Advancing cold-formed steel with thermal barrier coatings: buckling and fire resistance behaviours

Thin-walled cold-formed steel (CFS) members buckle prematurely under fire because their limited wall thickness heats rapidly, yet lightweight fire-protection options beyond bulky gypsum encasement remain largely unexplored. This gap motivated an experimental and numerical investigation of two thermal barrier coatings (TBCs) – a plasma-sprayed yttria-stabilised zirconia (YSZ) coating and an epoxy-based intumescent coating – applied to S355 lipped CFS channels (150 × 50 × 2 mm), with 10 specimens tested per group (uncoated, YSZ, intumescent) under the ISO-834 standard fire curve. Buckling progression was tracked with LVDT and thermocouple instrumentation, post-fire residual strength was measured through ASTM E8 tensile testing, and the observed behaviour was reproduced with nonlinear ABAQUS finite-element models. Both coatings delayed the onset of substrate buckling and improved post-fire load retention relative to uncoated specimens, with the intumescent coating performing marginally better due to its expanding char layer. A numerically modelled functionally graded material (FGM)-TBC configuration is also proposed as a means to further reduce interfacial thermal stress, though it has not yet been experimentally validated. The results suggest that current Eurocode 3 reduction factors may not capture the benefit of coated sections, though this finding should be treated as preliminary pending broader validation.