Study On Mechanical Analysis And Computation Method Of Cross Diaphragm In Continuous Box Girder

With the high-speed development of the city and transportation, The number of urban bridge and urban grade separation bridge continuously increase. With advantages such as superior mechanical properties, enrichment and beauty in structure form, high applicable performance, reinforced concrete continuous beam and prestressed concrete continuous beam become the main type of urban bridges and urban grade separation bridges. Cross diaphragm is an important component element in continuous box girder, it can increase the lateral stiffness of box girder, limit distortion stress of box girder, bear and disperse support reaction of box girder, transfer torque and shear to adjust and improve the holistic resistant behavior of the main beam, ultimately achieve the important role of improving the overall stability and deformation properties of the bridge. So in the design of a continuous box girder bridge, internal force calculation of the cross diaphragm is necessary to ensure it has sufficient strength and rigidity to play its due. But in present, researches on cross diaphragm of continuous box girder are less, and in the various bridge design specifications, there is no provisions and regulations.With the increasingly wide range of applications of box girder, bridge span, bridge width and loads are also greater and greater continuously, the design calculation of box girder bridge and cross diaphragm are particularly important. To provide references and basis for calculations of cross diaphragm in box girder, the researches on mechanical properties of cross diaphragm and put forward an accurate and practical design calculation method are more and more urgent.Combined with the health monitoring calculation of a 6-span prestressed concrete continuous box girder bridge, the following main research works on continuous box girder and cross diaphragm are been carried out:(1) A space finite element model of a full-bridge structure is established using large general-purpose finite element software ANSYS, and a baseline finite element model which is modified using the measured data is got. The baseline finite element model is very consistent with the actual stress conditions of the real bridge, so it can be the basis for health monitoring evaluation and analysis of mechanical properties of the bridge.(2) Main characteristics of mechanical behavior and stress distribution of this kind of box girder cross diaphragm in dead loads and live loads are got combining with the data calculated from space finite element model of the full-bridge structure and measured data, and got the mechanism of loads on box girder which is transported to cross diaphragm.(3) Research on the calculation cross-section and effective calculation width are carried out. By analyzing the stress distribution of the roof and floor plate which near to cross diaphragm in the loads case of the whole bridge, the conclusion that the effective width of this cross diaphragm is 1.5 times to 3times of the cross diaphragm itself is got. The effects of the effective width of roof and floor plate can be not ignored, so "å·¥"cross section is suggested in the calculation of cross diaphragm.(4) A new simplified calculation method is put forward according to the characteristics of mechanical behavior and mechanism of loads transportation of box girder cross diaphragm, by an example of cross diaphragm calculation verified the accuracy and advantages of this method. Reference and basis are provided for calculations of cross diaphragm in this kind of box girder.