Effect of transient strain on strength of concrete and CFT columns in fire – Part 2: Simplified and numerical modelling

This paper presents finite element analysis on columns of concrete and concrete-filled tubular section. This study has been conducted with Vulcan, a specialist structural fire engineering FE program, which has been further developed to incorporate the transient strain of concrete. The implementation of transient strain in Vulcan has been validated against a Shanley-like simplified model. A further extension of the simplified model has been carried out in order to provide direct comparability with the FE modelling. The effects of transient strain, considering thermal gradients through the column cross-section, have been evaluated with both the simplified and FE models. Finally, parametric studies on concrete-filled tubular columns, considering the effects of slenderness ratio, reinforcement, the steel casing and thermal gradient within the cross-section, have been conducted using Vulcan.

► Considering transient strain (TS) causes a reduction of the predicted buckling capacity.
► Both the simplified and numerical modelling indicated this reduction.
► The slenderness and the temperature distribution across cross-section control this effect of TS.
► TS should not be neglected, especially for columns of slenderness ratios higher than about 70.