Testing of Overhead Box Truss Chords and Flanges a Thesis

Testing of Overhead Box Truss Chords and Flanges

A thesis presented to

the faculty of the Russ College of Engineering and Technology of Ohio University

In partial fulfillment

of the requirements for the degree

Master of Science

S. Nicholas Sparks

August 2017

This thesis titled

Testing of Overhead Box Truss Chords and Flanges

S. NICHOLAS SPARKS

has been approved for

the Department of Civil Engineering and the Russ College of Engineering and Technology by

Eric P. Steinberg

Professor of Civil Engineering

Dennis Irwin

Dean, Russ College of Engineering and Technology 3

ABSTRACT

SPARKS, S. NICHOLAS, M.S., August 2017, Civil Engineering

Testing of Overhead Box Truss Chords and Flanges

Director of Thesis: Eric P. Steinberg

Overhead box truss structures are used every day by motorists to navigate through the interstate system. It is typical for an overhead box truss to experience multiple types of loading over its life span. One of the most common loading types an overhead sign structure will experience is wind loading. This study provides a synthesis of results from destructive testing of damaged overhead box trusses. Testing was done to provide a theoretical and experimental analysis in order to understand how damaged trusses would react under the most severe wind loads in Ohio.

Throughout the duration of this study two processes were used. First, an analytical model was developed using SAP2000 to model how an overhead box truss would react with the application of wind loads. From that full scale model, a sample model was created to mimic the loading from the full scale model. The sample model was used to create an experimental testing procedure. Secondly, full scale experimental testing was conducted to validate the analytical model.

It was hypothesized that the severity of the damage surrounding the bolted connections would result in catastrophic failure. Two trusses, one with a medium level of damage and one with high level of damaged were tested. The use of two trusses with different levels of damage was used to determine at what point catastrophic failure would occur. 4

It was determined from this study that damaged connections were able to transfer the load without increasing the level of damage. It was also found that failure occurred at the welds. This was seen from the failure of Test 2 at the interface between the chord and flange. It was also found that higher stresses were induced in the truss during the experimental testing compared to the stresses that were determined from the analytical analysis. Meaning, that the overhead box truss would be able to support higher loading than what was expected from the SAP2000 analysis.

ACKNOWLEDGMENTS

First, I would like to thank my graduate advisor, Dr. Eric Steinberg for all the time and support he provided to me throughout this entire process.

In addition, I would like to thank Dr. Ken Walsh, Dr. Issam Khoury, and Dr.

Annie Shen for serving as my thesis committee. I also want to take this time to thank

Josh Jordan, Dillon Strahler, Dominik Steinberg, and David Beegle who assisted throughout the testing process.

Next, I would like to express my gratitude towards my family. I want to thank my wife Kayla, and my parents Jayne and Stephen Sparks for the continuous support and encouragement throughout my years of study. Additionally, I want to take time to thank my grandfather Otis Bradley for sparking my interest in the engineering field in which I have come to enjoy greatly. I also want to recognize my other grandfather, Jerry Sparks, who unfortunately passed away during my time at Ohio University.

Finally, I want to thank all my friends that I made during my six years at Ohio

University. I made wonderful memories and will never forget my time here.

TABLE OF CONTENTS

Page

Abstract ...... 3 Acknowledgments...... 5 List of Tables ...... 8 List of Figures ...... 10 Chapter 1: Introduction ...... 14 1.1: Background ...... 14 1.2: Problem Statement ...... 16 1.3: Goal ...... 17 1.4: Presentation of Study ...... 18 Chapter 2: Literature Review ...... 19 2.1: Introduction ...... 19 2.2: Load Considerations ...... 21 2.2.1: Loading Types ...... 21 2.2.2: Dead Loads ...... 21 2.2.3: Live Loads ...... 21 2.2.4: Ice Loads ...... 22 2.2.5: Wind Loads ...... 22 2.3: Maximum Loading Conditions ...... 26 2.4: Fatigue ...... 27 2.5: Aluminum Structure Design ...... 31 2.5.1: Allowable Bending Stress ...... 32 2.5.2: Combined Stresses ...... 35 Chapter 3: Methodology ...... 37 3.1: Overhead Support Model Overview ...... 37 3.1.1: Material Properties ...... 37 3.1.2: Full Scale Overhead Sign Structure Model ...... 38 3.1.3: Locating Critical Section ...... 41 3.2: Sample Overhead Truss Structure ...... 42 7

3.2.1: Location of Provided Samples ...... 42 3.2.2: Sample Structure Computer Model ...... 45 3.3: Experimental Setup ...... 52 3.3.1: Framing and Truss Mounting ...... 52 3.3.2: Strain Gage Placement ...... 60 3.3.3: Strain Gage Mounting ...... 63 3.3.4: Sting Potentiometer ...... 65 3.3.5: Load Cell ...... 66 3.3.6: Testing Procedure ...... 66 Chapter 4: Results ...... 68 4.1: Sample SAP2000 Results ...... 68 4.1.1: SAP2000 Data ...... 69 4.1.2: Analysis of Sample Structure Computer Model Data ...... 71 4.2: Full Scale SAP2000 Results ...... 76 4.3: Experimental Test 1 Analysis ...... 78 4.3.1: Joint Analysis ...... 79 4.3.2: Load and Deflection Data ...... 81 4.3.3: Strain Gage Data ...... 87 4.4: Experimental Test 2 Analysis ...... 103 4.4.1: Joint Analysis ...... 104 4.4.2: Load and Deflection Data ...... 107 4.4.3: Strain Gage Analysis ...... 111 Chapter 5: Discussion ...... 122 Chapter 6: Conclusion...... 130 References ...... 132 Appendix A: General Information ...... 135 Appendix B: Testing Information ...... 137 Appendix C: Data from First Test ...... 142 Appendix D: Data from Second Test: ...... 153

LIST OF TABLES

Page

Table 1: Group Load Combinations (AASHTO 2013) ...... 26 Table 2: Fatigue Importance Factor (AASHTO 2013) ...... 28 Table 3: Allowable Stress Formulas (AASHTO, 2013) ...... 32 Table 4: Allowable Stress Formulas Continued (AASHTO, 2013) ...... 34 Table 5: Allowable Stresses for Cast Aluminum (AASHTO 2013) ...... 35 Table 6: Box Truss Material Properties ...... 38 Table 7: Overhead Truss Design (ODOT, T7-.65) ...... 39 Table 8: Truss Model vs. Section Model Axial Forces ...... 51 Table 9: Diagonal Rosette Gage Locations ...... 62 Table 10: Internal Member Forces ...... 71 Table 11: Shear Force to Shear Stress Calculation ...... 73 Table 12: Stresses on Chord Members ...... 75 Table 13: Internal Member Forces Full Scale Truss ...... 76 Table 14: Shear Force to Shear Stress Calculation ...... 76 Table 15: Full Scale Internal Stresses ...... 77 Table 16: Test 1 Sample Data of Load Cells (LC) and String Potentiometers (SP) ...... 82 Table 17: Test 1 String Potentiometer Data Transformation ...... 84 Table 18: Test 1 Sample Strain Gage Data ...... 88 Table 19: Test 1 Stresses of Uniaxial, Biaxial, and Bolt Gages ...... 89 Table 20: Test 1 Strain and Stress Calculations Rosette Gage R1 (Member 197) ...... 100 Table 21: Test 2 Load Cell (LC) and String Potentiometer (SP) Data ...... 108 Table 22: Test 2 Deflection Data ...... 109 Table 23: Test 2 Sample Strain Gage Data ...... 112 Table 24: Test 2 Stresses for Uniaxial and Biaxial Gages ...... 113 Table 25: Test 2 Strain and Stresses for R1 ...... 119 Table 26: Internal Stress (psi) ...... 126 Table 27: Deflections at Maximum Loading ...... 127 9

Table 28: Deflections after Test Completion ...... 128 Table 29: Aluminum Properties (AASHTO, 2013) ...... 136 10

LIST OF FIGURES

Page

Figure 1: Road Sign Dimensions (ODOT, 2012) ...... 15 Figure 2: Example Traffic Signs ...... 16 Figure 3: Decommissioned Truss Locations...... 17 Figure 4: Ice Load Region Map (AASHTO 2013) ...... 22 Figure 5: Basic Wind Speed Map for Eastern United States (AASHTO 2013) ...... 25 Figure 6: Stress Range vs. Number of Cycles (AASHTO, 2013) ...... 31 Figure 7: Overhead Sign Section ...... 40 Figure 8: Overhead Sign with Axial Loads ...... 42 Figure 9: Truss Connection (ODOT, 2015) ...... 43 Figure 10: Crack Criteria Used for This Study ...... 44 Figure 11: Model of Sample Section ...... 46 Figure 12: Cantilevered Section...... 48 Figure 13: Cantilever Section Results ...... 49 Figure 14: Load Distribution ...... 50 Figure 15: Final SAP2000 Model ...... 52 Figure 16: CAD Drawings of the Drilled Holes ...... 53 Figure 17: Frame Location and Beam Placement ...... 55 Figure 18: Slotted Connection ...... 56 Figure 19: Steel Tube Mounted to the Load Frame ...... 57 Figure 20: Added Steel Diagonal ...... 58 Figure 21: Connection Restraint ...... 59 Figure 22: Truss Setup ...... 60 Figure 23: Position of Biaxial Gages ...... 61 Figure 24: Rosette Gage Placement on Chord ...... 62 Figure 25: Prepared Aluminum Surface ...... 64 Figure 26: Truss Member Labels ...... 69 Figure 27: Member 197 Shear and Moment Data ...... 70 11

Figure 28: Tube Cross-Section ...... 72 Figure 29: Location of Stress Points ...... 74 Figure 30: Member 197 Stresses...... 75 Figure 31: Initial Joint Cracks (Joint 1 Left and Joint 2 Right) ...... 80 Figure 32: Test 1 Load vs. Time Graph ...... 83 Figure 33: Test 1 Before Testing Deformation ...... 85 Figure 34: Test 1 Permanent Deformation...... 86 Figure 35: Test 1 Load vs. Deflection ...... 87 Figure 36: Test 1 Uniaxial: Stress vs. Time ...... 90 Figure 37: Test 1 Position of Flange Connection ...... 91 Figure 38: Test 1 Bolt Gages Stress vs. Time ...... 92 Figure 39: Test 1 Location of Biaxial Gages ...... 93 Figure 40: Test 1 Joint Crack Locations ...... 93 Figure 41: Test 1 Longitudinal Biaxial Gage Stress vs. Time ...... 95 Figure 42: Test 1 Transverse Biaxial Gage Stress vs. Time ...... 96 Figure 43: Rosette Diagram Figure from (SM-06: Strain Gage Rosette 2016) ...... 97 Figure 44: Example Gage Layout ...... 98 Figure 45: Test 1 Longitudinal Stress from Rosette Gages R1-R3 ...... 101 Figure 46: Test 1 Transverse Stresses from Rosette Gages R1-R3 ...... 102 Figure 47: Test 1 Shear Stresses from Rosette Gages R1-R3 ...... 103 Figure 48: Test 2 Initial Joint Cracking (Joint 1 Left and Joint 2 Right)...... 105 Figure 49: Test 2 Cracked Weld ...... 106 Figure 50: Test 2 Change in Cracking (Before, During, and After Loading) ...... 107 Figure 51: Test 2 Load vs. Time ...... 109 Figure 52: Test 2 Load vs. Deflection ...... 111 Figure 53: Test 2 Longitudinal Stresses in Members 197 and 198...... 114 Figure 54: Test 2 Location of Biaxial Gages ...... 115 Figure 55: Test 2 Joint Crack Locations ...... 115 Figure 56: Test 2 Longitudinal Stress vs. Time Biaxial Gages ...... 117 Figure 57: Test 2 Transverse Stress vs. Time Biaxial Gages ...... 118 12

Figure 58: Test 2 Longitudinal Stresses Rosette Gages R1-R3 ...... 120 Figure 59: Test 2 Transverse Stresses Rosette Gages R1-R3 ...... 121 Figure 60: Test 2 Shear Stresses from Rosette Gages R1-R3 ...... 121 Figure 61: Fatigue Threshold for Steel Sections...... 135 Figure 62: ODOT Aluminum Truss Overhead Sign Support Standard Drawing (ODOT, TC-7.65) ...... 137 Figure 63: Joint Damage Index ...... 138 Figure 64: String Potentiometer 1 ...... 139 Figure 65: String Potentiometer 2 ...... 139 Figure 66: String Potentiometer 3 ...... 140 Figure 67: String Potentiometer 4 ...... 140 Figure 68: Load Cell ...... 141 Figure 69: Truss 100B Inspection Sheet ...... 142 Figure 70: Test 1 Longitudinal Stress Member 10 ...... 143 Figure 71: Test 1 Transverse Stress Member 10 ...... 143 Figure 72: Test 1 Longitudinal Stresses Member 4 ...... 144 Figure 73: Test 1 Transverse Stresses Member 4 ...... 144 Figure 74: Test 1 Longitudinal Stresses Member 2 ...... 145 Figure 75: Test 1 Transverse Stresses Member 2 ...... 145 Figure 76: Test 1 Longitudinal Stresses Member 11 ...... 146 Figure 77: Test 1 Transverse Stresses Member 11 ...... 146 Figure 78: Test 1 Longitudinal Stresses Member 14 ...... 147 Figure 79: Test 1 Transverse Stresses Member 14 ...... 147 Figure 80: Test 1 Longitudinal Stresses Member 19 ...... 148 Figure 81: Test 1 Transverse Stresses Member 19 ...... 148 Figure 82: Test 1 Longitudinal Stresses Gages R12-R14 Members 179 and 180 ...... 149 Figure 83: Test 1 Transverse Stresses Gages R12-R14 Members 179 and 180 ...... 149 Figure 84: Test 1 Longitudinal Stresses gages U7-U12 Members 179 and 180 ...... 150 Figure 85: Test 1 Bolt Gage H3 and H4 ...... 150 Figure 86: Test 1 Longitudinal Stresses for Biaxial gages Member 179 and 180 ...... 151 13

