Behaviours of column-in-column (CIC) system under axial compression: Experimental and theoretical studies

Previous researches showed that column-in-column (CIC) system has a favorable performance on controlling the dynamic responses of structures subjected to earthquake ground excitations. However, no study has been conducted to directly assess the static behaviours of this system yet. Since the primary function of a structural column is to resist the vertical load, it is imperative to understand the axial loading capacity of this innovative column form, besides vibration reduction capacity, for its practical applications. In this paper, axial compression tests were carried out to investigate the compressive behaviours of the CIC system. A total of 14 specimens were tested to investigate the effects of length-to-diameter ratio and diameter-to-thickness ratio on the loading capacity of the system. The failure modes, axial force-displacement behaviours and strain developments of the CIC system with different parameters were systematically tested and compared. Prediction equation for estimating the ultimate axial loading capacity of the CIC system is also developed following the codes GB 50936–2014 and T/CCES 7–2020. The predicted results are in good agreement with the experimental results, which can be easily used in design analysis of CIC system.