Title page for ETD etd-04042012-211349

Type of Document Dissertation
Author Zhang, Wei
Author's Email Address wzhan12@lsu.edu,wzhlsu@gmail.com
URN etd-04042012-211349
Title Fatigue Performance of Existing Bridges under Dynamic Loads from Winds and Vehicles
Degree Doctor of Philosophy (Ph.D.)
Department Civil & Environmental Engineering
Advisory Committee
Advisor Name Title
Cai, Steve C.S. Committee Chair
Barbato, Michele Committee Member
Levitan, Marc L. Committee Member
Wahab, Muhammad A Committee Member
Guzik, T. Gregory Dean's Representative
  • vehicle-bridge-wind dynamic system
  • road roughness index
  • cycles per truck passage
  • equivalent orthotropic material method (EOMM)
  • equivalent nodal force
  • stochastic random road profile
  • nominal live load stress range
Date of Defense 2012-03-12
Availability unrestricted
During the life cycle of bridges, varied amplitude of stress ranges on structural details are induced by the random traffic and wind loads. The progressive deteriorated road surface conditions might accelerate the fatigue damage accumulations. Micro-cracks in structural details might be initiated. An effective structural modeling scheme and a reasonable fatigue damage accumulation rule are essential for stress range acquisitions and fatigue life estimation. The present research targets at the development of a fatigue life and reliability prediction methodology for existing steel bridges under real wind and traffic environment with the capability of including multiple random parameters and variables in bridges’ life cycle.

Firstly, the dynamic system is further investigated to acquire more accuracy stresses for fatigue life estimations for short and long span bridges. For short span bridges, the random effects of vehicle speed and road roughness condition are included in the limit state function, and fatigue reliability of the structural details is attained. For long-span bridges, a multiple scale modeling and simulation scheme based on the EOMM method is presented to obtain the stress range history of structural details, while the calculation cost and accuracy are saved. Secondly, a progressive fatigue reliability assessment approach based on a nonlinear continuous fatigue damage model is presented. At each block of stress cycles, types and numbers of passing vehicles are recorded to calculate the road surface’s progressive deterioration and nonlinear cumulative fatigue damage, and the random road profiles are generated. Thirdly, this study discussed the fatigue design of short and long span bridges based on the dynamic analysis on the vehicle-bridge or vehicle-bridge-wind system. For short span bridges, a reliability-based dynamic amplification factor on revised equivalent stress ranges (DAFS) is proposed. For long span bridges, a comprehensive framework for fatigue reliability analysis under combined dynamic loads from vehicles and winds is presented. The superposed dynamic stress ranges cannot be ignored for fatigue reliability assessment of long-span bridges, although the stresses from either the vehicle loads or wind loads may not be able to induce serious fatigue issues alone.

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