Cross-laminated timber has been used in buildings since the 1990s. In the last years, there has been a growing interest in the use of this technology, especially with the adoption of the product in increasingly taller buildings. Considering that the product is manufactured from a combustible material, wood, authorities that regulate the fire safety in buildings and the scientific community have carried out numerous research and fire tests, aiming to elaborate codes which contemplate the use of cross-laminated timber in tall buildings. This paper discusses the main results obtained from the fire resistance test of a cross-laminated timber slab carried out in the horizontal gas furnace (3.0 m × 4.0 m x 1.5 m) from the University of Sao Paulo. A vertical load of 3 kN/m2 was applied over the slab and the specimens were exposed to the standard fire curve for 30 min. In addition to the 30-min test, the research also evaluated the thermal behavior of the samples during the 24 h after the burners were turned off. Throughout the test, the slab maintained the integrity and the thermal insulation, and no falling-off of the charred layer was observed. However, the 24-h test indicated that it is mandatory to consider the loss of stiffness and strength of timber caused by the thermal wave observed during the decay phase.
Fire safety remains a major challenge for engineered timber buildings. Their combustible nature challenges the design principles of compartmentation and structural integrity beyond burnout, which are inherent to the fire resistance framework. Therefore, self-extinction is critical for the fire-safe design of timber buildings.
This paper is the first of a three-part series that seeks to establish the fundamental principles underpinning a design framework for self-extinction of engineered timber. The paper comprises: a literature review introducing the body of work developed at material and compartment scales; and the design of a large-scale testing methodology which isolates the fundamental phenomena to enable the development and validation of the required design framework.
Research at the material scale has consolidated engineering principles to quantify self-extinction using external heat flux as a surrogate of the critical mass loss rate, and mass transfer or Damköhler numbers. At the compartment scale, further interdependent, complex phenomena influencing self-extinction occurrence have been demonstrated. Time-dependent phenomena include encapsulation failure, fall-off of charred lamellae and the burning of the movable fuel load, while thermal feedback is time-independent. The design of the testing methodology is described in reference to these fundamental phenomena.
This paper provides understanding of the fire performance of exposed cross-laminated-timber (CLT) in large enclosures. An office-type configuration has been represented by a 3.75 by 7.6 by 2.4 m high enclosure constructed of non-combustible blockwork walls, with a large opening on one long face. Three experiments are described in which propane-fuelled burners created a line fire that impinged on different ceiling types. The first experiment had a non-combustible ceiling lining in which the burners were set to provide flames that extended approximately halfway along the underside of the ceiling. Two further experiments used exposed 160 mm thick (40-20-40-20-40 mm) loaded CLT panels with a standard polyurethane adhesive between lamella in one experiment and a modified polyurethane adhesive in the other. Measurements included radiative heat flux to the ceiling and the floor, temperatures within the depth of the CLT and the mass loss of the panels. Results show the initial peak rate of heat release with the exposed CLT was up to three times greater when compared with the non-combustible lining. As char formed, this stabilised at approximately one and a half times that of the non-combustible lining. Premature char fall-off (due to bond-line failure) was observed close to the burners in the CLT using standard polyurethane adhesive. However, both exposed CLT ceiling experiments underwent auto-extinction of flaming combustion once the burners were switched off.
Timber buildings can now stand very tall using new products. As timber materials are expected to be easily ignitable, the fire hazard of timber is a concern. Charring of the timber surface would maintain structural stability, but would also be accompanied by smoke. Although treating timber products with fire retardants would delay the ignition time under low radiative heat flux, toxic combustion products and unburnt fuel would be emitted immediately upon burning. More smoke and higher toxic gas concentrations such as carbon monoxide would be given off upon burning some fire retardants under high flashover heat fluxes. Due to the fast upward movement of smoke under stack effect, spreading of toxic smoke in tall timber buildings would lead to a hazardous environment. Engineered timber consists of derivative timber products. New engineered timber products are manufactured with advanced technology and design, including cross-laminated-timber (CLT), laminated veneer lumber (LVL) and glue-laminated timber (Glulam). The fire behaviour of timber products has been studied for several decades. However, the smoke hazards of using new timber products in building construction should be monitored. The objective of this study is to inspire stakeholders in fire safety of timber buildings, inter alia smoke hazards, to use new timber products to build tall buildings.
