Fire-Induced Thermal Gradients in Cold-Formed Steel Flexural Members: A Numerical Parametric Study for Structural Application

The cold-formed steel (CFS) members are highly susceptible to the fire and the presence of full or partial insulation can significantly influence the overall thermal profile of the member. Unlike uniformly heated members, a gradient thermal exposure can reduce the member’s mechanical properties unevenly. This study investigated the effects of uniform and gradient thermal exposure on the structural behaviour of flexural members. The non-linear finite element (FE) model is developed and validated with the experimental and numerical results available in the existing literature. A series of numerical FE parametric studies on 1425 members is performed considering several member geometry and spans ranging for different beams covering non-dimensional slenderness ranging from 0.28 to 1.81. Two common loading patterns (4-point loading and uniform moment) and five thermal distribution patterns are considered, covering thermal bowing in the direction of loading as well as in opposite to that. Results of the extensive parametric study indicate the fact that the failure temperature of the member is largely dependent on the applied thermal profile of the member. Parameters like depth of the member cross-section, non-dimensional slenderness and thermal bowing of the member, which largely influenced the critical temperature of the CFS flexural member, are studied in detail. In several cases, the failure temperature of a partially heated member can be lower than that of the member fully exposed to fire. Parametric study results also highlighted the fact that the existing limiting temperature of 350° of the European design rules (Eurocode 3, Part 1.2) for CFS members is highly over-conservative.