Figure 87: Test 1 Transvers Stresses for Biaxial Gages Members 179 and 180 ...... 152 Figure 88: Truss 315A Inspection Sheet ...... 153 Figure 89: Test 2 Longitudinal Stresses Member 10 ...... 154 Figure 90: Test 2 Transverse Stresses Member 10 ...... 154 Figure 91: Test 2 Longitudinal Stresses Member 4 ...... 155 Figure 92: Test 2 Transverse Stresses Member 4 ...... 155 Figure 93: Test 2 Longitudinal Stresses Member 2 ...... 156 Figure 94: Test 2 Transverse Stresses Member 2 ...... 156 Figure 95: Test 2 Longitudinal Stresses Member 11 ...... 157 Figure 96 Test 2 Transvers Stresses Member 11 ...... 157 Figure 97: Test 2 Longitudinal Stresses Member 14 ...... 158 Figure 98: Test 2 Transverse Stresses Member 14 ...... 158 Figure 99: Test 2 Longitudinal Stresses Member 19 ...... 159 Figure 100: Test 2 Transverse Stresses Member 19 ...... 159 Figure 101: Test 2 Longitudinal Stresses Gages R12-R14 Members 179 and 180 ...... 160 Figure 102: Test 2 Transverse Stresses Gages R12-R14 Members 179 and 180 ...... 160 Figure 103: Test 2 Longitudinal Stresses Gages U7-U12 Member 179 and 180 ...... 161 Figure 104: Test 2 Longitudinal Stresses Biaxial Gages B7-B12 ...... 162 Figure 105: Test 2 Transverse Stresses Biaxial Gages B7-B12 ...... 163 14

CHAPTER 1: INTRODUCTION

1.1: Background

As automobiles became a popular mode for travel, people began to travel further from home. Due to the increase of motorists on the roadways, traffic controls system needed to be established. In 1922, a group of researchers planned to travel through the states to develop standards for signs and markings. Based on the research, the

Mississippi Valley Association of State Highway Department (MVASHD) developed the sign shapes that are used in today’s road signs. In the years following the initial research, organizations such as the American Association of State Highway Officials (AASHO, now known as AASHTO), and National Conference on Street and Highway Safety

(NCSHS) began to publish their own sign standards (Hawkins 1992).

In January of 1927, the first national signing manual, called the Manual and

Specifications for the Manufacture, Display, and Erection of U.S. Standard Road

Markers and Signs, was published. By 1930, it was determined that more work would need to be done to signing in both rural and urban areas. In 1935, the Manual on

Uniform Traffic Control Devices was established (Hawkins 1992).

Over the years, road signs have become an integral part of everyday travel.

Throughout the years these traffic signs have become larger to easily display information.

A typical highway road sign can be 11 feet in width and 10 feet in height (ODOT, 2012).

Figure 1 shows the typical measurements for highway signage. With road signs increasing in size, there is a demand for a structure that is able to support the signs and still be able to withstand external loading. For example, motorists can encounter overhead 15 signs that are supported by a bridge or overhead truss structure. Signs may also be supported with a cantilever structure. It is also common to see traffic signs presented on the side of the highway. The three common types of sign structures can be seen below in

Figure 2 (a: Two Small Span Overhead Sign Structure, b: Route 840 Extension, c: Red

Deer Lake).

Figure 1: Road Sign Dimensions (ODOT, 2012)

(a) (b) (c) Figure 2: Example Traffic Signs

One of the common sign structures used to support signs over the highways are overhead truss structures. The Ohio Department of Transportation (ODOT) uses two types of overhead truss sign structures, a steel box truss and an aluminum box truss. The overhead box truss is an effective structure due to its ability to span across multiple lane highways, which allows motorists to view the overhead signs clearly. These overhead box trusses are designed to last 50 years and over their design life, the structures are exposed to harsh weather conditions. Repeated wind loads from both nature and passing vehicles along with the age of the structure can begin to cause cracking; therefore, inspections are done periodically to ensure that these structures are reliable.

1.2: Problem Statement

The Ohio Department of Transportation conducted inspections of their overhead box trusses in Cleveland, Ohio during fall of 2015. From these inspections, ODOT found that cracks were beginning to develop on the flanges, which were used to bolt sections of the truss together. Based on the severity of cracking and due to concerns related to safety, ODOT removed seven existing overhead trusses from service. 17

1.3: Goal

The goal of this research was to determine if damaged connections of overhead box trusses could withstand maximum expected applied loads. To meet this goal, the first objective was to create a computer model using a finite element program. This program was used to model an actual overhead box truss to determine what kinds of loads are expected under Ohio conditions. From this computer model, a second model was created to simulate the full scale truss behavior in the sections provided from ODOT.

Finally, with the use of the second model, experimental testing was conducted to validate the computer model and to determine how a damaged truss would withstand service loading.

315-A 315-B

100-A 100-B

Figure 3: Decommissioned Truss Locations

1.4: Presentation of Study

Chapter 2: Literature Review discusses topics that are related to overhead sign structures. The Literature Review is used to explain loading, fatigue, and aluminum design. Chapter 3 continues with the Methodology. The Methodology chapter discusses the setup of the computer analyses. Following the computer analysis, the chapter continues with the experimental setup, which includes how the test frame was built, and how the truss samples were arranged for testing. Chapter 4: includes the results from the

SAP2000 computer analyses, experimental test 1, and experimental test 2. This chapter discusses the results with the use of tables and graphs to show how the trusses behaved under the loading conditions. Finally, Chapter 5: Discussion compares the results of both experimental results to the computer analyses results. Chapter 6: Conclusions, draws final conclusions based on the results and discussion.

CHAPTER 2: LITERATURE REVIEW

2.1: Introduction

This literature review provides an in depth knowledge of highway road sign structures along with various types of loading that the structure may experience. One of the most common road sign structures is the overhead box truss. The overhead box truss is widely used due to its structure capability of spanning multiple lanes of traffic and providing support for the road signs informing motorists. The large size of the structure along with the size of the sign causes the structure to experience multiple types of loading throughout its life span. As infrastructure ages, maintenance of these existing structures is a vital part of ensuring their reliability. During maintenance, the Ohio Department of

Transportation has recorded a number of cracks in the overhead sign structure joints.

These joints are a key structural aspect of an overhead box truss to bolt sections of the truss together. This raises the question, how do these cracks in the joints affect the structures ability to withstand loading?

A 2015 study by Leduc aimed to determine how the failure of one member would affect the entire structure. Leduc hypothesized, the failure of one member would result in extra stresses distributed throughout the truss. This would result in failure of other members. This study considered dead and wind loads applied to an overhead box truss modeled into a finite element computer program. To test this hypothesis, various aluminum members were removed one at a time to see when failure of the truss would occur. From Leduc’s analysis he found, when the diagonals were removed from the top front chord, failure of the truss would occur (Leduc, 2015). 20

Another study by Foutch in 2006 conducted field testing of sign structures. This study was conducted for the Illinois Department of Transportation in hopes to determine the design load capacity in addition to how the overhead box truss would resist fatigue.

This study investigated both overhead box trusses and cantilevered sign structures.

Foutch placed sensors on the structures and recorded data from truck induced wind loads.

Foutch found that the aluminum diagonal members are most likely to experience vibrations from wind loads. Over the lifespan of the structure these vibrations can cause cracking along the members. It was discussed that the newer sections used for Illinois sign structures would not experience as much cracking from these vibrations (Foutch,

2006).

Both of these studies considered how multiple types of loading affected the diagonal members. Neither study considered how the connections would affect the box truss structure. In this research, decommissioned box trusses were tested to determine how the load was transmitted through damaged joints under maximum expected load conditions. To understand the maximum loading conditions experienced by the sign structure, first the loading types are presented in section 2.2. Section 2.3 documents the maximum loading condition an overhead sign structure will experience. Section 2.4 considers fatigue calculations. Finally, the design of the aluminum structure along with allowable stresses through the members is considered in section 2.5. 21

2.2: Load Considerations

2.2.1: Loading Types

The American Association of State Highway and Transportation Officials or otherwise known as AASHTO hold standards for all structures and pavement seen on the

American highways. AASHTO has published the Standard Specifications for Structural

Supports for Highway Signs, Luminaires, and Traffic Signals. This publication lists the general design and analysis of the structure supporting signs and the use of materials such as wood, steel, concrete, and aluminum. It also specifies design requirements for fatigue, breakaway, and loading considerations. According to AASHTO (2013), the loading considerations that are of primary concern are dead load, live load, ice load, and wind load.

2.2.2: Dead Loads

Dead loads come from the structure itself. Dead loads include the weight of the support structure, luminaires, traffic signals, lowering device, and any other apparatuses permanently attached to and supported by the structure (AASHTO, 2013). For the overhead sign structure, the dead load was considered to be the weight of the structure, the signs mounted to the structure, and under some cases, maintenance walkways.

2.2.3: Live Loads

Live loads are used for the design of the maintenance walk ways or service platforms. Based on AASHTO (2013), a 500 lb. live load is estimated for one person and equipment. This 500 lb. live load is distributed over a two foot section on the walk way and service platforms. 22

2.2.4: Ice Loads

Ice loads are considered throughout the majority of the United States. Regions of the United States that factor ice loads into their design calculations can be found in

Figure 4. The regions that are required to consider ice loads use a load of 3.0 psf

(AASHTO 2013). The 3.0 psf load is to be applied to the surface of the structure supports, traffic signals, horizontal supports, and luminaires. Ice loads are also taken into consideration for the road signs. However, the ice load should only be considered on one face of the sign panel. AASHTO also states that an ice load of 3.0 psf can be increased in locations where historical data suggest a higher load is necessary.

Figure 4: Ice Load Region Map (AASHTO 2013)

2.2.5: Wind Loads

The final load consideration is wind loads. There are two types of natural wind loads that a structure could experience; static and dynamic wind loads. Dynamic wind loads introduce resonating vibrations. However, these vibrations are negligible and 23 therefore should be calculated using static load (Dyrbye, 1997). Wind loads are constantly changing, thus it is usually difficult to determine the maximum magnitude of load to apply to a structure. To accurately assess these changing winds, records from nearby weather stations are used to calculate the mean wind velocity (Dyrbye, 1997).

Static wind loads are then taken as the mean wind velocity and applied to the structure.

These wind loads are applied to the structure using pressure loads, which are applied horizontally to the structure. Due to their structural geometry, these structures will experience a wide range of loads (Dyrbye, 1997; Foutch, 2006). The largest static wind loads typically occur during storms. From these storms, a maximum wind load can be calculated. These loads are used as an equivalent wind load that is then evenly applied over the entire sign structure.

Other than static wind loads, an overhead sign structure can also encounter truck induced wind loads. A study by (Cali and Covert, 2000) found that a traveling vehicle creates an air bubble located near the top of the vehicle. This air bubble travels with the vehicle and can strike an overhead sign resulting in large wind forces on the structure.

This wind load is a fast acting force that quickly diminished as the vehicle continues past the sign. They also determined that the shape of the vehicle does not influence the magnitude of the wind load. Another study conducted by (Foutch, 2006) found that the truck configuration can induce a variety of wind loads. Foutch found that the largest wind gust can come from box trailers. AASHTO accounts truck-induced wind loads for fatigue design and natural wind gust when determining the wind loading. 24

The wind pressure is calculated using AASHTO (2013) wind pressure equation as seen in Equation 1. This equation is based on fluid-flow theory obtained from the

American Society of Civil Engineers (ASCE) publication of Minimum Design Loads for

Buildings and Other Structures (ASCE/SEI, 2005)

2 푃푧 = 0.00256퐾푧퐺푉 퐼푟퐶푑 (푝푠푓) (1)

Where 퐾푧= Height and Exposure Factor

G = Gust Effect Factor

V = Basic Wind Speed

퐼푟 = Wind Importance Factor

퐶푑= Drag Coefficients

The basic wind speeds are determined from three-second wind gusts. These three-second gusts are specific to regional location. AASHTO has basic wind maps for

10, 25, and 50 year mean recurrence. ASCE specifies that there are special wind regions, these special wind regions account for regions with higher wind speeds. The special wind regions are determined with the use of records that indicate higher wind gusts than what is seen in the chart. For example, mountainous terrains or gorges could experience higher winds. The 50 year mean wind speeds in kph (mph) for the eastern United States can be seen in Figure 5. From the figure, Ohio falls within 90 mph wind speed line. This specifies that roadway structures built in Ohio use 90 mph wind speeds for design

(ASCE/SEI, 2005). 25

Figure 5: Basic Wind Speed Map for Eastern United States (AASHTO 2013)

Basic wind speed is an important aspect of the wind pressure equation. However, there are other factors that need to be considered. AASHTO (2013) provides how to either calculate the factors or to determine them from various tables. To determine the factors, the assumption of a minimum design life of overhead sign structure is to be taken as 50 years. AASHTO uses a table to determine the wind importance factor for a 50 year design life. From the table the wind importance factor is 1.00 for a non-hurricane region.

The height and exposure factor can be also be found in a table or be calculated using an equation. A typical height and exposure factor for overhead sign structures is 1.00.

