Seismic Design And Evaluation Of Tall RC Frame-core Tube Buildings In China And U.S.

The frame-core tube structure is a typical type of tall reinforced concrete(RC) system widely constructed in China and the United States(U.S.). Evaluating the major differences of seismic design and performances of such structures between the two countries can be helpful to further improve the Chinese seismic design philosophies. Systematically comparisons are conducted on two groups of tall RC frame-core tube structures designed based on the Chinese and the U.S. code systems respectively. The main achievements of this study are as follows:(1) The development and status of the U.S. and the Chinese performance-based guidelines/specifications are summarized, including the main achievements of these current-generation performance-based guidelines/specifications, as well as the introduction of the next-generation performance-based seismic design procedures and guidelines.(2) Two groups of tall RC frame-core tube structures in high seismic regions, designed based on the Chinese and the U.S. code systems respectively, are selected as the research objects. The design outcomes in each group are compared and discussed in detail. The results of Case 1 indicate that if the two designs keep the identical seismic hazard level, the Chinese design costs a higher level of material consumption. Two reasons lead to the above difference. The seismic design forces determined by the Chinese response spectrum are larger than those determined by the US spectrum at the same seismic hazard level. In addition, the upper-bound restriction for the inter-story drift ratio is more rigorously specified by the Chinese code. Meanwhile, the results of Case 2 show that if the two designs have the same base shear forces, the load-carrying components of the U.S. design cost a slightly higher level of material consumption. This is because some frame columns and core walls of the U.S. design have larger cross sections; the confined area and the total amount of longitudinal reinforcement and stirrups in core wall boundary elements of the U.S. design are larger; the amount of stirrups in frame columns are also larger than that of the Chinese design.(3) The three-dimensional nonlinear finite element models of the studied structures are established to evaluate their collapse resistance capacity and seismic performances under three different earthquake intensities by nonlinear time history analysis. The results reveal that the Chines design exhibits slightly better seismic performances and higher collapse resistance capacity if the two designs keep the identical seismic hazard level(Case 1). In contrast, if the two designs have the same base shear forces(Case 2), the U.S. design yields superior seismic performances and collapse resistance capacity.(4) The seismic loss consequences(repair costs, repair times, and casualties) of the studied structures are evaluated using the next-generation performance-based seismic performance assessment methodology, i.e. the FEMA P-58 procedure. Results show that the repair costs and repair workload of nonstructural components account for the majority of the total costs and total repair workload. Except structural collapse, ceilings and elevators are the major cause of casualties under the maximum considered earthquake. If the two designs keep the identical seismic hazard level(Case 1), the Chinese design needs smaller repair costs under all three earthquake intensities and less repair workload under frequent earthquake and fortification level earthquake, but slightly larger repair workload under the maximum considered earthquake. While if the two designs have the same base shear forces(Case 2), both the repair costs and repair workload of the U.S. design are smaller than those of the Chinese design under all three earthquake intensities.