Failure Analysis of Continuous Highway Steel I-Multigirder Bridges under the Combined Effect of Fatigue and Overloading Events

A significant number of recent highway bridge failures have been attributed to the lack of financial resources that constrained owners to keep bridges in service under undesired circumstances. Given that many highway bridge failures were related to cyclic fatigue and overloaded trucks, or some combination thereof, the objective in this paper is to present an approach to assess the reliability of continuous highway steel I-multigirder bridge superstructures under the combined effects of fatigue damage and overloading. To that effect, Monte Carlo simulations were run for 42 short to medium-length steel I-multigirder bridges having configurations representative of bridges in North America. Fatigue damage locations, permanent loads, truck gross weights, and axle configurations were assumed to be random variables. The fatigue model used is consistent with the model implemented during calibration according to AASHTO’s specifications for a 75-year design life. Simple equations were constructed to quantify the probability of bridge system collapse resulting from the combined effects of fatigue and overloading events for typical continuous steel I-multigirder bridge superstructures. Accordingly, the expected service life of bridges would reduce by about 7 years if the percentage of overweight trucks increases from the national average of 5.1% to 12.0%. The proposed model can eventually be implemented in bridge management systems to account for the effects of truck loads, complementing these systems’ current focus on bridge condition ratings.