Research On Progressive Collapse Performance Of Steel Eccentrically Braced Frames

Eccentrically braced frame(EBF)integrates the advantages of both moment resisting frame and concentrically braced frame systems into a structural system.The EBF system provides high elastic stiffness and energy absorption capacity during severe earthquakes.The frame absorbs energy through plastic deformation of specific components,reduces stress of other components and ensures overall safety of the structure.However,the research on progressive collapse of this structure is very limited,and the content of relevant specifications is also relatively vague.In this paper,the research on progressive collapse resistance and lateral loading resistance of various eccentrically braced frames are developed through finite element simulation and analysis basing on the SAP2000 software.Firstly,2-D and 3-D eccentrically braced frame structural models are established and analyzed the progressive collapse capacity through nonlinear static(NS)analysis and nonlinear dynamic(ND)analysis respectively.The results show that braces can improve stiffness and bearing capacity of the structure,but it will also reduce deformation capacity and energy absorption capacity of the structure.2D analysis model has little difference compared with 3D model in calculating deformation,energy absorption and stiffness,but the bearing capacity has certain error.Secondly,influence factors of progressive collapse resistance of various eccentrically braced frames are studied by nonlinear static analysis.The results show that when the side column of single-span braced frame fails,the performance is similar to that of frame without braces.The IV-shaped eccentrically braced frame has the highest stiffness and bearing capacity against progressive collapse,the bearing capacity of D-shaped eccentrically braced frame is the worst and the Y-shaped eccentrically braced frame has the highest deformation and energy absorption capacity of the structure.Then,the progressive collapse resistance of various eccentrically braced frames is studied by nonlinear dynamic analysis.The results show that the bearing capacity,stiffness,energy absorption capacity,axial force of adjacent columns of failure members and vertical displacement obtained by nonlinear dynamic analysis are similar to those obtained by nonlinear static analysis,but the horizontal displacement error is large.The research on failure time of components shows that displacement factor is affected by vertical natural vibration period and natural vibration period of the structure.Finally,Pushover analysis method is used to analyze eccentrically braced frames to evaluate lateral resistance behaviour of the partial damaged frames and the importance of members to the structure.The results show that performance of the frame under uniform pattern is different from that under triangular pattern and model pattern.When members are damaged,the internal force of the frame will be redistributed,and the failure position of eccentrically braced frame with long links will be transferred from link to beam or column.In addition,the base shear capacity,stiffness,energy absorption capacity and robustness indexes of damaged frames are calculated,and the advantages and disadvantages of frame under different factors and evaluation indexes are compared.The results show that failure position of the frame has a great influence on the performance.