AASHTO states that the minimum gust factor is 1.14. Finally, the drag coefficient depends on the geometry of where the wind pressure is applied. In order to calculate the drag coefficient, AASHTO lists the various types of sign and structure members with the coefficient, or a formula to calculate the coefficient. This list is used when calculating the wind pressure on a single element. 26

2.3: Maximum Loading Conditions

AASHTO lists four groups of load combinations (AASHTO, 2013). The four groups and their load combinations can be seen in Table 1. The load combination takes into account multiple loads in order to determine the controlling load combination. As seen in Table 1, group load I through III all include the dead load of the structure. Group

II adds wind load and group III adds ice load. However, the wind load in group III is cut in half. For group load III, the wind load considered has a minimum wind pressure of

25psf. The last group load, group load IV, only considers fatigue loading.

Table 1: Group Load Combinations (AASHTO 2013)

For this research, group II loading, which is a combination of both the dead load and wind load, is considered when calculating the stresses in the critical members as well as through the flanges. 27

2.4: Fatigue

Structures that experience a variety of loading types and weather conditions are susceptible to fatigue. Fatigue is defined as, a weakening of material that is subjected to repeating cycles of stress. Over their life time, overhead signs and other traffic related structures are constantly experiencing periodic low to high wind loading. The changing magnitudes of the wind load will induce fatigue onto a structure, which is considered a major issue in design life of a structure. Structures can exhibit fatigue in a variety of ways including weakening critical members, to inducing cracks at welded or bolted connections. Understanding how fatigue will affect a structure will help during the design process.

Overhead signs structures are designed to resist wind-load-induced stresses

(AASHTO, 2013). The AASHTO 2013 standards recommend using the infinite life fatigue design. The infinite life fatigue design can be simplified into nominal stress- based design as expressed in Equation 2.

(∆푓)푛 ≤ (∆퐹)푛 (2)

Where:

(∆푓)푛 = the nominal wind-load-induced stress

(∆퐹)푛 = the nominal fatigue resistance

To use the nominal stress-based design, the strength of the materials are calculated by using simple strength calculations as determined by applied loads and section properties (AASHTO, 2013). AASHTO states that the calculations should use the gross section properties. 28

Fatigue importance is used to identify the reliability of a structure. AASHTO specifies three levels of importance. Level I is classified as a hazardous failure event.

Level I is to be considered on roadways with a speed limit over 35 mph, average daily traffic (ADT) over 10,000, and average daily truck traffic (ADTT) over 1000. Level III is for roads with a speed limit less than 35 mph. Level II is defined as anything that falls between level I and level III. Fatigue importance factors can be seen in Table 2.

Table 2: Fatigue Importance Factor (AASHTO 2013)

Table 2 shows the factors applied to the design loads of galloping, natural wind gusts, and truck-induced gusts. Galloping is only considered for cantilevered sections leaving only two factors for the noncantilevered sections. The applied loadings use an equivalent static wind load for calculations (AASHTO 2013). The first equivalent static wind load is the natural wind gust load. The natural wind pressure equation comes from a study performed by Kaczinski in 1998 (Kaczinski, 1998). Kaczinski found that 98 29 percent of cities mean wind speed was below 13 mph. The data collected from the 59 weather stations also showed 81 percent of cities also saw mean wind speeds less than 11 mph. Based on this study, it was determined that the mean wind speed was 11 mph. The mean wind velocity changes due to location. However, from AASHTO, most of the country falls under the mean wind velocity of 11 mph. The natural wind pressure equation can be seen in Equation 3.

The second equivalent static wind load is the truck-induced gust. This pressure equation is similar to the natural wind equation with only a change to the coefficient in front of the variables. The truck induced static wind pressure equation can be seen in

Equation 4. The truck-induced gust loads are applied both vertically and horizontally to the structure. Most commonly, the pressure loads are applied to the horizontal surfaces.

Equation 4 below is based on a truck traveling at 65 mph. If the speed limit greatly varies, the pressure load can be re calculated using the AASHTO equations. Truck- induced loads are not required for design. However, the owner can request it for fatigue design.

PNW = 5.2 ∗ 퐶푑 ∗ 퐼퐹 (3)

P푇퐺 = 518.8 ∗ 퐶푑 ∗ 퐼퐹 (4)

Where:

푃푁푊 = Pressure of the natural wind (psf)

푃푇퐺 = Pressure of the truck induced gust (psf)

퐶푑 = Drag coefficient based on the yearly mean wind velocity

퐼퐹 = Fatigue importance factor (see Table 2) 30

Now that the applied loads can be calculated with the use of Equations 3 and 4, the section properties need to be defined. In the Standard Specifications for Structural

Supports for Highway Signs, Luminaires, and Traffic AASHTO article 11.9.2 lists how to calculate the section properties based on the section criteria.

The nominal fatigue resistance, also known as the fatigue threshold, is used to compare to the nominal fatigue stress. The nominal fatigue resistance is calculated using

Equation 5 (AASHTO, 2013). Fatigue resistances are threshold values for steel structures. To convert the fatigue resistance values to apply for aluminum structures the values need to be divided by the factor of 2.6. A graphical representation of the fatigue resistance can be seen in Figure 6. AASHTO specifications also list the fatigue threshold for a verity of sections. A sample of the AASHTO table can be seen in Figure 61 in

Appendix A.

퐴 1/3 (5) (∆퐹) = ( ) TH 푁 Where:

A = the finite life constant

N = the number of wind load induced stress cycles 31

Figure 6: Stress Range vs. Number of Cycles (AASHTO, 2013)

2.5: Aluminum Structure Design

In AASHTO’s publication of Standard Specifications for Structural Supports for

Highway Signs, Luminaires, and Traffic Signals, the standard design criteria of aluminum structures are listed. This chapter lists types of aluminum with material properties along with yield and ultimate stresses. A portion of this table is provided in Appendix A Table

29. This chapter provides formulas to calculate allowable stresses for all types of member configurations. An example of the allowable stress formulas is provide in Table 3. 32

Table 3: Allowable Stress Formulas (AASHTO, 2013)

2.5.1: Allowable Bending Stress

An overhead sign structure is composed of four cords, which are expected to carry the majority of the forces. The maximum allowable bending stress in the cords can be determined using AASHTO aluminum design (2013). The equations for a round tube can be seen in Table 3 as Equation Set 6.4-3. From the aluminum design charts, the allowable tension stress in the extreme fiber should be calculated using the smaller of the two equations. The first equation in Equation Set 6.4-3 calculates allowable stress using tensile yield strength and a factor of safety on yield stress (AASHTO, 2013). The first equation calculated the allowable stress as 21.2 ksi. The second equation in Equation Set

6.4-3 uses the tensile ultimate strength, coefficient for tension members, and a factor of safety on ultimate strength. The allowable stress was calculated as 19.5 ksi; therefore

19.5 ksi allowable tension stress is used to design the aluminum chords. 33

The allowable compression stress uses a similar equation to the allowable tension stress. However, for the allowable compression stress, slenderness of the member must be considered. The allowable compression stress equations can be found in Table 4

as Equation Set 6.4-13. In Equation Set 6.4-13, the allowable stress equation is dependent upon the slenderness of the member. The slenderness limits were checked so that the correct allowable stress equation could be used. It was determined that S1 was

10.75 and S2 was 97.54. The slenderness of the truss was calculated as 13.39 meaning, the allowable compression stress is calculated between S1 and S2. The allowable stress equation in column c for Equation Set 6.4-13 was used. It was determined that the allowable compression stress was 30.5 ksi.

Table 4: Allowable Stress Formulas Continued (AASHTO, 2013) 35

AASHTO also lists the allowable stresses for casting alloys (2013). This is important because prior to ODOT’s most recent standard drawings for overhead signs the flanges could be cast aluminum, and the flanges that are tested in this research are cast aluminum. AASHTO does not provide allowable stress formulas for cast aluminum, but they do have a table that provides allowable stresses for cast aluminum. Table 5 provides the types of stress along with the type of cast aluminum. An allowable stress value can be obtained for both welded and non-welded castings based on the type of casting.

Table 5: Allowable Stresses for Cast Aluminum (AASHTO 2013)

2.5.2: Combined Stresses

Structural members can be subjected to a combination of stresses; such as bending, axial, shear, and torsion. AASHTO accounts for the combined stresses through an interaction equation. The interaction equation for axial compression, bending, and shear can be seen in Equation 6. The interaction equation for axial tension, bending, and shear can be seen in Equation 7. 36

2 fa 푓푏 푓푠 + + ( ) ≤ 1.0 (6) Fa0 퐶퐴퐹푏 퐹푠

2 fa 푓푏 푓푠 (7) + + ( ) ≤ 1.0 퐹푡 퐹푏 퐹푠

Where:

푓푎 = average compressive or tensile stress on the cross-section produced by an axial load

퐹푎0 = Allowable compressive stress for a member considered as an axially loaded column

푓푏 = Maximum bending stress produced by transverse loads or bending moments

퐹푏 = Allowable stress for members subjected to bending only

퐶퐴 = Amplification factor to estimate additional moments due to P-delta effects

푓푠 = Shear stress on cross-section caused by torsion or transverse shear loads

퐹푠 = Allowable shear stress for members subjected only to shear or torsion

퐹푡 = Allowable tensile stress for axial load only

CHAPTER 3: METHODOLOGY

3.1: Overhead Support Model Overview

3.1.1: Material Properties

Overhead box trusses are constructed using two types of materials, steel and aluminum. The structure under consideration was primarily aluminum. The materials used during construction are obtained from the ODOT standard drawings (TC-7.65,

2011). The material properties can be found in ODOT Construction and Material

Specifications. The sign was constructed using three types of materials; tube aluminum, cast aluminum, and stainless steel. The aluminum tubes are required to comply with

ASTM B 241 and needed to be built from 6061-T6 aluminum. The aluminum flanges were allowed to be composed of cast aluminum or fabricated. Aluminum castings had to comply with ASTM B 26, aluminum 356-T6 or T7. Finally, the stainless steel hardware was required to comply with ASTM A 320. Furthermore, the American Society for

Testing and Material (ASTM) standards classifies the material properties. Table 6 provides the material properties for the components of the box truss obtained from

ODOT material standards (ODOT, 2013).

Table 6: Box Truss Material Properties

3.1.2: Full Scale Overhead Sign Structure Model

To model a full scale overhead sign structure, the finite element computer

Structural Analysis Program (SAP2000), created by Computers and Structures, Inc. was utilized. This Program allows for three-dimensional modeling and performs analyses with linear and nonlinear static and dynamic loads.

The overhead sign structure was a recreation of the model used in Leduc (2015).

This recreation is an aluminum box truss structure supporting two traffic signs. The structure conforms to the ODOT standards for overhead sign structures. Additionally, tube sizes along with pole sizes, flange dimensions, and number of bolts can be seen in

Table 7. 39

Table 7: Overhead Truss Design (ODOT, T7-.65)

This overhead box truss is a simply supported box truss with two support structures. The box truss consists of four chords with diagonal connections spanning 54 feet over the roadway. Furthermore, sections of this truss were connected using six bolt flange connections. The two support structures are 26 foot tall steel frames. This model was designed using the ODOT Aluminum Truss Overhead Sign Support Standard

Drawing (see Appendix B, Figure 62). The SAP2000 model of the full scale layout is provided in Figure 7 below. 40

Figure 7: Overhead Sign Section

The model is completed when the desired applied loads are in place. The expected loads are stated in the design criteria specified in the AASHTO standard specifications.

In addition, the geometry of the signs was not shown in the model. However, the model considered how the signs would attach to the box truss and apply the loads at those same points. For example, the self-weight of the sign was applied and acted as a gravity load.

Then, the pressure load was distributed along the surface of the sign. The wind load pressure Equation 1 was used to calculate the applied loads. It was calculated that sign 1 would impart a 28.13 psf load and sign 2 would impart a 26.00 psf load.

Using the surface area of the signs, the pressure load was converted into a point load. Sign 1 was calculated at 381 pounds, which was applied at each point load location. These point loads were applied to the top and bottom chord at three locations spaced six feet apart. The first point load started at six feet from the left support. Sign 2 41 required eight point loads of 598 pounds at each point load location. These point loads were placed at four points along both the top and bottom chord. Additionally, the point loads for the second sign were applied to the chords 24 feet from the left support, with the same six foot spacing used for sign 1. Finally, a distributed wind load of 13.4 pounds per foot was applied to the exposed members of the truss. It should be noted, all of these loads were applied as wind loads in the horizontal direction.

3.1.3: Locating Critical Section

The greatest concern related to the overhead box truss connections, was the location of highest force. The locations of the connections vary for overhead sign structures. The length of each section determined these locations. When looking at this full scale model, there were two connection locations. This model’s critical forces were considered at mid span, placing the connection location at mid span, the connections would experience the highest possible loading. Therefore, the mid span was chosen due to the high internal axial load acting through the members.

SAP2000 computed the applied loads that were distributed to each individual member throughout the model and the forces that were transmitted through the connections. From the model, it was determined that the loads were primarily distributed through the four main chords. From the load distribution, it was noticed that the two chords on the front side of the model were subjected to compression forces; while the chords on the backside of the truss experienced tension forces.

Figure 8 below, displays the members near mid span with the member label.

Figure 8 also shows the magnitude of the axial force in the four chords. The forces are 42 shown as blue for compression and red for tension. The center of the truss is located between member 179 and 180.