While taller mass timber buildings continue to capture worldwide attention, the University of Idaho chose to pursue a different type of innovation with the Idaho Central Credit Union Arena by showcasing wood’s impressive long-span capabilities. Inspired by the rolling hills of the nearby Palouse, the undulating wood roof of this sports and events facility soars over the open space below, creating a visually stunning structure not typically associated with large arenas.
This project is also unique in that it was built through a collaboration of Idaho stakeholders, using wood harvested from the University of Idaho’s Experimental Forest, made into glue-laminated timber (glulam) beams by Idaho manufacturers. “The complex structure makes a strong statement, not only for what mass timber can do, but also for what Idaho’s timber industry can do,” said Lucas Epp, Vice President and Head of Engineering for StructureCraft.
It is fairly common for mid-rise wood buildings to include shaft walls made from other materials. However, wood shaft walls are a code-compliant option for both light-frame and mass timber projects—and they typically have the added benefits of lower cost and faster installation.
This paper provides an overview of design considerations, requirements, and options for light wood-frame and mass timber shaft walls under the 2018 and 2021 IBC, and considerations related to non-wood shaft walls in wood buildings.
Since the publication of the first edition of this guide, substantial regulatory changes have been implemented in the 2020 edition of the National Building Code of Canada: the addition of encapsulated mass timber construction up to 12 storeys, and the early adoption of the related provisions by several provinces are the most notable ones. The 2022 edition of this guide brings together, under one cover, the experience gained from recently built tall wood projects, highlights from the most recent building codes and standards, and research findings to help achieve the best environmental, structural, fire, and durability performance of mass timber products and systems, including their health benefits. The approaches to maximizing the benefits of prefabrication and building information modelling, which collectively result in fast, clean, and quiet project delivery, are discussed. Methods for addressing limitations controlled by fire requirements (through an Alternative Solution) or seismic requirements (through a hybrid solution using an Acceptable Solution in steel or concrete) are included. How best to build with mass timber to meet the higher performance requirements of the Energy Step Codes is also discussed. What makes building in wood a positive contribution toward tackling climate change is discussed so that design teams, in collaboration with building owners, can take the steps necessary to meet either regulatory or market requirements.
Midply shear wall, which was originally developed by researchers at Forintek Canada Corp. (predecessor of FPInnovations) and the University of British Columbia, is a high-capacity wood-frame shear wall system that is suitable for high wind and seismic loadings. Its superior seismic performance was demonstrated in a full-scale earthquake simulation test of a 6-storey wood-frame building in Japan (Peietal.,2010). Midply shear wall, however, had limited applications due to its low resistance to vertical load and difficulty to accommodate electrical and plumbing services. For broader applications of Midply shearwall, these limitations needed to be addressed.
In collaboration with APA–The Engineered Wood Association and the American Wood Council (AWC), a new framing arrangement was designed to increase the vertical load resistance of Midply shearwalls and make it easier to accommodate electrical and plumbing services. Consequently, structural, fire and acoustic tests have been conducted to evaluate various performance attributes of Midply shear wall with the new framing configuration. This InfoNote provides a summary of the structural, fire and acoustic performance of Midply shearwalls from the tests.
Cross-laminated timber (CLT) is one of the most widely utilized mass timber products for floor construction given its sustainability, widespread availability, ease of fabrication and installation. Composite CLT-based assemblies are emerging alternatives to provide flooring systems with efficient design and optimal structural performance. In this paper, a novel prefabricated CLT-steel composite floor module is investigated. Its structural response to out-of-plane static loads is assessed via 6-point bending tests and 3D finite-element computational analysis. For simply supported conditions, the results of the investigation demonstrate that the floor attains a high level of composite efficiency (98%), and its bending stiffness is about 2.5 times those of its components combined. Within the design load range, the strain diagrams are linear and not affected by the discontinuous arrangement and variable spacing of the shear connectors. The composite floor module can reach large deflection without premature failure in the elements or shear connectors, with plasticity developed in the cold-formed steel beams and a maximum attained load 3.8 times its ultimate limit state design load. The gravity design of the composite module is shown to be governed by its serviceability deflection requirements. However, knowledge gaps still exist on the vibration, fire, and long-term behaviour of this composite CLT-steel floor system.
