Seismic Performance of a 62-Story Steel Frame Hotel Tower

This paper introduces the seismic design and performance of a 62-story hotel tower in Beijing, China, and discusses conceptual conflicts that arose during the design process between code provisions and expected seismic behavior. For instance, while the IBC 2000 requires such a tower to be designed as a Special Moment Resisting Frame, pushover analysis studies (not permitted by FEMA 350 for such a tall building, but allowed by the design review board for collapse analysis during this design process) suggested that inelastic rotation demands were on the order of the 2002 AISC requirements for Intermediate Moment Resisting Frames. Furthermore, while axial force demands in the columns resulting from the pushover analyses exceeded the demands calculated according to the AISC building overstrength factor of 3.0, these high axial load demands clearly resulted from the pushover analysis loading pattern derived from the tower's fundamental mode shape. Time history analyses showed that both the extent of plastic hinging and the magnitude of overturning forces under actual earthquake demands were significantly lower than the levels produced from response spectrum and pushover analyses. Finally, in a capacity spectrum assessment under maximum considered earthquake (MCE) response spectrum loads, ductile capacity in the beams did very little to enhance the tower's performance. Several of these results were easily explained by the fact that the Chinese Code response spectrum controlling the design was artificially high for longer periods. This code requirement implied that increased strength, not increased ductility, would improve the tower's ability to withstand MCE demands according to a capacity spectrum assessment. The purpose of this paper is to identify these conflicts in the context of a real project where circumstances prevented the coordination of consistent seismic design criteria.