Figure 8: Overhead Sign with Axial Loads

The full scale model demonstrated the internal axial loads acting within the four chords were experiencing similar magnitudes. An axial load of ten kips was experienced by all four chords. For comparison between the full scale model and the modified section model, a ten kip axial force in the chords will be considered.

3.2: Sample Overhead Truss Structure

3.2.1: Location of Provided Samples

During the inspections of the box trusses on interstates 2, 90, 71, 273, and 480 it was found that 15 of the structures acquired cracks on the flanges. Figure 9 below shows an example of the cracks on the truss flange. A combination of the quantity of the cracks, along with the number of flanges that were identified with cracks, resulted in immediate 43 removal of seven structures, which were removed from service on September 30, 2015 and completed October 8, 2015.

Figure 9: Truss Connection (ODOT, 2015)

From the seven trusses removed from service, a damage index was created to identify what trusses were most damaged. This damage index accounts for three levels of cracking. The three levels of cracking can be seen in Figure 10. As shown in Figure 10 there is a small, medium, and big level of cracking. The small crack level accounts hairline cracks. The medium cracking level accounts for larger cracks where two cracks are seen around the same bolt. The big crack level accounts for three cracking types.

These three cracking types include, if there are three cracks, if a section of the flange is missing, or if the crack is large in nature.

Figure 10: Crack Criteria Used for This Study

The damage index applies an amplification factor for each level of cracking. A small, medium, or big crack is multiplied by a factor of 1, 2, or 3, respectively. The cracks are tallied then multiplied by their corresponding amplification factor and then summed together for each joint. Finally, all four joints are summed together to get the final overall damage. This damage index table is provided in Figure 63 (Appendix B). 45

The full length of the trusses can be quite large and therefore, difficult to transport. The trusses were cut down into seven smaller sections, approximately ten feet in length with the connections in the middle of each section. This allowed for the connections to remain bolted to prevent further damage attempting to unbolt the sections.

The approximate ten foot length also allowed for an optimal testing sample.

3.2.2: Sample Structure Computer Model

These sample sections were provided by ODOT in hopes of recreating internal stresses by the use of various loading conditions. The full scale model that was completed in section 3.1.2 helped determine the internal forces so in turn, these internal forces could be recreated in these sample sections. The sample section model was created by modifying the full scale model. First, the externally applied loads were removed from the full scale model. Once all the loads were removed from the structure, the truss was cut down to size by removing extra members. The members removed, included those located on the two support structure, along with some of the chords and diagonal members. The final model consisted of a small section of the full scale model as shown in Figure 11.

Figure 11: Model of Sample Section

Once the working model was created, the next step was to determine the best way to match the results from the full scale truss model to this new section model. In order to match the results and determine the best end conditions and placements of the loads, multiple models were made resulting in an iterative process. The first model created, tested multiple end conditions to recreate the internal loading from the full scale model to this section model. The first trial assumed a pinned support system applied to all eight chord ends. Two point loads of ten kips were applied, one ten kip load between members

179 and 180 and the other ten kip load between members 197 and 198. These applied loads were put into place to ensure that the load was acting toward the back of the section. In SAP2000, these loads were seen acting on the negative y-axis. From trial 1, the cords that were supposed to experience tension had no axial internal load. The load was transmitted through the diagonals and then right into the supports. Model 1 did not produce the desired behavior. As a result of this discrepancy, various end conditions were considered.

Trial 2 replaced all eight end restraints with fixed supports. The loading conditions were kept the same from trial 1 to trial 2. From SAP2000, the use of fixed end 47 supports did not have the desired effect. The axial force determined within the chords was minimal. Therefore, Trial 2 results were almost identical to trial 1’s results.

However, with the fixed supports, moments were registered in trial 2. Trail 1 and Trial 2 did not achieve the desired behavior that was being sought so other configurations of supports and load needed to be considered.

Trial 3 considered an approach by testing the sample section as a cantilever. By supporting the section as a cantilever, one end was restrained while the other end was free and subjected to the applied loads. The restraints were fixed supports, and the applied loads were the same as before, two ten kip loads. However, the loads acted at the end of member 180 and member 198. Trial 3 set up can be seen in Figure 12. To better understand the behavior, it was recognized that the chords in the front of the model would experience tension forces while the chords at the back of the model would be subjected to compression.

Figure 12: Cantilevered Section

Initially, Trial 3 model was yielding results that were comparable to the full truss model. The results from Trial 3 are provided in Figure 13. As stated before, the members that are highlighted in blue are the members under tension while those in red signify compression. The main focus of this analysis was to recreate the internal loads for the tension members. Using this cantilevered section, three out of the four chord members demonstrated an axial force. The two chords on the top closely match the complete truss model. However, one of the chords on the bottom experienced almost little to no axial load. On the other hand, the chord on the bottom experienced a larger axial load that was not comparable to the complete truss model. From Trial 3 it was determined that a cantilevered section was the method to use. However, more trials were necessary to see if other supports or members should be added to yield results more consistent with the complete truss model. 49

Figure 13: Cantilever Section Results

To build off of Trial 3, a member was added between various joints. An extra member was added between joints 127 and 165, joints 127 to 44, and joints 127 to 157.

These members were not added all at one time, rather, each member was added individually to see which added member produced results consistent with the complete truss model. After multiple SAP2000 analyses, it was determined a member needed to be added between joints 127 and 165. Using this additional member, the results from

SAP2000 exhibited the two upper chords’ axial force had decreased. The two lower chords axial force also changed. All the internal forces in the chords were lower than the complete truss model. However the internal forces were relatively similar for all four chords. The only member that was not comparable to the complete truss model was member 179. 50

To decrease the internal force in member 179 adding an additional member would not help, therefore, an external support was added. The external support was placed on at a time between the connection at members 179 and 180 and also between members 197 and 198. After both external restrains were examined in SAP2000, it was determined that an external restraint should be placed at the connection between members 179 and 180.

This external restraint should resist movement as the load was applied. With the added support in the SAP2000 model, the axial forces within the chords began to closely match the full truss model. The force in member 180 was the only force that varied from the full truss model. The difference between the section model and the full truss model with member 180 was only off by 1.5 kips. The axial force distribution can be seen in Figure

14.

Figure 14: Load Distribution

It was noticed that a diagonal member was missing in the model seen in the sample. A diagonal member needed to be added at the joint between members 197 and

198 to the joint between members 233 and 234. The member was then added to the

SAP2000 analysis. With the addition of this member, the SAP2000 the results were compared one last time to the full scale mode. It was found, with the addition of this member, the internal forces in the section model were more comparable to the truss model. The internal axial forces for both the full scale and sample truss models are provided in Table 8.

Table 8: Truss Model vs. Section Model Axial Forces

With the section model finalized, the model was rotated to match how the actual sample was tested. The final SAP2000 model can be seen in Figure 15 The two applied loads from the hydraulic cylinders were applied from the floor upward. The added support was at the lower backside of the sample section. This was a representation of how the sample was to be tested in the lab.

Figure 15: Final SAP2000 Model

3.3: Experimental Setup

3.3.1: Framing and Truss Mounting

This experiment was set up and conducted in the Structures Laboratory at the

Athens Campus of Ohio University; located on the ground floor of the Academic and

Research Center. The Structures Lab includes a four foot thick reinforced concrete strong floor, along with a hydraulic pump and two hydraulic cylinders. This strong floor contains four holes in a square pattern each containing threaded anchors. These threaded anchors located at the bottom of the holes and used to bolt the load frame to the floor.

Before any work was done for the experimental setup, an Auto CAD drawing was created to show the testing setup. To plan the initial setup of the experiment, the 53 positioning of the load frame needed to be confirmed. Drawings of both the columns and beams were placed in CAD. The original existing load frame was wider than the holes on the strong floor. The placement of the load frame needed to match the hold down holes in the strong floor. The CAD file with the location of the holes in the base plate of the frame columns can be seen in Figure 16. New holes had to be drilled into the base plates to match the hold down holes in the floor and to avoid the existing holes in the base plates. Avoiding the old holes ensured that the frame was secured to the strong floor.

Figure 16: CAD Drawings of the Drilled Holes

With the column locations established, the positioning of the load frame beams needed to be determined. The first step in this process was to place the bottom beams on the frame in order for the aluminum box truss to be mounted to the frame. Also, the box truss had to be placed high enough off the strong floor to allow load cells and the hydraulic cylinders to be placed under the other end of the truss. From the CAD design, the bottom flange of the bottom load frame beam was placed eighteen inches from the 54 strong floor. Additionally, the bottom chord of the box truss was twenty two inches off the strong floor. The twenty two inches gave room for the load cells, hydraulic cylinders, and steel channels for load distribution. The second beam to restrain the top chord of the truss was six feet and six inches from the strong floor to the bottom flange.

Next, the column holes were spaced to match the holes in the beams. There were two rows of holes on both sides of the flange. The holes started at the top of the column and extended down. The holes stopped four feet from the ground. More holes were required so that the bottom beam could be mounted. A total of 12 bolts, six on each side, were used to ensure the beams were mounted properly and the connection was strong enough to support the testing.

Once the columns were moved into place, the base plates of the columns needed to be restrained to the strong floor. Three holes were drilled in the base plates for the threaded rods to go through. Figure 16, shows the holes that were the drilled into the base plates. The hole locations were determined from CAD in order to line up with the stong floor hold down holes. The threaded rods were then threaded into the strong floor.

Finally, washers and nuts were used to fully secure steel base plates to the strong floor.

With the columns in place, the placment of the beams was completed. The frame with two beams attached can be seen in Figure 17. This first placement of the beams was to ensure that the truss would fit on the load frame. The next step was to determined how the truss would be mounted to the load frame.

Figure 17: Frame Location and Beam Placement

To create a fixed support, a male/female connection was devised in order to make the connection fit inside the aluminum chord of the truss. A square steel tube (3.5 in. by

3.5 in.) one foot was used. To limit the amount of movement between the aluminum chord and the steel tube, steel angles were welded to one side to reduce the amount of free space. The connection with the steel angles can be seen in Figure 18. A hole was drilled in both sides of the steel tube and matching identical holes were drilled in the aluminum chord of the truss. To prevent the truss from slipping when loaded, a bolt was threaded through the hole. This connection was used for all four chords.

Figure 18: Slotted Connection

Once the steel angles were welded to the steel tube, the tubes were welded to the beams. To ensure the corect placment of the tubes the truss, was hoisted into place and the tubes were tack welded to the beam. The truss was then removed to finish the welds of the tubes to the beams. The final load frame with the truss support connections can be seen in Figure 19. 57

Figure 19: Steel Tube Mounted to the Load Frame

To emulate the analytical modeling, it was necessary to add another support and member to the truss. These added fixtures were required to help the box truss section act as the full scale truss. A restraint on the back side chord located over the truss connection was needed. In addition, a member was added on the back side lower chord spanning 58 from the loading area to the top chord connection. This added member consisted of two square steel tubes (see Figure 20).

Figure 20: Added Steel Diagonal

The added support was placed at the lower back connection. For this support, a four by four inch steel tube four feet long was used. The support was located between two of the strong floor hold down holes. Furthermore, the threaded rods had to be seven 59 feet long so that they could be anchorded to the floor and extend past the steel tube. The restraint provided by the support was needed so the connection would not move vertically upward. This added support can be seen in Figure 21.

Figure 21: Connection Restraint

Figure 22: Truss Setup

3.3.2: Strain Gage Placement

Strain gages were placed throughout the lower half of the truss. To properly compare the experimental and analytical results, the location of the gage, the gage type, and the gage orientation was recorded. This information was used to correctly identify the results at the same location from the SAP2000 analysis. The correct gage transformation as well as using the right strain to calculate the stress, was also necessary.

Uniaxial gages were placed on the top and bottom of the two bottom chords. A total of twelve uniaxial gages were used. Four of the gages were located five inches from the connection, two on each side. Two gages were located 24 inches from the connection toward the free loading end of the truss section. The other six uniaxial gages were on the 61 other bottom chord and located at the same longitudinal positions. The uniaxial gages were placed parallel to the chords. Placing the uniaxial gages parallel allowed for the calculation of stresses in the top and the bottom of the chord.

There were a total of twelve biaxial gages placed on the two lower chord connections. The gages were placed so that the longitudinal and transverse stresses in the flange connections could be calculated. Two biaxial gages were placed at the same location on separate flanges so that the load between the two flanges could be compared.

The gage positions can be seen in Figure 23. The set of gages were placed at three locations along the bottom flanges, top, bottom, and side.

Figure 23: Position of Biaxial Gages

Nineteen strain gage rosettes were placed throughout the chords and diagonals. A total of six rosettes were placed in line with the uniaxial gages on the side of the chords.

The placement of the rosette on the chord can be seen in Figure 24. This placement allowed for the shear to be calculated. The other thirteen rosettes were placed on the diagonal members. The rosette gages were planted on the top and side of the diagonal 62 members. The locations of the rosette on the diagonals can be seen in Table 9. Rosette gages were also used for the two additional steel diagonal members. Two gages were arranged on the inside steel member and one was placed on the outside steel member.

Figure 24: Rosette Gage Placement on Chord

Table 9: Diagonal Rosette Gage Locations

Four bolt gages were used inside the top and bottom bolt of the two bottom connections. These gages were mounted by the process of drilling a hole into each bolt 63 and gluing the gage to the inside of the bolt. The bolt gages were used to understand how the load was transferred through the bolts. The top and bottom bolts were instrumented to account for possible bending stresses on the top and bottom of the chord. These gages along with the uniaxial gages would help show the load transfer along the whole chord.

