteria for the strength of

materials, dimensions, and construction methods. Along with these design specifications, the

AASHTO provides engineers with formulas and equations of how to estimate and predict the

behavior of the bridge under its own weight, and under external loading conditions.

Unfortunately, despite regular visual inspection by government officials, in 2007 the I-35

Minnesota Bridge did just that, resulting in several casualties. In the disaster, nine people lost

their lives and sixty were injured. Twenty people turned up missing after the collapse. Two years

earlier, an adjacent box girder bridge suddenly collapsed in Lakeview, Pennsylvania. In this case,

no vehicles or people were on the bridge during the collapse. In both cases, there were

substantial financial losses, and people were inconvenienced while the bridges were being

rebuilt. While it is safe and often correct to assume that deterioration of certain features of

bridges cause these collapses, certain aspects of bridge behavior as a result of these

deteriorations still remains a mystery.

In Ohio, a large percentage of bridges are built in the same fashion as the Lakeview

bridge. This presents a possible concern that necessitates thourough inspection procedure for

these types of bridges. As noted in the Minnesota I-35 bridge collapse, visual inspection is not

sophisticated enough to predict the behavior of bridges. In order to get a better understanding of

box girder bridge behavior, researchers often conduct destructive and non-destructive testing of

the bridges and observe the reactions of the members that comprise the bridge and its supports.

Through the use of special instruments, the researchers can measure and record these reactions.


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From these observations, the researchers continue to try to draw conclusions about bridge

behavior.

2. GOAL AND PROJECT OBJETIVESThe main goal of this project is to collect data in a benchmark test on the behavior of an

adjacent box girder bridge through the use of live (external) loads, measuring instruments and

recording software. The objectives for this project are as follows:

Learning Material Strength theory with Dr. Miller

Gather Research and Understanding of the Project

Assist in the Benchmark (baseline) tests

Create Models of the Bridge in Visual Analysis and run simulations

Compare Benchmark Test Results with Simulation Results

Tune the Model (find the true E & I of the bridge)

Compare the Continuous Tuned model to Discontinuous model

Tabulate and Analyze Results


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original un-tensioned length, they apply a compressive force. This pre-compression increases

load-carrying capacity to the beam and helps control cracking to specified limits allowed by

building codes (Precast/Pre-stressed Concrete Institute).

3.1.4. Adjacent Box Girder BridgesPre-stressed box beams are cast in pre-stressing plants. The beams are placed side by side

and held together by lateral tension rods. Grout and shear keys are then used to connect the

beams together (see Fig. 2) .

3.1.5. Deformation and DeteriorationDue to corrosion caused by water and heavy salt treatment during the winter time

corrosion can occur to the beams as well as the internal steel. Because of this the steel strands

begin to deteriorate and the bridge loses tensile support. As the deterioration level of these

strands increases pre-stress force decreases. This decreases the maximum load capacity and

could lead to total collapse of a beam or the bridge.

3.2. Preliminary Analysis of Bridge3.2.1. Bridge Information

The bridge that was tested was an adjacent box girder bridge with pre-stressed concrete

girders. The structure is located in Washington Court House in Fayette County in central Ohio.

The official number of the bridge is 36-17-6.80. The dimensions and material properties of the

bridge are as follows:


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Table 2: Bridge Facts and Figures

Property Value

Type: Adjacent Box GirderLocation: Washington Court House,

Fayette County, Ohio

Time Built: Approximately late 1960sSpans/Length: 3 spans, 48 feet each, 144 ft totalNumber of

Beams/Width:9 adjacent beams, each 3 feet

wide, 27 feet total widthDepth: 21 inchesSkew: 15 degrees left forwardMaterials used: Prestressed Concrete

Figure 1: Plan view of Bridge

Figure 2: Cross-Sectional View of the Adjacent Box Girders with the lateral tie


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3.2.2. Determination of Calculated and Derived ValuesFor the purpose of the preliminary analysis, the basic geometry of the cross-section was

taken into account when finding the moment of inertia (I) for the members. The formula for

determining this value is as follows:

(1)Also, the cross-sectional area of the girders itself was determined by basic geometry, using the

area formula for a rectangle.

