Research On Robustness And Reliability Of Fully-assembled Concrete Frame Structure Against Progressive Collapse

To study the behavior of progressive collapse performance of fully precast frame structures,based on the static and dynamic tests of two fully assembled specimens(PC1 and PC2)and one cast-in-situ specimen(RC),three sub-structural macro-models were established by using OpenSees finite element software,and the results of model verification were compared with this test results.Two seven-story fully assembled frame structures(PC1-Frame,PC2-Frame)and a cast-in-situ frame(RC-Frame)were designed.Progressive collapse analysis was conducted for the residual structure of which middle/exterior column at the bottom removed by using column removal method,respectively.The overall structural reliability analysis method based on stochastic Pushdown-moment method is used to evaluate the reliability and robustness of fully assembled frame structures.This paper mainly studies the following aspects:(1)Two assembly node macro-models and a cast-in-place macro-models are established by using OpenSees platform.The appropriate material constitutive model and nonlinear beam-column elements are selected to establish the beam and column section restoring force model,and then according to the structural characteristics of the fabricated nodes.The force characteristics are used to simulate the function of the beef leg and the bolt-plug.The numerical simulation results are compared with the frame structure against continuous collapse static load test.The results show that the finite element simulation results are in good agreement with the experimental results.The proposed modeling method can be applied to the study of continuous collapse of fabricated structures.(2)Based on the verified fully assembled node model,two fully assembled frame structures with seven layers and four spans and a cast-in-place structure are established.The instantaneous dynamic response analysis of the three frame structures after disassembling the column under different working conditions is carried out by means of the demolition component method.Then the nonlinear static analysis of the structure is carried out to further understand the continuous collapse mechanism of the structure,and finally the simplification based on the equal energy principle is used.The dynamic analysis method transforms the resistance curve of nonlinear static analysis,and obtains the nonlinear dynamic response and dynamic amplification factor of the structure.Therefore,the overall collapse resistance of the fully assembled and cast-in-place frame structures under different working conditions is evaluated.(3)Based on the concept of structural overall reliability,the global functional function of the structure is constructed by the difference between the ultimate bearing capacity of the structure and the total load of the structure.The point estimation method based on the Nataf transformation(also known as the improved point estimation method IPEM)is used to sample random variables that affect the carrying capacity of the structure.Combined with the IPEM method and the nonlinear static analysis Pushdown method,the high-order moment method can be used to calculate the reliability index of the complete structure and th e damage structure,so as to evaluate the reliability of the overall structure.(4)The structural robustness is quantitatively evaluated from the aspects of bearing capacity and reliability.In terms of bearing capacity,the robustness index of the structure of the most unfavorable A-axis column failure is calculated.In terms of reliability,the robustness of each structure under different moments is calculated.Through the robustness index,the continuous collapse resistance of the fully assembled structure and the cast-in-situ structure was compared quantitatively.