COLLAPSE CAPACITY ASSESSMENT OF RC FRAME STRUCTURES USING EXPLICIT ALGORITHM

Explicit algorithms have better performance with regarding convergence than implicit algorithms widely used in the conventional dynamic analysis. Explicit algorithms are more suitable for simulating the strong nonlinear behaviors of the structures close to a collapse state. It adopts an explicit algorithm based on a modified leapfrog format to evaluate the seismic collapse resistance of the reinforced concrete (RC) frames designed according to the current Chinese codes. OpenSees is used as the software platform. The seismic collapse fragility curves and the collapse margin ratios are obtained for the RC frames. Four criteria to describe collapse limit states are used and their effects on the collapse resistance of structures are investigated. The first two collapse criteria are corresponding to the inelastic inter-story drift ratio of 1/50 and 4% recommended by Chinese and US codes. The third collapse criterion is defined from the IDA (Incremental Dynamic Analysis) curve with the tangent slope equal to 20% of the initial elastic slope. The fourth collapse criterion is determined by the vertical displacement equaling to 1 m. The results show that explicit algorithms have better nonlinear simulation performance than implicit algorithms and can well approach to the collapse limit state. The first three criteria for the definition of collapse states are suitable for aseismic design to avoid the occurrence of structural collapse due to earthquake excitations. The fourth collapse criterion is derived based on the physical meaning of structural collapse, whose evaluation result is closer to actual structural collapse resistance.