3.2.3. Assumed and Approximated ValuesSome of the information of the bridge was either not readily available or subject to

unknown changes since the bridge's construction, or had to be determined experimentally. Such

values included the strength of the concrete, the modulus of elasticity of the concrete, the pre-

stressing tension in the steel strands, the diameter of the pre-stressing strands, and the level of

continuity of the bridge. The assumed values are as follows:

Property Initial value

Distribution Factor .11 (unitless)

Concrete strength 7 ksi

Moment of Inertia 23500 in

Cross Sectional Area 488 in

Strand Diameter 3/8 inch

Continuity Full continuity

Table 2: Property Values of the Girders

Figure 4: Fayette County Bridge (Test Bridge)Figure 3: Cross-Section of a Box Girder


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3.2.4. AASHTO Specifications: Finding the AASHTO specified Moment DistributionFactor

According to the following AASTHO specifications, bridges of this type must be design

with the appropriate distribution factor parameter. Based on the number of girders and several

other physical aspects of the design, AASTHOs equations give a distribution factor for design

only. The actual distribution factor of the bridge will be different since this is a design constraint

(these are usually over estimated). A comparison of between these two values would shed light

on how damaged the bridge is and how it performs according to its initial design.

(2)

Eq. 2 is the formula given by AASTHO for the Distribution factor of a bridge made of girders

that are Precast solid, voided, or Cellular Concrete Box, with Shear Keys and with or without

Transverse Post-Tensioning. All the mentioned physical characteristics coincide with the Fayette

County Bridge.

The following are formulas that facilitate the D.F. calculation (a sample of this calculation can be

found in Appendix III).

(3)

where

(4)


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Eq. 5 is a D.F. reduction factor for skewed bridges (the Fayette County Bridge is this type).

(5)where

When calculated with the appropriate values, the Distribution factor for design of this

type of bridge is 0.2413. This means that the interior girders of this bridge are designed to

distribute roughly 24% of any load to each girder.

3.3.

Simulation of loading

3.3.1. Purpose of SimulatingBefore conducting the on-site Benchmark tests, several simulations were run in order to

have an approximate estimate of how the bridge should behave under the given loads. These

simulations are designed to give internal moments, shear forces, and displacements at any point

along the modeled bridge. Once a model is designed and analyzed and the Benchmark test is

completed, a comparison between predicted and observed values can be done. Also, in the

model, several assumptions must be made regarding the physical characteristics of the bridge

itself (most of these are largely unknown). If the differences between these two values are too

dissimilar, a separate tuning procedure can be done in order to find the true characteristics of

the bridge. Using several iterations of a certain physical aspect of the bridge, the correct one can

be found that results in a displacement similar (within an acceptable error) to the displacement

observed in the Benchmark Test.

Visual Analysis V. 4 and V.7were used in this analysis. This software allowed for the

creation of a two-dimensional model of the Fayette County Bridge. The following section


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contains details on how the bridge was translated into a two-dimensional model, and how the

truck loadings were modeled.

3.3.2. Simulation SetupIn this setup, several steps had to be taken in order to adequately model the bridge in

Fayette County in Visual Analysis. First, since the model must be reduced to only one beam (2D

Model), the width of the bridge is disregarded. Also a distribution factor must be applied to any

real load on the bridge. For the purposes of this simulation a distribution factor of 11% was

applied. The assumption was made that since the bridge contains nine girders, ideally the weight

should be distributed evenly throughout the bridge (connecting grout in the shear keys and lateral

tie, as specified in the bridge plans, should facilitate this distribution, see Fig. 2). The model

contained the correct length and was separated into three spans (48 feet each). The model bridge

also has at one end, a pinned joint, and two roller joints (one at 48 feet and the second at 96 feet

from the leftmost end) that separate it into 3 spans (see Fig.5). The model was also treated as

continuous. As mentioned before, several physical characteristics of the bridge required

estimation for the purposes of this simulation. All of these estimated values were subject to

tuning later in the project.

