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The column-to-beam flexural strength ratio (CBFSR) has been used in many seismic codes to achieve the strong column-weak beam (SCWB) failure mode in reinforced concrete (RC) frames, in which plastic hinges appear earlier in beams than in columns. However, seismic investigations show that the required limit of CBFSR in seismic codes usually cannot achieve the SCWB failure mode under strong earthquakes. This study investigates the failure modes of RC frames with different CBFSRs. Nine typical three-story RC frame models with different CBFSRs are designed in accordance with Chinese seismic codes. The seismic responses and failure modes of the frames are investigated through time-history analyses using 100 ground motion records. The results show that the required limit of the CBFSR that guarantees the SCWB failure mode depends on the beam-column connection type and the seismic intensity, and different types of beam-column connections exhibit different failure modes even though they are designed with the same CBFSR. Recommended CBFSRs are proposed for achieving the designed SCWB failure mode for different types of connections in RC frames under different seismic intensities. These results may provide some reference for further revisions of the SCWB design criterion in Chinese seismic codes.

Strong columns and weak beams and "strong joints and weak members" are important concepts in the design of reinforced concrete ductile frame structures. However, many earthquake damages show that a large number of reinforced concrete frame structures still do not guarantee the realization of the above seismic concepts. In order to solve this problem, this paper designs and manufactures a beam column joint with plate, which includes the bottom column base and the moment increasing coefficient of the column end is 1.2. Through the quasi-static reciprocating loading test, the influence of the bearing capacity, ultimate deformation, stiffness degradation and hysteretic energy consumption of the specimen is investigated. The test results show that when the moment increasing factor at the end of the column is 1.2, the failure order of the specimen is bottom column base beam slab bottom column base, the plastic hinge occurs at the bottom of the column, and the position of the column in the beam column joint is not damaged; According to the seismic code, the overall failure mode of the beam column joints with slab and infilled wall at the bottom column base can be "strong column and weak beam" and "strong joint and weak member" under the action of reciprocating quasi-static loading.

In order to analyze the quantitative influence of the axial compression ratio on the seismic performance of reinforced concrete (RC) frame column, this paper carried out the numerical analysis of the quasi-static simulation of a RC frame column and analyzed its hysteresis performance, bearing capacity, stiffness degradation, energy consumption capacity and ductility capacity under different axial compression ratios, based on OpenSees finite element software, considering the buckling and fatigue damage model. The results show that the smaller the axial compression ratio, the fuller the hysteresis curve and the slower the stiffness degradation of the column. The ultimate bearing capacity of the column increases by 24.6% when the axial compression ratio increases from 0.3 to 0.8, but bearing capacity decreasing and stiffness degradation is faster and faster. When the deformation does not exceed the ultimate displacement, the equivalent viscous damping at each displacement level of high axial compression ratio column is greater than that of the low axial compression ratio, but the total hysteretic energy decreases about 64.2% at maximum amplitude. The ultimate displacement gradually decreases with the increase in the axial compression ratio, and the ductility factor decreases about 55.9% at maximum amplitude. The results can be referenced by the seismic design and analysis of RC frame.

This study investigates the role of masonry infill walls in the responses and failure modes of RC frames subjected to earthquake, by applying shaking table tests on two three-story, two-bay, 1/4-scale RC frame structures. Two types of RC frame structures, an infilled RC frame without infill walls in the first story (pilotis frame) and a bare RC frame, are constructed according to the seismic design codes of China. The pilotis and bare frames are simultaneously deployed on a shaking table when I-ELC180 ground motion and Wolong ground motion excitations are used. The two specimens are subjected to a sequence of dynamic tests with increasing intensity. This paper mainly presents and compares the phenomena observed from the shaking table tests of the pilotis and bare frames, including the dynamic properties, acceleration and displacement responses, evolution of damage and final failure mechanisms. The tests indicate that, compared with the bare frame, the infill walls in the pilotis frame can significantly affect the failure mode and damage distribution. Plastic hinges first appear in the 1st story columns for the pilotis frame under seismic loading, while plastic hinges first appear at the beam ends in the 1st story for the bare frame; The damage to the pilotis frame is increasingly concentrated in the 1st story as the earthquake intensity increases, while the damage distribution along the height of the bare frame remains almost the same as the earthquake intensity increases. The maximum interstory drift ratio of the pilotis frame is up to 50% larger than that of the bare frame under the same earthquake intensity.

As one of the basic parameters of strong ground motion, the duration of strong ground motion has not been considered in the seismic design codes over the world. To study the ground motion duration on the effects of the SDOF structure ductility demand, the Ds5-75 is chosen as the duration index, and the ductility demand ratio spectrum under long and short ground motion is calculated, then the effect of duration on structural ductility demand under different strength reduction factor is analyzed. The results show that the ductility demand of the structure under long duration ground motion is significantly greater than that under the short duration ground motion. For most periods, the ductility demand of long-duration ground motion is 1.3 times that of short-duration ground motion, and the maximum is 2.5 times. It is suggested that the effect of duration should be considered when the time history analysis of structure is carried out.