Based on the principle of minimum potential energy, choosing warping displacement function of parabolic displacement mode, using energy variational method to deduce Box beam shear lag effect analysis of differential equation to obtain shear lag warping stress. Through the calculation of simply supported box girder model and the analyse of the stress of Wide cantilever plate, box girder roof and box girder floor Assume a new warping displacement function. Through the analysis of measured results proved the rationality of this article assumes and research value.

The static load test schemes of Tiansheng bridge are briefly discussed . Through the comparative analysis of the theory values and the measured values , understand the actual work condition of bridge structure under test load and evaluate the bearing capacity of bridge structure .Through comparison of modeling datas and the measured values , test correctness of testing program, providing a scientific basis for the bridge safety and research in great depth.

This test took dynamic strain detection method depending on time history curve of the dynamic deflection or the dynamic strain analysis of moving load in the control section to obtain impact factor. Using the method of environmental random vibration testing tested vibration response signals of L / 4 section of bridge test span , the cross section and 3 L / 4 section to identify the dynamic characteristics parameters of the overall vibration of Bridge, so that to determine current situation of application , assess the carrying capacity of bridge and test design load bearing capacity. According to the results of load test,the bearing capacity of Tiansheng bridge meets the requirements of "road - grade I" load level.