Study on Axial Bearing Performance of Reactive Powder Concrete-Filled Square Steel Tube Columns After High Temperature

Abstract

This study investigated the axial compressive behavior of reactive powder concrete-filled steel tube (RPC-FST) columns after high temperatures. To evaluate the effects of heating duration, spiral stirrup spacing, and steel tube thickness on the post-fire performance of RPC-FST columns, ten specimens were first subjected to high-temperature tests and then subjected to axial compression load tests. The experimental results indicate that all specimens exhibited local buckling failure. The severity of local buckling decreased with increasing steel tube thickness and heating duration, as well as with decreasing spiral stirrup spacing. Compared with the unheated specimens, the specimens with heating times ranging from 140 to 260 min showed a reduction of 2.18–37.46% in the ultimate load and 11.00–38.51% in the elastic stiffness. Under identical heating conditions, the ultimate load increased with increasing steel tube thickness and decreasing spiral stirrup spacing. Specifically, when the steel tube thickness increased from 4 to 10 mm, the ultimate load capacity and elastic stiffness increased by 21.98 and 19.35%, respectively. Moreover, reducing the spiral stirrup spacing from 80 to 40 mm resulted in a 23.30% increase in ultimate load capacity. Based on the experimental results, a calculation method for predicting the axial bearing capacity of RPC-FST columns after high temperature was proposed. The proposed method was evaluated against the experimental results, existing design specifications, and previously reported prediction models, demonstrating its applicability and providing useful references for future research.