Full-coupled post-fire performance analysis of geopolymeric recycled aggregate concrete-filled steel tubular columns

This paper presents a numerical investigation into the post-fire performance of geopolymeric recycled aggregate concrete-filled steel tube (GRACFST) columns under a full-coupled fire and loading phase, including ambient temperature loading, heating, cooling, and post-fire loading. First, mechanical property models for passively confined geopolymeric recycled aggregate concrete (GRAC) in steel tubes were calibrated across the four temperature phases using existing test data. A refined finite element analysis (FEA) model was then developed and validated against existing test results, showing acceptable accuracy. This model was further extended to simulate a full-size GRACFST column, examining temperature distribution, deformation, stress development, load redistribution, and steel-concrete interaction. Using the proposed FEA model, a parameter analysis was conducted to identify key factors affecting fire resistance and post-fire bearing capacity. The results indicated that the column load ratio, section dimensions, and slenderness ratio significantly impact fire resistance, while post-fire bearing capacity is mainly influenced by column load ratio, heating time ratio, section dimensions, steel ratio, slenderness ratio, steel yield strength, and concrete compressive strength. Finally, simplified equations are proposed for fire design and post-fire evaluation of GRACFST columns.