Accurate and Rapid Determination of Fatigue Damage in Steel Bridges

Abstract

Fifteen representative bridges throughout the state of Illinois were instrumented with foil strain gages to determine their frequencies of loading and the magnitudes of stresses induced by traffic over a 3‐ to 8‐hour period, depending on traffic volume. Fatigue prone details, such as cover‐plated wide flanges, were instrumented. For each stress range increment gathered by the data‐acquisition system, the cumulative damage sustained over an extended number of years is compared with the number of available fatigue cycles for that stress range using published S=f(N) data for various details and the Palmgren‐Miner linear damage rule. A new equation for factor of safety for welded structures subject to fatigue is proposed, taking dead load, live load, and bridge detail fatigue strengths into account. A new method of assessing future fatigue damage in bridges that takes traffic growth and increased truck weights into account is also proposed.