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Research on Impact Factor of Simple Composite Box Beam under Vehicle Loads

Commonly the vibration due to vehicle loads has no apparently impact on highway bridges, but it is unneglectable when the heavy vehicles load on highway bridges. The impact factor is usually used to define the dynamic effect under vehicle loads in most design code. In this paper, the models of simple composite box beams with different span and the models of two simplified heavy vehicles are established respectively. The impact factors are calculated when the heavy loads pass though bridges at different speed under different load conditions. In addition, the change laws of the impact factors and the influence of different vehicle models on the impact factors are analyzed. Analysis results show that, not only the impact factor are increased with vehicle speed, but also the amplitude and period are all increased. In normal speed range, the influence of speed on the impact factors appears rising trend overall. For the bridge with same span, the impact factors under the double wheel load are smaller than that under single wheel load.