Live load spectra for girder bridges

The objective of this dissertation was to develop site specific static and dynamic live load models for bending moments and shear forces in steel girders. Steel girder bridges of various span lengths, girder spacings, and geometry were considered. Truck load data as well as bridge static and dynamic responses were collected.;Two sources of data were utilized: (1) bridge weigh-in-motion (WIM) measurements carried out as part of this study and (2) weigh station data collected by the Michigan DOT (over 600,000 trucks). The WIM system was used to collect unbiased truck load data. Multiple presence events were also recorded from WIM statistical information and truck survey observations. The moments and shear forces caused by the surveyed and WIM collected trucks were calculated for spans from 10 ft to 200 ft. From these results, the models for extreme truck load effects were developed for various time periods by extrapolations. The mean maximum 75 year moments and shear forces were established based on the single lane live load model.;Data on the Dynamic Load Factor (DLF) was collected under normal traffic loads using accelerometers, strain transducers, a data acquisition system and WIM system. Different truck positions and configurations were investigated. The effect of various truck parameters such as type, weight, speed, total length, lane position, and transverse distance on DLF was investigated. A numerical procedure was developed for data processing, filtering, smoothing and the calculation of DLF. This procedure utilizes the Fast Fourier Transform (FTT) numerical technique to obtain deflections from collected acceleration data. A similar procedure was applied to strain data collected from the WIM system. Results from measured strains and deflections were compared and confirmed conclusions obtained from theoretical simulations.;The experimental results were used to verify the available analytical models for bridge analysis. The results indicate that, in many cases, the current methods are too conservative and overestimate the load distribution and sharing in girder bridges.