Grunde Jomaas

Fire protection of bridge cable systems has been identified as an important mitigating action with respect to operational risk as well as the safety of existing and new bridges. In particular, cable supported bridges have been demonstrated to be vulnerable to vehicle fires.With the design of fire protection concepts for New Little Belt Bridge and Great Belt East Bridge, a process with development of fire protection of cable systems has been started. The project is based on the development of a fire protection concept for main cables based on insulation mats and currently a concept is being developed with use of intumescent coatings.The R&D project and handling of the design challenges on cable systems on suspension bridges is presented, and it includes details about the main cable, cable clamps and suspenders based on numerical modelling and testing of the steel performance during fires up to 1100°C.The fire protection relies on use of insulation mats and intumescent coatings and in developing the concept, one of the main challenges is to document the performance of the design concepts unique to each bridge. Furthermore, it is difficult to get access to information on material performance in such particular applications. Hence, in the current project, it has not been possible solely to rely on the supplier information and it has been necessary to carry out numerical modelling of performance during fire as well as use of laboratory testing.In summary, the objective is to investigate the combined performance of the steel cable and the applied insulation concept. For solutions, design has not only to consider the fire protection of steel but also to address issues regarding cable durability and allowance for operation and maintenance.

Long‐span suspension bridges provide vital support to society and its development. With ever increasing road traffic, such bridges are increasingly exposed to greater risks from fires. Experience shows that a significant fire in a truck without dangerous goods (like the 2013 New Little Belt Bridge fire in Denmark) can grow rapidly to reach temperatures above 1000°C, thereby making it a fire comparable to the hydrocarbon fire test standard. Compared to fuel tankers, the relatively high frequencies of trucks carrying normal (but flammable) goods make such significant truck fires more likely. Significant fires on a suspension bridge can lead to strength reduction or cable failure that could result in a reduction in bridge load rating and a need for long‐lasting repairs. Such outcomes mean high societal costs due to long‐term disruption of the connectivity provided by the bridge. Hence, there is a need to systematically assess fire risks in suspension bridges, focusing on a) fire frequencies and proportion of significant fires that can affect key bridge elements, b) fire consequences to key bridge elements and c) implementing mitigation measures when needed. Main cables in a suspension bridge are vital for structural integrity and at the same time difficult and expensive to replace during the bridge lifetime. This means that, in addition to ensuring no cable failure and no bridge collapse during fire, non‐exceedance of critical temperatures that could result in extensive damages and/or irreversible strength loss after fire is also important. Evaluating cable performance with respect to such criteria requires a detailed modelling of heat transfer into the cable, taking into account the nature of fire, multiple heat transfer modes, packing arrangement within the cable and geometrical exposure conditions.The above issues are addressed and useful insights are provided to help in understanding the fire risk picture for suspension bridges.