FATIGUE-LOAD MODELS FOR GIRDER BRIDGES

A fatigue-live-load model is developed for steel girder bridges. The d atabase for the model is obtained by weigh-in-motion (WIM) measurement s. Five bridge structures were selected for testing to determine the s ite-specific truck parameters' and component-specific stress spectrum. The database includes 22,000 truck files, each consisting of gross ve hicle weight (GVW), axle weights, and axle spacing. Stress cycles were measured at the midspan of all bridge girders and results are present ed as cumulative distribution functions. The WIM measurements confirm that truck bads are strongly site-specific. The results also indicate a significant variation in stress spectrum between girders. A three-ax le truck is proposed to represent the truck traffic. For sites with 10 - and 11-axle trucks, an additional four-axle truck is proposed. The d eveloped fatigue live load model is verified using fatigue-damage anal ysis to compare the model with measured results.