Study On Yield Mechanism Of Reinforced Concrete Frame Structure's Strong Column-Weak Beam Under Rare Earthquake Action

The practical phenomena of Wenchuan earthquake damage indicates that the frame designed by Chinese code for seismic design buildings(GB 50011-2001) could not realize the expected"strong column-weak beam"yield mechanism. Therefore, it's necessary to find out the reason for the failure of"strong column-weak beam"and analyze the factors which affect the realization of"strong column-weak beam"yield mechanism. On the base of the above background, this paper carries out the research on the"strong column-weak beam"yield mechanism of reinforced concrete frame under rare earthquake and discuss the rationality of related measures in current code for seismic design buildings.This paper first analyzes and summarizes the factors which affect the realization of"strong column-weak beam"yield mechanism, it can be seen that the axial compression ratio is one of the very important factors. Secondary reinforced concrete frame in the religion of 8 degree(0.20g) is regarded as the research object and 5 six-layer reinforced concrete frame models(3×2 span) were designed by general structure design software PKPM according to Chinese code for seismic design buildings (GB 50011-2001), in which the axial compression ratios n are 0.77, 0.73, 0.62, 0.49 and 0.39 respectively. Non-linear dynamic time-history analysis under bidirectional rare earthquake was carried out on these five models in nonlinear dynamic analysis software SeismoStruct respectively, which investigates the whole reactions and local reactions of structures. Analysis results indicate that the space secondary frame in the religion of 8 degree which is designed according to code for seismic design buildings (GB 50011-2001) forms the beam-column hinge hybrid yield mechanism which is dominated by column hinge under rare earthquake. The related measures in the current code about the limited value of the axial compression ratio etc are feeble. With the decrease of the axial compression ratio, the seismic reaction of the column end comes to be weaker compare with that of the beam end comes to be stronger step by step. When the axial compression ratio was adjusted to 0.39 and the column reinforcement area was multiplied by 1.15, the structure can form favorable and acceptable the beam-column hinge hybrid yield mechanism. At last, a six-layer secondary frame (3×2 span) in the religion of 8 degree was designed according to latest code for seismic design buildings (GB 50011-2010), on which non-linear dynamic time-history analysis was carried out. Analysis results indicate that the space secondary frame in the religion of 8 degree which is designed according to code for seismic design buildings (GB 50011-2010) still forms the beam-column hinge hybrid yield mechanism which is dominated by column hinge under rare earthquake, but the plastic rotation at column end is smaller and beam hinge appears more general.