Research On Collapse Mechanism And Collapse Resistant Technology Of Truss String Structure

The long-span spatial structure has the advantages of light and beautiful shape,reasonable force and large span,which is widely used in convention center,airport and other important public buildings.With the wide application of the long-span spatial structure,structural collapse accidents occur from time to time.As a typical long-span spatial structure,the truss string structure has low redundancy and high importance of cable,and cable failure will make the force transfer path of the structure change greatly,so progressive collapse of the truss string structure is worthy of analysis and research.At present,there are few studies on the progressive collapse mechanism of the russ string structure.Most of the initial failure members in the existing research are cables,while there are few studies on other types of initial failure members,and there is a lack of research on the ultimate load and progressive collapse mechanism of the residual structure.This paper takes the long span plane truss string structure as the research object,analyzing its progressive collapse mechanism under four working conditions,and then proposing collapse resistant technology based on compression buckling of key members.The research content of this paper is as follows:(1)The cable,the lower chord of the support,the upper chord of the middle span and the middle strut are selected as the initial failure members and LS-DYNA is used to analyze the progressive collapse mechanism of residual structure under ultimate load.The results show that the ultimate load coefficients of the cable and the lower chord of the support are much lower than those of the upper chord and the middle strut,which are of high importance.After the cable failure,the compression buckling of the top chord in the middle of the span causes the plastic hinge in the middle of the upper truss,and the structure collapses rapidly.After the failure of the lower chord of the support,the web member of the support buckles and causes the support failure,and the structure collapses rapidly.After the buckling of the members,the axial force decreases rapidly and cannot continue to bear the load,which has an important impact on the progressive collapse process of the structure.So,a collapse resistant sleeved column with secondary stiffness is proposed.(2)The components and working mechanism of the collapse resistant sleeved column are described,and two unidirectional loading tests of the collapse resistant sleeved column are completed.The results show that the buckling modes of collapse resistant sleeved column include second-order buckling and first-order buckling.When the second-order buckling occurs,the sleeved column has larger bearing capacity and secondary stiffness,and when the first-order buckling occurs,the sleeved column has larger secondary stiffness.The experimental buckling modes is in good agreement with that obtained from the simplified calculation model of the inner tube.(3)Based on the finite element software ABAQUS,a sleeved column solid model is established,and the finite element analysis results are in good agreement with the test results.The finite element parametric analysis shows that the smaller the initial defect amplitude ratio,the larger the cross-sectional area ratio of steel strand,the higher the height ratio of middle brace plate,the larger the stiffness ratio of inner and outer tube,the smaller the slenderness ratio of inner tube,the larger the secondary stiffness and maximum bearing capacity of axial force curve and the the second-order buckling occurs.Then,the theoretical formulas of the three key points on the axial force curve are derived when the sleeved column occurs second-order buckling,and the correctness of the theoretical formulas is verified by the results of finite element parametric analysis.(4)The collapse resistant sleeved column is applied to the truss string structure,and the key buckling member is replaced by the collapse resistant sleeved column.The results show that after the cable failure,the collapse resistant sleeved column can effectively prevent the progressive collapse caused by the buckling of the top chord of the mid span.The ultimate load of the structure is increased by 24% and 36%,and the effect of improving the collapse resistance of the structure is obvious.After the failure of the lower chord of the support,the collapse resistant sleeved column can effectively prevent the progressive collapse caused by the buckling of the web member of the support.The ultimate load of the structure is increased by 28.6%,and the effect of improving the collapse resistance of the structure is obvious.After replacing the buckling member with the collapse resistant sleeved column in the truss string structure with different support stiffness,the collapse resistance of the structure is improved.