engleski

Reliability of timber structures exposed to fire

Until recently, the fire resistance of buildings was based on the ISO standard curve. The only option for determining the fire resistance was to carryout tests in laboratories. ISO standard curve used by the current norm is too simple, unrealistic and lead to uneconomic situations with no guarantee of security proportional to the invested money. Unlike the fire design of the steel, concrete or composite structures, methods for fire design of timber structures have been greatly simplified. Generally, it is not necessary to check the reduction of strength in the residual section because each increase of temperature is considered small and it is ignored. Global fire safety concept of timber structures is presented according to the recommendations from Eurocode norms. Special attention was given to natural fire design with two different methods of parametric exposure which are given in EN1995-1-2. Method of design according to EN 1995-1-2 is a two stage process. First, the calculation of charring depth, and then determine the strength of the residual section. This paper presents reliability analysis of a glulam load-bearing beam in a fire. The limit-state functions for maximum bending stress of glulam beam in fire conditions are formed. The charring rate of wooden beam is calculated by a model that includes explicitly the principal sources of uncertainties and variability. Reliability indexes are obtained from the limit state of the beam exposed to 30 min fire. Reliability index in the Eurocodes (reliability class RC2) compared to the calculated reliability indexes obtained by the methods of reduced strength and effective section were described.

fire design; reliability; Eurocode; timber structure; glulam beam

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