3.3.3: Strain Gage Mounting

To properly use a strain gage, the gage needed to be bonded to the material, in this case the aluminum members. Through the bonding process the strain gage acts as the material would under load. This is necessary so that data can be recorded on how the material is behaving under an applied load. Therefore, the installation procedure used followed the recommendations from Kyowa.

Before the bonding of the strain gage could be executed, the cleaning of the aluminum was required. The first step was determining the best location on the aluminum where the strain gage would give the desired data. Next, 400 grit sand paper was used to sand off the aluminum and remove years of weathering in the field. Enough of the aluminum was sanded off when the material returned to its bright shiny finish. The sanding also roughened up the surface so that the glue was able to adhere to the aluminum. Next, a guideline was essential for the proper placement of the gage. To successfully create a guideline, a ballpoint pen was used to burnish a line and not to leave any ink residue behind. Once the guideline was draw on the aluminum, the surface was cleaned with acetone. Acetone was used to remove all the small particles and oils during the sanding process along with the large ink particles. The aluminum was then ready for gage installation. A prepared aluminum surface can be seen in Figure 25. 64

Figure 25: Prepared Aluminum Surface

A piece of tape was placed over the gage with the tape being longer than the gage.

The tape helped with placing the gage so that the guidelines on the aluminum match the guidelines on the gage. With the gage adhered to the tape, it was then placed and aligned on the aluminum. The tape held the strain gage in place until the adhesive was added.

One edge of the tape was peeled back to expose the underside of the gage and allowed placement of a drop of strain gage cement (CC-33A) between the gage and the aluminum. The gage was carefully rolled back down so that the strain gage cement spread over the underside of the gage. It was important to ensure that the adhesive covered the whole gage to ensure complete successful bonding. The gage was held in place for thirty seconds to one minute to achieve full bonding. Once the gages were in place, wiring the gages to the Optim Electronics, Megadac data acquisition began. These steps were repeated for all the uniaxial, biaxial, and rosette gages.

In addition to the three types of gages used, there were also four strain gages drilled into the top and bottom bolts of the two bottom chords. A hole was drilled into the stainless steel bolt using a titanium drill bit. The hole was drilled two and one quarter inches into the bolt past the center of the connection so that the strain through the bolts 65 could be recorded. Then, degreaser was sprayed into the hole to remove all the debris.

The gage was then pushed into the hole so that the middle of the gage was at center of the connection. A two part strain gage cement (EP-180 A and EP-180 B) was mixed together, then injected into the hole. After 48 hours, the gage was secure and the gage wires could be attached. A tab was glued to the bolt head and the gage wires were then soldered to the tab. Then extra lead wires were also soldered to the tab. These lead wires were then connected to the boards, which were later connected to the Megadac data acquisition system.

3.3.4: Sting Potentiometer

String potentiometers were used to record the deflection data. Two of the string potentiometers were placed at the free end of the truss to record the maximum deflection.

A string potentiometer was also placed at the truss connection between members 197 and

198 and members 179 and 180. Data from the string potentiometers used to compare the experimental deflections to the deflections from the SAP2000 analyses. Each string potentiometers had their own set of calibration data. This calibration data is used to create a conversion equation to convert the recorded data from millivolts to a displacement in inches. The calibration data of the four string potentiometers are shown in Appendix B. With the use of the calibration data the displacement and measured output were graphed. From this graph, a linear equation was determined. This was done for each string potentiometer due to variation for each one.

SP1 푦 = 2.0563푥 − 0.1988 (8)

SP2 푦 = 2.0594푥 − 0.2241 (9) 66

SP3 푦 = 2.0542푥 − 0.2184 (10)

SP4 푦 = 2.0573푥 − 0.1270 (11)

3.3.5: Load Cell

A load cell was placed under each of the hydraulic cylinders. Each load cell had a

75,000 lbs. capacity. A computer program, in the data acquisition system that recorded the data, converted the voltage reading automatically into a load. For both load cells, the output was three millivolts per volt. The use of the computer program to convert the load cell readings into load was necessary to know the applied load during the experimental testing.

3.3.6: Testing Procedure

The testing began with the initial setup of all sensors. The sensors were wired into the data acquisition system. Eight sensors could be wired to a board then, using ribbon cables, a total of fourteen boards where connected to the Megadac data acquisition system. After all sensors were connected a sensor test was run to check if the sensors were recording data. There was also a test on the load cells and string potentiometers to ensure load and deflection would increase while load was applied. Once these steps were completed, all sensors were ready for testing.

With the sensors working, the hydraulic cylinders were then checked. The need for a slow flow rate was to ensure that the sensors did not miss any data. First, the hydraulic pump needed to be turned on to test that the cylinders were working. The pump flow rate was set to ensure a desired loading rate. The flow rate was assumed by a visual observation. The cylinders were now prepped and ready to begin testing. 67

With the initial setup completed, the test was ready to be performed. First, recording on the sensors began. Next, the hydraulic cylinders were activated. The load was applied gradually. As the load was being applied, it was being recorded on the computer. Once a total load of 20,000 lbs. was achieved, the hydraulic cylinders were halted. The 20,000 lbs., 10,000 lbs. on each load cell, was the desired loading as calculated from the finite element analyses. The deformed shape was then recorded. The load was then released until no load was being recorded. Finally, the data was saved for analysis.

CHAPTER 4: RESULTS

4.1: Sample SAP2000 Results

With the finite element analysis completed, review and interpretation of the results was necessary. The assessment focused on the two lower chords and the attached diagonals. For ease of comparison, Figure 26 below shows how the members were labeled. In the field, the chord on the bottom of the backside was labeled in two sections, one before and one after the flange connection. For testing, the truss needed to be rotated a quarter turn, which resulted in a position change of the members. The bottom back chord from the field was now located at the bottom front for testing. The new position for this chord can be seen in the Figure 26 and is labeled as member 197 and 198. With the rotation of the truss for testing, the chord on the top of the backside in the field was now the chord on the bottom back in Figure 26. This chord was labeled as members 179 and 180. The diagonal members are also labeled in Figure 26. The diagonal member labels are red distinguish them from the chord labels. The primary joints are also shown in Figure 26, labeled in blue. 69

11 180 179 19 10 4

197

Joint 1 2

Joint 2

198

Figure 26: Truss Member Labels

4.1.1: SAP2000 Data

The axial forces, stresses, and shear forces of the members were determined using

SAP2000. This was based on the sample structure computer model developed in section

3.2.2. The shear and moment data provided from SAP2000 for member 197 can be seen in Figure 27. Furthermore, SAP2000 has the ability to calculate the shear force and moment at any location along the member. Figure 27 was used to show the shear force and moment at 31 inches from the support frame. These values obtained from SAP2000 will be used later to compare to the experimental results. 70

Figure 27: Member 197 Shear and Moment Data

The internal forces of the two bottom chords are provided in Table 10. Table 10 lists the axial force, shear force, and the moment at three specific locations for each chord. The locations are expressed as the distance from the support frame. These locations were selected so results could be compared to strain gage data at the corresponding locations on the experimental tested sections. 71

Table 10: Internal Member Forces

4.1.2: Analysis of Sample Structure Computer Model Data

The shear force data from the SAP2000 analyses were converted to shear stress.

Therefore, a conversion was required so that the shear stresses could be easily compared between the analytical and experimental results. In order for the comparison, the shear force obtained from SAP2000 was transformed into shear stress using Equation 12

(Hibbeler, 2014).

푉푄 (12) 휏 = 푥푦 퐼푡 Where:

휏푥푦 = the shear stress at a location from the neutral axis

V = the shear force for SAP2000

I = moment of inertia for a hollow tube

t = thickness of the member at the location where τ was needed

Q = the first moment of the area about the neutral axis for the hollow tube 72

Shear stresses were calculated by multiplying the shear force by the first moment of the area. Then it was divided by the thickness of the member and the moment of inertia of the hollow tube section. The first moment of the area was calculated using Equation

13 (Hibbeler 2014).

푄 = 푦̅′퐴′ (13)

Where:

A’ = area of the member above or below where the stress was being determined

푦̅′ = the distance from the neutral axis to the centroid to A’

The cross-section of the aluminum chord can be seen in

Figure 28. The following three equations were used to calculate the geometric properties of the hollow tube. Equation 14 and 15 were used to calculate the moment of inertia and cross sectional area, respectively. Equation 16 was used to calculate the distance from the neutral axis to the centroid of the area being considered.

Figure 28: Tube Cross-Section

1 (14) 퐼 = 휋(푟 4 − 푟 4) 4 표 푖

1 (15) 퐴′ = 휋(푟2 − 푟2) 2 표 푖

2 (16) 푦̅′ = 푟 휋 푚

Where:

푟표 = outside radius

푟푖 = inside radius

푟푚 = average of the outside radius and the inside radius

The shear force and the calculated shear stress values are provided in Table 11 at the designated locations as discussed earlier.

Table 11: Shear Force to Shear Stress Calculation

The normal stresses were provided directly from the SAP2000 analysis.

SAP2000 allows for normal stresses to be obtained at eight points along the circumference of the tube. The locations of the eight stress points for the tubes are shown in Figure 29.

5 4

Figure 29: Location of Stress Points

Maximum and minimum normal stresses were determined based on the eight stress point locations. Stresses for member 197 can be seen in Figure 30. These stresses were obtained from SAP2000 at the top and bottom of the chord. In addition, stresses from the diagonals were obtained from the top and side of the member. The internal stresses of the chords can be seen in Table 12. 75

Figure 30: Member 197 Stresses

Table 12: Stresses on Chord Members

4.2: Full Scale SAP2000 Results

The internal forces determined by SAP2000 for the full scale model were determined in a similar way as the sample model. The internal forces of the backside chords of the full scale model are provided in Table 13. From the provided internal forces it is noticed that the shear force is minimal. When the shear stress is calculated from the shear force, the maximum shear stress was calculated as -2.00 psi for member

179 and -0.19 psi for member 197. The shear stresses can be seen in Table 14.

Table 13: Internal Member Forces Full Scale Truss

Table 14: Shear Force to Shear Stress Calculation

The internal stresses throughout the truss model were obtained from the finite element analysis similar to the sample model stresses. The stresses of concern consisted of the stresses along the backside of the model. Those members were undergoing tensile stresses. The stresses are provided in Table 15. The internal stresses were obtained from stress point 4 and stress point 5. Stress points 4 and 5 were located along the front face and the back face of the member, respectively. The testing setup changed the orientation of the truss stress points 4 and 5 that correspond to stress points 1 and 8 on the sample truss. The SAP2000 stress locations can be seen from Figure 29.

Table 15: Full Scale Internal Stresses

The stresses provided in Table 15 show that the stress in the backside chords all experienced tension. It can also be seen that the stresses along the chord members experienced similar stresses at all locations. This means that the stresses are transferred through the members uniformly. 78

4.3: Experimental Test 1 Analysis

The damage index values were used to determine which trusses to test. The damage index values ranged from 25 for the least amount of damage to 86 for the most amount of damage. The primary concern was the two back joints. This is due to the assumption that the two chords in tension from wind loading were the controlling chords.

A second damage joint index was created only considering the backside joints. The damage of the backside joints ranged from a low value of 3 to a high of 38. Using the damage index of the backside joints, it was decided that the first experimental test would be conducted on a truss with medium to high damage. It was determined that the first experimental test was to be conducted on truss 100B.

Truss 100B was located over highway 480 in Cleveland, Ohio after mile marker

17 with the traffic heading in the easterly direction. Truss 100B had a calculated damage index of 73 with a backside damage index of 22. In addition, the backside top and bottom joints had the same damage value of 11.

Test 1 was conducted on August 26, 2016. Prior to testing, the experimental setup discussed in section 3.3 was also followed. Following the experimental setup, strain gages were attached to the truss at locations discussed in section 3.3.2. Testing began by using the procedure discussed in section 3.3.6. The overall test duration took 7 minutes. Data was recorded at 600 readings a second. After the data was recorded, it was then filtered to remove some of the noise. The data was filtered at 30 hertz and then resampled to 100 hertz to reduce the magnitude of information. 79

4.3.1: Joint Analysis

Before physical testing, inspection documentation of the joints was reviewed. The

University of Toledo completed ODOT’s inspection forms with the use of visual observations. From the completed inspection sheet it was documented that three big cracks and one medium crack were seen on the joint between members 197 and 198. The inspection sheet also indicated that parts of the joint were unable to be seen, therefore, the level of damage was not indicated on the inspection. The left photo of Figure 31 shows the locations of cracks on the first joint. The second joint between members 179 and 180 was documented with one large crack, two medium cracks, and one small crack. The photo of the right of Figure 31 exhibits the location of the largest crack on the second joint.

Figure 31: Initial Joint Cracks (Joint 1 Left and Joint 2 Right)

The cracks were deep, however, they appeared to not extend to the bolt. As seen in Figure 31, the cracks extended horizontally from bolt face to the interface between the castings. In some cases like the photo in the left, the crack extended through both flanges. It appeared that the bolt was being pulled out. Locations seen with multiple cracks also showed larger cracks widths. These sections looked as if the cast aluminum was loose. However, the cracked section did not move after the application of manual force. The smaller cracks demonstrated limited crack width. Also, some of the smaller cracks also extended longitudinally through the flange section.

The joints were inspected after the completion of the test to see if the application of load caused new cracks to appear or if existing cracks expanded and/or propagated. 81

The visual inspection of the joints showed that the joints did not show any obvious signs of changes to the pre-existing cracks.

4.3.2: Load and Deflection Data

String potentiometers and load cells were placed and the locations were recorded.

Load cell 1 and string potentiometer 1 were placed near the free end of member 198.

