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Thai truck weights are different from the highway live loadings specified by the American Association of State Highway and Transportation Officials (AASHTO) standard specifications, which are popularly used for bridge design in Thailand. This article has studied the load-carrying behavior of simple supported bridge with the length ranging from 5-60 meters due to Thai truck loads and the AASHTO highway loads. This study aims to compare the maximum shear and bending moment of the simple beam bridges. The appropriate ratios of the shear, also bending moment, between Thai truck loads and AASHTO loads are proposed. The results show that, in each span, the maximum shear and bending moment caused by different types of trucks. In addition, the largest trucks produce the maximum responses for some analysis cases. In associated with various bridge span length, the shear ratios and the moment ratios are varied from 1.12 to 1.89 and 1.26 to 1.67, respectively. For bridge design practice in Thailand, these ratios could be applied as multiplier to the AASHTO loads, therefore, the maximum shear and bending moment of simple beam bridge caused by the proportioned AASHTO loads and Thai truck loads are comparable.