Experimental analysis on post-fire performance of GRAC filled steel tubular columns and thermal properties of GRAC

This paper presents experimental investigation on the post-fire performance of geopolymeric recycled aggregate concrete filled steel tube (GRACFST) columns and temperature field of GRAC cubes. A total of 10 GRACFST column specimens were tested to investigate their post-fire performance. A total of 10 GRACFST column specimens were tested to evaluate their performance after exposure to fire, considering various parameters: (a) cross-section type (circular and square); (b) testing conditions (ambient temperature test, post-fire test without initial load, and full-coupled post-fire test); (c) target temperatures (20 ℃, 600 ℃, and 800 ℃); and high-temperature exposure durations (30 min and 180 min). The study examined failure modes, temperature evolution, deformation and strain patterns, and post-fire ultimate bearing capacities. The test data revealed the commendable post-fire performance of GRACFST columns, as evidenced by the residual strength index typically falling within the range of 0.83 to 1.11. To calibrate the thermal properties of GRAC materials, a series of temperature field tests of GRAC cubes at different target temperatures (200 ℃, 400 ℃, 600 ℃ and 800 ℃) were conducted. These tests provided data on temperature distribution within the cubes and mass loss due to high temperatures. Using back analysis of these temperature field tests, thermal property models for GRAC, including thermal conductivity, specific heat, and density, were developed and validated by simulating temperature data from existing fire and post-fire tests of GRACFST columns. The proposed thermal property models are crucial for designing this novel composite column type for fire resistance applications.