In 2015, the National Building Code of Canada (NBCC)  adopted prescriptive provisions to allow the construction of mid-rise (5- and 6-storey) buildings using combustible construction. These types of buildings were already permitted under the British Columbia Building Code, as of 2009 . In2014 the Province of Ontario filed an amendment to also allow mid-rise wood buildings, however, it required that the exit fire separations be built using noncombustible construction having a fire resistance rating (FRR) of not less than 1.5-hr, which was an increase from the 1-hr requirement in the NBCC. The Québec Construction Code has also filed amendments to allow mid-rise wood construction and also limits exit stairwells to use noncombustible construction.
FPInnovations conducted a research project to study the construction of mid-rise wood exit shafts in Ontario and Québec. The scope of the project included an investigation into the concerns that have been raised in regards to the use of wood exits in mid-rise buildings, an analysis of recent Canadian fire statistics in residential multi-family structures, and a fire demonstration of a mass timber wall and supported light-frame floor. This report describes the fire demonstration completed as part of this project; this report acts as a supplement to the full project report.
FPInnovations carried out a survey with consultants and researchers on the use of analytical models and software packages related to the analysis and design of mass timber buildings. The responses confirmed that a lack of suitable models and related information for material properties of timber connections, in particular under combination of various types of loads and fire, was creating an impediment to the design and construction of this type of buildings. Furthermore, there is currently a lack of computer models for use in performance-based design for wood buildings, in particular, seismic and fire performance-based design.
In this study, a sophisticated constitutive model for wood-based composite material under stress and temperature was developed. This constitutive model was programmed into a user-subroutine and can be added to most general-purpose finite element software. The developed model was used to model the structural performance of a laminated veneer lumber (LVL) beam and a glulam bolted connection under force and/or fire. Compared with the test results, it shows that the developed model was capable of simulating the mechanical behaviour of LVL beam and glulam connection under load and/or fire with fairly good correlation.
With this model, it will allow structural designers to obtain the load-displacement curve of timber connections under force, fire or combination of the two. With this, key design parameters such as capacity, stiffness, displacement and ductility, which are required for seismic or fire design, can be obtained.
It is recommended that further verification and calibration of the model be conducted on various types of wood products, such as CLT, glulam, SCL and NLT, and fasteners, e.g. screw and rivet. Moreover, a database of the thermal and structural properties of the wood members and fasteners that are commonly used in timber constructions need to be developed to support and facilitate the application of the model.
The key objective of this study is to analyze full-scale fire-resistance tests conducted on structural composite lumber (SCL), namely laminated veneer lumber (LVL), parallel strand lumber (PSL) and laminated strand lumber (LSL). A sub-objective is to evaluate the encapsulation performance of Type X gypsum board directly applied to SCL beams and its contribution to fire-resistance of wood elements.
The test data is being used to further support the applicability of the newly developed Canadian calculation method for mass timber elements, recently implemented as Annex B of CSA O86-14.
The report concludes with the recommendation that it would be useful to run an extensive set of cone calorimeter tests on SCL, glue-laminated timber and CLT products. The fundamental data could be most useful for validating models for predicting flame spread ratings of massive timber products and useful as input to comprehensive computer fire models that predict the course of fire in buildings. It is also argued that the cone calorimeter would be a useful tool in assessing fire performance during product development and for quality control purposes.
The present work aims at evaluating the combustibility characteristics (i.e. reaction to fire) of structural composite lumber (SCL) when tested in compliance with the cone calorimeter standard ISO 5660 [7, 8, 9]. More precisely, this study evaluates the heat release rate, total heat release, mass loss, effective heat of combustion, smoke obscuration as well as the presence of toxic gases when SCL products are tested in conformance with ISO 5660.
Moreover, this study is solely focused on SCL elements that are thick enough to act as semi-infinite solids (thermally thick solids), as opposed to typical thin combustible finish products. Tests data are also compared to those obtained for visually-graded solid wood specimens of the SPF species group.
Laminated products - Fire resistance
Structural Composites - Properties
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Le bois lamellé-croisé (CLT), un système de construction relativement récent pour lequel l’intérêt ne cesse de croître dans le secteur de la construction d’Amérique du Nord, contribue à la définition d’une nouvelle classe de produits massifs en bois. Le CLT est un composant structural à base de bois très prometteur, qui présente un potentiel élevé pour fournir des solutions de construction rentables pour les bâtiments résidentiels, commerciaux et institutionnels ainsi que pour les grandes installations industrielles. L’acceptation de la construction en CLT dans l’environnement réglementaire canadien requiert la conformité aux dispositions relatives à la protection incendie du Code national du bâtiment du Canada (CNBC), entre autres choses.
Des essais au feu approfondis ont démontré la capacité du CLT à fournir un degré de résistance au feu pouvant atteindre près de 3 heures lorsque le matériau est mis à l’essai dans des conditions de plein chargement conformément à la norme CAN/ULC S101. De plus amples renseignements sont également fournis sur les propriétés de sécurité incendie connexes, y compris l’indice de propagation des flammes et les dispositifs coupe-feu.
