In current bridge engineering an idealized model is used to apply the parapet load to the bearing pads of a bridge. In this idealized model it is assumed that the parapet load is evenly distributed across all of the bridge bearing pads. However, this assumption is incorrect. The purpose of this study is to demonstrate that the parapet load distribution is more complicated than an evenly distributed load. Instead, this study shows that a majority of the parapet load is applied to the exterior bearing pad. This means that the real world exterior bearing pad reactions will be much larger than the reactions found using the idealized, evenly distributed model. This study utilizes the finite element program, NISA, to model and analyze a simple span bridge. The bridge used in this study was developed using a prestressed concrete girder design example from the Texas Department of Transportation. The design example specified the span length, clear roadway width, prestressed girder type, and girder spacing of the bridge. The bridge is modeled under two different loading conditions to ensure a comprehensive array of results is obtained. The two loading conditions were carefully designed to compare the idealized model, utilized by the Federal Highway Administration, to the real world parapet load distribution. The focus of this study is to determine how the parapet load distribution will affect the bearing pad reactions in a simple span bridge. The results of this study are provided in several tables depicting the bearing pad reactions obtained from the finite element models. The results of each parapet load distribution are compared to one another and percent differences are calculated between each condition. This allows for the use of a single number to define the effect the parapet load distribution has on the bearing pad reactions. A secondary focus of this study is to determine how a bearing pad's deformation, and thus its stiffness, will affect the bearing pad reactions of a simple span bridge. The results of this study are provided in several tables depicting the bearing pad reactions obtained from the finite element models. The results of each bearing pad stiffness condition are compared to one another and percent differences are calculated between each configuration. This allows for the use of a single number to define the effect of bearing pad stiffness on the parapet load distribution. This portion was completed first and the best model was chosen to be used in the main part of the study.

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The effect of a number of variables upon prestress anchorage length was investigated. The end zones of prestressed pretensioned concrete members were simulated by casting against steel bulkheads. 3/8" diameter strands and .276" diameter wires were used. Fifty specimens were tested. The variables investigated were; surface condition of prestressing steel, speed of release of prestress, water/cement ratio of concrete, age of concrete, stress in concrete, and vibration. A relationship between free end pull-in and anchorage length was found and is compared with the results of other investigators. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The purpose of this investigation was to compare the behaviour of real prestressed concrete columns to the predictions of a mathematical model. A previously developed computer programme, based on the mathematical model, had suggested several problems which needed examination. The programme indicated that, in some circumstances, an unstable equilibrium configuration could occur. The existence of this unstable loading path meant that a snap-through type of buckling was a possibility. To check these hypotheses, six T-shaped prestressed concrete columns were constructed and tested at the University of British Columbia. In most instances, experimental observations closely matched the predictions of the mathematical model. The computed and observed peak loads compared well and the presence of an unstable equilibrium path was confirmed. Unfortunately, attempts to measure curvatures and to compare them with mathematically obtained values were unsuccessful. No satisfactory explanation for this problem was found. Having established the validity of the mathematical model through the experimental programme, an examination of snap- — through buckling was made. It was concluded that prestressed concrete columns are not prone to snap-through buckling, although sufficient additional energy applied to a column might result in a jump from a stable equilibrium configuration to an unstable one. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

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Corrosion on bridges is a common issue since it can be caused by multiple agents such as marine environments or deicing chemicals. The damages caused by these agents, if left unmitigated, may lead to failure of the superstructures. If corrosion is present in the end regions of the beams, failure of the girders will likely be in shear, which is a sudden failure mode and not the preferred limit state. Therefore, it is beneficial to study repair practices and their advantages, as repairs are often more cost-effective than building entirely new structures. Repairing prestressed girders for shear is not common practice, but with the number of superstructures considered structurally deficient in the United States, additional consideration should be given to repair methods. In this study, two beams were extracted from two decommissioned bridges and were repaired using Carbon Fiber Reinforced Polymer (CFRP) to investigate how well proposed repairs functioned. One of the beams is an American Association of State Highway and Transportation Officials (AASHTO) Type II beam, while the second one is an adjacent box beam. Before repairs were done, the beams had their ends further damaged with accelerated corrosion induced via electrolysis to ensure that the beams would have enough deterioration in their shear span to simulate the worst-case scenario found in the field. Afterwards, the girders had their damage and residual strength estimated, and repairs were designed using guidelines from the American Concrete Institute (ACI) and AASHTO for CFRP repairs. Since the adjacent box beam could only be repaired in flexure, it failed in shear with a load similar to previous studies done in beams from the same bridge, which indicates that repairs for box beams need further investigation. The repairs on the AASHTO Type II beam worked well for shear, and both ends failed in flexure, which is an improved failure mode since failing in flexure is more ductile and predictable than shear failures. One end of the AASHTO Type II beam failed by concrete crushing and CFRP rupturing, and the other end failed by strand rupturing, which shows that the accelerated corrosion worked as was predicted. / Master of Science / Corrosion on bridges is a major problem across the United States, especially in marine environments and in cold areas where deicing chemicals are needed to ensure the safety of the drivers. These external agents typically accelerate the deterioration of bridges and lead to expensive repairs and sometimes total replacement of structures. In order to study repair methods for bridges that have been exposed to corrosive agents, bridge girders were extracted from two decommissioned bridges in Virginia. The level of damage in these girders was assessed and it was determined that more corrosion had to be induced into the girder to ensure repairs were needed. After that process, the strength of the girders was estimated using guidelines from the American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO), and the girders were repaired for shear using sheets of Carbon Fiber Reinforced Polymers (CFRP). These repairs were done by using two different wrapping schemes, one that enveloped the sides of the girder, and one that was only at the bottom of the girder. The girders then had their ends tested under three-point bending to evaluate the effectiveness of the repairs. The girder that had the sides repaired as well performed better since the failure mode of it changed from shear to flexure. The girder that only had its bottom repaired did not do as well since its failure mode was still shear.

published_or_final_version / abstract / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Philosophy

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.