The load-bearing performance of sandwich bridge decks comprising a balsa core and fiber-reinforced polymer composite face sheets exposed to fire is a main concern regarding the application of these deck systems. In order to obtain the thermal responses of the balsa core exposed to fire, the temperature-dependent values of thermal conductivity and specific heat capacity are required. Furthermore, information about the char depth and charring rate and the temperature-dependent coefficient of thermal expansion is also needed for the subsequent thermomechanical modeling. In the current study, the effective thermal conductivity and specific heat capacity of balsa up to 850 °C were obtained from one-dimensional transient heat transfer models and experimental data using an inverse heat transfer analysis. The results showed that both properties depend significantly on the stages of combustion, direction of heat flow (in the tracheid or transverse direction) and density. Moreover, charring temperatures and rates were obtained, again as a function of direction and density. Finally, the coefficient of thermal expansion was measured in the transverse direction during evaporation and pyrolysis.
The building industry consumes a lot of material, which causes depletion of material stocks, toxic emissions, and waste. Circular building design can help to reduce this impact, by moving from a linear to a circular design approach.
To reach a circular build environment, all disciplines should be involved, including fire safety design. However, there is a contradiction between the objectives of circular and fire safety design, either affecting the aim of protection of material sources, or protection against fire risk.
Timber is a material that has high potential in contributing to a circular building industry, as it is renewable, recyclable and can store CO2. However, timber is combustible, which increases the risk of fire. Therefore, mass timber building design has traditionally been restricted by building regulations. To enhance mass timber building design research on timber buildings has increased, to allow understanding of the risks. However, yet general guidelines or understanding on the fire behaviour and risk in timber buildings is lacking. This is a problem for the fire safety design and the potentials of timber contributing to a circular building industry.
Until now, there was no specific method available that quantifies this relation between material use and fire risk in mass timber buildings. This limits the possibility of fire safety design and mass timber design to contribute to a more circular building industry. By creating a method that allows comparison between the economic and environmental impact of material use and fire risk, a well-founded choice of building materials is easier to make.
The design tool created in this research quantifies the impact on material use for fire safety measures relating to CLT, encapsulation and sprinkler availability and their effect on the fire risk in mass timber buildings. This way insight is provided between the balance of material use and fire risk. By the sum of the impact on material use and fire risk, the total “circular fire safety impact” value is calculated. This value represents the total economic and environmental impact of the design based on the choice of building materials. By changing the fire safety design, the most optimal design variant can be determined. This is the variant with the lowest total impact value.
This way, a circular design approach is used to steer fire safety design in mass timber buildings towards a design solution that does not only provide sufficient safety for people, but also provides maximum economic and environmental safety from a material point of view.
Mass timber continues to be a hot topic of discussion within the development industry in British Columbia. The International Building Code now allows for mass timber to be used for buildings up to 18 storeys. The change allows developers to consider it for residential multi-family projects and prompts one big question: “What will it cost to build my high-rise project with mass timber in our market?”
The team that developed this report represents an independent team of architects, structural engineers, quantity surveyors, and a general contractor. Consultants from fire, building code, and acoustic industries also provided expertise to the study. In late Fall 2020, we formed an industry group in Vancouver to answer this question with an exclusive focus on the local market. We identified a need for a significant shift in the local industry’s building philosophy when using mass timber as a structural material.
Our goal was to assess the viability of mass timber for this product type in British Columbia by comparing the cost, construction methods, and schedules of a typical concrete high-rise in Vancouver to those for the same building using mass timber as the principal structural material. To undertake the study, the group created virtual models of the base building and conceptual models for side-by-side detailed comparisons.
While gaining in popularity, building a high-rise with engineered mass timber remains an unconventional method in British Columbia. To support the industry, we wanted to fill in gaps in data to better understand and help solve the challenges of working with new materials and techniques needed for mass timber construction at scale.
This study presents what we learned about cost, schedule, and code implications as well as methodology efficiencies. It must be noted that the study took place over a period in Q2 and Q3 of 2021 when lumber and steel prices – two of the principal materials – experienced high volatility in supply and record increases in price.
Since every building project and market is unique, the report makes no claims concerning specific cost or time frame. Rather, it identifies what to consider in creating a reliable framework for optimizing costs and schedules while meeting code requirements when building residential high-rise mass timber buildings.