Load cell 1 was located four inches from the end and string potentiometer 1 was 11 inches from the end. Load cell 2 and string potentiometer 2 were placed near the free end of member 180. Load cell 2 was located five inches from the end and string potentiometer 2 was 13 and ¾ inches from the end. String potentiometer 3 was paced two inches from the joint casting interface between member 179 and 180.

First, the load cells and string potentiometer data was analyzed. The data acquired from the load cells did not require data transformation. Next, the string potentiometer data was recorded mV/V/inch requiring a transformation of the data to obtain the initial and final deflections along with the deflections throughout the test. A sample of the data for the load cells and string potentiometers near maximum loads can be seen in Table 16 at the maximum loads. 82

Table 16: Test 1 Sample Data of Load Cells (LC) and String Potentiometers (SP)

The test procedure required each hydraulic cylinder to apply a load of 10,000 pounds to match the computer model. As seen in Table 16, Load Cell 1 (LC1) recorded a maximum load of 10,735.7 pounds while Load Cell 2 (LC2) recorded a maximum load of

10,022.1 pounds. For the ease of the data analysis, the maximum applied load was taken at 286.27 seconds. The load at each load cell during the duration of the test can be seen in Figure 32.

During the initial stages of the test, the loads were applied at a constant rate allowing for the load to increase at a constant rate. At approximately 150 seconds, the loading rate changed. That can be noticed by the pause in the loading after 150 seconds.

The pause in the loading was due to concerns related to creaking and sound heard from the truss. With the concerns of possible catastrophic failure, load was applied, then 83 paused for short periods. The two quick spikes around 200 seconds were the result of the truss shifting during loading. The loads measured by the two load cells also began to differ. LC1 showed higher values than LC2. However, the behavior shown by the load cells was very similar with loading peaks occurring at the same time. At approximately

300 seconds, the unloading process began. As load was removed from the truss, the load cells showed the loading to decrease at the same rate. The truss was completely unloaded at less than 400 seconds.

Figure 32: Test 1 Load vs. Time Graph

The string potentiometer data required a transformation so that the millivolt (mV) reading was transformed into a displacement reading. The equations from section 3.3.4 84 were used in the data analysis. In Table 17, the string potentiometer displacement data is provided.

Table 17: Test 1 String Potentiometer Data Transformation

Table 17 shows the deflections recorded from the string potentiometers as the maximum load was achieved. Table 17 also lists the final displacement once all loads were removed. String potentiometer 1 (SP1) was located near the end of member 198.

String potentiometer 2 (SP2) was positioned near the end of member 180. The maximum deflections near the ends of member 198 and member 180 were 6.40 inches and 5.83 inches, respectively. The total permanent deformation of the truss near the end of member 198 was 1.81 inches. Additionally, the total permanent deformation of the truss 85 near the end of member 180 was 2.27 inches. Figure 33 shows the truss at the initial stages prior to loading, Figure 34 shows the deformed truss shape once testing was complete.

Figure 33: Test 1 Before Testing Deformation

Figure 34: Test 1 Permanent Deformation

The truss deformation throughout the loading process can be seen in Figure 35.

The graph shows the three string potentiometers during the loading and unloading of the truss. The permanent deformation can be seen once unloading is completed.

Figure 35: Test 1 Load vs. Deflection

4.3.3: Strain Gage Data

There were four types of strain gages used during this test. A sample of the raw strain gage data has been placed in Table 18. The data was recorded in micro-strain. The four types of gages were labeled as follows: the uniaxial gages were labeled with a U; rosettes were labeled with an R with the use of A, B, and C to denote the three gages in the rosettes; the biaxial gages were labeled with a B, and like the rosettes A and B are to help distinguish the two gages within the biaxial gages; finally, the hole gages are labeled with a H.

The primary concern of the truss was the behavior of members 197 and 198 and the connection between them. This was the result of the position the truss in the field. In 88 the field, members 197 and 198 experienced the maximum tension forces due to applied wind loads and gravity loads. The following data analysis consisted of gages that were placed on members 197 and 198 along with the joint between those members. The data and graphs from the diagonal members and members 179 and 180 can be found in

Appendix C.

Table 18: Test 1 Sample Strain Gage Data

The data was selected at maximum load, which occurred at the time of 286.27 seconds. Four values before and after the maximum load are also shown in Table 18.

The uniaxial gages U1 and U2 were located on the top and bottom of member 197, respectively, at 31 inches from the support frame. The rosette gage R1 was located on the side of member 197, also 31 inches from the support frame. The hole gages, H1 and

H2, were placed inside the top and bottom, respectively, of the connection bolts located between members 197 and 198. Finally, the biaxial gage was placed on the top of the 89 flange connection between members 197 and 198. The data from the strain gages was then transformed into stresses.

The process began with obtaining the stress values from the uniaxial and hole gages. For the strain to stress transformation, Equation 17 was used for the uniaxial, biaxial, and hole gages. For the transformation to be conducted, the correct Young’s modulus needed to be applied. The overhead truss used four different materials.

Young’s modulus for the four materials can be found in Table 6. Using the data from

Table 18, Equation 17 was applied to the uniaxial, biaxial, and hole gages. The stresses can be found in Table 19.

σ = ϵE (17)

Where: σ = stress (psi)

ϵ = strain (in/in)

E = Young’s modulus of the material at gage location (psi)

Table 19: Test 1 Stresses of Uniaxial, Biaxial, and Bolt Gages

There were a total of six uniaxial gages placed on members 197 and 198. A gage was placed on the top and bottom of the chord at 31, 41, and 60 inches from the support frame. The load/stress verse time graph for the uniaxial gages can be seen in Figure 36.

Gage U1, U3, and U5 were placed on the top of the chord at 31, 41, and 60 inches, respectively. Gage U2, U4, and U6 were placed on the bottom of the chord at the same locations as the other uniaxial gages.

Figure 36: Test 1 Uniaxial: Stress vs. Time

Figure 36 demonstrates the relationship of the uniaxial gages during testing. The uniaxial gages are shown reflecting the applied loading throughout the various gage locations. The hydraulic cylinders were located 72 inches from the support structure. 91

When comparing the gage locations to the location of the hydraulic cylinders, it is important to note, as the distance from the hydraulic cylinder increased the stress was lower. The magnitudes between the gages located on the top of the chord to the gages on the bottom of the chord exhibit that there was an induced negative moment.

The flange connections consisted of six bolt hexagonal cast aluminum flanges positioned with a bolt at the top and a bolt at the bottom leaving the four remaining bolts for the sides. The flange position and gage locations can be seen in Figure 37. The stress inside the bolts during the test can be seen in Figure 38. The stresses inside the bolts between maximum compression and maximum tension have relatively the same magnitude. After 350 seconds the stresses flipped directions compression turned to tension and visa-versa. Once the load was completely removed it was noticed that the stresses did not return to the same stress as when testing begun. These changes in the stresses are the result of the permanent deformation.

Figure 37: Test 1 Position of Flange Connection

Figure 38: Test 1 Bolt Gages Stress vs. Time

During the construction of the overhead truss, flanges were welded on the ends of the truss chords, then later used to bolt sections together. To further understand how load was transferred through the two flanges, three biaxial gages were installed at the same location on each flange edge. Biaxial gages were placed at the locations shown in Figure

39 for the connection between members 197 and 198. Figure 40 shows the circumference of the joint in plan view. With the use of the inspection sheet and visual observation, Figure 40 was created so that locations of the gages can be seen compared to the locations of the cracks shown in red.

B1-B2

B3-B4

B5-B6

Figure 39: Test 1 Location of Biaxial Gages

Figure 40: Test 1 Joint Crack Locations

Biaxial gages B1, B3, and B5 were situated on the flange closest to the support frame, while B2, B4, and B6 were placed further from the support frame. The gages were positioned so that gage one was reading strain in the flange along the longitudinal axis of the chord and the second gage was in the transverse direction of the chord. An example of how the biaxial gages were positioned on the flanges can be seen in Figure 23 in section 3.3.2.

The data from the longitudinal gages at corresponding locations for each flange are plotted Figure 41. The results from the transverse gages are provided in Figure 42.

The data provided for gage B3B was determined unusable and therefore, the transverse 94 stress at this location was not provided in Figure 42. All longitudinal gages showed tensile stress and the transverse gages provided compressive stress in the flanges while loading occurred. In general, the stresses increased as load increases. Higher stresses were typically obtained in the flange closer to the support frame. The plots for the transverse stresses were a mirror image, however, with an increase in magnitude of the longitudinal stress to the transverse stress was in the range of approximately 0.25-0.30.

This may have been due to Poisson’s effect.

Figure 41: Test 1 Longitudinal Biaxial Gage Stress vs. Time

Figure 42: Test 1 Transverse Biaxial Gage Stress vs. Time

The rosette gages required further transformations. Strain gage rosettes are commonly composed of three gages. These gages can be oriented in a verity of ways but are most commonly oriented with a 45 degree angle between the longitudinal axes of the gages. In addition, strain gage rosettes are used to determine the stain components at specific locations. The strain components include the longitudinal normal strain, the transverse normal strain, and the shear strain. These three strain components can be calculated by transforming the gage readings. Figure 43 shows how the rosette could look with any angle between the gages.

Figure 43: Rosette Diagram Figure from (SM-06: Strain Gage Rosette 2016)

The three gage rosette transformation equations can be seen in Equation 18. This equation was used for each gage resulting in three equations with three unknowns. This allowed for solving simultaneous equations to calculate the unknowns.

2 2 휖푖 = 휖푥 푐표푠 휃푖 + 휖푦 푠푖푛 휃푖 + 훾푥푦 푠푖푛 휃푖 푐표푠 휃푖 (18) 98

Where:

휖푖 = recorded strain from gage 푖

휖푥 = longitudinal normal strain

휖푦 = transverse normal strain

훾푥푦 = shear strain

휃푖 = angle of the gage 푖 from the longitudinal axis of the chord

The orientation of the rosette was critical so that the appropriate transformation was applied to the data. The various positions could yield multiple transformation equations. Figure 44 shows the position of a rosette on a diagonal member. The gage was positioned perpendicular to the longitudinal axis of the diagonal member. However, the rosettes positioned on the chords were lined up with the longitudinal axis of the member. Equations 19 through 21 were used to transform the gage data into plane strain.

Figure 44: Example Gage Layout

휖푦 = 휖푏 (19) 99

휖푥 = 휖푎 + 휖푐 − 휖푏 (20)

훾푥푦 = 휖푐 − 휖푎 (21)

Where: 휖푎 = strain gage 1

휖푏 = strain gage 2

휖푐 = strain gage 3

Once the plane strains were calculated, the next step consisted of converting the strains into stresses. The process of converting the strains to stresses was a form of

Hooke’s Law. Hooke’s Law uses superposition and Poisson’s ratio to relate the strain to stress (Hibbeler, 2014). The general form of Hook’s Law can be seen in Equation 22 and

Equation 23 for a biaxial stress state.

1 (22) 휖 = [휎 − 휈휃 ] 푥 퐸 푥 푦

1 (23) 휖 = [휎 − 휈휃 ] 푦 퐸 푦 푥

Hooke’s Law also can relate shear strain to shear stress. The following equations were used to calculate the shear stress (Hibbeler, 2014). Equation 24 was used to relate the material properties, Young’s modulus and Poisson ratio, in order to obtain the shear modulus. Then, the shear modulus and the shear strain were used to calculate the shear stress by equation 25.

퐸 (24) 퐺 = 2(1 + 휈)

휏푥푦 = 퐺 ∗ 훾푥푦 (25)

Where: G = shear modulus

휏푥푦 = shear stress 100

The experimental stress data transformed from the strain measured by the stain gage rosettes is shown in Table 20.

Table 20: Test 1 Strain and Stress Calculations Rosette Gage R1 (Member 197)

With the completion of the data analysis of the rosette gages the longitudinal, transverse, and shear stresses were calculated for the rosettes located on the members 197 and 198. Figure 45 shows the longitudinal stresses in rosette R1, R2, and R3 positioned at 31, 41, and 60 inches, respectively, from the support frame. These locations were similar to the uniaxial gage locations. However, these gages were place on the side of the chords. As the gage location increased from the support frame, the longitudinal stress went from compressive stresses to tensile stresses. The highest stress magnitude occurred in rosette R1B, which is located furthest from the applied load. 101

Figure 45: Test 1 Longitudinal Stress from Rosette Gages R1-R3

Figure 46 shows the transverse stresses along the sides of the chords at the locations provided. From the transverse stresses it is important to note that R1 and R2 located at 31 and 41 inches, respectively, exhibit the same magnitudes. Gage R2 was closest to the applied load reading compressive transvers stresses, while R1 further from the applied load experienced tension transverse stresses. R3 was the closest to the applied load and the transverse stresses experienced minimal stresses compared to R1 and

R2.

102

Figure 46: Test 1 Transverse Stresses from Rosette Gages R1-R3

Shear stresses were calculated using the rosette transformation equations. The shear stresses are provided in Figure 47 throughout experimental test 1. Compared to the longitudinal and transvers stresses the shear stresses are minimal. It was observed that after, approximately 150 seconds, the shear stress at R2 and R1 share a similar relationship where the values were mirrored. The shear stress in R1 did not experience the similar mirrored relationship when compared to the shear stresses in R2 and R3. 103

Figure 47: Test 1 Shear Stresses from Rosette Gages R1-R3

4.4: Experimental Test 2 Analysis

The damage index used for truss selection in experimental test 1 was used to select the truss for the second experimental test. Truss 100B tested for experiment 1 reached the design load determined from the SAP2000 analysis without catastrophic failure. This achievement of the design load required a truss with a higher damage index to be tested. Truss 315A had the highest damage index of 86 with a backside damage index of 38. With the high amount of damage, Truss 315A was selected for the second experimental test. Truss 315A was located over interstate 90 in Cleveland, Ohio after mile marker 173.2 with the traffic heading in the westerly direction.

