January 26-28, 2009, San Francisco, California, USA
Fire-resistive wood construction is achieved either by having the structural elements be part of fire-rated assemblies or by using elements of sufficient size that the elements themselves have the required fire-resistance ratings. For exposed structural wood elements, the ratings in the United States are calculated using either the T.T. Lie method or the National Design Specifications (NDS) Method. There is no widely accepted methodology in the United States to determine the fire-resistance rating of an individual structural wood element with the protective membrane directly applied to the exposed surfaces of the element. In these tests, we directly applied one or two layers of 16-mm thick fire-rated gypsum board or 13-mm thick southern pine plywood for the protective membrane to the wood element. The wood elements were Douglas-fir laminated veneer lumber (LVL) specimens and Douglas-fir gluedlaminated specimens that had previously been tested without any protective membrane. The methodology for the tension testing in the horizontal furnace was the same used in the earlier tests. The fire exposure was ASTM E 119. For the seven single-layer gypsum board specimens, the improvements ranged from 25 to 40 min. with an average value of 33 min. For the three double-layer specimens, the improvement in times ranged from 64 to 79 min. with an average value of 72 min. We concluded that times of 30 min. for a single layer of 16-mm Type X gypsum board and at least 60 min. for a double layer of 16-mm Type X gypsum board can be added to the fire rating of an unprotected structural wood element to obtain the rating of the protected element.
The fire-resistance rating of a building element in an assembly has traditionally been assessed by subjecting a replicate of that assembly to the standard fire-resistance test ULC S101 in Canada, ASTM E119 in the USA and ISO 834 in most other countries. This paper presents two (2) calculation procedures for determining the fire-resistance of massive timber members in an attempt to develop a suitable calculation method that would provide accurate fire-resistance predictions when compared to test data and potentially be an alternative design method to conducting fire-resistance tests in compliance with ULC S101 and to the current Appendix D-2.11 of the National Building Code of Canada. Comparisons between the proposed methodologies and the experimental data for beams, columns and tension members show generally good agreement. Predicted failure times have been compared to experimental data that are publicly available.
Fire-resisting wood structural elements for building were developed. It is composed of three layers made of glued laminated timber, “a load-bearing part, a self-charring-stop and a surface layer”. Tree species of load-bearing part is limited to the only kind. In order to enable a species different, this research was carried out. Fire resistance test was performed to demonstrate the effect on fire resistance of the wood density. The relationship of fire resistance and wood density of the load-bearing part was clear. Usage of high wood density of the load-bearing part was obtained a conclusion that is advantageous to fire performance.
This paper discusses the principles of performance based structural design and motivates the need for probabilistic assessment of the response of structures and an assessment of the consequences of failure. Using the results from a series of tests carried out at SP in Sweden, we extrapolate data required for the assessment of timber structures under a range of parametric fires. This data also includes information required to develop probabilistic models of the response of timber elements under different parametric fires. Using methodologies from the literature, we then carry out a reliability analysis of timber structures, considering uncertainties the timber response to fire. This is carried out using the first order reliability method. We show that the opening factor has an influence on the reliability of timber structures, as a result of the rate of heating in a parametric fire exposure. A minimum reliability, evolving over time, is seen to occur at an opening factor of 0.14m 1/2.
Finally, we propose a modification to the Eurocode target reliability indices that allows these to be used as a target reliability index for structures exposed to fire. The proposed modification is dependent on the floor area and the method is exemplified here for a range of floor areas and its application to timber structures is illustrated.
International Journal of Civil and Environmental Engineering
Cross-laminated timber is increasingly being used in the construction of high-rise buildings due to its simple manufacturing system. In term of fire resistance, cross-laminated timber panels are promoted as having excellent fire resistance, comparable to that of non-combustible materials and to heavy timber construction, due to the ability of thick wood assemblies to char slowly at a predictable rate while maintaining most of their strength during the fire exposure. This paper presents an overview of fire performance of cross-laminated timber and evaluation of its resistance to elevated temperature in comparison to homogeneous timber panels. Charring rates for cross-laminated timber panels of those obtained experimentally were compared with those provided by Eurocode simplified calculation methods. Keywords—Timber structure, cross-laminated timber, charring rate, timber fire resistance.
This paper presents a numerical model for heat transfer in timber structures. The thermal behaviour is described by the standard Fourier heat equation. The chosen model integrates the three modes of heat transfer; namely: conduction, radiation and convection during the fire exposure. The theory and the boundary conditions associated with the model are briefly discussed. The identification of the model parameters is carried out with the experimental data available in literature. The simulation results are compared with experiments carried out on laminated veneer lumber (LVL) panels.
Fire safety has always been a major concern in the design of timber construction. Even though wood is a highly combustible material, timber members can perform adequately under elevated temperatures. The thermal response of timber connections, however, is in most cases poor and determination of their fire resistance is usually the crucial factor in evaluating the overall load-bearing capacity of wood structures exposed to fire. The analysis of timber joints under fire conditions can be challenging due to their complexity and variety. After presenting the variation of the properties of timber with temperature, this paper reviews the fire performance of various connection types, such as bolted or nailed wood-to-wood and steel-to-timber joints. Results from relevant experimental programs and numerical studies are discussed in detail and future research needs are highlighted. The effect of several factors on the fire resistance of timber connections, such as the fastener diameter, timber thickness and joint geometry, is investigated and useful conclusions are drawn. Based on these, preliminary guidelines for the efficient design of timber connections under fire exposure are presented.