The Anti-Collapse Capacity Of RC Frame Structures Based On Pushover Analyses

During an earthquake,the main threats to people's life and property are caused by the severe damages and collapse of the buildings.The current Chinese seismic code proposes the so-called "Two stages,three levels" design criterion,that is,using the linear elastic design method to calculate the internal forces and displacement of the structures under frequent earthquake,and using the combinations of internal forces to determine the cross-sections of the structural members to meet the requirements.However,the anti-collapse capacity check were only carried out for a few structures with high level of importance,for the vast number of structures,the collapse resistance mainly depends on the seismic concept design and detailing.The quantitative methods and evaluation indexes are insufficient.Therefore,it is of great significance to study the ability of the structures to resist collapse under earthquake excitations.In this paper,the anti-collapse capacity of the RC frame structures designed according to Chinese code were analyzed using Pushover method:(1)11 RC frame structures with 5 or 8 stories were designed under different seismic fortification intensities,the finite element analysis software SAP2000 were used to apply Pushover analyses using 3 different lateral force patterns to the frames.(2)The base shear-top displacement curve obtained from the analyses were used to build the overstrength factor,yield ratio,overall ductility coefficient and extension coefficient to investigate the anti-collapse capacity of the frame structures quantitatively.(3)The influence of the seismic fortification intensities and number of stories on the anti-collapse capacities were investigated.It is concluded that the lateral force pattern has a great effect on the anti-collapse capacity of the structures.Generally,the overstrength factor decreases with the increase of the seismic intensity.The minimum value of the overstrength factor of the RC frame structures is assumed to be 1.3.The average value of the yield ratio is larger than 1.25 regardless of the seismic intensity,which is the minimum value required by the seismic code.The overall ductility coefficient of the structures is between 3.8 and 5.3,and the extension coefficient is between 1.7 and 2.1.