The Benchmark Test involved six different loadings (trucks were used for this), and each

load comprised of different configuration to the truck locations on the bridge. In the Visual

Analysis model, each tire of the truck was treated as a point load, so if there were 4 trucks on a

particular loading configuration, there would be 24 point loads on the modeled beam (each truck

has 3 axles). These point loads would be located on the model based on their distance from the

abutment (the distance from the side guard rail edges of the bridge were disregarded for the

purposes of creating a 2D model). Figure 6 shows an example of this model and its point loads.


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The six different loadings were simulated, and the following section displays the results from

this analysis.

3.3.3. Simulation ResultsAs stated before, Visual Analysis shows the internal forces and moments throughout the

modeled bridge as well as displacements at every point of the bridge. The max value (in

magnitude) is 0.399 inches at 22 feet (this occurred in Run 3). This simulation does not take into

account the dead load the bridge experiences from its own weight. In light of this and the other

assumptions necessary in order to simulate the behavior of the bridge, the observed

displacements will not be exact.

144 ft

Figure 5: Sketch of Bridge Supports


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Table 3: Simulation Results

7 KSI Strength Concrete Simulation

I = 25300

in^4

A = 488 in^ 2

Max Negative Max Positive

Run Deflection (in) Location (ft) Deflection (in) Location (ft)

1 0.125 22.08 0.04 67.2

2 0.389 22.08 0.142 67.2

3 0.399 22.08 0.144 67.2

4 0.171 22.08 0.03 115.2

5 0.389 22.08 0.14 67.26 0.171 22.08 0.031 115.2

Figure 6: Simulation of Bridge Behavior under load

Figure 7: Visual AnalysisModel

Figure 8: Moment, Shear, and Displacement reactio

from simulation


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4. MEASURING INSTRUMENTS4.1. Strain Gauges

Strain gauges were used to measure and record the strain while the concrete girders

underwent in response to the external load of the ODOT trucks. The gauges that were used were

resistance gauges and measured two inches in length. They were manufactured in Japan, and

were affixed to the bridge using an epoxy solution.

Table 4:Strain Gauge Properties

Property Value

Type: WFLM-60-11-2LT

Gauge Length: 60mm

Gauge Resistance: 120 0.5

Temp Compensation For: 1110-6/oC

Transverse Sensitivity: -5.%

Quantity: 10

Gauge Factor: 1.96 1%

Test Condition: 23C 50%RH

Batch No.: IE28K

Lead Wires : 7/O.127 3W 2m

4.2. String PotentiometerString potentiometers (also known as "wire pots") are generally used to measure linear

displacement. For this project, they were put to use in measuring and recording the deflections of

the individual girders during the tests.


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Table 5: Wire Potentiometer Sensitivities

Beam Wire Pot Model Seal (Series) Sensitivity

(mV/V/inch)

1S A1 (W) PA-15 3708148 64.70

2 A2 PA-20 32010211 46.65

3 A3 PA-15 37080147 64.64

4 A4 PA-15 37080149 64.69

5 A5 PA-15 37080150 64.63

6 A6 PA-10A 9007-5885 97

7 A7 PT-10A 9007-5883 96.6

8 A8 PT-10A 9007-5886 96.8

9N A9 PT-10A 9007-5884 96.6

1S B1(E) PT-108 9007-5887 97.8

2 B2 PT101-0010-111-1110 B0952696 91.39

3 B3 PT101-0015-111-1110 H1003996 61.227

4 B4 PT101-0010-111-1110 J0962400 92.61

5 B5 PT101-0010-111-1110 J0962401 91.96

6 B6 PT101-0015-111-1110 H1003994 62.647

7 Not Applied8 B8 PT101-0010-111-1110 K0866500 91.83

9N Not Applied

5. BENCHMARK TEST5.1. Initial Preparation

The initial preparation of the benchmark test consisted of the following: marking all of

the key locations on the bridge (locations of instruments, span endpoints, origin location datum

Figure 9: Instrumentation Position


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(the southwest corner of the bridge where the bridge begins on the west abutment and on the

white traffic line), etc.), removing the top layer of asphalt at the location of the strain gauges,

setting up the frame for the wire pots below the bridge, gluing all of the strain gauges in place,

testing all of the instruments, and opening the recording software. Much of the aforementioned

preparation was carried out on July 14, 2010. The rest was completed on July 15, 2010.

