| In recent years, the research of reinforced concrete frame to resist progressive collapse under accidental load had become a hot topic. While, most of the studies focused on the progressive collapse because of sudden failure of the local support member of the lower floor. and there were a few research of the progressive collapse caused by impact load from the upper collapsed floors. With the development of the high-rise building, it is very important to study the behaviors of the RC frame structures to resist progressive collapse under impact load.(1)The hammering method was used to finish the dynamic experiment of a 2-bay, 1-story RC plane frames under no load and uniformly distributed load, and based on the tests results, the dynamic behaviors of RC frame under hammering load was analyzed. The tests results showed that the frame beam's stiffness increased slightly after the arch effect was formed. The maximum hammer load exceeded the frame beam's maximum resistance force, but the frame beam did not collapse because of the small impact energy.(2)A new impact test system was used to conduct a small equivalent impact experiment on a 2-bay, 1-story RC plane frame. Study the dynamic response, internal force distribution, strain rate of steel bar of the RC frame under impact load, and the dynamic load coefficient and the effect of strain rate on the strength of steel bar were analyzed. The tests results showed as follows: The strain rate had a little influence on the increase of the strength of steel bar, the maximum amplification factor of yield strength were between 1.09 and 1.11, the maximum amplification factor of ultimate strength were between 1.06 and 1.07. Under impact load, with the increasing of the impact height, the dynamic load coefficient of the frame beam was increased, and it was decreased with the increasing of the degree of structural damage.(3)Based on the finite element software LS-DYNA, the collapse process of two one-story RC frame and four three-story RC frame under impact load were simulated. The mechanical behavior and failure mode of the RC frame under impact load were studied, and the collapse process, dynamic response and internal force were analyzed. The analysis results showed as follows: Under impact load, the reinforced concrete frame had experienced significant arch effect and catenary mechanism stage. and the maximum internal force of frame beam was larger than it's static carrying capacity. By comparing the resist-collapse capacity of four three-story frame, it can be seen that it should give full pay to the material properties and didn't affect resist-collapse capacity of the frame to strengthen the first floor.(4)The static performances of two one-story RC frame and four threestory RC frame were analyzed by using the finite element software ATENA. The analysis results showed that the frame's stress process from elastic stage to catenary mechanism stage was simulated well by using the ATENA. and the failure mode of the frame were similar with its under impact load. By comparing the carrying capacity of four three-story frame, it can be seen that the frame's carrying capacity was obviously different in the plastic stage, while it was closely in the catenary mechanism stage. Based on the frame's carrying capacity under impact load and static load, it can be seen that the load amplification factor of the frame were between 1.22 and 1.82.(5)Based on the load-displacement cure which was simulated by using the ATENA. the nonlinear time-history analysis method was used to calculate the dynamic response of the RC frame under small equivalent impact load, and the calculation results agreed well with the test results. The energy method and nonlinear history analysis method were used to calculate the resist-collapse capacity of the six frames, the calculation results showed that the energy method can be used to estimate the resist-collapse capacity to guide the design. |
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