Prestressed concrete is a popular construction material for highway bridges. A variety of girder span values, cross-sectional shapes, and prestressing strand layouts has been used in bridges across the United States. A major concern for such bridges is the possibility of corrosion damage in the prestressing strands or reinforcing bars, which is commonly caused by the use of deicing salts on the deck or saltwater spray in coastal regions. The present study aims at establishing analytical tools for the accurate simulation of chloride ingress, corrosion and mechanical damage (cracking) in the concrete, and for the evaluation of the impact of corrosion on the flexural and shear strength of bridge girders. First, an efficient and accurate analytical scheme is formulated to enable the calculation of the load-carrying capacity of corrosion-damaged girders. The analyses rely on two types of models, namely, beam models and nonlinear truss models. The latter are deemed necessary to obtain reliable estimates of the shear capacity, as beam models are not well-tailored for capturing shear failures. A procedure to account for the reduction in area and deformability of corroded strands, based on visually observed corrosion damage, is proposed and implemented. The models are calibrated and validated with the results of experimental tests on prestressed girders which exhibited varying levels of corrosion damage. Further analyses allow the comparison of the capacity of corrosion-damaged girders to that of their undamaged counterparts. The accuracy of a simplified procedure, using equations in the AASHTO code to determine the flexural and shear capacity of the damaged girders, is also determined. Subsequently, a computation scheme was proposed to describe the intrusion of chloride ions in prestressed bridge girder sections. The approach accounts for multiple, coupled processes, i.e., heat transfer, moisture transport, and chloride advective and diffusive transport. The constitutive models for moisture and chloride transport rely on previous pertinent work, with several necessary enhancements. The modeling scheme is calibrated with data from previous experimental tests on concrete cylindrical and prismatic specimens. The calibrated models are then validated using data from chloride titration tests conducted on girders removed from two bridges in Virginia after 34 and 49 years of service. The results indicate that the proposed framework can accurately reproduce the experimentally measured chloride content. The modeling approach also allows the evaluation of the accuracy of simplified, design-oriented tools for estimating the evolution of chloride content with time. The multi-physics simulation scheme is further refined to account for the corrosion-induced mechanical damage (cracking), by incorporating a phenomenological description of the electrochemical reaction kinetics, generation of expansive corrosion products, and subsequent development of tensile stresses and cracking in the surrounding concrete. The impact of cracking on the chloride and moisture transport mechanisms is also taken into account. The last part of this dissertation pursues the quantification of the uncertainty governing the chloride ingress in bridge girders, through the use of a stochastic collocation approach. The focus is on understanding how the inherent uncertainty in the value of input parameters (e.g., material transport parameters, ambient conditions etc.) is propagated, leading to uncertainty in the evolution of chloride content and the expected corrosion initiation time for a given bridge. / Doctor of Philosophy / Prestressed concrete is widely utilized in the construction of highway bridges in the United States. A significant concern arises regarding potential corrosion damage in the prestressing strands or reinforcing bars, which is commonly attributed to the application of deicing salts on the deck or exposure to saltwater spray in coastal regions. This study aims to develop analytical tools that can accurately simulate the intrusion of corrosive agents (namely chloride ions), and subsequent damage (cracking) in concrete. Furthermore, the research seeks to assess the impact of corrosion on the bearing capacity of bridge girders. Two different classes of analytical approaches are pursued. The first class employs purely mechanical (stress/deformation) models for capturing the strength, deformability and failure modes of girders with visual corrosion damage. These models rely on two approaches to capture the flexural and shear capacity of specimens, namely, beam-based models and truss-based models. The impact of corrosion is established through appropriate modification of the model parameters, based on the extent of visually observed corrosion damage. The analytical approaches are validated through a series of experimental tests previously conducted on corrosion-damaged girders. The second class of analytical approaches employs multi-physics models, to describe the mechanisms leading to corrosion-induced damage. The models account for heat transfer, moisture transport, and chloride transport in prestressed beam sections. Model parameters are calibrated with experimental tests in literature. The computational scheme is used to quantitatively describe the chloride ingress on bridge girders decommissioned from two different bridges in Virginia, after 34 and 49 years of service. The analysis results are found capable of capturing the actual chloride content at various depths from the exposure surface, as determined by chloride titration tests. The temporal evolution of chloride on the surface of prestressing strands indicates that corrosion has been taking place over a period of time for the two bridges. The multi-physics simulation approach is further enhanced to account for the corrosion-induced mechanical damage (cracking), by explicitly incorporating a description of the reaction kinetics, generation of expansive corrosion products and subsequent development of cracking in the surrounding concrete. The last part of this dissertation pursues the quantification of the uncertainty in the expected service life of prestressed concrete bridge structures. Given the inherent uncertainty to key values of model parameters, a parametric study is employed to investigate the propagation of uncertainty to the time history of chloride content at particular locations of the section and the probability of corrosion initiation at specific age values.