5.2. Placement of InstrumentsThe location of the instruments was predetermined during the preliminary analysis

(where the location of maximum moment and displacement was found, using Visual Analyis).

Strain gauges were placed on top of the bridge along the midspan (22 ft from the leftmost edge

of the bridge) of the bridge; one located on the center of each beam, with the exception of the

northernmost beam. An additional line of gauges was set out an additional 14 feet 6 inches east

of the first set of strain gauges, which is location of the anticipated inflection point (see Figure

9). On this line, all of the beams had strain gauges affixed to them. Underneath the bridge on the

same lines as on the top, strain gauges were glued to the underside of the bridge, with a gauge on

each beam. Finally, supported by a wooden frame beneath the bridge, wire pots were arranged

along the aforementioned lines, with a wire pot on each beam on the midspan (22 ft from the

leftmost edge of the bridge) line and one on each beam on the inflection line, with the exception

of the northernmost beam and the third northernmost beam.


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5.3. Collection of DataThe collection of data involved applying external or "live" loads in the form of trucks

provided by the Ohio Department of Transportation. TCS for the MegaDec data acquisition

system was used to record the reading of the array of instruments over time in regular intervals.

For this test, the rate of collection was 1200 scans per second. The test involved six static tests

(see Figures 11 and 12), where the four trucks were placed in different locations to investigate

the different reactions. Following the static tests came two dynamic tests, each involving one of

the trucks traveling across the bridge, from west to east, first at 10 miles per hour, and again at

35 miles per hour. Testing began after all of the preparation on July 15, 2010.

Table 6: Truck Dimensions and Weights

License Plate: OF 1050 OF 5591 OG 2791 OD 6634

Number: 41 47 8 31

L R L R L R L R

Front Axle Weight

(lbs)

7500 6900 7250 7250 7350 7700 5400 6650

Middle Axle Weight

(lbs)

9450 10700 9150 9600 9800 11150 9800 11500

Rear Axle Weight

(lbs)

8850 10750 8950 9850 10050 11200 10000 11300

Distance - front axleto middle axle: 13-0 130 13-0 12-6

Distance - font axle to

rear axle:

17-8 178 17-8 1610

Front axle width*: 6-10 6-10 6-10 6-7

Middle and Rear axle

width**:

6-0 6-0 6-0 6-1

*(middle of tire to middle of tire)

** (space between tire pair to space between tire pair)


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5.4. ResultsThe following are figures displaying the displacements found in Test 3 and Test 4

(involving Truck positions 3 and 4). However, only the wire potentiometers in Row A (located at

22 ft) functioned properly.

Figure 12: Bridge DeflectionTest 3 Load

Beam 9

Beam 8 Beam 7 Beam 6 Beam 5 Beam 4 Beam 3 Beam 2Beam 1

-0.4

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

Deflection(in)

Beam

Bridge Deflection - Test 3 Load

Row A

Figure 10: Truck Position 1 Figure 11:Truck Position 2


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Figure 13: Bridge DeflectionsTest 4 Load

6. ANALYSIS OF RESULTS6.1. Tuning the Data to Find Experimental Physical Characteristics.

The results from the Benchmark test showed that the displacements are slightly different

from the predicted values found using VisualAnalysis. This could be due to some of the

assumptions made for the physical characteristics being slightly inaccurate. For this reason

through the iteration of the moment of inertia, and the concrete strength and matching the

displacements produced in their simulations to those found in the Benchmark Test. Below are the

Tables that contain these displacements.

