Abstract
Thin-walled steel tube confined reinforced concrete (STCRC) columns are increasingly used in high-rise and heavily loaded structures. One concern is whether concrete shrinkage affects the load resistance of STCRC columns, as the confinement to the concrete may become less effective when the concrete shrinks. This paper presents ultimate tests on STCRC columns after subjected to 490-day-sustained-loading or 490-day-shrinkage. The compression tests are conducted on specimens with different steel ratios, reinforcement ratios, concrete strengths and steel-concrete interfacial bonding conditions, or with long-term load first applied at different concrete ages. The sustained load history and the shrinkage effects on the short-term axial stiffness, ultimate strength, and peak strain of STCRC columns are investigated. The development of confinement effects and the tube's axial stiffness contribution after shrinkage and creep history are compared against those test results without experiencing shrinkage or long-term load history. A non-linear finite element model is finally developed for the ultimate response prediction of STCRC columns with the consideration of the creep and shrinkage history, and its accuracy is compared against the test data. The results show that concrete shrinkage and creep significantly affect the occurrence and development of the confinement effects, but not the confining pressure at the peak load. The axial stiffness and peak strain of STCRC columns are sensitive to time effects, while the ultimate strength is not. Under service loading, the tube's contribution to the axial stiffness of STCRC columns is negligible due to concrete shrinkage, while at the ultimate strength limit state condition, the column compression resistance is barely influenced by shrinkage and creep effects. The proposed FE model achieves reasonable accuracy in evaluating the ultimate responses of STCRC columns considering the shrinkage and creep effects.
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