Theoretical Study On Seismic Collapse Capacity Of Moment Steel Frames Supported By Stepped Foundations

Especially since China's western region features,many mountain towns architectural style is very common.In the past,there have been in-depth studies on the seismic collapse resistance and safety reserve of moment frames supported by foundations,however,with the development of society and the construction industry,the steel structure building is known as the new energy saving and environmental protection building system in the 21 st century,it has many advantages such as good ductility,good seismic performance,etc.,the steel frame structure system is bound to be introduced gradually in the future.However,the research on steel frame supported by foundations is still in the blank stage.In order to further study the seismic collapse resistance and seismic collapse safety reserve of layered steel frame supported by foundations,to provide reference and design basis for the future development of steel structure in mountain buildings in central and western China.In this paper,the report results of SAP2000 about steel frame structures are used to verify the simulation effect of Perform-3D package on seismic response of steel structures,and on the basis of the existing specifications,two examples of ordinary steel frame,two examples of steel frame supported by foundations,two examples of strengthening steel frame supported by foundations with beam.The seismic collapse vulnerability analysis of structures based on incremental dynamic analysis is used to evaluate quantitatively the seismic collapse capacity and the collapse margin ratio of each example model under different seismic waves,the seismic collapse vulnerability analysis of structures based on incremental dynamic analysis method is used to quantitatively evaluate the seismic collapse resistance and seismic collapse safety reserve of each example model under the action of different seismic waves,and the response results of each steel frame model are compared.Finally,the collapse capacity and the collapse margin ratio of the ordinary steel frame,steel frame supported by foundations and steel frame supported by foundations with strengthening measures are investigated by analyzing the failure modes of each calculation example,this provides the corresponding reference for the development and design of steel stripper structure in the future.The main conclusions of this paper are as follows:(1)For steel frames and steel frames supported by foundations with the same number of floors,its seismic the collapse margin ratio is weaker than ordinary steel frame.For the steel frame structure with different dropped layer number,the influence of the number of dropped layers on the upper grounding side of the steel frame supported by foundations is very small on seismic collapse capacity and the collapse margin ratio,however,it will affect the seismic collapse capacity and the the collapse margin ratio on the lower grounding side of the steel frame supported by foundations which will increase with the increase of the number of layers.(2)Compared with the steel frame supported by foundations with no additional steel strengthing beam,the seismic collapse capacity and the collapse margin ratio of the one which add pull beam on the upper grounding are better.However,this pattern is just the opposite on the lower grounding,that is to say the seismic collapse capacity and the collapse margin ratio of the one which add pull beam on the lower grounding are even get worse.Moreover,the number of additional beam has little influence on the seismic collapse capacity and the collapse margin ratio.(3)Compared with the ordinary steel frame which is only grounded,the seismic collapse capacity of the steel frame supported by foundations is much closer to that of the ordinary steel frame which is filled with dropped layer.In addition,for the same steel frame supported by foundations,the failure form of the upper grounding is different from that of the lower grounding,the upper grounding will be damaged before the lower grounding,and the difference in seismic collapse capacity between the two sides will increase with the increase of the number of dropped layers in the steel frame supported by foundations.(4)For the collapse probability of the upper grounding side of the steel frame supported by foundations,the first upper grounding layer is the layer with the highest probability,the rest of the layers are much less likely to collapse.Therefore,the first upper grounding layer of the steel frame structure is the weakest one on the upper grounding side.For the collapse probability of the lower grounding side of the steel frame supported by foundations,the second upper grounding layer is the layer with the highest probability,the rest of the layers are much less likely to collapse.Therefore,the second upper grounding layer of the steel frame structure is the weakest one on the lower grounding side.The collapse failure modes of the two ultimate states of the layered steel frame structure with beam strengthening measures are consistent,and the probability of collapse failure of the second upper grounding layer is the highest.Therefore,in the future study of the falling floor structure,the strengthening measures of the rigid pull beam can be considered.That is to say,the rigid pull beam will change the failure mode of the structure.(5)It can be seen from the results of the analysis,if according to the requirement of rules to design the out layer of steel frame structure,must increase the out layer column section size(meet minimum stiffness ratio),but in fact off layer column interlayer displacement Angle is small,so the design according to the requirements of resistance to gauge the steel frame structure supported by foundations is not the most economic way.It is suggested that the special steel frame structure should be adjusted properly.