Study On Seismic Collapse Analysis Of Single-bay RC Frame Structure

As a special type of reinforced concrete(RC)frame structure,single-span frame structures are widely used in municipal buildings such as lifting pumping station,blower room and so on.However,it is inconsistent with the provision in the Code for Seismic Design of Buildings(GB50011-2010)that “single-span frame structure should not be used in Class A and B buildings”.Based on the this phenomenon,this paper analyses and estimates the single-span frame structure from the aspect of the seismic collapse safety margin capacity,and compares it with the five-story three-span frame structure.Whether the provision for single-span frame structure in the Code for Seismic Design of Buildings needs to be further refined.At the same time,it is of great significance to deepen the knowledge of earthquake resistance and disaster reduction capability of single-span frame structure.Firstly,13 frame structures in 7 degree(0.1g)zone,included 6 single-story singlespan frame structures with different axial compression ratios,6 three-story single-span frame structures with different axial compression ratios and a five-story three-span ordinary frame structure,which are designed according to the current China codes.Then,the finite element software SeismoStruct is used to establish the numerical models for 13 frame structures,and the incremental dynamic analysis(IDA)method is used to investigate the seismic collapse performance of single-span frame structure under 23 earthquake waves.The distribution trends and characteristics of IDA curve(s)under single(multi)-ground motion(s),IDA fractile curves and collapse fragility curves are investigated.The collapse margin ratio(CMR)is calculated to quantitatively estimate the seismic collapse safety margin capacity of single-span frame structure.Meanwhile,in order to compare the effect of the number of stories under the same axial compression ratio on the seismic collapse performance of single-span frame structures,a five-story single-span frame structure with an axial compression ratio of 0.32 is added in this paper.Finally,on the basis of the previous analysis,the influences of two strengthening schemes on the seismic collapse performance of single-story single-span frame structure are considered.One is to study the effectiveness of seismic strengthening measures for existing single-story single-span frame structure.The other is to improve the seismic grade of structure on the basis of meeting the code and compare with five-story threespan frame structure,which study relevant provisons for single-story single-span frame structure.The main conclusions of this study are summarized as follows:(1)Based on the IDA fractile curves,collapse fragility curves and CMR values,it can be found that the seismic collapse capacity and the seismic collapse safety margin capacity of single-story single-span frame structure or three-story single-span frame structure increase gradually with the decrease of the axial compression ratio.(2)For single-story single-span frame structure within the limit of axial compression ratio,the seismic collapse safety margin capacity of structure is weaker than that of the five-story three-span frame structure.Therefore,this result from the aspect of the seismic collapse safety margin capacity can explain why the Code for Seismic Design of Buildings makes this provision that single-span frame structure should not be used in class A and B bulidings.(3)For three-story single-span frame structure,it is found that there is a fixed axial compression ratio,which makes the structure’s seismic collapse safety margin capacity the same as that of the five-story three-span frame structure.Furthermore,the structure’s seismic collapse safety margin capacity is greater than the five-story three-span frame structure when the axial compression ratio is smaller than the fixed value.Furthermore,for the design of the single-story single-span frame structure,it is found that the seismic collapse safety margin capacity of the structure is also larger than that of five-story threespan frame structure by improving the one-level on the seismic grade.Therefore,it is suggested that the use of single-span frame structure in class B building on the Code for Seismic Design of Buildings can be considered to increase the seismic grade or limit the axial compression ratio.(4)The seismic strengthening measures are adopted for existing single-story singlespan frame structure.The research results show that the single-story single-span frame structure strengthened by wing-wall and bilateral frame columns can significantly improve the seismic collapse safety margin capacity of the structure and is larger than the five-story three-span frame structure.It is shown that the two seismic strengthening measures are effective.