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Abstract: Lateral–torsional buckling (LTB) is a stability failure mode that occurs in unbraced segments of flexural members and is associated with simultaneous out-of-plane lateral defection and cross-section rotation. The LTB behaviour of doubly symmetric I-shaped members is generally well understood. However, there is concern that current understandings of inelastic LTB in welded steel girders may be inaccurate and not representative of the current fabrication methods employed in Canada. Moreover, recent studies (MacPhedran and Grondin 2011; Kabir and Bhowmick 2018) have indicated the current Canadian design provisions for LTB may be inaccurately estimating the inelastic LTB resistance of welded steel girders. The purpose of this study is to address these concerns and assess the LTB behaviour of modern welded steel girders through experimental and numerical means. Additionally, to assess the LTB behaviour and load-carrying performance of heat-straightened welded steel girders. The experimental portion of this study includes the large-scale testing of four welded steel girders and five heat-straightened girders of intermediate slenderness. The test results were used to examine the LTB behaviour of welded steel girders and assess the stability response of heat-straightened girders through comparison with the as-built response. A continuum finite element model was developed and calibrated against the experimental test results and was used to simulate the experimental specimens for two loading conditions: top flange and shear centre. The adequacy of the CSA S16-19 design provisions for welded steel girders was then evaluated by comparing the code-predicted moment resistances with those of finite element analysis. The CSA S16-19 design equation is found to adequately estimate the moment resistance of modern welded steel girders; however, CSA S16-19 can overestimate the moment resistance of girders with large web width-to-thickness ratios and high initial geometric imperfection.

The Inverted Tee (IT) girder bridge system was originally developed in 1996 by the University of Nebraska–Lincoln (UNL) and Nebraska Department of Roads (NDOR) engineers. This bridge system currently accounts for over 110 bridges in Nebraska used for both state highways and local county roads. Excessive transverse and longitudinal deck cracking has been observed and noted in numerous bridge inspection reports. Since the IT girder bridge system is relatively new, limited data and knowledge exist on its structural performance and behavior. This study evaluates the IT girder bridge system by conducting twenty field observations as well as recording accelerometer time histories and lidar scans for a selected subset of these bridges. The field observations included visual inspection for damage and developing deck crack maps to identify a trend for the damage. System identification of the bridge deck and girders helped investigate the global and local structural responses, respectively. Operational modal analysis quantified the natural frequencies, damping ratios, and operational deflected shapes for the instrumented IT girder bridges. These results helped diagnose the reason for the longitudinal deck cracking. The IT girders respond nonuniformly for the first operational deflected shape and independently for higher modes. Two comparable bridges, namely one slab and one NU girder bridge, were instrumented to verify and demonstrate that the IT girder behavior is unique and undesirable. An advanced geospatial analysis was conducted for the IT girder bridges to develop lidar depth maps of the deck and girders elevations. These depth maps help identify locations of potential water/chloride penetration and girders set at various elevations and/or where the deck thickness is nonuniform. Advisor: Richard L. Wood

Many older bridges in Texas are constructed with floor systems consisting of a concrete slab over steel girders. A potentially economical means of strengthening these floor systems is to connect the existing concrete slab and steel girders using post-installed shear connectors to change the behavior of the beam from non-composite to partially-composite. Since fatigue is one of the main concerns in designing bridges, investigating the fatigue properties of these post-installed shear connectors becomes crucial. Results from direct-shear testing show that post-installed shear connectors have a better fatigue life compared to conventional welded shear studs. However, based on currently available data from direct-shear tests, fatigue life of post-installed shear connectors is still inadequate for economical retrofit in some cases. Furthermore, it is unclear if direct-shear tests provide an appropriate means of evaluating fatigue performance. The objective of this dissertation is to develop new and more accurate approaches for evaluating the fatigue characteristics of post-installed shear connectors. This objective is addressed through large-scale beam fatigue tests and computational studies. The focus of the work is on evaluating fatigue life of shear connectors based on both slip and stress demands.

