Nonlinear Analysis Of Failure Behavior Of Longspan Two-Way Beam String Subjected To Strong Earthquake Under Cable Corrosion

Long span two-way beam string structure belongs to prestressed long-span spatial structure system,and the importance of prestressed cables is self-evident.When the structure is in bad service environment for a long time,the corrosion of cables will affect the structural performance,and then threaten the safety of the whole structure.At the same time,some of these long-span structures are located in areas with high seismic intensity.The generation of high-intensity ground motion will still affect the safety of the structure.At present,the domestic research mainly focuses on the single effect of corrosion research and seismic research,which will overestimate the performance of the structure,while considering the joint effect of the two is in the blank stage.Therefore,it is necessary to carry out the research and analysis of two-way beam string structure considering both cable rust and strong earthquake.It plays an important role in understanding the safety performance of long-span two-way beam string under the combined action of the two.In this paper,two aspects of cable corrosion and strong earthquake action are taken as the benchmark to carry out the research,focusing on the form finding and optimization of cable net of two-way beam string,and the corrosion tests of different types of cable steel wires are carried out,the vulnerability of cables is analyzed,and the simulation parameters of cable failure are systematically discussed,Based on the "dynamic time history analysis method of multiple response load domain under different degrees of corrosion",the strong earthquake analysis under different degrees of corrosion is carried out（1）In this paper,the form finding optimization of cable net for two-way beam string structure is studied.Through the formula derivation of continuous cable net stress state,the analytical solution is compared with the ANSYS solution.The results show that the ANSYS solution of cable net form finding is more uniform and reasonable than the theoretical solution,and the maximum displacement limit is smaller.（2）The size optimization analysis of three components of bidirectional beam string structure is carried out.Taking the best stress state and the lowest cost of steel consumption as the goal,the final optimization result is that the size of the top chord box hollow beam is 900×500×18×18.The size of stay bar is Φ196×5.The specification of the lower chord cable is Φ5×121,saving 83.7 tons of steel.displacement are still within the allowable range,and the structure is in a safe state.（3）The corrosion test of different kinds of cable steel wires of beam string is carried out.Three kinds of nickel chromium stainless steel wire with straight diameter of 5mm,galvanized steel wire on the surface and steel wire without any antirust treatment were used for electric corrosion test.The corrosion degree of steel wire was judged according to the corrosion phenomenon,mass loss and corrosion rate.The results show that the corrosion degree is 10%,15%,20%,25%and 30%respectively.（4）The vulnerability of two-way beam string cables is studied.According to the definition of vulnerability,the vulnerability of cables is analyzed.According to the calculation example in Chapter 2,the influence of cable corrosion on the mechanical properties of the structure is calculated,and the number of vulnerable cables of twoway beam string is determined.Finally,the regional division of the structure is carried out to analyze its robustness.The results show that:even under the maximum corrosion degree of 30%,the cable stress and maximum The determined vulnerable cables are X3,X5,X6 and X7.The regional robustness of the structure is region 1>region 5>region 4>region 2>region 3.（5）The dynamic analysis of cable failure is studied.Firstly,the natural vibration period of the whole structure and the remaining structure is calculated to provide the basis for the follow-up.Secondly,the simulation method of cable fracture,the duration of cable fracture and the duration of initial load are systematically discussed.The results show that:Based on the natural vibration period of 1s,the cable fracture is simulated by the full dynamic equivalent load instantaneous unloading method considering the initial state,and the simulated cable fracture duration is 0.01s,and the initial load duration is 30t.（6）The "dynamic time history analysis method of multiple response load domain under different corrosion degrees" is proposed.Based on the unrealistic time history analysis,through the study of strong earthquake analysis under the corrosion degree of cables,and based on the characteristics and stress mode of bidirectional beam string structure,a method suitable for analyzing the seismic effect of this structure is proposed,Compared with the traditional IDA incremental dynamic time history analysis method,it is mainly through increasing the external environmental factors.Compared with the former method,the advantage of this method is mainly to change the properties of the structure itself and constantly reduce its own performance factors,which is more in line with the objective basis of the structure in the service environment.（7）The influence of structure under strong earthquake is studied.According to the stress characteristics of the structure,the characteristic response indexes of the structure under different corrosion degrees are extracted.The failure behavior of the structure under different cable breaking modes can be judged by selecting appropriate seismic records.According to the domestic and foreign codes,the seismic performance level and damage state of the structure are divided ωm、λg、εb、δs、ux and uy.When the earthquake intensity is 7 degrees,8 degrees and 9 degrees respectively,the results of single cable fracture are safe.When the double cable fracture occurs,the strength failure occurs at 30%of the corrosion degree.When the three cable fracture occurs,the strength failure occurs at any corrosion degree,which eventually leads to instability failure.The seismic performance level and damage state of all 210 kinds of strong earthquake and corrosion actions are divided.This paper has 80 pictures,29 tables and 58 references.