Fire Performance of Structural Cables: Current Understanding, Knowledge Gaps, and Proposed Research Agenda

Structural cables are widely used on large-scale structures such as bridges and stadia around the world. This paper presents a review of current research and development associated with the thermal and mechanical performance of structural cables when subjected to fire loading. The findings of this study highlight key knowledge gaps, which are subsequently used to propose the future research agenda. The particular focus of the review is on large-diameter cables, composed of both multiple strands and multiple wires, which are commonly used on structures of concern to civil and structural engineers. It is determined that the fire performance of structural cables is influenced by several factors such as the cable shape, diameter, metallurgical characteristics, uniformity of thermal exposure conditions, time-dependent effects of fires, and their terminal characteristics. The thermal expansion coefficients and reduction of material properties provided in EN 1992-1-2 and other research studies may not be appropriate for exposed prestressed cables because they were developed for tendons encased in concrete construction and creep is not accounted for. In particular, the material characterization at elevated temperatures may not necessarily be the same as that of normal high-strength steel owing to the different cold-working process of cable wires. Very limited studies have investigated experimentally or numerically the fire performance of structural cables with a shape and diameter different to the typically studied seven-wire strands used for concrete construction, leading to a number of knowledge gaps. The experiments conducted so far have shown that for unprotected cables a significant thermal gradient develops and early failure occurs with an increase in the cable diameter leading to an increase in its failure time. A range of simplified and advanced methods have been proposed in the literature; however, these generally lack extensive validation against experimental evidence. Numerical studies have shown that the presence of air cavities between strands can lead to larger thermal gradients in particular for unprotected cables because the cavity acts as insulation, unlike protected cables, where the temperature is more uniform within the section. The testing procedure of PTI DC45.1-12, which is the only available standard for stay cables, lacks extensive verification and validation to ensure that the aims of the standard are achieved. Further research is required to confirm that the two-phase procedure adequately captures all underlying physics under realistic fire exposures and its applicability for cables with characteristics different from the sample tested.