Fire resistance of timbers from tropical countries and comparison of experimental charring rates with various models

Abstract

Tropical hardwood species are more and more used in the field of construction due to the particular qualities they can offer. Presently it is no longer possible to envisage the development of construction materials and products without taking into consideration the problem of their fire behaviour, and more particularly of their fire resistance. In the case of timber elements, this characteristic is mainly influenced by the charring rate of the external layers of the element. On the other hand this parameter is influenced by the density of the material. Limited information is available on the charring rate of tropical hardwood species. Therefore experimental investigations have been conducted at the University of Liege to study this characteristic. Seven tropical and three timber species from temperate countries have been examined. Two types of test have been used, one on small specimens, the other on a construction element made of one single material. In the first type, 20 specimens have been manufactured by gluing several laminates together. The specimens were instrumented with four thermocouples inserted at various depths in four different laminates. In the second type, a non-loaded wall made of 12 glued-laminated spruce beam profiles was instrumented with thermocouples embedded at different depths in the panel for the evaluation of the charring rate. Experimental charring rates have been compared with the results derived from Eurocode EC5-1.2 recommendation [ENV 1995-1-2. Eurocode 5: Design of timber structures – Part 1–2: General rules – Structural fire design. European prestandard; 1994], Australian standard AS 1720.4 relation [AS 1720.4. Timber structures Part 4: fire resistance of structural timber members. North Sydney, Australia: Standards Australia; 1990] and White’s model [Charring rates of different wood species. PhD dissertation. Madison University of Wisconsin, Madison, WI, 1988; White RH, Erik V, Nordheim EV. Charring rate of wood for ASTM E119 exposure. Fire Technol 1992;28(1)]. This comparison shows that the results obtained from these three models are not entirely satisfactory for tropical hardwood species. Therefore a new model has been proposed.