DAMAGE ANALYSES AND REPAIRABILITY EVALUATION OF IN-SERVICE RC FRAMES DESIGNED BASED ON DIFFERENT CODES

Most of the in-service reinforced concrete (RC) frame structures in China were designed based on the three seismic codes of GBJ 11−1989, GB 50011−2001 and GB 50011−2010. Due to the functional requirement, the height of the first story for common RC frame structures is obviously larger than that of other stories, which may result in inter-story drift concentration. Three in-service RC frames, characterized by larger-height first story, were selected as prototypes and their three-dimensional finite element models were built via OpenSees software, considering the factors such as out-of-plane deformation of infilled walls, shear deformation of beam-to-column joints and bond slip of steel bars in columns. The static analyses under cyclic loading and nonlinear dynamic analyses under a larger number of ground motions were conducted for the three models to investigate the damage degree, the distribution pattern of inter-story drift and the repairability performance of the structures under rare and very rare earthquakes. The results show that compared with the structures designed based on GBJ 11−1989 and GB 50011−2001, the structure designed based on GB 50011−2010 suffers minimum damage, and obvious strengthening effect for the potential soft story is observed. Under rare earthquakes, the collapse probabilities of the structures designed based on the three seismic design codes are relatively low, while the structure designed by GBJ11−1989 may develop serious damage and the repairing is impracticable. Under very rare earthquake, the structures designed based on GBJ 11−1989 and GB 50011−2001 have high risk of collapse; while the structure designed based on GB 50011−2010 shows small collapse probability, but the repairing cost is high. With the successive revision of the seismic code, the failure ratio of structural components under very rare earthquakes decreases gradually for the structures designed based on them. The columns of the structures designed based on GB 50011−2001 and GB 50011−2010 mainly present ductile damage, while the columns of the structure designed based on GBJ 11−1989 exhibit obvious brittle damage.