Transverse load distribution behavior amongst bridge girders is influenced by many parameters including girder material properties, spacing, skew, deck design, and stiffening element interactions. In order to simply and conservatively approximate the bridge superstructure load distribution between girders, the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications contain load distribution factor (LDF) equations for many common bridge types. The Texas Department of Transportation (TxDOT) had recently developed a new design for bridge superstructures that utilizes a spread configuration of prestressed concrete slab beams. AASHTO does not contain LDFs for this type of bridge so the load sharing behavior of this superstructure must be investigated further. TxDOT has funded the Texas A&M University Transportation Institute (TTI) to design, model, construct, test, and analyze a full scale spread slab beam bridge. In addition to this testing, an existing slab beam bridge in Denison, Texas will be instrumented and observed for supplementary slab beam behavior data. To predict bridge behavior, computer models of the Riverside experimental bridge and of the Denison field bridge were developed using both the grillage and finite element methods of analysis. The experimental results from the Riverside and Denison bridges will not be collected by the conclusion of this thesis so a third bridge with existing experimental data, the Drehersville, Pennsylvania bridge, was also modeled for calibration purposes. The work presented by this thesis focuses on how to accurately model transverse load distribution relationships and LDFs for use in bridge design. The analysis covered is concentrated primarily on the grillage method, with the finite element analysis as part of the larger project scope. From this analysis it was determined that the grillage method was able to accurately model bridge LDFs as compared to FEM modeling and experimental results, for spread slab beam and spread box beam bridges. The critical loading configurations for all bridges placed two trucks side by side and as far to one edge of the bridge as possible. It was also determined that at an ultimate loading case, the load is distributed much more evenly across the deck than at service loading.

A test program for the Hybrid-Composite Beam (HCB) was conducted prior to its use for the replacement of a skewed, simply-supported bridge (Tide Mill Bridge). The HCB is an innovative combination of conventional materials and ideas in a structural beam. The beam consists of a concrete arch tied with prestressing strand that is placed within a Fiber-Reinforced Polymer (FRP) box. Behavior in individual HCB's and a three HCB-system was examined to determine the appropriateness of the current design methodology developed by John Hillman and the simplifying assumptions made within it. Such assumptions include strain compatibility and linear-elastic behavior. Three HCB's were tested at the structures laboratory at Virginia Tech. During individual beam tests, the predicted behavior of the FRP box and prestressing strand agreed with experimental results. The tests revealed the arch was susceptible to local bending and behaved far differently from predicted. Overall, the beams were shown to behave linearly. A final test was performed to apply the design live load to the system. Slight non-linear behavior was observed in the beams. Distribution factors for the system were also investigated and compared to AASHTO and Hillman's model. AASHTO factors were conservative for exterior girders but unconservative for interior girders. Hillman's factors were often conservative but were in agreement for the shear in the exterior girder. The current design procedure appeared to predict FRP and strand behavior well, but the behavior of the arch appeared to differ greatly from the other components of the HCB. / Master of Science

The Long Term Bridge Performance (LTBP) Program is a 20-year program initiated by the Federal Highway Administration to better understand the behavior of highway bridges as they deteriorate due to environmental variables and vehicle loads. Part of this program includes the periodic testing of selected bridges. The Lambert Road Bridge was subjected to nondestructive testing in the fall of 2009. Part of this testing included a live load test. This test involved driving two heavy trucks across the instrumented bridge on selected load paths. The bridge was instrumented with strain, displacement, and tilt sensors. This collected data was used to calibrate a finite element model. This finite element model was used to determine the theoretical live load distribution factors. Using the controlling distribution factor from the finite element model, the inventory and operating ratings of the bridge were determined. These load ratings were compared to those obtained from using the controlling distribution factor from the AASHTO LRFD Specifications. This thesis also examined how different parameters such as span length, girder spacing, parapets, skew, continuity, deck overhang, and deck thickness affect the distribution factors of box girder bridges. This was done by creating approximately 40 finite element models and comparing the results to those obtained by using the AASHTO LRFD Specifications.

Live load distribution factors are used to determine the live-load moment for bridge girder design when a two dimensional analysis is conducted. A simple, analysis of bridge superstructures are considered to determine live-load factors that can be used to analyze different types of bridges. The distribution of the live load factors distributes the effect of loads transversely across the width of the bridge superstructure by proportioning the design lanes to individual girders through the distribution factors. This research study consists of the determination of live load distribution factors (LLDFs) in both interior and exterior girders for horizontally curved concrete box girder bridges that have central angles, with one span exceeding 34 degrees. This study has been done based on real geometry of bridges designed by a company for different locations. The goal of using real geometry is to achieve more realistic, accurate, and practical results. Also, in this study, 3-D modeling analyses for different span lengths (80, 90, 100, 115, 120, and 140 ft) have been first conducted for straight bridges, and then the results compared with AASHTO LRFD, 2012 equations. The point of starting with straight bridges analyses is to get an indication and conception about the LLDF obtained from AASHTO LRFD formulas, 2012 to those obtained from finite element analyses for this type of bridge (Concrete Box Girder). After that, the analyses have been done for curved bridges having central angles with one span exceeding 34 degrees. Theses analyses conducted for various span lengths that had already been used for straight bridges (80, 90, 100, 115, 120, and 140 ft) with different central angles (5º, 38º, 45º, 50º, 55º, and 60º). The results of modeling and analyses for straight bridges indicate that the current AASHTO LRFD formulas for box-girder bridges provide a conservative estimate of the design bending moment. For curved bridges, it was observed from a refined analysis that the distribution factor increases as the central angle increases and the current AASHTO LRFD formula is applicable until a central angle of 38º which is a little out of the LRFD`s limits.

