Acomparative study between dynamic behaviour of steel and composite bridges over open channels

Abstract

The current highway bridge design codes treat the dynamic effect of traffic loads by applying an empirical amplification factor, called the “impact factor” which is a function of span length only and has little theoretical basis. This procedure is an imprecise because it is known that, the increase in bridge response due to dynamic effects is a function of vehicle characteristics, pavement surface conditions and bridge type. This paper aims to study and compare the dynamic behavior of steel and composite bridges over open channels under the same truck loads. A finite element dynamic analysis is performed to achieve the desired calculations. The highway bridge is modeled as a beam element, while the traffic loads are modeled as a series of concentrated moving loads. The standard trucks given by the New Egyptian Code of practice are considered in this study. A computer program is developed to generate the standard traffic loads and to perform the required dynamic analysis. The FE model and the developed computer program are calibrated using the available results in previous works. A practical steel and composite bridge cases with the same span lengths traveled by the Egyptian standard traffic loads are analyzed. A comparison between the dynamic response of each pair of the steel and the composite bridge cases has been made. Accurate values for the dynamic effect factors for these bridges are calculated and compared by the approximate values for the impact factors given by the Egyptian bridge design code. Finally a summary of conclusions and useful recommendations concerned the bridge designers are highlighted.