Experimental test 2 was conducted on November 18, 2016. Prior to testing, strain gages were attached to the truss at similar locations as Truss 100B that was tested first. 104

However, four bolt gages were not used for this second test. The test began using the procedure discussed in section 3.3.6. Test 2 took approximately 6 minutes. The shorter test time was the result of a failure that occurred at the weld between the chord and the flange. This weld is located at the joint between members 179 and 180. The data was recorded, filtered, and resampled the same as was done in test 1.

4.4.1: Joint Analysis

Prior to test 2, inspection documentation of the joints was reviewed. The inspection sheet completed by the University of Toledo revealed that the joints had severe cracks. The inspection sheet is provided in Appendix D (Figure 88). It was observed that the joint between members 197 and 198 had one large crack and six medium cracks as documented on the inspection sheet. The left photo of Figure 48 shows the largest crack at the bottom of joint 1 between members 197 and 198. Joint 2 between members 179 and 180 was documented to have five large cracks and six medium cracks. The right photo of Figure 48 shows the severity of joint 2 cracking.

105

Figure 48: Test 2 Initial Joint Cracking (Joint 1 Left and Joint 2 Right)

Truss 315A failed before achieving the desired applied load. However, this failure occurred at the interface between the weld and the flange at joint 2. The failure while the load was applied to the truss can be seen in Figure 49. 106

Figure 49: Test 2 Cracked Weld

After failure, a visual inspection of the other joints was conducted. While load was applied to the truss, the cracked region in locations of large cracks expanded, and in some instances, a gap developed between the two flanges. Figure 49 shows a comparison of joint 2 before loading (photo on the left), during loading (photo in the center) and after loading (photo on the right). As shown in the center photo, the crack above the gages propagated into the other flange, and the crack below the gages widened. The bolt also appeared to have rotated. When the load was completely removed the gap between the flanges had grown and the cracks widened. No other significant changes were noticed in the other cracked sections. 107

Figure 50: Test 2 Change in Cracking (Before, During, and After Loading)

4.4.2: Load and Deflection Data

String potentiometer 1 and load cell 1 were placed near the free end of member

198. String potentiometer 1 was placed eleven inches from the end and load cell 1 was located five inches from the end. String potentiometer 2 and load cell 2 were placed ten inches and five inches, respectively, from the end of member 180. String potentiometer 3 was placed at joint 1 similar to the location for the experimental test 1. There was an additional string potentiometer for experimental test 2 to see if joint 2 deflected while being restrained. String potentiometer 4 was placed at joint 2 between members 179 and

180.

Similar to experimental test 1, the load cell and string potentiometer data was first analyzed. The data from the load cells and string potentiometers at the maximum achieved load can be seen in Table 21. 108

Table 21: Test 2 Load Cell (LC) and String Potentiometer (SP) Data

The test procedure required a load of 10,000 lbs. to be reached in each load cell.

However, due to the failure at joint 2, the maximum achieved load was 8,277 lbs. in Load

Cell 1 (LC1) and the maximum recorded load in Load Cell 2 (LC2) was 8,250 lbs. This maximum load was achieved in both load cells at 244.11 seconds. The data collected from the load cells throughout the duration of the test can be seen in Figure 51. During the initial stages of the test the loading measured in both load cells was the same. Before approximately 200 seconds, the load in LC2 began to increase at a slightly faster rate.

However, the difference between LC1 and LC2 was minimal. Additionally, at 244.11 seconds the load in both load cells experienced a drastic drop in load due to the failure that occurred. Once failure occurred, the experiment was stopped. At approximately 280 seconds the applied load was decreased with the entire load removed after 350 seconds. 109

Figure 51: Test 2 Load vs. Time

The string potentiometer data was transformed using the equations stated in section 3.3.4. The displacement at maximum load and final testing of Truss 315A is provided in Table 22.

Table 22: Test 2 Deflection Data

110

Table 22 provides the deflection of the truss when the maximum load occurred at

244.11 seconds and the final truss deflection at 350.93 seconds. String potentiometer 1

(SP1), near the fee end of member 198 experienced the highest deflection of 3.38 inches at the maximum load. String Potentiometer 2 (SP2), located near the free end of member

180, experienced the highest permanent deflection of 0.90 inches which was likely due to the failure of the connection along this member. String potentiomenter 3 (SP3), plaed between members 197 and 198, experienced a 2.09 inch deflection at maximum load and almost no permanent deformation. String Potentiometer 4 (SP4) was placed between members 179 and 180 recorded little defelction due to the restraint preventing movement in the vertical deflection. Therefore, the permanent deformation was not significently noticed once testing was completed. The average applied load verses the deflection can be seen in Figure 52.

111

Figure 52: Test 2 Load vs. Deflection

4.4.3: Strain Gage Analysis

Gage identification was similar to experimental test 1 to eliminate confusion between the two tests. Gage placements and locations were also similar to test 1 for easy comparison between the two experimental tests and the SAP2000 analysis. Sample data for the uniaxial, biaxial, and rosettes for test 2 at the time of maximum load is shown in

Table 23. Note the abrupt change in most of the gage readings at 244.13 seconds right after peak load was obtained at 244.11 seconds. 112

Table 23: Test 2 Sample Strain Gage Data

The longitudinal stress in the top and bottom of the chords were first calculated at the uniaxial gage locations. There were uniaxial gages on the top and bottom of members

197 and 198 placed at 31, 41, and 60 inches from the support frame similar to the gage locations of test 1. The uniaxial gages were converted from strain to stress using

Equation 17. Also, biaxial gages were placed at three locations on the flange. Gages were placed on both sides of the flange with one strain gage in the same direction of the uniaxial gages and the other perpendicular to longitudinal axis. The longitudinal stresses for U1 and U2 along with the longitudinal and transverse stresses for B1A and B1B are provided in Table 24. As shown in Table 24, the stress at U1 changed from tension to compression and the stress at U2 increased in tension after the peak load was obtained.

Gage B1A changed from compression to tension and B1B showed an increase in compression after peak load was reached. 113

Table 24: Test 2 Stresses for Uniaxial and Biaxial Gages

The longitudinal stresses were also determined for the six uniaxial gages placed on members 197 and 198. The stress of these uniaxial gages can be seen in Figure 53.

U1, U3, and U5 were placed on the top of members 197 and 198, while U2, U4, and U6 were placed on the bottom of those members. The weld interface cracking occurred between members 179 and 180, however the failure was experienced throughout the entire truss. The crack resulted in a shift of the data before 250 seconds. Similar to test

1, the uniaxial gage placed at the same longitudinal locations experienced opposite stresses but similar magnitudes. Failure caused the data to fluctuate once peak load was achieved. Data after the peak load was removed to allow for better data analysis. Strain gage U3 was removed due to the gage malfunction. 114

Figure 53: Test 2 Longitudinal Stresses in Members 197 and 198

Biaxial gages were placed on the flanges of joint 2 between the two bottom chords. Three sets of biaxial gages were placed on each flange similar to test 1. Biaxial gages B1, B3, and B5 were placed on the flange welded to member 197 closest to the support frame. Biaxial gages B2, B4, and B6 were placed on the flange welded to member 198 furthest away from the support frame. The location of the biaxial gages can be seen in Figure 54. Figure 55 was created to show the locations of the cracks compared to the location of the biaxial gages. 115

B1-B2

B3-B4

B5-B6 Figure 54: Test 2 Location of Biaxial Gages

Figure 55: Test 2 Joint Crack Locations

The results of the biaxial gages were graphed so that the longitudinal and transvers stresses could be compared to the same location on opposite flanges. The longitudinal and transverse directions are defined in relation to the axis of the chords.

Figure 56 shows the longitudinal stresses in the biaxial gages at the locations provided between members 197 and 198, while Figure 57 shows the transverse stresses. Stain gages B1A and B2A in Figure 56: Test 2 Longitudinal Stress vs. Time Biaxial Gages experienced similar behavior. However, the stress in B1A experienced a tensile stress for the majority of the test and B2A experienced primarily compressive stress. Gage B3A 116 and B4A also showed opposite stress behavior. Only gages B5A and B6A both showed similar compressive stress with similar magnitudes. The inconsistent behavior from the biaxial gages may have been caused by the variety of cracking in the flanges. In general, the stresses in the transverse gages shown in Figure 57 were lower than the longitudinal stresses and were likely from Poisson’s effect.

117

Figure 56: Test 2 Longitudinal Stress vs. Time Biaxial Gages

118

Figure 57: Test 2 Transverse Stress vs. Time Biaxial Gages 119

The rosette gages used in test 2 were placed in the same locations as the rosette gages in test 1. Table 25 provides the strain transformation for R1 located on the side of member 197, 31 inches from the support frame. Equations 19, 20, and 21 were used to transform the gage strain readings into the longitudinal normal strain, transverse normal strain, and shear strain. Then Equations 22 and 23 were used to convert the longitudinal and transverse strain into longitudinal and transverse stresses. Equation 25 was utilized to transform the shear strain into shear stress.

Table 25: Test 2 Strain and Stresses for R1

The longitudinal stress on the side of members 197 and 198 can be seen in Figure

58. It is noted that gage R3 was closest to the applied loading and resulted in the largest stress. The gages placed further from the applied load experienced lower stresses. Figure

59 shows the transverse stresses from the rosette gages. R1 was furthest from the applied load and experienced the highest stresses. Figure 60 shows the shear stresses obtained 120 from the rosette gages. The shear stress from R1 and R3 show a similar rate of increase to when max load was achieved.

Figure 58: Test 2 Longitudinal Stresses Rosette Gages R1-R3

121

Figure 59: Test 2 Transverse Stresses Rosette Gages R1-R3

Figure 60: Test 2 Shear Stresses from Rosette Gages R1-R3

122

CHAPTER 5: DISCUSSION

The experimental tests were conducted based on the results of the analytical assessment. From the analyses, it was determined that a total of 20,000 lbs. should be applied to the truss. The desired load of 20,000 lbs. was reached for the truss in Test 1.

The truss in Test 2 failed at 16,500 lbs. To compare the analytical and the experimental test results, internal stresses and deflections were used. The internal longitudinal and shear stresses are provided in Table 26, the deflections at maximum loading and after loading are provided in, Table 27, and Table 28.

The internal stresses are shown in Table 26. First, the longitudinal stresses from all locations were compared between the SAP2000 models and the experimental tests.

The longitudinal stresses from the full scale SAP2000 model are shown as all tension stresses. When the stresses are compared between the two SAP2000 models it can be seen that the sample SAP2000 model shows higher stresses than the full scale model.

The closest relationship between the top longitudinal stresses can be seen at 60 inches.

The ratio between the two top longitudinal stresses is 0.87.

The top longitudinal stresses at 31 and 41 inches for Test 1 are 6632 and 6914 psi, respectively. These stresses are one thrid greater than the stress values from the full scale model. However, it is also noticed that the stresses at those locations from Test 1 experience similar magnitudes as the full scale model. The stresses obtained from the

SAP2000 sample model at those locations are 5643 and 6444 psi. When the top longitudinal stresses at 31 and 41 inches are compared to the sample model it can be seen that the stresses are closer in maginutude. The SAP2000 sample model and the Test 1 123 values are compared to determine the ratio between them. At 31 inches a ratio of 0.85 was calculated and at 41 inches a ratio of 0.92 was calculated. The stresses at 41 inches are the best comparison between Test 1 and the sample SAP2000 model. The top longitudinal stress at 60 inches for Test 1 is about 2 times larger than the stress in the full scale model and 2.25 times larger than the SAP2000 sample model.

The top longitudinal stress at 41 inches for Test 2 was not provided in Table 26 due to gage malfunction. However, the top longitudinal stresses at 31 and 60 inches for

Test 2 were lower than the stresses experienced at the same locations for Test 1. These stresses were the result of Test 2 reaching 16,500 lbs. of applied load before failure. The stresses from Test 1 and the SAP2000 sample model exhibits the stresses obtained from

Test 2 did not compare. The closest relationship between for the top longitudinal stresses for Test 2 occurred at 60 inches. The top longitudinal stress was compared to the top longitudinal stress for the full scale SAP2000 model. The ratio between the values was

0.85. This was the best relationship between Test 1 and the full scale model. The trend of the data increasing at the time of failure for Test 2, gage U5 located at 60 inches, should have continued to increase until maximum load was achieved. The stress at 60 inches for Test 1 was 5877 psi. at the same loading as Test 2. When the top longitudinal stresses at 60 inches are compared at a similar loading, the ratio of 0.87 was calculated.

The stresses obtained from the full scale SAP2000 model shows that all the stresses in the chords were tensile stresses. The SAP2000 values from the sample model experienced different stresses throughout the chord. At some locations the chords experienced tension on the top and compression on the bottom. The wide range of 124 stresses experienced by the sample SAP2000 model are due to higher moments than the full scale model. The higher moments caused higher bending in the experimental tests than what was expected in a full scale model.

The longitudinal stresses on the bottom of the chords did not experience similar stresses between the tests and the SAP2000 models. The bottom longitudinal stresses also experienced similar stress magintudes. The stress magintudes on the bottom of the chords at 31 and 41 inches for Test 1 have similar values. The bottom longitudinal stresses from the SAP2000 sample model experience compression at 31 and 41 inches.