This research provides quantitative data to aid engineers in the selection of various attributes to facilitate fit-up during I-girder bridge construction. Concepts and procedures for explicit calculation of locked-in forces due to cross-frame detailing are developed and discussed. Fit-up forces are evaluated and discussed for a suite of bridge cases analyzed in this research. Bridge cases with difficult fit-up are highlighted. Recommendations for erection procedures are provided to facilitate fit-up. The research investigates and recommends beneficial staggered cross-frame framing arrangements that are applicable to straight skewed bridges, framing arrangements with liberal offsets around bearing lines at interior pier in continuous spans bridges, and the use of staggered versus lean-on cross-frame arrangements in straight skewed bridges. The research also addresses the impacts of cross-frame detailing methods, that is, the “fit condition” of the structure, on cross-frame forces, girder elevations, girder layovers, girder stresses, and vertical reactions in the completed bridges.

O presente trabalho faz uma comparação entre resultados obtidos por um método prático e simplificado e o Método dos Elementos Finitos na determinação de esforços solicitantes em pontes celulares curvas em planta, submetidas à protensão. Na primeira parte, teórica, apresenta-se os conceitos fundamentais das vigas celulares curvas, mostrando-se principalmente as diferenças de seu comportamento em relação ao das vigas retas. Em seguida discute-se a protensão de peças de concreto com ênfase no seu efeito em vigas curvas. Finalmente, são apresentados os métodos a serem utilizados no cálculo, percorrendo as diversas situações de carregamento, mas sempre enfatizando o carregamento de protensão. Na segunda parte, prática, é elaborado um estudo comparativo, tomando-se como exemplo duas pontes rodoviárias em viga unicelular, sendo uma biapoiada e outra contínua, submetidas a protensão. Após a construção de modelos, tais vigas são processadas através de um programa comercial de elementos finitos. Alguns resultados são então comparados com aqueles obtidos através do método simplificado, elaborando-se assim observações práticas e que possam ser utilizadas nos projetos corriqueiros de engenharia. / This work compares the results from a practical and simplified method and the Finite Element Method to determinate section efforts in prestressed box-girder curved bridges. The first part, theoretical, introduces the basic principles of the cellular curved beams, showing the differences of its behavior comparing with straight beams. Next, prestressing of concrete members is discussed, emphasizing its effects in curved beams. Finally, calculation methods are presented, covering many loading situations, but always emphasizing the prestressing load. In the second part, practical, a comparative study is elaborated, taking two road unicellular bridges, one simply supported and another continuum, submitted to prestressing load. After models construction, such beams are calculated using a commercial software of Finite Element Method. Then, some results are compared with those calculated by simplified method, thus elaborating practical comments that can be used in the current designs of engineering.

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.

The majority of the bridges in the United States are already reaching the years that the design process took into account when determining the time the structure would be functional. This means that many of the bridges in the nation are in need of increasing maintenance, and in some cases, major retrofitting. Researchers at Utah State University in conjunction with the Long-Term Bridge Performance (LTBP) Program, under the direction of the Federal Highway Administration’s (FHWA’s) Office of Infrastructure Research and Development, directed dynamic testing on the New Jersey Pilot Bridge, structure number 1618-150. The purpose of the LTBP Program is to monitor the nation’s highway bridges for a 20-year period to analyze and understand the behavior over time of the selected bridges and then promote the safety, mobility, longevity, and reliability on those bridges. In order to perform the monitoring of the bridge, ambient vibration analysis was selected for this structure, which was instrumented with an array of velocity transducers to record the response coming from the excitation. A finite element model was also created to compare the results from the ambient vibration testing. The results of this testing will be used with the LTBP Program to improve the knowledge of the bridge performance and foster the next generation of bridges and bridge management in the nation.

After September 11, 2001, government officials and the engineering community have devoted significant time and resources to protect the country from such attacks again. Because highway infrastructure plays such a critical role in the public’s daily life, research has been conducted to determine the resiliency of various bridge components subjected to blast loads. While more tests are needed, it is now time to transfer the research into tools to be used by the design community. The development of Anti-Terrorism Planner for Bridges (ATP-Bridge), a program intended to be used by bridge engineers and planners to investigate blast loads against bridges, is explained in this thesis. The overall project goal was to build a program that can incorporate multiple bridge components while still maintaining a simple, user-friendly interface. This goal was achieved by balancing three core areas: constraining the graphical user interface (GUI) to similar themes across the program, allowing flexibility in the creation of the numerical models, and designing the data structures using object-oriented programming concepts to connect the GUI with the numerical models. An example of a solver (prestressed girder with advanced SDOF analysis model) is also presented to illustrate a fast-running algorithm. The SDOF model incorporates the development of a moment-curvature response curve created by a layer-by-layer analysis, a non-linear static analysis accounting for both geometric non-linearity as well as material non-linearity, and a Newmark-beta-based SDOF analysis. The results of the model return the dynamic response history and the amount of damage. ATP-Bridge is the first software developed that incorporates multiple bridge components into one user-friendly engineering tool for protecting bridge structures against terrorist threats. The software is intended to serve as a synthesis of state-of-the-art knowledge, with future updates made to the program as more research becomes available. In contrast to physical testing and high-fidelity finite element simulations, ATP-Bridge uses less time-consuming, more cost effective numerical models to generate dynamic response data and damage estimates. With this tool, engineers and planners will be able to safeguard the nation’s bridge inventory and, in turn, reinforce the public’s trust. / text