American Association of State Highway and Transportation Officials (ASHTO) specifications have prescribed lateral load distribution factors to calculate the bending moments and shear forces for the design of highway bridges for civilian highway traffic. The maximum bending moments and shear forces caused by a wheel line load (or the entire vehicle) placed on the girders are multiplied by the distribution factors to calculate the design forces to include the effect of the load distribution laterally to the girders by the bridge deck. However, the use of these AASHTO distribution factors may not provide accurate estimate of the maximum forces for military vehicles, which usually have significantly different loading pattern than those of the civilian vehicles. Therefore, this study was conducted to develop new formulas for the lateral load distribution factors for military vehicles. The study considered six different types of military vehicles, three wheeled vehicles and the other three tracked vehicles. The bridge database used for developing AASHTO distribution factors formulas was also used in this study. The focus of this study was to develop the distribution factors formulas for three different types of bridges: steel girder bridges, pre-stressed concrete bridges, and concrete T-beam bridges. The bridges in each category were analyzed for the six types of military vehicles by the harmonic decomposition approach to calculate the distribution factor. This thesis provides a total of 52 new formulas for different types of vehicles, different types of bridges, bending moment and shear force values, interior and exterior girders, and for single and multiple lane loading cases. The distribution factors calculated with the formulas were compared with those calculated by direct analyses of the bridges to evaluate the accuracy of the proposed formulas. Comparisons were also made between the values calculated by the new formulas, post-LRFD formulas prescribed in 1996 AASHTO Standard Specification, and simple pre-LRFD formulas that were prescribed by AASHTO before 1994. / Master of Science

The Hampton Roads Bridge-Tunnel is one of the oldest prestressed concrete structures in the United States. The 3.5 mile long twin structure includes the world's first underwater tunnel between two man-made islands. Throughout its 60 years in service, the harsh environment along the Virginia coast has taken its toll on the main load carrying girders. Concrete spalling has exposed prestressing strands within the girders allowing corrosion to spread. Some of the more damaged girders have prestressing strands that have completely severed due to the extensive corrosion. The deterioration has caused select girders to fail the necessary load ratings. The structure acts as an evacuation route for the coast and is a main link for the local Norfolk Naval Base and surrounding industry. Because of these constraints, load posting is not a viable option. Live load testing of five spans was performed to investigate the behavior of the damaged spans. Innovative techniques were used during the load test including a wireless system to measure strains. Two different deflection systems were implemented on the spans, which were located about one mile offshore. The deflection data was later compared head to head. From the load test results, live load distribution factors were developed for both damaged and undamaged girders. The data was also used by the local Department of Transportation to validate computer models in an effort to help pass the load rating. Overall, this research was at the forefront of the residual strength of prestressed concrete girders and the testing of in-service bridges. / Master of Science

The inverted T-beam bridge system provides an accelerated bridge construction alternative for short-to-medium-span bridges. The system consists of adjacent precast inverted T-beams finished with a cast-in-place concrete topping. The system offers enhanced performance against reflective cracking, and reduces the likelihood of cracking due to time dependent effects. The effects of transverse bending due to concentrated wheel loads are investigated with respect to reflective cracking. Transverse bending moment are quantified and compared to transverse moment capacities provided by a combination of various cross-sectional shapes and transverse connections. A design methodology for transverse bending is suggested. Tensile stresses created due to time dependent and temperature effects are quantified at the cross-sectional and structure level and strategies for how to alleviate these tensile stresses are proposed. Because differential shrinkage is believed to be one of the causes of deck cracking in composite bridges, a study on shrinkage and creep properties of seven deck mixes is presented with the goal of identifying a mix whose long terms properties reduce the likelihood of deck cracking. The effects of differential shrinkage at a cross-sectional level are numerically demonstrated for a variety of composite bridge systems and the resistance of the inverted T-beam system against time dependent effects is highlighted. End stresses in the end zones of such a uniquely shaped precast element are investigated analytically in the vertical and horizontal planes. Existing design methods are evaluated and strut-and-tie models, calibrated to match the results of 3-D finite element analyses, are proposed as alternatives to existing methods to aid designers in sizing reinforcing in the end zones. Composite action between the precast beam and the cast-in-place topping is examined via a full scale test and the necessity of extended stirrups is explored. It is concluded that because of the large contact surface between the precast and cast-in-place elements, cohesion alone appears to provide the necessary horizontal shear strength to ensure full composite action. Live load distribution factors are quantified analytically and by performing four live loads tests. It is concluded that AASHTO's method for cast-in-place slab span bridges can be conservatively used in design. / Ph. D.

Accelerated Bridge Construction (ABC) has gained substantial popularity in new bridge construction and bridge deck replacement because it offers innovative construction techniques that result in time and cost savings when compared to traditional bridge construction practice. One technology commonly implemented in ABC to effectively execute its projects is the use of prefabricated bridge components (precast/prestressed bridge components). Precast/prestressed bridge components are fabricated offsite or near the site and then connected on-site using small volume closure pour connections. Diaphragms are also commonly used to strengthen the connection between certain prefabricated components used in ABC, such as beam elements. Bridges containing closure pour connections and diaphragms can be designed using AASHTO LRFD live-load distribution factor formulas under the condition that the bridge must be sufficiently connected. However, these formulas were developed using analytical models that did not account for the effects of closure pours and diaphragms on live-load distribution. This research study investigates live-load distribution characteristics of precast/prestressed concrete bridges with closure pour connections and diaphragms. The investigation was conducted using finite element bridge models with closure pour joints that were calibrated using experimental data and different configuration of diaphragms. The concrete material used for the closure pour connections was developed as part of a larger project intended to develop high early-strength concrete mixtures that specifically reach strength in only 12 hours, a critical requirement for ABC projects.

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