Study On Calculation Method Of Prestressed Concrete Invisible Cap Beam

With the high-speed development of our economy,highway and urban traffic construction is also in full swing.The application of a large number of prestressed concrete Bridges has made China’s bridge design theory mature day by day.The bridge design theory mainly focuses on the longitudinal bridge to the main beam,while the research on the transverse bridge,especially the invisible cap beam is less.In this paper,the invisible cap beam of prestressed concrete continuous beam bridge is taken as the research object,and the spatial solid model is established by ABAQUS software to study the calculation method of the invisible cap beam of prestressed concrete.The main work contents are as follows:(1)The spatial solid model of prestressed concrete continuous box girder bridge is established to study the mechanical characteristics of the invisible cap beam under the action of dead weight,prestress,vehicle and phase ii constant load.When the number of supports,the distance between supports and the thickness of the top,bottom and web of the box girder change under the self-weight load,the distribution law of vertical shear in the cross section between the invisible cap beam and the box girder is studied.The results show that the number of supports has the greatest influence on the vertical shear distribution of the junction section between the invisible cap beam and the box girder.The more the number of supports,the more uniform the vertical shear distribution of the webs on the junction section will be.The vertical shear in the web area on the junction section of the invisible cap beam and the box girder takes up the largest proportion of the total section,followed by the top and bottom plates,and the smallest flange and inclined plates.(2)By changing the thickness of the invisible cap beam,the thickness of the top and bottom plates of the box girder and the thickness of the web,the effective working width of the invisible cap beam under constant load and vehicle load was studied,and the selection method for calculating the section of the simplified model of the invisible cap beam was summarized.The elastic support with certain stiffness is set to modify the current simplified model of invisible cap beam,and the influence of the stiffness value of elastic support and the position of elastic support on the mechanical characteristics of the simplified model of invisible cap beam is studied.The results show that the effective working width of the invisible cap beam decreases with the increase of the thickness of the invisible cap beam under the constant load and vehicle load.Under constant load,the thickness of the top and bottom plates and the web of the box girder have little influence on the effective working width of the invisible cap beam.The calculation section of the simplified model of the invisible cover beam should be selected according to the effective working width at the flange plate and the thickness of the invisible cap beam.The actual working state of the invisible cap beam can be accurately simulated by setting the elastic support model of the invisible cap beam with certain rotational stiffness in the outermost web of the junction section between the invisible cap beam and the box girder and the web area near the bearing.(3)The topology optimization method based on SIMP interpolation model was used to establish the strut-and-tie model of the invisible cap beam.The strut-and-tie model method was used to calculate the reinforcement of the invisible cap beam in combination with the bridge design specification,and the method was compared with the traditional design method.The results show that the topological optimization results are best when the equivalent load is loaded in the form of concentrated force and the residual volume is 20%.At the bearing of the invisible cap beam of strut-and-tie model,several press-rods meet,and the node at the bearing is the control node of the invisible cap beam of strut-and-tie model.Under the condition that the bearing capacity of the invisible cap beam does not change much,the strut-and-tie model method uses less steel than the traditional design method.