Shm-based fatigue reliability evaluation of steel bridges: Methodology, experiment, and application

The present investigation is concerned with the development of a systematic method for fatigue reliability assessment of welded details at steel bridges by making use of long-term measurement data from the structural health monitoring (SHM) system. An analytical fatigue reliability model is proposed by uniquely integrating the probability distribution of hot spot stress range with a continuous probabilistic formulation of Miner's damage cumulative rule, and applied for fatigue life and reliability evaluation of the instrumented Tsing Ma Bridge (TMB). A monitoring-based standard daily stress spectrum accounting for highway traffic, railway traffic, and typhoon effects is derived by use of the monitoring strain data, from which a multi-modal probability density function (PDF) of the stress range data is obtained using the finite mixed Weibull distributions in conjunction with a novel hybrid mixture parameter estimation approach. Then the global and local finite element models (FEMs) of the bridge are developed for numerically calculating the stress concentration factors (SCFs) at fatigue-susceptible locations, while the stochastic characterization of the SCF for a typical welded bridge T-joint is perceived by conducting full-scale model experiments of the railway beam section of TMB which reveal that the SCF for typical welded connections conforms to a normal distribution. The failure probability and reliability index versus fatigue life are achieved from the obtained joint PDF of the hot spot stress range in terms of the nominal stress range and SCF random variables.