PRE-TENSIONED STEEL CABLES EXPOSED TO LOCALISED FIRES

Pre-tensioned steel cables are often used in hybrid string structures, suspended roofs and cable suspended bridges. When subjected to localised fire, the tensile force in the steel cables reduces due to thermal expansion, and thus, the geometry of the structure and the internal force distribution in the cable-tensioned structure will be affected. The mechanical behavior of pre-tensioned steel cables is sensitive to the elevated temperature history. In this paper, a set of analytical formulation has been proposed to determine the transient tension force in a cable subjected to localised heating considenng the mechanical properties at elevated temperature and the effects of loading configuration, pre-tensioned force level, and thermal expansion at elevated temperature. The fire resistance of a pre-tensioned steel cable can be determined when the cable tension force is equal to its effective yield strength at elevated temperature. Meanwhile, the proposed method is able to capture the relationship between the transient tension forces with each influence parameter in order to study the behavior of steel cables subjected to localised fire. The mechanical responses predicted by the proposed analytical method of pre-tensioned cables exposed to localised fires are validated against the numerical results obtained from nonlinear finite element software. Finally, a design flow chart is proposed for fire resistant design of pre-tensioned steel cables and the calculations can be implemented using a spreadsheet program.