The Minnesota Department of Transportation has typically used epoxy coated straight legged stirrups anchored in the tension zone as transverse reinforcement in prestressed concrete bridge girders. With the straight legs of the U-shaped stirrups anchored into the bottom flange of the girders, this configuration is readily placed after stressing the prestressing strands. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) specifications require stirrups with bent legs that encompass the longitudinal reinforcement to properly anchor the stirrups. Such a configuration is specified to provide mechanical anchorage to the stirrup, ensuring that it will be able to develop its yield strength with a short anchorage length to resist shear within the web of the girder. AASHTO specifications for anchoring transverse reinforcement are the same for reinforced and prestressed concrete; however, in the case of prestressed concrete bridge girders, there are a number of differences that serve to enhance the anchorage of the transverse reinforcement, thereby enabling the straight bar detail. These include the precompression in the bottom flange of the girder in regions of web-shear cracking. In addition, the stirrup legs are usually embedded within a bottom flange that contains longitudinal strands outside of the stirrups. The increased concrete cover over the stirrups provided by the bottom flange and the resistance to vertical splitting cracks along the legs of the stirrups provided by the longitudinal prestressing reinforcement outside of the stirrups help to enhance the straight-legged anchorage in both regions of web-shear cracking and flexure-shear cracking. A two-phase experimental program was conducted to investigate the anchorage of straight legged epoxy coated stirrups that included bar pullout tests performed on 13 subassemblage specimens which represented the bottom flanges of prestressed concrete girders in a number of configurations to determine the effectiveness of straight legged stirrup anchorage in developing yield strains. Additionally, four girder ends were cast with straight legged stirrup anchorage details and tested in flexure-shear and web-shear. The straight leg stirrup anchorage detail was determined to be acceptable for Minnesota Department of Transportation M and MN shaped girders as nominal shear capacities were exceeded and yield strains were measured in the stirrups prior to failure during each of the tests.

Bridges are critical pieces of infrastructure important to public safety and welfare. Fires have the potential to damage bridges and have been responsible for taking many bridges out of service. The hazard fire poses to bridges is a little studied risk unlike more common threats such as impact, scour and earthquake. Information on the rate of occurrence of bridge fires and the mechanisms of structural response of bridges subjected to fire are both vital to policy makers seeking to address the hazard rationally. The investigation presented developed frequency statistics of bridge fire incidents from several sources of vehicle accident and fire statistics. To further investigate the fire hazard a computational model integrating the simulation of large fires and the simulation of bridge superstructure mechanical response was created. The simulation was used to perform a parametric study of fire size and location to investigate the relationship between these parameters and damage tot bridge super-""structure. The statistics investigation resulted in an observed rate of fires due to vehicle accidents of approximately 175 per year. Approximately one of these per year was the result of a tanker truck carrying a flammable liquid leading to extensive superstructure damage. The simulation showed that a tanker fire resulted in permanent damage to the bridge by several measures where as the affects of a bus fire were minimal. The simulations also demonstrated the mechanisms of bridge response; the importance of girder temperature in that response; and the differences in the response to a tanker fire that can lead to collapse.

The Innerbelt Bridge (CUY-90-1524) carries Interstate Route 90 over the Cuyahoga River Valley in Cleveland, Ohio. The bridge was opened to traffic in 1959 and is a cantilevered steel deck truss with nine spans for a total length of 2,721 feet and a main span of 400 feet. Historically there have been several structural concerns with this particular bridge. Some of the concerns that have been noted are section loss due to corrosion, slope stability of the west bank, thermal strains due to inoperable expansion joints, and possible fatigue concerns due to out-of-plane vibrations in the web of a plate girder. The plate girder was added to widen the west end of the south side of the bridge.The research presented here will discuss four investigations into the condition of the bridge. The first investigation consisted of instrumentation and live load testing of several members. The purpose of the investigations was to assess the condition of the members and to validate a finite element model of the bridge. An investigation into out-of-plane vibrations in the web of a plate girder was then conducted. This investigation’s aim was to determine the cause of and severity of the vibrations. The third investigation consisted of monitoring the structure during repairs and modifications. Due to slope movement, the expansion joint located in Span 2 had “closed” and was inoperable. Several members were monitored during operations to “open” the expansion joint. The final investigation also involved structural monitoring. Several members were instrumented during the removal of the previously mentioned plate girder and the changes in the loads on the bridge were calculated. The results of this work were used to determine the condition and to aid in developing load ratings for the bridge. This work shows the importance of structural monitoring and investigation.

