Browsing by Subject "bridge"
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Item Calculation of Extreme Wave Loads on Coastal Highway Bridges(2010-01-14) Meng, BoCoastal bridges are exposed to severe wave, current and wind forces during a hurricane. Most coastal bridges are not designed to resist wave loads in such extreme situations, and there are no existing analytical methods to calculate wave loads on coastal highway bridges. This study focuses on developing a new scheme to estimate the extreme wave loads on bridges for designing purpose. In order to do this, a 2D wave velocity potential model (2D Model) is set up for the deterministic analysis of wave force on bridge decks. 2D Model is a linear wave model, which has the capability of calculating wave velocity potential components in time domain based on wave parameters such as wave height, wave period and water depth, and complex structural geometries. 2D Model has Laplace equation as general equation. The free surface boundary, incoming and outgoing wave boundary conditions are linearized, decomposed first, and then solved by the finite difference method. Maximum wave forces results calculated by the linear 2D Model are compared with results from CFD software Flow3D that is using Navier Stokes theory up to the 5th order; and 2D Model is validated by comparing results with experiment data. A case study is conducted for calculating extreme wave forces on I-10 Bridge across Escambia Bay, Florida during Hurricane Ivan in September 2004.SWAN model is adapted to investigate the parameters of wave heights and wave periods around bridge sites. SWAN model has the capability of predicting or hindcasting significant wave heights and wave periods as long as the domain and input parameters are given. The predicted significant wave heights are compared with measurements by Buoy Station 42039 and 42040 nearest to Escambia Bay. A new prediction equation of maximum uplift wave forces on bridge decks is developed in terms of wave height, wave period, water depth, bridge width, water clearance and over top water load. To develop the equations, the relationship is investigated between maximum uplift wave forces and wave parameters, water clearance, green water effects and bridge width. 2D Model is used for up to 1886 cases with difference parameters. Flow3D model is adopted to determine coefficients of water clearance and green water effects, which cannot be calculated by 2D Model.Item Connection of modular steel beam precast slab units with cast-in-place closure pour slabs(Texas A&M University, 2005-02-17) Brush, Natalie CamilleJointless bridges are advantageous in removing mechanical joints which are a known cause of bridge deterioration. Elimination of joints provides a smoother riding surface and removes the possibility of de-icing salts penetrating the deck and corroding the deck reinforcing and underlying bridge superstructure. Jointless bridges are traditionally constructed by monolithically casting the entire bridge deck on beams after they have been erected. However, this process requires extensive in-field formwork and lengthy traffic closures. The Texas Department of Transportation proposes a new method of constructing jointless bridges using prefabricated girder-and-deck units connected on-site with cast-in-place closure pours. This new system will expedite construction and reduce disturbances to the traveling public. The objective of this experimental study was to investigate the behavior of the cast-in-place closure pour slab and to determine if it responds to wheel loads in the same way as a traditional monolithic continuous deck. The effects of the cold joints and discontinuous steel details are the focus of the research work.Item Fault modeling, delay evaluation and path selection for delay test under process variation in nano-scale VLSI circuits(Texas A&M University, 2006-04-12) Lu, XiangDelay test in nano-scale VLSI circuits becomes more difficult with shrinking technology feature sizes and rising clock frequencies. In this dissertation, we study three challenging issues in delay test: fault modeling, variational delay evaluation and path selection under process variation. Previous research of fault modeling on resistive spot defects, such as resistive opens and bridges in the interconnect, and resistive shorts in devices, lacked an accurate fault model. As a result it was difficult to perform fault simulation and select the best vectors. Conventional methods to compute variational delay under process variation are either slow or inaccurate. On the problem of path selection under process variation, previous approaches either choose too many paths, or missed the path that is necessary to be tested. We present new solutions in this dissertation. A new fault model that clearly and comprehensively expresses the relationship between electrical behaviors and resistive spots is proposed. Then the effect of process variations on path delays is modeled with a linear function and a fast method to compute coefficients of the linear function is also derived. Finally, we present the new path pruning algorithms that efficiently prune unimportant paths for test, and as a result we select as few as possible paths for test while the fault coverage is satisfied. The experimental results show that the new solutions are efficient and accurate.Item Rehabilitation Techniques and Assessment of a Historic Reinforced Concrete Variable Depth Girder Bridge(2013-05-08) Ortiz, Laura MarieHistoric bridges are an important part of the nation's infrastructure. However, many historic bridges are not being maintained to a level that will ensure their continued use. In 2007, the I-35 W Mississippi River Bridge collapsed demonstrating significant issues with the safety of older bridges in service. Currently there are so many bridges that are considered structurally deficient that transportation authorities are continuously faced with the dilemma of distributing limited bridge funds. This situation underscores a need for cost effective and reliable maintenance and rehabilitation strategies. This thesis promotes historic preservation in two main tasks: (1) rehabilitation and repair methods are determined to guide engineers, preservationists, and other stakeholders and (2) an assessment is performed for a prototype historic bridge. More specifically, the assessment is performed in three tasks: (1) modeling of the historic bridge, (2) evaluation of the bridge using load rating procedures, and (3) rehabilitation strategies are recommended based on the results of the assessment. The prototype bridge is a 1930s variable depth T-beam bridge. The bridge did not meet requirements for flexural capacity at the mid-sections of the approach and main span interior girders. Three rehabilitation methods considered were support modification at the cantilever ends, external fiber reinforced polymer (FRP) plies, and external post-tensioning. The support modification raised the bridge to a 75-year exposure period, the highest level of evaluation, without disrupting the historical integrity of the bridge. The FRP plies raised the positive moment capacity of the bridge to legal load standards, a 5-year exposure period. The FRP retrofit was limited by de-bonding issues. The external post-tensioning raised the positive capacity to design load standards at the inventory level, a 75-year exposure period. The external post-tensioning was limited by the use of a straight tendon, but is less visible than a draped tendon. From the information in the assessment, support modification is more effective than the other methods and will not negatively affect the bridge?s historic integrity. Other factors such as the projected effects on other bridge elements including the substructure, cost, installation procedures, and durability should be considered and might lower the benefits of the considered methods.