A. James Clark School of Engineering
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Item Development of a Fatigue Life Assessment Model for Pairing Fatigue Damage Prognoses with Bridge Management Systems(IntechOpen, 2018-12-18) Saad, Timothy; Fu, Chung C.; Zhao, Gengwen; Xu, ChaoranFatigue damage is one of the primary safety concerns for steel bridges reaching the end of their design life. Currently, US federal requirements mandate regular inspection of steel bridges for fatigue cracks; however, these inspections rely on visual inspection, which is subjective to the inspector’s physically inherent limitations. Structural health monitoring (SHM) can be implemented on bridges to collect data between inspection intervals and gather supplementary information on the bridges’ response to loads. Combining SHM with finite element analyses, this paper integrates two analysis methods to assess fatigue damage in the crack initiation and crack propagation periods of fatigue life. The crack initiation period is evaluated using S-N curves, a process that is currently used by the FHWA and AASHTO to assess fatigue damage. The crack propagation period is evaluated with linear elastic fracture mechanic-based finite element models, which have been widely used to predict steady-state crack growth behavior. Ultimately, the presented approach will determine the fatigue damage prognoses of steel bridge elements and damage prognoses are integrated with current condition state classifications used in bridge management systems. A case study is presented to demonstrate how this approach can be used to assess fatigue damage on an existing steel bridge.Item Fatigue Assessment of Highway Bridges under Traffic Loading Using Microscopic Traffic Simulation(IntechOpen, 2018-11-13) Zhao, Gengwen; Fu, Chung C.; Lu, Yang; Saad, TimothyFatigue is a common failure mode of steel bridges induced by truck traffic. Despite the deterioration caused by environmental factors, the increasing truck traffic volume and weight pose a premier threat to steel highway bridges. Given the uncertainties of the complicated traffic loading and the complexity of the bridge structure, fatigue evaluation based on field measurements under actual traffic flow is recommended. As the quality and the quantity of the available long-term traffic monitoring data and information have been improved, methodologies have been developed to obtain more realistic vehicular live load traffic. A case study of a steel interstate highway bridge using microscopic traffic simulation is presented herein. The knowledge of actual traffic loading may reduce the uncertainty involved in the evaluation of the load-carrying capacity, estimation of the rate of deterioration, and prediction of remaining fatigue life. This chapter demonstrates a systematic approach using traffic simulation and bridge health monitoring-based fatigue assessment.Item Truck Loading Simulation for the Fatigue Assessment of Steel Highway Bridges(2015) Zhao, Gengwen; Fu, Chung C.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fatigue is a common failure mode for steel bridges. About 80-90% of failures in steel structures are related to fatigue and fracture. Despite the deterioration caused by environmental factors, the increasing traffic volume and weight pose a premier threat of steel highway bridges. The total number of truck passages in the 75-year life of a highway bridge could exceed 100 million. With the aging of existing steel highway bridges and the accumulated damage under truck loading, the fatigue assessment for continuing service has become important for decisions making on the structure maintenance, component replacement, and other major retrofits. This research seeks to develop a framework for the fatigue assessment of steel highway bridges based on simulated truck loading. The I-270 Bridge over Middlebrook Road was numerically studied with the proposed methodology. With the help of the available long-term monitoring traffic data and information, truck loading was obtained through the probability-based full velocity difference model. Then, the three-dimensional finite element (FE) global and local bridge models were studied subjected to the simulated truck loading. Meanwhile, the preliminary field test and the long-term monitoring test were also been conducted. The FE models were calibrated by the collected field measurements through monitoring systems, and the simulated numerical structural responses were validated. Lastly, Miner's rule and the rainflow counting algorithm were used in the analysis of simulated numerical structural responses to estimating the fatigue life. Thus, the proposed methodology could be used to realistically simulate the fatigue behavior of steel highway bridges under current or future truck loading, to direct the experimental designs and instrumentation plans before performing experiments on laboratory or on site, and to better understand the fatigue mechanism and prevent the fatigue damage of steel highway bridges.