Ultra High Performance Concrete (UHPC) is a class of cementitious materials that share similar characteristics including very large compressive strengths, tensile strength greater than conventional concrete and high durability. The material consists of finely graded cementitious particles and aggregates to develop a durable dense matrix. The addition of steel fibers increases ductility such that the material develops usable tensile strength. The durability and strength of UHPC makes it a desirable material for the production of highway bridge girders. However, UHPC's unique constitutive materials make it more expensive than conventional concrete. The cost and lack of appropriate design guidelines has limited its introduction into bridge products. The investigation presented in this thesis developed several optimization formulations to determine a suitable bridge girder shape for use with UHPC. The goal of this optimization was to develop a methodology of using UHPC in highway bridge designs that was cost competitive with conventional concrete solutions. Several surveys and field visits were performed to identify the important aspects of girder fabrication. Optimizations were formulated to develop optimized girder cross sections and full bridge design configurations that utilize UHPC. The results showed that for spans greater than 90 ft UHPC used in the proposed girder shape was more economical than conventional girders. The optimizations and surveys resulted in the development of a proposed method to utilize UHPC in highway bridges utilizing existing girder shapes and formwork. The proposed method consists of three simple calculations to transform an initial conventional design to an initial design using modified UHPC girders.

High Performance Steel (HPS) has quickly gained popularity in bridge applications due to its high yield strength and better weldability, toughness, ductility, and weathering characteristics when compared to conventional grades of 50 ksi (345 MPa) structural steel. However, a great deal of information is missing from the body of knowledge on HPS performance and design criteria, especially concerning HPS-70W (485W) produced by thermo-mechanical controlled processing (TMCP). This research examines material characteristics and fatigue performance of HPS-70W (485W) TMCP, as well as its performance in inelastic loading ranges. Data from 96 tensile tests show that yield and ultimate strengths of HPS-70W (485W) TMCP are dependent upon plate thickness and orientation. 75 Charpy V-Notch (CVN) specimens were tested, and all met ASTM A709 requirement. Twenty-nine specimens were tested to investigate the fatigue resistance of HPS-70W (485W) continuous plate with punched holes. Specimen thickness, hole diameter, and hole-making method were varied to examine their effect upon fatigue resistance of punched connections utilizing HPS. Results from this investigation suggest that current restrictions mandated by some state DOTs concerning punching holes are not overly restrictive when HPS-485W (70W) is utilized. Performance of drilled and sub-punched and reamed specimens met or exceeded AASHTO (2004) requirements. Performance of Submerged Arc Weld (SAW) and Narrow Gap Improved Electroslag Weld (NGI-ESW) welded butt-splices utilizing HPS-70W (485W) were examined. Five SAW and five NGI-ESW specimens were tested in fatigue and all reached infinite life. All ten specimens performed considerably better than predicted by AASHTO. Results from this study suggest that it is reasonable to include HPS-70W (485W)welded butt-splices created using NGI-ESW in the AWS D1.5 specification (2001). Moment redistribution properties were also examined through a finite element investigation in conjunction with an inelastic AASHTO analysis. All analyses dealt with a girder from an HPS-70W (485W) TMCP bridge located near Lancaster, Ohio. The HPS-70W (485W) TMCP girder exhibited comparable inelastic moment redistribution when finite element results and AASHTO predictions were examined. Peak moment capacity was found to be significantly lower for model results than for AASHTO predictions, and this difference is likely attributable to low yield strengths and roundhousing in thicker HPS-70W (485W) TMCP plates.

