Impact Factors for Fatigue Design of Steel I-Girder Bridges Considering the Deterioration of Road Surface Condition

Abstract

The purpose of this paper is to evaluate the impact factor (IM) in LRFD bridge design specifications for fatigue design and to propose a method for determining reasonable IMs for the fatigue design of steel I-girder bridges that can more rationally consider the effect of the deterioration of the road surface condition (RSC) during its whole lifecycle. The deterioration process of the RSC was investigated under the given traffic and environmental conditions, and the number of truck passages taken for the RSC to deteriorate from one class to the next was investigated. A three-dimensional coupled vehicle–bridge model was developed to simulate the interaction between the bridge and vehicle, with both the bridge and fatigue load models adopted from an existing LRFD code. The IM of the stress range (IM_SR), which is calculated using the stress range instead of the maximum stress used traditionally, was used for the fatigue analysis of steel girders. Numerical simulations were performed to study the IM_SR of steel I-girder bridges under different RSCs while taking into consideration the effect of two other important parameters: bridge span length and vehicle speed. Results show that the RSC has a greater impact on the IM_SR than on the traditional IM, and the IM_SR is greater than the traditional IM calculated using the maximum stress. By considering the cumulative fatigue damage caused by the passage of each truck under different RSCs and the deterioration process of the RSC during its whole lifecycle, simple and reasonable expressions were proposed for the IMs for fatigue design of steel I-girder bridges under the given traffic and environmental conditions.