Effects of structural continuity on fire resistant design of steel columns in non-sway multi-storey frames

Abstract

Abstract This paper discusses two aspects of the effect of structural continuity on the fire resistant design of steel columns in non-sway multi-storey steel frames. One is beneficial and the other is detrimental. The beneficial effect is to enhance the rotational restraint to the column and thus to reduce its effective length and increase its load carrying capacity. The detrimental effect is to increase the column compressive load due to axial restraint to its thermal expansion. This paper attempts to put forward a simple design method to reconcile these two effects. A comprehensive parametric study is performed to evaluate these two effects on the column limiting temperature and its fire protection thickness. It is found from the results of this parametric study that for buildings with a practical range of axial restraint to columns, these two effects almost cancel each other out. This paper therefore proposes that for the calculation of column limiting temperature, the additional compressive force in the column may be discarded provided the original column slenderness ratio at the cold condition is used for elevated temperature design. The fire protection thickness of the column may be conservatively obtained by increasing by 20% that calculated using the above limiting temperature.