From Flames to Resilience: New Perspectives for the Design of Structures Against Fire Hazards

The catastrophic consequences of fire events in singular buildings (e.g. Nôtre Dame Cathedral) and tunnels (e.g. Hsuehshan and Mont Blanc tunnels) have significantly changed the public perception of fire risk. During a fire, materials and structures are pushed to the limit, and ensuring an adequate fire response can be very challenging. Fires pose a range of detrimental effects also on bridges (see e.g. the fire induced collapse of the Interstate 95 bridge in Northeast Philadelphia, USA), including the potential weakening of structural components and the compromising of the bridge load-bearing capacity and overall stability. This special issue is aimed at showing innovative and useful perspectives to address these challenges.

The first contribution¹ contains a detailed review of past fire events affecting cable-supported bridges and analyses the performance of decks, cables, girders, and pylons when exposed to fires. The article compiles probabilistic and deterministic methods to enhance the fire resilience of cable-supported bridges and concludes by pointing out to areas where more research is needed.

The second article² proposes a methodology for modelling the thermal response of a critical component of cable-supported structures: spiral strand and locked coil cables. The methodology is experimentally validated and enables to understand the temperature distribution and thermal deformation in the cables cross-section. It also enables to estimate the cables post-fire resilience.

Moving forward, the third contribution³ discloses a framework to assess the fire performance of cable-supported bridges. The framework includes the identification of potential fire scenarios, simulations of potential fire events using computational fluid dynamics, simulations of the bridge thermomechanical response using finite element analysis and, finally, definition of fire prevention and protection measures. The framework is applied to a two-level bridge with a main span of 708 m built in China.

The fourth contribution⁴ proposes a methodology that considers fire probability, incident location uncertainty, and wind effects, to assess the probability of structural failure due to fire in cable-supported bridges. The methodology enables informed decision making regarding fire preventive/protective measures and is applied to a 450 m long cable-stayed bridge submitted to fuel tanker fire scenarios.

Shifting the focus to tunnel structures, the fifth paper⁵ proposes a quantitative fire damage assessment framework for RC tunnel linings that integrates advanced modelling with visual inspections, non-destructive testing, and material sampling. The framework is applied to a case study and includes a damage classification system based on international guidelines and feedback from industry experts.

Lastly, the sixth paper⁶ explores the consequences of fires in urban areas following earthquakes and their potential impact on reinforced concrete frames. Using validated numerical models, the study investigates the post-earthquake fire behavior of damaged and undamaged RC frames. Results show that the difference in time until collapse between an undamaged frame and a heavily damaged frame can be higher than 2 hours, which poses significant challenges considering the potential delay in response times due to overwhelmed rescue teams following a large earthquake. The findings underscore the need to consider the combined effects of earthquakes and fires in designing resilient structures.

Collectively, these articles shed light on the multifaceted aspects of fire resilience and post-earthquake fire behaviour in structures. By presenting novel methodologies, design frameworks, and damage assessment approaches, they constitute an important contribution to the ongoing efforts to mitigate the consequences of fires in our infrastructure.