Post-fire residual strength of steel tubular T-joint with concrete-filled chord

The post-fire behavior of steel tubular T-joints with a concrete-filled chord (CFC) was experimentally and numerically investigated. One specimen was tested at ambient temperature while the other two were tested after a heating and cooling process. The experimental results revealed that the failure mode was chord plastification, rather than local buckling of the chord wall, due to the support provided by the in-filled concrete. A finite-element (FE) method was then developed to simulate the structural response of the post-fire joints under compressive load. The comparison between the FE simulation and experimental data illustrated that the FE method reliably and accurately predicted the failure modes, the measured load-displacement curves and the residual strength of the T-joints. The verified FE method was then used in a detailed parametric analysis, which systematically varied the geometric and material parameters including α, β, τ, γ, fc, fy and the highest temperature of fire exposure-Tmax. The results indicated that filling concrete into the chord increased the fire resistance and bearing capacity of the joints, but had an appreciably negative impact on the post-fire behavior, as the damage to concrete in fire was irreparable. Moreover, the residual strength increased significantly with increasing fy, but decreased with increasing α and γ. β and fc showed slight influence, while changing τ had negligible effect. The effect of each parameter could be quantitatively simulated by a function. A parametric equation based on the effect was proposed, and its accuracy was verified through error analysis against the numerical and experimental results.