An experimental study of the influence of an exposed combustible ceiling on compartment fire dynamics has been performed. The fire dynamics in compartments with combustible cross-laminated timber ceilings vs non-combustible reinforced concrete ceilings in otherwise identical compartments with three different ventilation factors were investigated. The experimental results are compared against predictions from two theoretical models for compartment fire dynamics: (a) the parametric fire model given in EN 1991-1-2, and (b) a model developed at Technische Universität Braunschweig, which are the parametric fire models currently used in Germany. It is confirmed that the introduction of a combustible timber ceiling leads to higher temperatures within the enclosure, both under fuel-controlled and ventilation-controlled scenarios. It is also demonstrated that the theoretical models considered in this article require refinement in order to adequately represent all relevant scenarios when combustible ceilings are present. A refinement of the German model, by adding the fuel from the combustible ceiling to the occupancy fuel load, was shown to not adequately capture the response for the ventilation-controlled fires.
This paper describes selected observations, measurements, and analysis from a series of large-scale experiments on cross-laminated timber (CLT) slabs that were exposed to fire from below, using four different heating scenarios, with a sustained mechanical loading of 6.3 kN m per metre width of slab. The deflection response and in-depth timber temperatures are used to compare the experimental response against a relatively simple structural fire model to assess the load bearing capacity of CLT elements in fire, including during the decay phase of natural fires. It is demonstrated that the ventilation conditions in experiments with a fixed fuel load are important in achieving burnout of the contents before structural collapse occurs. A mechanics-based structural fire model is shown to provide reasonably accurate predictions of structural failure (or lack thereof) for the experiments presented herein. The results confirm the importance of the ventilation conditions on the fire dynamics, burning duration, and the achievement of functional fire safety objectives (i.e. maintaining stability and compartmentation), in compartments with exposed CLT.