Self-Consolidating Concrete (SCC) was first developed in Japan almost 15 years ago, and it was not until the late 1990's that the U.S precast concrete industry applied the technology to architectural and structural building elements. This study describes the first experience of using SCC for prestressed concrete bridge girders in North Carolina. A multiple-span bridge is currently under construction in eastern North Carolina using one hundred thirty AASHTO Type III girders, each 54.8 ft (16.7 m) long (NCDOT Project 8.1170903). Three girders from one production line of five girders were selected for evaluation. Two of the girders were cast with SCC and one with conventional concrete as the control. The plastic and hardened properties of both the SCC and the conventional concrete were monitored and measured. The fresh properties of SCC included unit weight, air content, slump flow, Visual Stability Index (VSI), and passing ability as measured by J-ring and L-box. Hardened concrete tests on SCC and conventional concrete included compressive strength, static elastic modulus, elastic modulus based on resonance frequency ('dynamic' modulus) at different ages, along with creep and shrinkage. The prestressing force in the girders was monitored by load cells. Finally, the three girders were tested in flexure up to the design service load to determine and compare their load-deformation characteristics. In general, two AASTHO Type III girders were successfully cast without any vibration using SCC, and exhibited virtually identical load-deflection relationships up to the design service load than that of the conventional concrete girder. SCC showed lower elastic modulus after strength adjustment, and higher creep and shrinkage than conventional concrete.

The objective of this dissertation was to develop site specific static and dynamic live load models for bending moments and shear forces in steel girders. Steel girder bridges of various span lengths, girder spacings, and geometry were considered. Truck load data as well as bridge static and dynamic responses were collected. Two sources of data were utilized: (1) bridge weigh-in-motion (WIM) measurements carried out as part of this study and (2) weigh station data collected by the Michigan DOT (over 600,000 trucks). The WIM system was used to collect unbiased truck load data. Multiple presence events were also recorded from WIM statistical information and truck survey observations. The moments and shear forces caused by the surveyed and WIM collected trucks were calculated for spans from 10 ft to 200 ft. From these results, the models for extreme truck load effects were developed for various time periods by extrapolations. The mean maximum 75 year moments and shear forces were established based on the single lane live load model. Data on the Dynamic Load Factor (DLF) was collected under normal traffic loads using accelerometers, strain transducers, a data acquisition system and WIM system. Different truck positions and configurations were investigated. The effect of various truck parameters such as type, weight, speed, total length, lane position, and transverse distance on DLF was investigated. A numerical procedure was developed for data processing, filtering, smoothing and the calculation of DLF. This procedure utilizes the Fast Fourier Transform (FTT) numerical technique to obtain deflections from collected acceleration data. A similar procedure was applied to strain data collected from the WIM system. Results from measured strains and deflections were compared and confirmed conclusions obtained from theoretical simulations. The experimental results were used to verify the available analytical models for bridge analysis. The results indicate that, in many cases, the current methods are too conservative and overestimate the load distribution and sharing in girder bridges.

The live load models for girder bridges have been developed for bending moments and shear forces with considerations of various span lengths and girder spacings, using specially calculated truck influence line factors. To develop the live load model, the Ontario truck survey results were used as a basic statistical data. The moments and shear forces caused by the surveyed trucks were calculated for a wide range of spans from 10ft to 800ft. From these results, extreme truck load effects were extrapolated for various time periods. Statistical approach has been used to predict the effect of multiple presence based on the truck survey observations. Finally, the live load model were developed for single lane and multilane bridges. Also, equivalent uniformly distributed loads for mean maximum 50 year moments and shear forces were established based on the single lane live load model. Structural analysis methods were reviewed to model the girder bridges. An advanced finite element method using computer program MSC/NASTRAN was adopted to reduce the uncertainties involved in structural modeling procedures and to produce wheel influence envelopes. Parametric studies of live load distribution on girder bridges were performed. Effects of structural modeling, bridge geometry, structural design parameters, and truck load randomness were investigated by the sensitivity analysis. As a basic data set, the influence surfaces for one pair of wheel load were developed for bridge models selected from parametric studies. Different truck positions and configurations were investigated to identify the effects of various truck parameters. The truck influence lines of moments and shear forces were generated for the Ontario truck configuration. The load effect on girders for moment and shear forces were developed based on the bridge live load model and truck influence lines. The developed values of moments and shear forces will be used as a basis for changes in bridge design criteria. Some of these results are already implemented.