A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item STRUCTURAL PERFORMANCE ASSESSMENT ON PREVENTIVE MAINTENANCE/REHABILITATION OF STEEL GIRDER BRIDGE SYSTEMS(2022) Zhu, Yifan; Fu, Chung C.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bridge maintenance, including preventive maintenance, rehabilitation, and replacement keeps the structure safe in its service life. Bridge maintenance methods have developed and expanded to bridge inspection, bridge condition assessments, structural health monitoring technologies, service life prediction, and maintenance with new materials or technologies. This dissertation proposes two structural performance assessments, (1) a rapid machine learning assessment classifying whether the design is under an acceptable range; and (2) comparing the structural health monitoring data with engineers’ predictions to evaluate the current structural performance.The first part of this dissertation focuses on preventive maintenance evaluation. This part discusses and plans a specific topic to instrument a newly constructed link slab system on a multiple simply-supported bridge. Before any simulation and field test of the general steel I-girder bridge model was conducted, literature regarding bridge maintenance, performance assessment, the durability of bridges, structural health monitoring method, current condition assessment methods, and research on the material and structural behavior of link slabs were reviewed and investigated. Then comprehensive experimental programs on the new materials HPFRC and ECC were conducted, and the extensive hands-on laboratory results update the nonlinearity and accuracy of the structure model. Moreover, a series of data analyses of the current steel bridge in the United States was conducted for further database establishment. Two sets of simulation-based finite element parametric analyses of the bridge with protective maintenance or structural repairing were introduced to generate preferred designs and further be used for rapid performance assessment. The inputs are the configuration of the bridge and the proposed work or deteriorated location, which generate the dataset for the training, validating, and testing of the evaluation model. The resulting regression model allows for quick assessment of the function developed by taking advantage of machine learning. This research verifies the assessment’s results using the Maryland Transportation Authority (MDTA) pilot HPFRC link slab system on the bridge overpass I-95 as a case study by comparing the prediction and actual structure health monitoring data after the assessment’s results were verified, and its performance was evaluated. This dissertation also examines one case from the Maryland State Highway Administration (MDSHA) bridge over the Patapsco River, which has several frozen expansion rocker bearings. This restrained the longitudinal movement of the superstructures due to thermal expansion and contraction. It has partially recovered to its normal condition after repairing and strengthening the pier under this bearing. In this study, we combined the finite element analysis and monitoring data to simulate structural behavior, and evaluate repair work using the proposed methods. Finally, This research evaluates the repaired bridge with partially strengthened structural components (i.e., deck, girders, or piers) and forecasts its wear and tear. In this study, the original and deteriorated bridges were numerically modeled first and simplified to 3D grid models. Then, the current condition rating process was used to determine the structural performance at the element level. After establishing the evaluation criteria and investigating the corresponding condition ratings, the rapid assessment models for the repaired bridges were carried out. The condition prediction relied on historical ratings and (if any) monitoring data.Item NUMERICAL SIMULATION STUDY OF VIBRATION MITIGATION EFFECTIVENESS OF TUNED MASS DAMPERS FOR TRAFFIC SIGNAL MAST ARM STRUCTURES(2016) Zhu, Yifan; Zhang, Yunfeng; Fu, Chung C; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fatigue damage in the connections of single mast arm signal support structures is one of the primary safety concerns because collapse could result from fatigue induced cracking. This type of cantilever signal support structures typically has very light damping and excessively large wind-induced vibration have been observed. Major changes related to fatigue design were made in the 2001 AASHTO LRFD Specification for Structural Supports for Highway Signs, Luminaries, and Traffic Signals and supplemental damping devices have been shown to be promising in reducing the vibration response and thus fatigue load demand on mast arm signal support structures. The primary objective of this study is to investigate the effectiveness and optimal use of one type of damping devices termed tuned mass damper (TMD) in vibration response mitigation. Three prototype single mast arm signal support structures with 50-ft, 60-ft, and 70-ft respectively are selected for this numerical simulation study. In order to validate the finite element models for subsequent simulation study, analytical modeling of static deflection response of mast arm of the signal support structures was performed and found to be close to the numerical simulation results from beam element based finite element model. A 3-DOF dynamic model was then built using analytically derived stiffness matrix for modal analysis and time history analysis. The free vibration response and forced (harmonic) vibration response of the mast arm structures from the finite element model are observed to be in good agreement with the finite element analysis results. Furthermore, experimental test result from recent free vibration test of a full-scale 50-ft mast arm specimen in the lab is used to verify the prototype structure’s fundamental frequency and viscous damping ratio. After validating the finite element models, a series of parametric study were conducted to examine the trend and determine optimal use of tuned mass damper on the prototype single mast arm signal support structures by varying the following parameters: mass, frequency, viscous damping ratio, and location of TMD. The numerical simulation study results reveal that two parameters that influence most the vibration mitigation effectiveness of TMD on the single mast arm signal pole structures are the TMD frequency and its viscous damping ratio.