Periodic Reporting for period 1 - FIReSafeTimber (Fundamental advances for the fire safety of tall timber structures including the fire decay phase)
Reporting period: 2022-10-01 to 2024-09-30
Urban densification, sustainability drivers and technological advances foster the development of high-rise structures using bio-based materials like engineered wood products. Their main worldwide barrier relates to fire safety. Although a natural fire has a decay phase, structural capacity is traditionally assessed according to a standard fire curve: an unrealistic ever-increasing thermal exposure with time, conceived as worst-case design scenario. This results in inadequate assessment for timber, often disqualifying it as potential material. Also, the decay phase, deemed less onerous due to its lower temperatures, is generally omitted from structural calculations. However, for structural performance it is of crucial importance for timber. Unlike traditional non-combustible construction materials, wood loses its mechanical properties at relatively low temperatures. Thus, the precise interaction between fire and structure needs to be understood because the temperature propagation through the load-bearing timber can unexpectedly lead to structural collapse, even after a fire seems extinguished. Current regulations fail to consider this hazardous issue and available literature on the matter is limited. Fundamental technical issues still need to be resolved and pertain to the nature of the fire dynamics and the resulting deterioration of the engineered timber mechanical properties. FIReSafeTimber investigates key challenges related to the fire dynamics inside timber buildings and the resulting deterioration of the timber mechanical properties. Computational models are built to simulate the thermal exposure to structural elements for various fire dynamics conditions (e.g. fuel and compartment characteristics). Bench-scale and full-scale fire tests are conducted on loaded timber structural elements with varying fire decay phase. FIReSafeTimber aims at formulating a novel constitutive model to predict the heat transfer and the structural capacity of timber elements and developing performance-based methodologies for the fire-safe design of timber structural systems including the fire decay phase.
Due to the early termination of the action, the fellowship had little progress, with respect to what foreseen in the Grant Agreement (GA). When the action was terminated, the project has just commenced, and the research fellow had just started working towards the research objectives and carrying out the Work Packages (WPs). During its short duration, the research fellow advanced in defining the main characteristics of the fire decay and cooling phases of post-flashover compartment fires, and a simplified numerical model based on energy-conservation equations was developed to estimate the fire exposure to building elements within an enclosure during these phases.
The research fellow demonstrated the importance of considering the fire decay and cooling phases in structural fire engineering design procedures for load-bearing elements so as to avoid partial or total structural collapse. The fire decay and cooling phases of post-flashover compartment fires were characterised in detail, and a simplified numerical model based on energy-conservation equations was introduced to simulate the thermal exposure to load-bearing structural elements during these phases. A parametric study also enabled to understand how the fuel and compartment characteristics affect the fire dynamics within a compartment, hence the temperatures and heat fluxes in the event of a fire.