Study On Failure Mechanism Of Grid Structure With Intersecting Nodes Considering Damage Accumulation Effect Under Strong Earthquake

The research object of this paper is a new type of grid structure--intersecting node grid structure.This kind of structure combines the characteristics of some steel pipe truss structure,and solves the problem of large amount of steel used in traditional grid structure node,and reduces the weight of roof structure.With the continuous progress of space steel pipe structure design theory and construction technology,the engineering application prospect of this kind of structure is good.At present,the stress analysis theory of this kind of structure under static load is mature,but considering the dynamic response and failure mode of damage accumulation effect under strong earthquake,it is still in the exploratory stage.In order to study the failure mechanism of this kind of structure considering damage accumulation under strong earthquake,the finite element model of 44 m × 44 m intersecting node grid structure is established by using ABAQUS finite element analysis software.The beam31 beam element that can output the stress and strain at 8 integral points of the cross section of the member is selected as the member of the example model.The main chord of the example is through rigid connection,and the connection between the main chord and the secondary chord is set to hinge.The material nonlinearity and geometric nonlinearity are considered in the static and dynamic analysis of the whole structure.Static analysis applied vertical static load.The dynamic analysis selects four actual seismic waves,which are Tianjin seismic wave,El-Centro(1940)seismic wave,Taft(1952)seismic wave and Wenchuan seismic wave.According to the peak value of each seismic wave,the corresponding seismic waves are adjusted,and four groups of seismic load amplitude are obtained.The multi-response incremental dynamic time history analysis of the example is carried out,that is,increasing the amplitude of each seismic load.The time history analysis of the example structure of each seismic intensity of each wave is carried out.The multiple dynamic response indexes of the example structure under each load amplitude time history analysis are investigated,and the plastic development is analyzed.Until the dynamic failure of the example structure occurs,and according to multiple dynamic responses,the failure category of the example structure is determined.The main research contents and conclusions are as follows :1)Under the action of vertical static load,the internal force of the main members and the displacement of the main nodes of the example structure are mainly observed and compared with those of the rigid connection model.In each direction,the displacement of the nodes of the example structure is slightly larger than that of the rigid connection model.Compared with the rigid connection model,the axial force values of the upper and lower chords of the main truss increase slightly;For the secondary truss,because the secondary chord of the model example is hinged on the main chord,the overall stiffness of the secondary truss is weakened under load,and the internal force redistribution of the member occurs,which makes the axial force of the main truss of the model increase and the axial force of the secondary truss decrease.2)According to the material toughness parameters and damage cumulative fracture model CVGM criterion,the damage factor D is defined to predict the fracture of bars.3)Using ABAQUS nonlinear dynamic implicit analysis,t The dynamic time history analysis of the whole structure model under four groups of different seismic waves and different load amplitudes is carried out,and the four dynamic response indexes of the maximum node displacement of the structure,the proportion of different yield bars in the structure,the number of broken bars in different degrees and the relative strain of the maximum element are mainly investigated.By analyzing the whole process variation of different response indexes with the increase of load amplitude,the strong earthquake failure mode of the example structure is judged.In this paper,combined with the maximum node displacement response and the yield condition of beam element 8 integral point,the ratio of bars with different yield degrees and the fracture of bar section can well reflect the plastic development of the example structure.4)According to the CVGM criterion and damage factor D,the fracture prediction of each member of the example is carried out,and the fracture of each member of the whole structure is predicted.The dynamic response of the number of members with different fracture degrees of the example structure is investigated.It provides an idea for considering damage accumulation effect in the overall seismic simulation of TJ grid.5)It is found from the dynamic time-history analysis of multiple responses that under four groups of different seismic waves,each dynamic response of the example structure has a similar development trend,which is shown as follows : with the increase of load amplitude,the maximum node displacement of the example structure increases continuously,its stiffness decreases continuously,the proportion of members with different yield degrees increases continuously,and the plasticity develops continuously until it is fully developed.Finally,due to the large sag,the normal use ability is lost.Based on the analysis of multiple response indexes,it can be judged that the failure mechanism of the example structure in this paper under strong earthquake is dynamic strength failure.6)Based on the analysis of four dynamic response indexes and empirical statistics,this paper comprehensively and comprehensively analyzes the dynamic strength limit load of the structure under strong earthquake Tianjin wave.