Efficient Fire Hazard Mitigation for Suspension Bridge Cables

Abstract

Increasingly, large suspension bridges are exposed to fire risks as the traffic they carry increases. A truck fire on a suspension bridge may lead to main cable failure or a strength reduction that will either cause down-graded classification of the load carrying capacity or need for long lasting repairs of the main cable with large costs and traffic disruption as severe consequences. A serious fire in a truck occurred in 2013 on the New Little Belt Suspension Bridge in Denmark, and caused rapidly rising flame temperatures to above 1000 °C, somewhat similar to a hydrocarbon fire. Based on this accident and a number of other incidents with fires on roads and bridges, a risk and cost–benefit study focusing on fire risks for this bridge was carried out. Based on the result of the study, it was decided to provide fire protection to the main cables on the New Little Belt Bridge. Due to the large socio economic importance, the need for similar mitigation of fire hazards has been considered for bridges such as Alvsborg Suspension Bridge (Sweden), Great Belt East Bridge (Denmark) and A.L. MacDonald Suspension Bridge (Canada). Current status is that fire retro protection projects have been decided and are being prepared for the latter two bridges. Based on the accident on New Little Belt Bridge, a fire protection concept for main cables has been developed after detailed studies of the fire impact on this occasion. This has resulted in advanced modelling of the fire loading on a main cable and in design elaboration of an efficient fire hazard mitigation concept for main cables. This paper describes the systematic process for evaluation of the fire accident on New Little Belt Bridge and how this has evolved into a very efficient fire hazard mitigation concept for main cables. The concept may be used on existing as well as on new suspension bridges being essential elements in national road infrastructure systems.