| RC stilted frame structure has obvious vertical irregularity,and the influence of floor stiffness of bottom suspended feet on seismic performance of RC suspension frame structure needs to be studied.In this paper,the ratio of the stiffness of the adjacent upper layer to the bottom layer of the structure was defined as the stiffness ratio of the bottom layer.The relationship between the story stiffness ratio and the seismic performance of RC frame structures with suspended legs was studied by combining the experimental and numerical methods.In this paper,a 3-story substructure of RC stilted frame with a story stiffness ratio of0.025 was designed with a scale ratio of 1:3.Compared with the test results of the suspended frame structure with the story stiffness ratio of 0.99,the influence of the bottom floor stiffness ratio on the seismic performance indexes such as failure mode,bearing capacity and ductility of RC stilted frame structure was studied.Based on the prototype stilted frame structure,a group of 11 RC frame models with different story stiffness ratios(1.58 to 0.04)were designed,and the influence of story stiffness ratio on the elastic seismic response characteristics of RC stilted frame structures was analyzed.The elastic-plastic analysis model was established by Open Sees software.The validity of the finite element model have been verified by comparing the results of finite element simulation and test.Based on 11 elastic analysis models,a total of 22 elastic-plastic analysis models were established for high axial compression ratio(maximum axial compression ratio is 0.66)and low axial compression ratio(maximum axial compression ratio is 0.32).The static elasto-plastic analysis was carried out to study the influence of story stiffness ratio on the failure mode,hysteretic curve and skeleton curve of RC stilted frame with high and low axial compression ratio,and the recommended range of story stiffness ratio was given.IDA(incremental dynamic time history analysis)analysis was carried out on two prototype frame structures with suspended legs designed in the test,and the vulnerability curves of RC frame structures with suspended feet were drawn.The main conclusions are as follows:(1)The test results show that:For the test specimen with story stiffness ratio of0.025,the damage degree of the structure hanging foot layer is small,the failure state of the upper floor is similar to the overall failure mode of the frame,and the lateral displacement mechanism is formed by the hinge at the bottom of the column in the second floor.However,for the test specimen with story stiffness ratio of 0.99,the damage of the hanging foot layer is more serious,and the hinge time of the short column is earlier,and the damage degree is larger,and the structure is easy to form the failure mechanism of local collapse.the Peak bearing capacity of the specimen with story stiffness ratio of0.025 is greater than that of the specimen with story stiffness ratio of 0.99,and its ductility performance is worse than that of the specimen with story stiffness ratio of 0.99,and its energy dissipation capacity is stronger than that of the specimen with story stiffness ratio of 0.99.(2)The results of elastic-plastic analysis show that: With the decrease of the story stiffness ratio,the damage degree of the stilted suspension layer of RC scaffold frame is gradually reduced,the hinge time is gradually delayed,the damage degree of the upper two story column end is gradually increased,and the hinge out time is gradually advanced.In order to prevent serious damage of short column and 2-story column end under earthquake action,the floor stiffness ratio of suspended frame structure can be controlled.For RC stilted frame structures with high axial compression ratio,the stiffness ratio of the bottom layer should be between 0.85 and 1.14.For RC stilted frame structures with low axial compression ratio,the stiffness ratio of the bottom layer should be between 0.75 and 1.16.(3)The collapse resistance of RC stilted structure with stiffness ratio of 0.99 is slightly stronger than that of structure with story stiffness ratio of 0.025.According to the current code,the collapse probability of the stilted frame structure with different story stiffness ratio under rare earthquake is small,and the maximum collapse probability is0.12.All of structures can achieve the design goal of not collapsing in large earthquake. |
PDF Full Text Request