This paper proposes to assess the vehicle carrying safety of in-service highway grillage girder bridge considering structure redtmdancy and lumped plasticity of components under bending.The highway bridge considered is a two-lane simply-supported RC bridge composed of 5 main girders and 5 diaphragms.The structure is modeled as a grillage girder system and all of its main girders and diaphragms are modeled as 6DOF grid elements.The vehicle load on each lane is modeled to be the summation of a uniform distributed force and a concentrated force.