Research On Stiffness Calculating Method Of Reinforced Concrete Beam Bridge Based On Loading Tests

The existing traffic volume and vehicle loads are increasing with the rapid development of transportation and social economy. These factors cause a heavier burden to the existing RC bridges and bring structural potential safety hazard. Therefore, it is pretty necessary to evaluate the bearing capacity of RC bridges reasonably and effectively. Usually, there are a variety of calculation methods for theoretical strain and deflection in the theoretical arithmetic of RC simple-supported beam bridge, and most of the theories take the section stiffness as a constant value after cracking, but it is not so. The section stiffness of RC should decrease as the loads increase, namely the stiffness is related to imposed vehicle loads. Meanwhile, the stiffness formulas in the relevant specifications are semi-empirical and semi-theoretical formulas base on the test of two symmetrical concentrated loads on simple-supported beam bridge. The influence of different load forms on the stiffness and deflection is not presented. And the calculation formula of stiffness in the specification is complex and experimental, and, the stiffness formulas specified in the various specifications are used to calculate and check the deformation of the most unfavorable stress cross section, however, it is not clear that the stiffness formulas can be used for the calculation of any cross section stress(strain) and the deflection. So it is worth further research on how to calculate the theoretical stiffness accurately and select of calculation method, thus it has important theoretical significance and practical value to study the stiffness calculation method for RC beam bridge and analyze the influence of different calculation methods on testing coefficient.This paper starts from the actual loading condition, combined with the crack development mechanism of cracking section and the nonlinear property of concrete material, then the relationship between theoretical stiffness and external bending moment is established, and the formula of the cracking section stiffness of RC beam is derived. On the foundation, the paper presents the equivalent stiffness for RC beam based on the form of loading vehicle and analyzes the calculation method and the formula. Besides, the reliability of stiffness calculation method is verified by the finite element analysis.Based on 4 pieces of model beams, the theoretical strain values of the model beams are calculated by linear algorithm, concrete specification method, the nonlinear algorithm, respectively; and the theoretical deflection values of the model beams are calculated by 85 specification, 04 specification, concrete standard and curvature integral method,respectively. According to comparing the theoretical deflection and strain values with the measured value, some reasonable suggestions of theoretical calculation method of RC beam is given. Finally, based on several real RC bridges, the different theoretical calculation methods are further verified by loading test, and the influence degree of different methods on the testing coefficient of strain and deflection is given. Finally, the program is compiled to calculate stiffness and deflection, with high efficiency.The paper is important part of the “Small and Medium Span Bridges Loading Test Key Technology Research and Promotion Project”(14-26T), which belongs to Shanxi Provincial communications department.The research results will provide technical support to load test result and bearing capacity assessment of RC beam bridge.