Fatigue analysis for steel bridge deck sections under blocked cycles of traffic loading

An effective approach for fatigue analysis of bridge-deck sections under traffic loading is proposed. It allows fatigue damage and predicted life of bridge deck under variable amplitude stress history due to traffic to be evaluated on the basis of health monitoring data. Based on the measurement of bridge traffic and the analysis on the property of strain-time histories recorded by strain gauges set at a bridge-deck section, the variable-amplitude strain-time history can be modeled as block repeated cycles. A representative block used as a standard of the blocks of repeated strain history is defined and obtained from the statistical analysis of many samples of daily strain-time data measured by the health monitoring system. Fatigue damage rate generated by a representative block of cycles is then derived, and computational approach for fatigue analysis based on the damage model and Miner's law is developed, in which the updating of the representative block is included for considering the increase of traffic volume in the future. Finally, as an example to show how the approach proposed in this paper is applied to revaluate the fatigue damage of a long-span suspension bridge, some results calculated for the critical location in the deck section are given.