Experimental research on fire behavior of L-shaped CFST columns under axial compression

Six L-shaped concrete-filled steel tubular (LCFST) stubs were designed and tested under the axial compression and ISO-834 standard for fire. The temperature distribution, axial deformation development, fire resistance, and failure modes of LCFST columns under fire were investigated. The fire test results show that the fire resistance of the specimen decreases with the increasing axial compression ratio and increases linearly with the thickness of the fire protection layer; and the tension-bar stiffened column has slightly higher fire resistance than multi-cell columns. The fire behavior of LCFST columns was then analyzed using the finite element program ABAQUS and the simulated temperature distributions and fire resistances were found to be in good agreement with the test results. Moreover, the LCFT column has slightly higher fire resistance than the square CFST column specified in the design code GB50936–2014. The parametric analysis results show that slenderness ratio, column limb thickness, eccentricity ratio, and fire protection layer thickness all affect the fire resistance of LCFST columns. It was discovered that the first level fire-resistance rating of LCFST columns could be achieved by adopting a reasonably thick fire protection layer. Lastly, simplified formulas for the fire resistance and fire protection layer are proposed, which can reduce the fire protection layer thickness by 50% compared to the current fire design requirements for CFST columns.