Beam 1

Beam 2 Beam 3 Beam 4 Beam 5 Beam 6 Beam 7 Beam 8Beam 9

-0.25

-0.2

-0.15

-0.1

-0.05

0

Deflections(in)

Beam

Bridge Deflections - Test 4 Load

Row A


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Table 7: Moment of Inertia

Iterations for I

Test 3 Test 4

I (in^4) Displacements

(in)

24800 -0.285 -0.17

24900 -0.284 -0.169

25000 -0.283 -0.169

25100 -0.282 -0.168

25150 -0.281 -0.168

25200 -0.281 -0.167

25300 -0.28 -0.167

Table 8: Concrete Strength

Test 3 Test 4

Strength

(PSI)

Displacement (in)

6800 -0.284 -0.169

6900 -0.282 -0.168

7000 -0.28 -0.167

7100 -0.278 -0.167

7200 -0.276 -0.165

7300 -0.274 -0.163

7400 -0.272 -0.162

7500 -0.27 -0.161

6.2. Tests for ContinuityBelow, Fig.15shows of the dynamic test done in the Benchmark Test. The graph displays

how strain in the first span changes as the truck moves along the bridge. One can infer that the

bridge is continuous due to the positive strain seen. Since the gauge is at the top of the beam of

the first span, when the truck is on the third span, the strain should read as negative (if it is

continuous) and positive when on the second span.


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In Figures 16 and 17,a comparison is done between a continuous tuned model of the

bridge versus a discontinuous tuned model. The discontinuous model has a displacement that is

much larger than the one observed in the Benchmark Test. Also the observed displacement is

within 5% of what the tuned model displays.

Figure 14: Dynamic Test

-1.40E+02

-1.20E+02

-1.00E+02

-8.00E+01

-6.00E+01

-4.00E+01

-2.00E+01

0.00E+00

2.00E+01

4.00E+01

1

549

1097

1645

2193

2741

3289

3837

4385

4933

5481

6029

6577

7125

7673

8221

8769

9317

9865

10413

10961

11509

12057

12605

13153

13701

microStrain

ms


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Figure 16: Test 3 LoadTuned Continuous Model vs. Tuned Discontinuous Model (Bottom)

Figure 15: Test 4 LoadTuned Continuous Model (top) vs. Tuned Discontinuous Model (Bottom)


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Table 9: Comparison of the Tuned Continuous and Discontinuous Models

Test 3 Test 4

Model Displacements (in)

Continuous -0.28 -0.168Observed -0.282 -0.167

Discontinuous -0.405 -0.356

% Difference 0.711744 0.597015

7. CONCLUSION AND APPLICATIONFrom the analysis of the wire-potentiometer data and the dynamic data (Fig. 14) from the

strain gauges most of the basic physical characteristics of the Fayette County Bridge. The

Moment of inertia can be approximated to be roughly 25300 in^4 and the Concrete Strength,

~7000PSI. However, the only way to confirm these two values is to first, take a look at the cross

section (when Dr. Miller and OU conduct the destructive test) to confirm the design from plans,

and second, take core sample and test for strength.

The bridge also seems to be at least partially continuous. The dynamic tests suggest this

and the continuous tuned models show the same displacement as the observed displacement from

the Benchmark Test.

8. RECOMMENDATIONSFirst, it is highly recommended that the cross sectional area and the concrete strength be

tested and recorded.

More testing is needed in order to confirm continuity by 1) observe behavior during the

destructive test 2) synchronize a timer along with the data acquisition to pinpoint exactly when

and where the truck is when positive displacement occurs on the first span (when the truck


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passes the third span) and 3) place truck on the third span and check for any kind of reaction in

the first span where the instruments are installed.

Instruments on the third and possibly second (middle span) should be considered.

Although on the middle span this would be difficult since it crosses the water and no kind of

support would be available for wire-potentiometers and strain gauge attaching, placing strain

gauges on the tops of the beams (after grinding off the asphalt) of the middle span would help in

observing behavior throughout the whole bridge and not just one span.

The strain gauge data did not allow for the examination of the distribution of the load

throughout the girders simply because of the nature of the test. In all tests a combination of four

trucks was used, making difficult to relate one truck to a specific displacement in a beam. To

explore this phenomenon, it is recommended that only truck be used. The location should be

varied so that the effect on displacement/strain in one beam can be observed.

9. FUTURE WORKThe bridge will be subject to further tests. The date and time of these tests is to be

determined. The aforementioned instruments will be used to collect data of the responses to live

loads, as in the benchmark test, but after the girders have sustained intentional damage. After

these series of tests, special equipment will be used to apply increasing loads until the bridge

fails. This will tell the researchers the ultimate load capacity of the bridge after damage. After all

of the tests, including the ones covered in this report, researchers shall have a better idea of the

distribution of forces among the adjacent members, establish a connection between apparent

damage and the effect on the ultimate load capacity, and use the findings to improve bridge

design and inspection methods.


