COMPARISON ON THE SEISMIC DEISGN OF BASE-ISOLATED RC FRAMES USING TWO CHINESE CODES

There will be two seismic design codes for the base-isolated structures in the near future in China, including Code for Seismic Design of Buildings and Code of Design for Seismic Isolated Buildings. It is notable that significant differences exist in terms of design methods and critical design indexes between these two codes. However, comparisons on the seismic design of base-isolated structures using these two codes are rarely reported. The seismically isolated reinforced concrete (RC) frame structure is herein selected as the study subject. Using three pairs of structure cases with different heights which were designed according to the two codes, the controlling factor for the seismic design of such structures using Code of Design for Seismic Isolated Buildings was identified. In addition, the seismic responses and economic investment of such structures designed according to the two codes were compared and analyzed. The results indicate that the abovementioned controlling factor is base shear ratio. For the superstructure, a smaller stiffness is selected if Code of Design for Seismic Isolated Buildings is adopted, and the corresponding seismic load reduces by approximately 15%~20% in comparison with that designed following Code for Seismic Design of Buildings. However, because the degree of stiffness reduction of superstructure is greater than that of seismic load reduction, a significant increase of maximum inter-story drift ratio (i.e., θ_max) of superstructure is observed. Furthermore, the increment of θ_max basically increases with the increase of total height of structure. As for the material consumption, the concrete consumption is reduced by 7.7%~12.1% while the reinforcement consumption is increases by 11.02%~26.29% if Code of Design for Seismic Isolated Buildings is adopted. With the increase of total height of structure, the reduction of concrete consumption increases, while the increment in reinforcement consumption decreases. The research outcome will assist in providing a useful reference for seismic design of base-isolated RC frame structures.