Impact of wood species on the timber beam strength and stiffness under fire

Abstract

A lot of different types of wood can be used to build the structure. Main constructions are usually built of solid wood or glued laminated timber. The division into design classes depends on the strength and mechanical properties of wood. One of the most important aspects to consider when designing timber structures is to provide fire resistance. In contrast to other construction materials such as concrete, steel, ceramics, wood is a combustible material. When timber member is subjected to fire, the surface of the wood initially ignites and burns rapidly. At 300°C the pyrolysis takes place which cause loss in mass and decrease the strength and mechanical properties. Charring rate and decreasing of properties depend on the wood species. As a consequence, it has a significant impact on the timber member strength in fire conditions. This article presents a summary from numerical simulations on impact of wood species on the timber beam strength and stiffness in fire conditions. Numerical models of timber beams were made in the SAFIR software. All modeled beams have the same dimensions. Each beam was loaded with a bending load. Also the fire load from four sides of the elements according to the ISO fire curve was given. Species and classes of wood were differentiated. Using the isotherm 300°C from the SAFIR program, time-dependent residual cross-sections were determined. As a result, the reduction of bending capacity and the increase in deflections of timber beams were obtained. It was noticed that higher class wood had a relatively lower load-bearing capacity reduction under fire.