Les éléments de CLT sont utilisés dans les systèmes de construction d’une façon similaire aux dalles de béton et aux éléments muraux massifs ainsi qu’aux éléments utilisés dans la construction en gros bois d’œuvre en limitant les vides de construction créés grâce à l’utilisation des éléments massifs en bois, ce qui contribue à réduire le risque d’incendies dans ces vides de construction. En outre, la construction en CLT utilise généralement des panneaux de CLT pour les planchers et les murs porteurs, ce qui permet d’obtenir une compartimentation ayant une résistance inhérente au feu et contribue une fois de plus à réduire le risque de la propagation d’un incendie au-delà de son point d’origine (compartiment d’origine).
Le présent document propose une méthodologie visant à déterminer la résistance au feu des éléments de CLT. En tant que modèle déterministe fondé sur les concept de calculs aux états limites, cette méthode permet de calculer la résistance des éléments de CLT soumis à une exposition au feu standard (soit la norme CAN/ULC S101) à l’aide des mécanismes techniques de base du bois pour les calculs de résistance au feu allant jusqu’à 3 heures, qui ne sont limités que par la disponibilité actuelle des données. La méthode utilise un ajustement linéaire échelonné de la vitesse de carbonisation, une épaisseur de la couche carbonisée de 7 mm dont la résistance et la rigidité sont supposées nulles, un coefficient de résistance égal à l’unité, un coefficient de durée d’application de la charge de courte durée, et des résistances spécifiées ajustées à leurs valeurs moyennes pour prédire les temps moyens de résistance au feu des éléments de murs et planchers de CLT qui suivent étroitement les temps réels de résistance au feu des éléments testés. Bien que certaines améliorations à cette méthode soient encore possibles, ces comparaisons suggèrent que la méthodologie prédit de façon prudente la résistance au feu des éléments de CLT.
Building regulations require that key building assemblies exhibit sufficient fire-resistance to allow time for occupants to escape and to minimize property losses. The intent is to compartmentalize the structure to prevent the spread of fire and smoke, and to ensure structural adequacy to prevent or delay collapse. The fire-resistance rating of a building assembly has traditionally been assessed by subjecting a replicate of the assembly to the standard fire-resistance test, (ULC S101 in Canada, ASTM E119 in the USA and ISO 834 in most other countries).
Massive wood elements such as solid sawn timbers, glued laminated timber (glulam) and structural composite lumber (SCL) can provide excellent fire-resistance. This is due to the inherent nature of thick timber members to char slowly when exposed to fire allowing massive wood systems to maintain significant structural resistance for extended durations when exposed to fire. Calculating the fire-resistance of massive wood elements can be relatively simple because of the essentially constant and predictable rate of charring during the standard fire exposure. Charred wood is assumed to no longer provide any strength and stiffness; therefore the remaining (or reduced) cross-section must be capable of carrying the load.
This report presents two (2) mechanics-based design procedures as alternative design methods to conducting fire-resistance tests in compliance with ULC S101 or to using Appendix D-2.11 of the NBCC, which is limited to glulam members stressed in bending or axial compression. The procedures are applicable to solid sawn timber, glulam or SCL structural members and aim at developing a suitable calculation method that would provide accurate fire-resistance predictions when compared to test data. The long-term objective is to provide recommendations for incorporating either method into CSA O86 and/or NBCC.
The comparisons between the proposed methodologies and the experimental data for beams, columns and tension members show good agreement. While further refinement of these methods is possible, these comparisons suggest that the use of the CSA O86 equations and a load combination for rare events adequately address fire-resistance design of massive wood members.
This report is divided into six (6) subsections related to different building performance attributes. It presents a review of current design provisions as well as an investigation and identification of gaps in current knowledge with respect to performance criteria for wood-based building systems.
Lastly, suggestions related to performance criteria are given with respect to, among others, structural, sound, vibration, fire, building enclosure, energy efficiency, durability and environmental performance. The development of such criteria is fundamental for reducing the burden on early adopters and AHJs in demonstrating regulatory acceptance of innovative building systems.
Currently, mass timber building designs commonly incorporate a concrete floor topping. This can improve building accoustics by increasing the mass of the assembly, reduce floor vibration and create a smooth flat surface to install finish flooring on. The installation of concrete requires formwork, pouring and finishing the concrete and time to cure which adds to project schedules. One way to address this is to use mass timber elements that are prefabricated with concrete toppings preinstalled. Replaceing the concrete floor toppings wiht dry alternatives, such as cement board, may also reduce construction timelines, while still ensuring adequate acoustic and vibration performance. Cement board needs only to be screwed in place and can be walked on immediately after installation; this reduction in construction time may reduce overall project costs and help make wood buildings more cost competitive than other types of construction.