Live-load models for girder bridges.

Abstract

The live load models for girder bridges have been developed for bending moments and shear forces with considerations of various span lengths and girder spacings, using specially calculated truck influence line factors. To develop the live load model, the Ontario truck survey results were used as a basic statistical data. The moments and shear forces caused by the surveyed trucks were calculated for a wide range of spans from 10ft to 800ft. From these results, extreme truck load effects were extrapolated for various time periods. Statistical approach has been used to predict the effect of multiple presence based on the truck survey observations. Finally, the live load model were developed for single lane and multilane bridges. Also, equivalent uniformly distributed loads for mean maximum 50 year moments and shear forces were established based on the single lane live load model. Structural analysis methods were reviewed to model the girder bridges. An advanced finite element method using computer program MSC/NASTRAN was adopted to reduce the uncertainties involved in structural modeling procedures and to produce wheel influence envelopes. Parametric studies of live load distribution on girder bridges were performed. Effects of structural modeling, bridge geometry, structural design parameters, and truck load randomness were investigated by the sensitivity analysis. As a basic data set, the influence surfaces for one pair of wheel load were developed for bridge models selected from parametric studies. Different truck positions and configurations were investigated to identify the effects of various truck parameters. The truck influence lines of moments and shear forces were generated for the Ontario truck configuration. The load effect on girders for moment and shear forces were developed based on the bridge live load model and truck influence lines. The developed values of moments and shear forces will be used as a basis for changes in bridge design criteria. Some of these results are already implemented.