Research On Progressive Collapse Resistance Of High-rise Diagrid Structures

Current trends in the design of tall buildings are driven by diverse factors such as the demand for taller height,the need for enhanced safety against fire and terrorist attacks and the characteristic forms that can provide distinct identity for the buildings.High-rise diagrid structure system as a new and efficient structural system is often shown in the structural scheme of landmark buildings due to its large lateral stiffness and significant aesthetic potential.However,the research on progressive collapse resistance of this type of system is still in the exploratory stage at present.Based on the existing research,the dynamic response,progressive collapse resistance and its influencing factors of the structure under the failure of key bearing components based on the alternate load path method are studied in this paper.The main research contents are as follows:(1)The SAP 2000 finite element software was used to establish the analysis model of high-rise diagrid structures.The typical conditions of progressive collapse analysis were selected.The nonlinear static analysis and vertical incremental dynamic analysis method were used to analyze the progressive collapse resistance of the structure.The alternative load transfer path of the structure is clarified.The influence of different progressive collapse conditions and analysis methods on the results is compared.It is found that after the failure of a pair of tilted columns on the center or corner of the facade,the ultimate bearing capacity of diagrid structures against progressive collapse is large,and the ultimate displacement is small.(2)Dynamic analysis of diagrid structures based on the removal of tilted columns was carried out.The effect of design variables such as slope of diagrids,the location of removed members and the existence of corner columns on the dynamic response of diagrid structures in the case of sudden failure of tilted column is also investigated.The displacement and internal force responses of residual structures under various failure conditions are compared,and the progressive collapse potential of diagrid structures is discussed.It is found that the displacement response and the axial force response of adjacent tilted columns of diagrid structure with corner columns are significantly reduced when the inclined columns in central part of the diagrid facade is removed.The opposite is true when the inclined columns at the corner part of the diagrid facade is removed.(3)The vertical Pushdown analysis was carried out on the diagrid structures after the removal of tilted column members.The effect of design variables such as slope of diagrids,the location of removed members and the existence of corner columns on the progressive collapse resistance of diagrid structures is analyzed.The plastic development process and yield mode of residual structure under various failure conditions are summarized,and the robustness index based on bearing capacity is proposed to evaluate the robustness of diagrid structures against progressive collapse.The results show that the ultimate bearing capacity of the diagrid structures against progressive collapse is the smallest when the removed tilted columns is located at the bottom,and the largest when the slope of diagrids is close to 71°.The existence of corner columns makes the yield mode of diagrid structures change significantly when the tilted columns in the central part of the diagrid facade fails,and consequently improves the ultimate bearing capacity of the structure against progressive collapse.Under the studied damage state,the diagrid structures can withstand the original design load without progressive collapse,and has good robustness against progressive collapse.