Test 1 experiences similar compression stresses at those locations. However, the magintudes of the stresses from Test 1 are larger than the values from the SAP2000 sample model. Test 2 experienced the opposite affect were the stresses at 31 and 41 inches were tension, stresses and the stress at 60 inches was a compression stress.

The longitudinal stress along the side of the chords were compared next. The side longitudinal stresses from the SAP2000 sample model showed a similar relationship to the full scale SAP2000 model where the stresses were all tension stresses. The full scale

SAP2000 model and the SAP2000 sample model stresses showed a ratio of 0.78, 0.63, and 0.61, at 31, 41 and 60 inches, respectively.

The side longitudinal stresses from Test 1 and Test 2 varied from the SAP2000 sample model stresses. Test 1 only experienced tension stresses at 60 inches and Test 2 experienced tension stresses at 41 and 60 inches. However, Test 2 showed almost no longitudinal stress at 41 inches. This widely differs from the SAP2000 model and Test 1.

The side longitudinal stress at 60 inches is the location were the stress values are the 125 closest. It can be seen that there is about 1100 psi. difference bewteen the SAP2000 full sacle model and the experimental tests.

The shear stresses were experience both positive and negative values, this is due to the direction of the shear stress. The shear stresses from SAP2000 shows the same stresses at 41 and 60 inches for both the SAP2000 sample model and the full scale model.

However, the values are very different between the models. The shear stress were much higher for the sample SAP2000 model. The shear stresses for the full scale model were all small negative values. It can be seen that the shear stresses for both Test 1 and Test 2 are lower than the shear stresses obtained from the SAP2000 sample model. Test 1 exhibits similar attributes as the shear stresses from the SAP2000 model, the shear stresses at 31 inches is a positive stress, while the stresses at 41 and 60 inches were negative. The shear stresses for Test 2 were positive stresses at all locations. The closest related shear stresses are between Test 1 and the SAP2000 model at 60 inches. The ratio between the two values was 0.56. No other shear stresses from the experimental tests were closely related to the values from the SAP2000 models. 126

Table 26: Internal Stress (psi)

The deflections exhibited by both experimental tests showed much higher deflections than what were expected from the SAP2000 computer model. It can be seen from Table 27 that the deflection recorded from the SAP2000 analysis was less than 0.25 inches. Test 1 demonstrated a deflection of 6.40 inches and 5.82 inches at the free ends.

Test 2 also exhibited high deflections at the free ends, 3.38 and 2.65 inches. It can be seen that the highest deflection occurred at the end of member 198 for both experimental tests. However, the highest deflection in the analytical model occurred at the end of member 180.

127

Table 27: Deflections at Maximum Loading

When the deflection from Test 1 was observed at a similar applied load as the maximum applied load in Test 2, the deflection at the free ends of members 198 and 180 were 4.49 and 3.50 inches, respectively. The ratio of the deflections was calculated between member 198 and 180. From the calculation the ratio of the deflections was 1.28 for Test 1 and 1.27 for Test 2.

Table 28 shows the final deformations after the load was removed at the completion of the test. Since the SAP2000 analysis was a linear elastic model, all the deflections returned to their starting point. Test 1 experienced higher permanent deformations than Test 2. However, a comparison between the permanent deformations between Test 1 and Test 2 shows that the highest deformation occurred at the end of member 180. The permanent deformations were higher for Test1 than Test 2 due to the recorded internal stresses along the chords from Test 1 exceeded the yield strength of the aluminum. Exceeding the yield strength of aluminum resulted in material deformation.

Test 2 did not exceed allowable stresses. However, Test 2 did recorded minimal permanent deformation. The failure at the weld by the connection could have resulted in 128 the permanent deformation experienced by Test 2. The deflections from the tests compared to the deflections from the SAP2000 model are widely different due to the

SAP2000 assumption that the support frame was a fixed connection. From testing, it was observed that the load frame experienced its own deflection causing the truss to have such higher deflections than the truss in the SAP2000 model.

Table 28: Deflections after Test Completion

From Chapter 2 Literature Review, the allowable aluminum design strength was calculated. It was found that the aluminum was able to resist 19.5 ksi. in tension and 30.5 ksi. in compression. The stresses calculated from Test 1 and Test 2 showed that the stresses along members 197 and 198 were well below the allowable stresses. However, the stresses recorded from test 1 for members 179 and 180 were higher than the allowable stresses. For example, the allowable stress along the bottom of member 179 at 31 inches reached 19.5 ksi at 86.24 seconds. The allowable stress along the top of the member at

31 inches reach 30.5 ksi until 118.42 seconds with the stress increasing due to the applied 129 load. These stresses conntinued to increase until the max load was achieved at 286.27 seconds. Yield stress of aluminum for both tension and compression is 35 ksi. this stress was reached at 112.48 sceonds. The stresses exceeding the yield strength of aluminum was represented by Test 1 experiencing such large permanent deflection. The stresses recorded in Test 2 did not exceed the allowable stresses.

130

CHAPTER 6: CONCLUSION

This research was conducted to test how applied loads such as wind loads were transferred through the sign structure, specifically at the chords and flanges. Testing was conducted to see how previously damaged truss flanges would resist the maximum expected design load. The full scale testing of a section of the truss would help compare results from an analytical model to the results experimental testing.

With the use of the sample sections provided by the Ohio Department of

Transportation, experimental analyses were conducted to simulate the overhead box truss in the field. In the field, it was expected that an overhead box truss would experience 90 mph. wind loads. The sample sections were tested in a laboratory environment in hopes of understanding how the chords and damaged flanges of an overhead box truss would transfer the loading. The use of a cantilever testing method was determined to be the best way to recreate the loading of the critical flanges in the overhead box truss in the field.

Experimental testing of the sample truss demonstrated that the chords experienced both tension and compression stresses. When those stresses were compared to the

SAP2000 full scale model it was determined that Test 1 experienced higher stresses.

Test 1 showed that the flanges were able to transfer load without an increase in the existing crack width. However, Test 2 experienced a crack expansion during the application of loads and once loading was removed there was a permanent increase in crack width. Test 2 also showed that the truss failed at the welds even though cracking existed around the bolts. 131

Overall, the experimental analysis showed that a damaged aluminum truss would be able to support more load than what is required from design loading. This was observed from the data acquired from the experimental analysis. The data showed that higher moments were induced experimentally than what was calculated from the

SAP2000 full scale model.

132

REFERENCES

AASHTO. (2013; 2014). Standard Specifications for Structural Supports for Highway

Signs, Luminaires, and Traffic Signals (6th Edition). Washington, D.C.:

American Association of State Highway and Transportation Officials

http://app.knovel.com/hotlink/toc/id:kpSSSSHS01/standard-

specifications/standard-specifications

ASCE/SEI (2005) Minimum Design Loads for Buildings and Other Structures (4th ed.).

Reston, VA: The American Society of Civil Engineers.

Cali, P. M., & Covert, E. E. (2000, January). Experimental Measurements of the loads

induced on an overhead highway sign structure by vehicle-induced gusts. Journal

of Wind Engineering and Industrial Aerodynamics, 84(1), 87-100. Retrieved

November 5, 2016, from

http://www.sciencedirect.com/science/article/pii/S0167610599000458

Dyrbye, C., & Hansen, S. O. (1997). Wind loads on structures. Chichester: J. Wiley.

Foutch, D. A., S.E., Rice, J. A., LaFave, J. M., P.E., Valdovinos, S., & Kim, T. (2006).

Evaluation of Aluminum Highway Sign Truss Designs and Standards for Wind

and Truck Gust Loadings (Rep. No. FHWA/IL/PRR 153). Urbana, IL.

Hawkins, H. G., Jr. (july 1992). Evolution of the MUTCD: Early Standards for Traffic

Control Devices. ITE, 23-26. Retrieved January 27, 2017, from

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.417.2566&rep=rep1&t

ype=pdf 133

Hibbeler, R. C. (2014). Mechanics of materials (9th ed.). Upper Saddle River, NJ:

Pearson Prentice Hall.

Hibbeler, R. C. (2001). Engineering mechanics Statics (9th ed.). Upper Saddle River, NJ:

Prentice Hall.

Kaczinski, M., Dexter, R., & Dien, J. V. (1998). Fatigue-resistant design of cantilevered

signal, sign and light supports. Washington: National Academy Press.

Leduc, P. D. (2015). Critical Members of Aluminum Overhead Box Truss Sign Supports

(Unpublished master's thesis). Athens Ohio, Ohio University.

Red Deer Lake. (n.d.). Retrieved January 25, 2017, from

http://www.sharecom.ca/poet/mapdetails.html

Route 840 Extension [Photograph found in New York]. (n.d.). Retrieved January 25,

2017, from

http://dihighway.com/products/overheadsignstructures/gallery.php?id=37

SAP2000 (Version 15) [Computer software]. (2011). Retrieved 2016.

SM-06: Strain Gage Rosette. (2016). Retrieved October 11, 2016, from

https://www.ecomputingx.com/SM-06.jsp

Strain Gages. (2015, May). Retrieved September 14, 2016, from http://www.kyowa-

ei.com/eng/

Ohio Department of Transportation (ODOT). (2012, April 20). OHIO’S FREEWAY AND

EXPRESSWAY GUIDE SIGN DESIGN METHOD. Retrieved from

http://www.dot.state.oh.us/Divisions/Engineering/Roadway/DesignStandards/traff 134

ic/SDMM/Documents/SDMM_Chapter09_AppendixC_071516Revision_041916.

pdf

Ohio Department of Transportation (ODOT). (2013). Construction and Material

Specifications. Columbus, Ohio. Ohio Department of Transportation

Ohio Department of Transportation (ODOT). (2015). 90 wb chester Truss (315) 008

[Photograph]. Cleveland, Ohio.

TC-7.65 [Aluminum Truss Overhead Sign Support]. (2011, January 21), Ohio Department

of Transportation. (Author). Retrieved January 24, 2016,

https://www.dot.state.oh.us/Divisions/Engineering/Roadway/DesignStandards/traf

fic/SCD/Documents/TC_00765_2016-01-15.pdf

Two Small Span Overhead Sign Structure [Photograph found in New York]. (n.d.).

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http://dihighway.com/projects/past/gallery.php?id=53

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APPENDIX A: GENERAL INFORMATION

Figure 61: Fatigue Threshold for Steel Sections

136

Table 29: Aluminum Properties (AASHTO, 2013)

137

APPENDIX B: TESTING INFORMATION

Figure 62: ODOT Aluminum Truss Overhead Sign Support Standard Drawing (ODOT, TC-7.65) 138

Figure 63: Joint Damage Index 139

Figure 64: String Potentiometer 1

Figure 65: String Potentiometer 2

140

Figure 66: String Potentiometer 3

Figure 67: String Potentiometer 4

141

Figure 68: Load Cell

142

APPENDIX C: DATA FROM FIRST TEST

Figure 69: Truss 100B Inspection Sheet 143

Figure 70: Test 1 Longitudinal Stress Member 10

Figure 71: Test 1 Transverse Stress Member 10

144

Figure 72: Test 1 Longitudinal Stresses Member 4

Figure 73: Test 1 Transverse Stresses Member 4

145

Figure 74: Test 1 Longitudinal Stresses Member 2

Figure 75: Test 1 Transverse Stresses Member 2

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Figure 76: Test 1 Longitudinal Stresses Member 11

Figure 77: Test 1 Transverse Stresses Member 11

147

Figure 78: Test 1 Longitudinal Stresses Member 14

Figure 79: Test 1 Transverse Stresses Member 14

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Figure 80: Test 1 Longitudinal Stresses Member 19

Figure 81: Test 1 Transverse Stresses Member 19

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Figure 82: Test 1 Longitudinal Stresses Gages R12-R14 Members 179 and 180

Figure 83: Test 1 Transverse Stresses Gages R12-R14 Members 179 and 180

150

Figure 84: Test 1 Longitudinal Stresses gages U7-U12 Members 179 and 180

Figure 85: Test 1 Bolt Gage H3 and H4

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Figure 86: Test 1 Longitudinal Stresses for Biaxial gages Member 179 and 180 152

Figure 87: Test 1 Transvers Stresses for Biaxial Gages Members 179 and 180

153

APPENDIX D: DATA FROM SECOND TEST:

Figure 88: Truss 315A Inspection Sheet 154

Figure 89: Test 2 Longitudinal Stresses Member 10

Figure 90: Test 2 Transverse Stresses Member 10

155

Figure 91: Test 2 Longitudinal Stresses Member 4

Figure 92: Test 2 Transverse Stresses Member 4

156

Figure 93: Test 2 Longitudinal Stresses Member 2

Figure 94: Test 2 Transverse Stresses Member 2

157

Figure 95: Test 2 Longitudinal Stresses Member 11

Figure 96 Test 2 Transvers Stresses Member 11

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Figure 97: Test 2 Longitudinal Stresses Member 14

Figure 98: Test 2 Transverse Stresses Member 14

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Figure 99: Test 2 Longitudinal Stresses Member 19

Figure 100: Test 2 Transverse Stresses Member 19

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Figure 101: Test 2 Longitudinal Stresses Gages R12-R14 Members 179 and 180

Figure 102: Test 2 Transverse Stresses Gages R12-R14 Members 179 and 180

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Figure 103: Test 2 Longitudinal Stresses Gages U7-U12 Member 179 and 180

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Figure 104: Test 2 Longitudinal Stresses Biaxial Gages B7-B12 163

Figure 105: Test 2 Transverse Stresses Biaxial Gages B7-B12 ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

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