Research On The Progressive Collapse Performance Of The Steel Frame Considering The Mechanical Behavior Of Beam-to-column Joints

With the high-speed development of national economy,our country has entered a period of large-scale construction.Steel production grows rapidly during this period.Steel structures got great development in the field of construction in our country due to the advantages such as light-weight and high-strength.Steel structures have been widely applied in constructions.Due to the increasing role of steel structures,the performance of steel structures is studied widely.But the current studies are performed mostly under the normal load of the steel structures.When the structures subjected to accidental loading(such as earthquake,explosion,shock,fire and others),some local components may be destroyed and lead to a disproportionate break of the structure and then cause the progressive collapse.Therefore,in order to avoid the progressive collapse of steel structures under accidental loads,it is necessary to study the structural progressive collapse performance and puts forward some suggestions for improvement to improve the structural progressive collapse performance.In this paper,the finite element software was used to establish model and the rotational spring element was used in the model to simulate the rotational stiffness of joints.According to the rotational stiffness of joints,the model was classified into rigid model and linear joint model without considering the stiffness degradation of joints and nonlinear joint model considering the stiffness degradation of joints.The alternate path method was applied to analyze the progressive collapse.At first,Static analysis was analyzed to solve the axial force of failure column and then modal analysis was analyzed to solve the vertical vibration cycle of the failure column structure.At last,dynamic analysis was analyzed to evaluate the progressive collapse performance through the dynamic magnification factor.The different dynamic magnification factor could be obtained by parametric analysis.Meanwhile the influence of rotational stiffness of joints on the progressive collapse performance of steel frame under the elastic and plastic states could be obtained.In order to study the influence of stiffness degradation of joints on the progressive collapse performance,the linear joint model without considering stiffness degradation was compared with the nonlinear joint model considering stiffness degradation.Finally,the structure and member energy consumption could be changed due to the change of rotational stiffness of joints.Therefore,it is necessary to study the influence of rotational stiffness of joints on the structure and member energy consumption.Through the above analysis,the measures could be proposed to improve the structural progressive collapse resistance which can provide references for practical engineering application.The analytical results show that the dynamic magnification factor will increase if joint stiffness degradation occurs.The dynamic magnification factor remains at about 2.0 and the model without considering joint stiffness degradation can be adopted to the progressive collapse analysis when the structure is in the elastic state.The dynamic magnification factor decreases with the increase of rotational stiffness and Demand-capacity ratio during the plastic state and the model considering joint stiffness degradation can't be adopted to the progressive collapse analysis during the plastic state.With the increase of joint rotational stiffness,the ratio of joint energy consumption to total energy consumption is decreased,while that of beam is increased.Therefore,it is suggested that the joint deformation ability should be reinforced to improve the structural progressive collapse resistance when joint rotational stiffness is decreased.Otherwise the beam deformation ability should be reinforced.