The inherent nature of structural timber components to be charred slowly and at a predictable rate makes solid wood systems capable of maintaining significant structural capacity for extended periods of time when exposed to fire. Solid systems such as cross-laminated wood (CLT), glulam (GLT), nail-laminated timber (NLT) and dowel laminated timber (DLT) have prove that they can provide excellent fire resistance, often comparable to that of typical non-combustible heavy structures.
To facilitate greater acceptance of solid wood systems in international building codes, many topics still need to be studied. This session will cover the most recent topics related to fire safety for medium- and high-rise buildings.
Moderator : Christian Dagenais, FPInnovations, Canada
Tall Mass Timber Provisions in the 2021 I-Codes
Speaker: Jason Smart, American Wood Council, USA
Fire safety of CLT buildings
Speaker: Martino Negri, CNR Ivalsa Trento, Italy
European countries are harmonizing their respective codes and rules in trade, industry, environment, agriculture, food, and health—and the wooden building sector is within this process. The CEN (European standards body) has been producing a plethora of technical standards for sorting, grading, and characterizing wood, timber, adhesives, and the whole set of materials and products in the wood/building chain.
Even structural design in Europe is coordinated by the CEN. In recent years, it has been working to achieve further harmonization of the rules for structural design through implementation of the Eurocodes, with a view to ease of use and reduction in the adoption of nationally determined parameters. This is because national fire prevention codes are in force in many countries.
Until a few years ago, wooden construction in Italy represented a solution strongly linked to the geographic location. In many cases, the combustible nature of wood limited its use in the design and construction of buildings, which required compliance with strict fire safety codes. Buildings must provide an adequate level of protection for occupants and property in order to guarantee a safe exit and without becoming a source of danger.
The fire behaviour of the structural and finishing elements in wood is now known and predictable, thanks to the results of national and international scientific research. As well, experimental tests were carried out at the CNR laboratories, conducted on wall elements and a building in real scale composed of cross-laminated timber supporting structures. This represents a modern technology for resolving environmental and anti-seismic problems, as well as being a valid alternative to traditional constructions.
Fire Performance of Laminated Mass Timber Assemblies
Speaker: Lindsay Ranger, FPInnovations, Canada
Mass timber systems have many applications in medium- and high-rise construction. A significant amount of research has been done to demonstrate the safe fire performance of mass timber and its ability to meet various fire-related code requirements.
In Canada, the construction industry and the regulatory framework are becoming more accepting of wood construction, which is stimulating the realization of numerous wood projects. This has led to further research and development of innovative mass timber products which can be chosen for specific applications, based on their strengths, to ensure efficient design. Some of these mass timber systems were more commonly used decades ago, but their construction processes and design methods are being modernized for the current market.
The fire performance of CLT has been well studied, with a fire resistance calculation method available in the CLT Handbook. Several other types of mass timber products have recently been investigated for their fire performance, including nail-laminated timber (NLT), dowel-laminated timber (DLT), glued-laminated timber (GLT), screw-laminated timber (SLT), and cross-laminated veneer lumber (X-LVL). This presentation will focus on the results of full-scale fire resistance testing of these types of product and will also cover pertinent design considerations to ensure adequate fire safety.
Title to be confirmed
Speaker: Mathieu Létourneau Gagnon
Structural elements in a building must provide sufficient fire resistance to prevent collapse and provide safe means of evacuation for the occupants. In a building, the critical area often lies in connections, because they are responsible for transferring efforts between the main elements. Hybrid steel-wood connections in mass timber construction provide great strength and excellent ductility. However, under fire conditions, steel and timber behave differently and their interaction makes the assembly difficult to evaluate. Until now, designers have used the approach defined in CSA 086, which determines a charred layer around the exposed faces that will be reduced from the initial section of the element. It is presumed that metallic fasteners located within the remaining cross-section remain protected from fire and thus not affected mechanically. However, this approach does not consider failure modes and interactions between materials, e.g. localized heat transfer from the fasteners into the timber elements.
With new innovative fasteners such as self-tapping screws, design principles for connections have greatly changed. Thus, several research projects were carried out in the past years in order to increase the knowledge on the fire behaviour of these connections. Although a large amount of information is publicly available in the literature, it is often limited to short fire exposure (± 30 minutes), which is largely insufficient for buildings that need to provide 1-hour and 2-hour fire resistance ratings. The main objective of this research project is to model the fire performance of screwed-timber connections in order to develop design principles facilitating the determination of their level of fire performance.
Jason joined the American Wood Council in 2013 as manager of engineering technology. He is involved in a number of projects related to the fire performance, acoustics, and structural aspects of wood construction. Prior to joining the American Wood Council, he worked for the International Code Council’s Evaluation Service (ICC-ES), a subsidiary of the International Code Council (ICC), where he primarily evaluated new wood products and systems for equivalency and compliance with U.S. model code provisions. Jason also worked for three years at the Institute for Business & Home Safety as a project engineer/building code specialist prior to his tenure at the ICC-ES. He is a licensed professional engineer and a graduate of Virginia Tech with degrees in civil engineering as well as wood science and forest products. From 2017 to 2019, Jason provided technical support to the ICC Ad-Hoc Committee on Tall Wood Buildings regarding the development and execution of multiple fire test series which were deemed necessary to justify ICC code change proposals.
Martino Negri has a forestry degree from the University of Turin, doctoral studies at the University of Florence and has done post-doctoral work at École des Arts et Métiers in Cluny, France.
He leads the Wood Quality Lab at the Trees and Timber Institute – National Research Council CNR IVALSA, located in San Michele all’Adige, Italy. In the last years, the laboratory activities include work on timber quality, gluing, testing and wood quality, which led him toward research projects specifically dealing with Cross Laminated Timber in buildings such as Sofie (six-storey CLT building with full dimension seismic and fire testing), ChiQuadro (a wood school building), Made in Italy (light building elevation) and CNR Pisa (applied building site).
Lindsay Ranger is a Professional Engineer and has worked as a scientist at FPInnovations since 2010, conducting research on the fire performance of wood-based products and systems. Most of her work has related to understanding fire behaviour of mass timber for construction applications. She is a co-author of the fire design chapter in the Mid-Rise Wood-Frame Construction Handbook and the fire chapter in the new CLT Handbook. Ms. Ranger holds a master’s degree in fire safety engineering from Carleton University, where she is currently a Ph.D. candidate.
Mathieu holds a bachelor’s degree in wood engineering from Laval University, with a specialization in wood structure. Currently a master’s student in wood science at Laval University in the Chaire industrielle de recherche sur la construction écoresponsable en bois (CIRCERB), his research project focuses on the fire performance of screwed-timber connections using finite element modelling.