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Fatigue Behavior And Fatigue Life Evaluation Of Structural Details In Welded Steel Girder Bridges

Posted on:2009-06-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:W P RenFull Text:PDF
GTID:1102360272478590Subject:Bridge and tunnel project
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Fatigue cracks initiated from various connection details are common problems in welded steel bridge structures. Though extensive research has been performed in the past few decades, various fatigue problems are still occurring on a frequent basis. With truck weight increase and traffic volume growth, the fatigue problem in welded steel bridge structures is becoming more and more serious. This dissertation discusses a few most common types of fatigue cracks, and develops two fatigue reliability approaches for estimating fatigue lives of details in welded steel bridges. The main research contents and results are as follows.The dissertation analyses the fatigue failure mechanism of the most common connection details in welded steel bridges, and summarizes the research on fatigue of steel bridges in the world, which give an important reference to fatigue reseach and design of steel bridges in our country.Due to the absence of fatigue vehicle models in current Chinese highway bridge design specifications, the fatigue load models of BS5400, AASHTO, and Eurcode 1 bridge design code are introduced and analysed. Based upon the traffic data collected from five representative national highway sites, the main vehicle types included two types of buses and eight types of trucks for estimating fatigue damage accumulation are developed. The vehicle axle weights, axle spacings, and gross weights are measured with weight-in-motion (WIM) system. The load spectrum data were simulated over analytical bridge models, including simple and two-equally continuous spans. Based on the simulation results, the 3-axle and 4-axle standard fatigue truck models were developed. A discussion of the accuracy of fatigue vehicle models of AASHTO, BS5400, and Eurcodel bridge design code in estimating fatigue damage and the new developed standard fatigue vehicle models also presented.Based upon the load spectrum data collected from some representative national highway sites, the fatigue life curves (S-N curve) of four typical details in welded steel bridges subjected to random, variable-amplitude traffic cycles are computed using linear elastic fracture mechanics (LEFM) approach. Eighty results are finished by utilizing a FORTRAN program that is writted to simulate the random process. Based on the simulation results, the corrected S-N design curves are developed.Two fatigue reliability formulations that can be applied for most details in steel bridges are developed. One model is based on S-N Curve approach which is used for details classified according to fatigue categories in bridge design codes; the other is based on LEFM approach which is used for details not classified according to fatigue categories in bridge design codes. The variables needed for fatigue reliability analysis in either the S-N or the LEFM approaches is also studied and statistics on these variables have been compiled in this dissertation to assist in performing reliability analyses.Through two typical case studies, Shijiazhuang Overbridge in Zhang-Shi highway and Zhanjiang Gulf Bridge, a convenient fatigue evaluation procedure for welded steel bridge structures is developed. The fatigue design and scheduling of inspections and repairs can be performed according to the analytical result.Finally, the relationship between the fatigue life of some key welded details, N, and the main span length, L, is discussed based on analysis for four long-span cable-stayed bridges with steel box-girder.
Keywords/Search Tags:welded steel bridge, fatigue, load spectrum, S-N curve, fracture mechanics, fatigue reliability evaluation
PDF Full Text Request
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