Research On "Strong Column-weak Beam" Failure Mode Factors Of Reinforced Concrete Frame Structure

The devasting ludian earthquake, ya’an earthquake, yushu earthquake and wenchuan earthquake showed that there were many problems in structure design. Post earthquake investigation indicated that RC frame structures could not achieve ductile damage and “strong column-weak beam” failure mode was not realized.Based on the space frame nodes test of BIAD, this paper will mainly start from the factors of “strong column-weak beam” failure mode affecting structure seismic capacity with axial compression ratios, slab reinforcement, moment augment factor of column and sesmic wave input angles. The main works are summarized as follows:Firstly, axial compression ratios: this part mainly discusses the realization of “strong column-weak beam” failure mode of RC frame structures under the influence of different axial compression ratios. The axial compression ratios of eight finite element models vary from 0.75 to 0.31 by changing concrete grades. Nolinear dynamic time analyses were carried out to get plastic hinges at beam ends and columns, include precedence order on the basis of program ABAQUS, and investigate the realization of “strong column-weak beam” failure mode of RC frame structures. Research in this paper is aimed to propose reasonable value of axial compression ratios and guarantee the realization of “strong column-weak beam” failure mode.Secondly, slab reinforcement:static nonlinear analyses were carried out on the basis of program ABAQUS. Eight contrast models were established using frame strucures with and without floor slab, and different cut sizes across the beam end and mid-span, to investigate the effects on moments of beam end or mid-span of floor slab. According to the analyses of slab reinforcement stress at different joint types and different layers, the change trend of effective flange width value was proposed.Thirdly, moment augment factor of column: this part mainly discusses the realization of “strong column-weak beam” failure mode of RC frame structures under the influence of different moment augment factors of column. Five finite element models were establised by changing column reinforcement ratios. According to the analyses of shear-top displacement curve, lateral drift and plastic hinges under rare earthquake, reasonable moment augment factor of column was proposed.Fourthly, seismic wave input angles: the prototype was a three-layer RC frame structure, nonlinear dynamic time analyses were carried out based on program ABAQUS to investigate the distribution of top-displacements and plastic hinges. Seismic wave input angles were taken as 0°、15°、30°、45°、60°、75°and 90°, aiming at investigating the effects of seismic wave input angles actions on “strong column-weak beam” of RC frame structures. Also, the effect of bi-directional horizontal seismic should be considered seriously, the results indicated the plastic hinge distributions under bi-directional horizontal seismic actions were worse than that responding single-component earthquake excitation.Finally, a simplified calculation method for checking the realization of “strong column-weak beam” failure mode of RC frame structures was proposed. In this paper, a four-layer actual frame structure was used. By calculating the flexual capacity at beam end based on the actual reinforcement, investigate the realization of “strong column-weak beam” failure mode under increasing force levels.