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APPENDIX I: NOMENCLATURE AND GLOSSARY OF TERMS

Glossary

Moment of Inertia - A property, based on its geometry (most generally based on the

object's centroid or cross sectional area) of an object's (or member) resistance to bending.Usually expressed in units of length, i.e. in^4

Concrete Strength This is the compressive strength of concrete, determined

experimentally, and given in units of PSI. This value can be calculated from the Modulus ofElasticity

Modulus of Elasticity - A measure of an object's tendency to be deformed elastically

under an applied force.

Distribution Factor - A design parameter given by AASTHO (can be approximated by

dividing the number of lanes by the number of beams) that specifies the amount of load eachbeam experiences when the bridge is loaded.

Continuity or Discontinuity - If the bridge is separated into several spans, the beams in

each span could be connected to each other making the entire structure continuous. If theyare not, then the structure would be considered discontinuous. These two characteristics

change the response of the bridge from a load.

Tuning - Through several iterations of a simulation, the characteristics of the bridge are

changed until the response matches up with the response seen at the Fayette County Bridge.

This approximates or "tunes" the characteristic in question.

Cross-Sectional Area - This is the area of the inside cross section of a beam.

SkewThe amount of angle given to a bridge with respect to whatever it is over passing.For example if a bridge were placed perpendicular to a river, then there is no skew. However,

if the bridge is placed 15 off the perpendicular then is it considered a 15 degree skew.

Nomenclature

E = Youngs modulus of elasticity

I = Moment of InertiaJ = Polar Moment of Inertia

b = width of the beam (in)

d = depth of beam (in)

L = span of the beam (ft)Nb = number of beams or girders

= skew angle (degrees)

A*

= Area of the body (from parallel axis theorem)z = Distance from the centroid of the body to the axis (from parallel axis theorem)


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APPENDIX II: RESEARCH TIMELINE

Informational Session 06/21-22/2010

Information was provided an introduction to the research. This information told of previous tests

that were done from other research projects and why.

Literature and Lectures 06/24-28/2010

Lectures were given by Dr. Richard Miller and Mr. Dawit on the basics of the physics and

mechanics of bridge structures. Some homework and reading material was provided.

Procurement of Materials and Resources 06/30/2010 to 0713/2010

Materials needed for the experiment were gathered while researching was being done. These

materials consisted of available trucks, wire pots, gauges, etc.

Research Application to Bridge 07/02-07/2010

The information learned from the literature and lectures was then applied to the project bridge in

preparation for visual analysis simulations. This consisted of how the internal forces act in the

bridge such as moment and shear. Also, known characteristics and properties of the bridge were

obtained and documented.

Simulations 07/07-09/2010

Using known information and some assumptions simulations were done for maximizing

deflections on the bridge using Visual Analysis. This was done by finding the precise position to

place the trucks. Simulations were done for continuous and discontinuous cases to model

possible deflections and to obtain deflection results for comparison.

Benchmark Test 07/14-15/2010

This part of the project consisted of benchmark test set-up followed by the benchmark test. This

was a two day event at the bridge located in Washington Court House. Data was collected to be

analyzed at a future time (*see Benchmark Test).

Post-Benchmark Test Analysis 07/16-26/2010

Data was obtained and analyzed. After results for the actually benchmark test were found theses

results where then compared to the simulations to determine the continuity of the bridge. Other

useful Information which could possibly help with future tests were then documented by UC and

OU students and faculty. All possible errors experimental, electronic and environmental were

documented so that they could be fixed or prevented in future tests.


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Conclusion 08/02-06/2010

All Information for this project was then put together in a note book, report, poster and power

point for documentation and presentation needed in the future.

APPENDIX III: SAMPLE CALCULATIONS

AASTHOs Distribution Factor

b=36 in d=21 in

L=48 ft =9 beams

( )

( )

final paper reu summer2010

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