Research On Modeling Of Small Supported Box Beam Based On Rigid-jointed Girder Method And Application

The small box, having been used widely in china, has advantages of resistance to torsion and economy as well as convenience construction. In order to calculate the small box girder, based on load transverse distribution, the spatial bearing performance can be changed into plane stress analysis. Rigid-jointed girder method is suitable for calculating the small box girder. In the process of calculating the small box's load transverse distribution, the coefficient matrix increase as the number of the main girder grows. It can be only solved by programming software, so it's difficult to master by technical staff.Besides, the box beam has been gradually applied in the widening and strengthening of old bridges. The conventional rigid-jointed girder method is performed using the assumption that the main girders are the same. The conventional can't be used in the structure of the T-shape section bridge with small box beam, because the same box beam stiffness is not the same as the T-shape section bridge.The paper uses the research ideas, combining the rigid-jointed method and finite element model. The paper proposes the beam grillage model by setting virtual crossmember, based on the small box girder's construction. The model is applied to analyze the static load test of small box girder. And the paper researches the change rule of load distribution of the T-shape section bridge with box beam. The main contents and conclusions are as follows:(1) The small supported box beam is calculated by rigid-jointed girder method and beam grillage model. The measuring criterion is the transverse distribution influence line of main girder.The maximum relatively error between the results of two methods is less than 5%. The results verify that this model is acceptable and valid.(2) The beam grillage model is applied to analyze the static load test of small box girder,according to the calculation results, loading project and rule of measuring-point arrangement for bridge static test are presented. The measured deflections and strains are less than the theoretical values. The measured load distribution curve values coincide with the theoretical ones. Based on above analysis, the carrying capacity of the bridge satisfies the design requirement.(3) Based on the beam grillage model, the paper analyzes the change rule of load distribution of the T-shape section bridge with box beam, and the effect among main parameters.The analysis shows that setting small box girder can improve the overload ability of T-beam bridge, the small box girder torsional stiffness does not much affect the load distribution of Tshape section bridge. It can be viewed from complicatedness and mechanical property that 3diaphragm plates can be setted between side box beam and T-beam.(4) The sectional dimension of big box girder is bigger, by analysis and calculation of big box girder, the split concept is introduced. Based on the shear-flexible beam grillage model, the change rule of load distribution of the T-shape section bridge with big box beam. The analysis shows that: setting big box beam reduces the load distribution curve amount by 1/4, the big box beam can effectively reduce vehicle load eddect. The diffence between two webs of big box girder is 8%, there exists stress distribution unevenness in two webs.