Analysis Of Anti-collapse Mechanism And Strengthening Measures Of Long-span Grid Structures

long span structure has many advantages and superior performance.It is widely used in practical life.However,due to its rapid development,there are also some problems,especially in the face of collapse.Based on the results of previous studies on large-span structures,combined with the analysis of an actual grid structure,this paper puts forward a collapse judgment criterion combining displacement response and plastic hinge failure,and introduces the selection of analysis theory and analysis method.Firstly,this paper analyzes the characteristics of the grid structure itself,then analyzes the members with different stress characteristics in different parts of the grid structure by using the simplified sensitivity analysis method,and initially obtains the sensitive members of the grid structure.Based on the results of the analysis,dynamic incremental method(IDA)is used to carry out collapse simulation analysis on the lossless and damaged structures,and further judge The importance of different members in grid structure.Finally,through the reinforcement of important components,the most appropriate reinforcement measures are obtained by judging the reinforcement effect.The specific research contents are as follows:(1)Using the finite element software SAP2000,the modal analysis and linear harmonic response analysis show that the fundamental frequency of the structure is0.78 hz,the horizontal vibration mode of the structure is more easily excited and more sensitive to the horizontal load.The maximum node displacement of the structure under harmonic excitation is about 1.5Hz;according to the sensitivity analysis results,the weak part of the structure is located at 1 / 5 of the structure and around the bottom support,among which the upper chord tension compression member,the web compression member and the lower chord compression member are more sensitive.(2)The dynamic time history analysis method is used to simulate the collapse of the grid structure under the lossless condition,and the ultimate collapse load of the grid structure under the one-way action is the highest,while the two-way and three-way action are very close to about 320 gal,so in order to reduce the workload,the two-way simple harmonic excitation is used to simulate the collapse process;the structure under six conditions is simulated respectively The results show that the damage of Web tie rod and bottom chord tie rod has little effect on the collapse resistance of the structure,while the damage of the other four members will reduce the ultimate collapse load of the structure,and further get the important components of the grid structure.(3)When the replacement member method is used to reinforce the important members,the most effective method is to reinforce the compression chord with the same number of members to reduce the stress and the maximum displacement of the structural members.According to the dynamic analysis of the original structure and the structure after taking four kinds of reinforcement measures,the maximum displacement frequency of the structure under different reinforcement measures remains basically unchanged between 1.4hz-1.6hz,and the structure collapses only when the structure is about 325 gal after the top chord compression bar and webcompression bar are reinforced,which is about 5gal higher than the collapse limit load before reinforcement,while the member lifting effect of the rest reinforcement is about 5 Gal higher General.