Fire behaviour of slender, highly utilized, eccentrically loaded concrete filled tubular columns

• Effect of large eccentricities combined with high slenderness and utilization is investigated.
• Explicit solver successfully captured descending part of the axial shortening curve to enable FRR to be evaluated.
• The FRR reduces significantly as the bending moment increases on the column.
• For highly utilized columns, the FRR was less sensitive to changes in the magnitude of the bending moments.

This paper investigates the fire performance of highly utilized and eccentrically loaded concrete filled composite columns with slendernesses greater than currently permitted by the simple calculation model in Eurocode 4 Part 1.2. The fire resistance rating was calculated by applying implicit as well as explicit finite element analyses and undertaking sequentially coupled thermal-stress analyses. Initially, published fire tests on concentrically loaded columns as well as columns with a modest load eccentrically (e/h ≤ 0.25) were analysed with normal (NSC) and high strength concrete (HSC). Following the validation of the numerical model against the test data, a parametric study was undertaken on a composite column using a 400 mm square hollow section with a fixed-pinned boundary condition and a relative slenderness at room temperature of λ̅=0.6. Load levels ηfi,t of 0.47, 0.35 and 0.24 were considered and, using a constant eccentricity of e/h = 0.5, a combination of concentric and eccentric loading was applied to the column, as would occur in practice. The results from the parametric analyses show that the FRR reduces significantly as the bending moment increases on the column. Moreover, although the FRR reduced as the utilization increased, it was found that for highly utilized columns the FRR was less sensitive to changes in the magnitude of the bending moments.