Numerical Simulation Analysis Of Working Box Girder Bridge With Crack

Prestressed concrete box girder bridge is widely used in China due to its own performance advantages.Under the influence of the disease,cracks may occur in the box girder of this bridge during the construction and operation stages.Domestic scholars have deeply researched the causes of cracks and expounded the mechanism of cracks,but there are few researchs on the state of prestressed concrete box girder bridge after cracking,which cannot reflect the real state of box girder with cracks.In this thesis,the No.0 block of a continuous rigid frame bridge is taken as the research object to establish the spatial solid model of the structure,and the Cohesive constitutive relationship is established to simulate the crack interface behavior.The completed work includes:(1)The main concepts of CDP constitutive model simulating concrete mechanical behavior and Cohesive constitutive model simulating crack interface behavior are expounded.The definition parameters of the model are determined by comparing the relevant literature.(2)The spatial solid model of No.0 block is established for finite element analysis,and verified with the actual bridge results.The spatial stress distribution of No.0 block under two construction stages of concrete pouring and prestressed tension is analyzed.The results show that the prestressed tendons anchoring area will cause the performance loss of regional materials.Based on the finite element analysis data and field investigation results,four typical crack models are presented: oblique crack of web,vertical crack at the top of diaphragm manhole,longitudinal crack of box girder roof,vertical crack at the web.(3)Cohesive linear constitutive model is used to realize the implantation of cracks in the solid space model.By trial calculation,the damage criterion of crack interface — the maximum nominal stress,is 0.135 MPa.Taking the internal force at the most unfavorable stage of the construction stage as the loading external force,the spatial stress distribution of No.0 block after the failure of each typical crack and its corresponding combined crack is investigated.The results show that the typical cracks only affect the region within a certain range,and the maximum change of normal stress value is 1.00 MPa,and the maximum change of principal stress value is 0.73 MPa;and the multi-crack model not only has an impact in a certain range at the crack interface,but also radiates to the whole structure of No.0block,and the stress value of the whole section changes greatly,which makes the tensile stress of the whole structure increase,and the maximum change of the normal stress value is4.20 MPa,and the maximum change of the principal stress value is 0.77 MPa.The load-displacement curves of each crack model are obtained by ultimate load,and the maximum bearing capacity loss rate is 20.00 %.The stiffness loss rate of No.0 block structure is quantified by secant stiffness method,and the maximum stiffness loss rate is 6.47 %.(4)The stiffness loss rate is introduced into the frame model of whole bridge,and the response of the whole bridge structure under the condition of partial structural performance loss is analyzed.The deflection and stress of the key sections are researched respectively.The results show that during the construction,the performance loss of the damaged structure only affects the beam section near itself,and the farther the distance is,the smaller the influence is.With the increase of the number of damaged structures,the loading effect at each stage increases accordingly.In the operation stage,the overall performance of the bridge will be affected,which is the result of the load-bearing response of the damaged area and diffusion to the whole bridge.Under D5 damage scheme(0#、8#-11# blocks structure damaged),the maximum deflection value and stress value variation are located at the 11# block beam section,which are 2.69 mm and 1.59 MPa during the construction;during the operation,the maximum deflection variation is 2.59 mm(section 1 – 1),and the maximum stress variation is 1.00 MPa(section 2 – 2).