Cross frames are critical components in steel bridge systems. Cross frames brace girders against lateral torsional buckling and assist in distributing live loads to girders during the service life of the bridge. In curved bridges, cross frames also serve as primary structural members in resisting torsion generated by the traffic loads. The conventional cross frames are often constructed in X- or K- type shapes with steel angle sections. However, the actual stiffness of these cross frames are not well understood or quantified, leading to potentially inaccurate prediction of bridge behavior and safety during construction and in service. Previous studies have shown the possibility of employing new sections, such as tubular members and double angles, in cross frame designs. In addition, a type-Z cross frame, or single diagonal cross frame was also found to be a potential use to simplify the design. However, the effectiveness of these innovative cross frame types has not been completely examined. And these new cross frames have yet compared with the conventional ones in terms of their stiffness and strength capacity. This dissertation documents the results of a study on the stiffness of various types of cross frame systems. Full size cross frames were tested to establish actual stiffness of the cross frames specimens. The tests results revealed a significant discrepancy between the actual measured stiffness and the stiffness calculated using methods commonly employed by bridge designers. The research showed that the major source of this discrepancy was eccentricity in the connection. The stiffness reduction was quantified by employing analytical derivation and finite element modeling. As a result, methods were developed to account for the stiffness reduction. / text

This thesis describes part of the work associated with Project 0-6719 sponsored by the Texas Department of Transportation (TxDOT). The primary objective of the project is to examine the feasibility of strengthening older continuous multi-span steel girder bridges through the use of post-installed shear connectors. Bridges potentially eligible for retrofit have noncomposite floor systems, where the concrete slab is not attached to the steel girders with shear connectors. Many of these bridges were designed in the 1950's and 1960's for loads smaller than the standard design loads used today. A secondary objective of the project, and the main focus of this thesis, is to examine the design of post-installed shear connectors for fatigue. Of particular interest in this study is the adhesive anchor, given its convenient installation procedure but relatively poor fatigue performance in previous tests. The objectives of this thesis were to quantify the fatigue strength of the adhesive anchor, as well as quantify the shear force and slip demands on adhesive anchors in realistic bridge conditions. In regards to the first objective, twenty-six direct shear fatigue tests were performed on adhesive anchors. Each test was conducted on a single adhesive anchor in order to capture its individual cyclic load-slip behavior. Results indicate that adhesive anchors have considerably higher fatigue strength than conventional welded shear studs, making partial composite design feasible in the strengthening of older steel bridges. In regards to the second objective, analytical and computational studies were conducted on composite beams with adhesive anchors. Results show that the shear force and slip demands are typically smaller than the endurance limits determined from direct-shear testing. This suggests that fatigue failure of adhesive anchors under service loads may not be a primary concern. Based on the results, preliminary recommendations for the design of adhesive anchors for fatigue are provided. / text

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Commercially available glass fiber-reinforced polymer (GFRP) off-the-shelf structural shapes have great potential as stay-in-place open structural forms for concrete structures, including bridge decks and girders. The system simplifies and accelerates construction, and the non-corrosive GFRP forms can fully or partially replace steel rebar. In this study, eight concrete slabs were constructed using flat pultruded GFRP plates, and nine girders were constructed using trapezoidal pultruded GFRP sheet pile sections as stay-in-place structural forms. No tension steel reinforcement was used. All specimens were tested in four-point monotonic uniaxial bending. Four adhesive and mechanical bond mechanisms were explored to accomplish composite action. The most effective mechanism, considering structural performance and ease of fabrication, was wet adhesive bonding of fresh concrete to GFRP. Although failure was by debonding, no slip was observed prior to failure. Other parameters studied were concrete slabs’ thicknesses and their shear span-to-depth ratios. For the girders, three different cross-sectional configurations were examined, namely, totally filled sheet piles, one with a voided concrete fill, and an all-GFRP box girder developed by bonding flat GFRP sheets to the upper flanges of the sheet piles with a cast-in-place concrete flange. Girders were tested in positive and negative bending to simulate continuity. The built-up box girders showed superior performance, with up to 70% higher strength and 65% lower weight than the totally filled sections. It was found that similar size conventional steel-reinforced concrete sections of comparable stiffness have considerably lower strength, while those of comparable strength have considerably higher stiffness than FRP-concrete members. An analytical model was developed to predict the behaviour and failure loads of slabs and girders, using cracked section analysis. A unique feature of the model is a multi-stepped failure criteria check that can detect flexural, shear, or bond failure. The model was successfully validated using the experimental results, and used in a parametric study. It was shown that using the typical value of 1MPa for shear strength of cement mortar predicts debonding failure, which occurs slightly above the interface, quite well. Also, in practical applications of longer spans, flexural failure is likely to occur prior to bond failure. / Thesis (Master, Civil Engineering) -- Queen's University, 2008-07-14 15:12:48.405