Determination of design fires in compartments with combustible structure – modification of existing design equations

Abstract

The determination of the fire development, i.e. the temperature-time curve, is an essential input for the fire design of structural elements when performance based design (PBD) is used. PBD uses the particular boundary conditions (i.e. geometry, openings, and fire load) of a compartment to define a relevant temperature development. This may be done according to EN 1991-1-2 Annex A or another method such as the corresponding German National Annex. Regardless the method, the consideration of the contribution of the structural fire load is required by EN 1991-1-2. The increase of the movable fire load by the structural fire load for timber corresponding a charring depth was mentioned by several authors (K. Leikanger -Friquin 2012, Brandon 2018, McNamee et al 2019). However, various approaches exist. This paper gives guidance about how to include the contribution of unprotected timber surfaces in the actual framework of EN 1995-1-2. Here, the estimation of the a) maximum heat release and b) the calculation of the fire load density are extended and c) the amount of heat re-leased at the façade is given.