UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
3 results
Search Results
Item THERMO-MECHANICAL FATIGUE OF STEEL PILES IN INTEGRAL ABUTMENT BRIDGES(2012) Razmi, Jafar; Aggour, M.Sherif; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The issue of fatigue in steel piles of Integral Abutment Bridges (IABs) is investigated. A three-dimensional, non-liner finite element (FE) model is constructed for a bridge located in a harsh climate. Historic temperature data for the region is obtained and a sinusoidal model was developed to represent the daily and seasonal temperature changes. The FE is parametrically run for 5 cases with bridge lengths varying between 400 and 1800 feet under the cyclic load of daily and seasonal temperature variations. The pile behavior and stresses in the piles are evaluated and a fatigue model is used to determine the fatigue life of the piles. The Palmgren-Miner rule is used to evaluate the combined effects and contribution of both types of temperature cycles. The critical location of the pile is modeled locally utilizing a global-local modeling approach. "Successive initiation" in conjunction with a strain-based fatigue damage model is implemented in the local model to determine the thermo-mechanical fatigue crack initiation site, propagation path, and rate in the piles. The results show that maximum stress occurs in the pile furthest from the center of the bridge in its flange right below the concrete abutment. Plastic deformation is observed in all the piles and in all the cases studied indicating the possibility of low cycle fatigue. Lateral displacement and maximum plastic deformation in the piles increases as the length of the bridge increases. A linear relationship was found between the length of the bridge and the lateral displacement for both seasonal and daily temperature variations. The longer the bridge is the shorter the fatigue life. The crack modeling results indicate that the crack initiates in the tip of the flange. Multiple cracks form in the flange, which causes an increased propagation rate. The propagation rate decreases when the crack reaches the web. The crack could initiate in the pile in the first decade, but it will take several decades to reach the web. The final failure of the pile may not occur for several decades.Item Behavior and Analysis of an Instrumented Slab Bridge(2009) Jeong, Sungki; Fu, Chung C.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Because of quick construction and cost effectiveness, adjacent precast, prestressed box girder bridges have been used nowadays more often for short-span bridges, and the standardization of this modular bridge is highly desired. Maryland intends to revise its current practice of using tie-rods for the transverse post-tensioning in slab bridge design. The new design of using high strength rods will provide a more tightly integrated modular slab bridge system with higher post-tensioning forces. With the new design, the Maryland State Highway Administration is highly interested in the performance of the new design, especially compared with the old design. This thesis presents the procedure of test, live load test results and analysis results in association with the finite-element model simulated in a newly-built bridge.Item GAS-FILLED AXISYMMETRIC ACOUSTIC RESONATORS(2005-12-05) El-Sabbagh, Adel; Baz, Amr; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation, the harmonic oscillations of gas-filled axisymmetric acoustic cavities near resonance conditions are considered. This problem has gained considerable interest during the last decade when compression ratios of up to 340% have been achieved. The objective of this dissertation is to develop theoretical models that can predict the performance of resonators of complex geometries in a straightforward manner to enable the selection of optimal resonator configurations that yield high compression ratios. With this goal in mind, a mathematical model is developed based on the equations of conservation of mass, linear momentum, and state equation for ideal gas. The model accounts for the full nonlinear behavior of the gas oscillations. The equations are cast in a weighted residual form which can be solved provided that the exact mode shapes for the linear problem can be determined. The model is proved to be accurate in capturing experimental phenomena such as the formation of shock waves at large excitations. However, it is solvable only for resonators with simple geometries. In order to overcome these deficiencies, a finite element model is developed based on the weak form of the governing equations. The finite element model enables the prediction of resonators of complex geometries with either body or boundary excitation sources at different flow conditions. Furthermore, the model is integrated with the dynamics of axisymmetric piezoelectric bimorphs that are used to actuate the acoustic cavity instead of the conventional actuation systems. The coupling between the cavity and piezoelectric bimorph models is achieved by considering their mutual interactions. The validity of the coupled model is validated experimentally and against the predictions of a commercial finite element software (ANSYS) that deals with linear acoustic equations. Close agreement is obtained between theory and experiment indicating that the developed analytical and experimental tools can be confidently used in the design of axisymmetric acoustic resonators that possess a high potential of applicability in designing smart structures and vibration control.