| The researches on strong column-weak beam of reinforced concrete (RC) frame structures are reviewed and the damage mode of strong beam-weak column is discussed. The failure mechanism of 3-D beam-column joints in RC frame structures is studied by the low cycle loading test and the numerical simulation. The seismic design, guaranteeing the strong column-weak beam mechanism, is proposed. The main research works are as follows:(1) Analyze the curvature ductility of beams. It is proved that the ductility at beam end decreases with the increasing of the reinforcement strength and the steel ratio of the tensile bars, however, increases with the increasing of the compression strength of concrete and the steel ratio of the compression bars. But when compression steel ratio exceeds 2%, the ductility decreases rapidly and at the same time the ductility increases with the ratio of the reinforcement amounts between the tensile to the compression.In the seismic design for frame beams, it is suggested that the reinforcement ratio of the compression longitudinal bars does not exceed 2%, and the ratio of compression steel reinforcement to tensile to steel reinforcement should be adjusted according to the strength of the reinforcement. For HPB235 steel, the ratio should be greater than 0.3; for HRB335 and HRB400 steel, the ratio should be greater than 0.5.(2) Analyze the curvature ductility of columns. It is proved that the total steel ratios in columns have no effect on the ductility when it satisfies the Code's requirements. The ductility decreases with increasing of the axial-force-ratio of columns. Therefore, it should be specified that the axial-force-ratio could not exceed a certain value. The limit values for the axial-force-ratio of columns (grade 3 and grade 4) specified by seismic design code (2011 version) probablely leads to weak ductility of columns due to its over-high assignment. In the seismic design for frame columns, it is suggested that the axial-force-ratio of columns for grade 1st,2nd,3rd and 4th could not exceed 0.6,0.7,0.8 and 0.85 respectively.(3) Propose a concept of beam-column line stiffness ratio. The theory equation of beam-column line stiffness ratio, guaranteeing the strong column-weak beam mechanism, is derived. The beam-column line stiffness ratio and its applications on strong column-weak beam design are verified by comparing earthquake examples and numerical calculation. (4) Two RC frame structures were designed by using the equation of beam-column line stiffness ratio.6 beam-column joints with the scale (1:1.6), extracted from the RC frames, were tested to prove that the beam-column line stiffness ratio greatly influence on the node yield mechanism.(5) The two RC frame structures is analyzed by the elasto-plastic dynamic time history analysis. The results show that the yield mechanism of the RC frames in simulation consistents with the test.(6) For the multistory RC frames, the elastio-plastic dynamic analysis for three dimensional earthquake action are conducted. The adjustment factor, ratio of column-to-beam strength, guaranteeing the strong column-weak beam mechanism without considering the limit value of beam-column line stiffness ratio, is suggested. The factor should be 2.4,2.1,1.9 and 1.6 for the frame with seismic design level of 1st,2nd,3rd and 4th, respectively.(7) The seismic capacity of the frame 1 and frame 2 is analyzed by static elasto-plastic Pushover analysis and IDA analysis. It is proved that the yield mechanism of strong column-weak beam is better than that of strong beam-weak column. At the same cross-section of frame columns condition, the smaller beam-column line stiffness ratio the frame has the lower lateral resistance capacity the frame performs. But the frame has higher deformation capacity redundancy and collapse-resisting capacity. The factors which influence the seismic performance of the RC frame structures, such as the axial-force- ratio of the columns in the first story, the maximum story drift and the ratio of vertical stiffness of the structure are investigated. It is found that the increasing axial-force-ratio of the columns on the ground floor decreases the ductility of the structures and therefore greatly effect the seismic performance of the RC frame structures. So the ratio should be limited to product enough ductility redundancy that enhance the safety of structures in earthquake. The structures with uniform vertical stiffness along vertical direction have the optimal seismic performance. The seismic performance of the multi-storey RC frame in this paper is the best if the maximum value of elastic story drift is 1/ 800.The above research indicates the following innovative achievements:(1) The relationship between yielding mechanism of beam-column joints and beam-column line stiffness ratio is firstly proposed. The theoretical equations describing the relationship are derived.(2) The 3-D beam-column joint seismic test and nonlinear finite element analysis on those joints is conducted. When the beam-column line stiffness ratio of interior columns is 0.8 or the ratio of the exterior columns or corner columns is 0.62, the strong beam-weak column mechanism is observed in the samples. When the beam-column line stiffness ratio of interior columns is 0.41 or the ratio of the exterior columns or corner columns is 0.3, the strong column-weak beam mechanism is observed.According to the test, the failure mechanism under earthquakes is proved.(3) For the RC frame structures which are designed according to the code for seismic design of building (GB50011-2010) with capacity adjustment, it is suggested that the beam-column line stiffness ratio should be examined. For the RC frame structures with seismic design level of 1st,2nd,3rd and 4th, the line stiffness ratio between beams to column should not exceed 1.1,1.0,0.6 and 0.6, respectively.
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