Collapse risk-targeted seismic design of concrete-filled steel tube frame-RC core tube structures

Abstract

The concrete-filled steel tube (CFST) frame-reinforced concrete (RC) core tube composite structure is a widely-used structural system of high-rise buildings due to its high compressive strength, good plasticity, and convenient construction. The cross-sectional dimensions and bending stiffness of CFST frames are smaller than those of RC frames with the same vertical load-bearing capacity. Since the seismic forces are distributed in proportion to stiffness for components, the assigned seismic forces of CFST frames are smaller, which may result in CFST frames not meeting the minimum load-bearing capacity requirement for the frame part in a dual system. If the CFST frame-core tube structure is designed adopting the dual system seismic design method which is applicable to RC frame-core tube structure, forcefully increasing the design seismic force of the frame, this will significantly increase the amount of material consumed and reduce the available area of the building. In this study, the CFST frame-RC core tube structure is designed according to different seismic design methods and compared through incremental dynamic analysis-based (IDA) fragility analysis. Then, an improved collapse risk-targeted seismic design method is proposed. The study results indicate that the structure designed according to the proposed method can achieve the excellent collapse resistance capacity, low collapse probability, and less material cost, which may provide a reference for seismic design of CFST frame-RC core tube composite structures.