Mass timber is gaining momentum in the US, with developers interested in exploring the technology as a solution for their projects—especially as the material is now code-approved for up to 18 stories. Yet, the Architecture, Construction and Engineering (AEC) industry is notably hesitant to adopt new building methods. The primary obstacle preventing developers from committing to mass timber is the associated risk that results from uncertainty and unfamiliarity with these systems. To address this, Generate has partnered with a seasoned consortium of mass-timber specialists: Swinterton’s Timberlab; KL&A Engineers and Builders; Niles Bolton Associates; Jordan & Skala Engineers; Waugh Thistleton Architects; Mass Timber Strategy; Olifant LLC; and WoodWorks. The team established that the main obstacles holding back mass timber from widespread use are:
1. Costs: Project stakeholders do not have cost data on which to base rule-of-thumb estimates of construction and operational costs. The US timber supply chain, lacking demand, fails to become a mature, reliable, and cost-effective industry.
2. Constructability: General Contractors are often unfamiliar with the means and methods to build mass timber and are unwilling to rely on a new supply chain. Project stakeholders are concerned by the upfront effort needed for the implementation of innovative, sustainable systems.
3. Design Limitations: Stakeholders do not have experience with mass timber structures to compete in the residential market against concrete/steel. Architects struggle to find compatible floor assemblies with acoustic and fire properties and lack the know-how to design efficient lateral systems.
Certainty and predictability are needed in the mass timber construction space. An open-source, code-compliant, cost-effective, replicable system developed by an industry-leading consortium will streamline cost analysis and supply chain integration to enable large-scale deployment across the US. The target market for the proposed system will be the US multifamily sector in the 7-12 story range, which accounts for a total addressable market of 200M sf/year. The system will be designed for the major housing markets of Boston, Atlanta and Denver, and will serve as a template for the AEC industry.
Forest Service/USDA Wood Innovations Grants
Recipient Point of Contact: Stefan Schneider
Location: Portland, Oregon
CutMyTimber, a wood and mass timber fabricator since 2010, is seeking funding to research and develop a Modular Mass Timber Skeleton (MMTS) system with accompanying software. Mass timber includes innovative and structurally engineered wood products such as glue-laminated beams (GLB) and cross-laminated timber (CLT). Glulam beams consist of layers of dimensional lumber, bonded together with moisture-resistant adhesives. Pound for pound, this product is stronger than steel. Despite growing interest among builders and investors, developing a mass timber building currently involves too much time and uncertainty due to lack of knowledge and experience. Our team will draw from two decades worth of experience in successful mass timber projects to develop a system of standard and engineered connections that will be made available to the industry.
The project goals are to:
(1) research and optimize a standard, yet modular, skeleton system of glulam and connection hardware based on potential load scenarios, number of levels in the structure, grid distances, etc.
(2) produce an available design guide detailing standardized, engineered solutions
(3) review and obtain structural approval of all standard connection types by partnering with engineers and fire safety and code compliance experts
(4) develop and release the MMTS system in an intuitive and free-to-use software tool in partnership with software designers. This will be made available for early-stage design by the mass timber industry.
CutMyTimber expects the MMTS system will reduce the market barriers of risk, time, and cost of mass timber projects at all levels, including design, engineering, fabrication, and installation. In turn, we expect to stimulate and expand opportunities for the mass timber building market in the United States.
Forest Service/USDA Wood Innovations Grants
Recipient Point of Contact: Karl R. Englund
Location: Pullman, Washington
The durability of wood has always limited mass adoption into many markets. With CLT, wood’s perceived ineffective performance when exposed to bio-deterioration and fire has many customers hesitant to commit to a mass timber structure. Our project will evaluate a commercial ready process to pretreat the lamstock of CLT panels with a variety of borate-based treatment options. By treating the lamstock prior to CLT fabrication, a more homogeneous treatment is realized, making a more durable panel that can be implemented in areas prone to high humidity and mitigate risks associated with durability. Our work will provide a commercial-ready solution that can be easily implemented in-line, lowering costs and not interrupting process flows or outputs.
Fire safety greatly contributes to feeling safe, and it is a key parameter for the selection of building materials. The combustibility of timber is one of the main reasons to have the strict restriction on timber for use as a building material, especially for multistory buildings. Therefore, the main prerequisite for the use of timber in buildings is to ensure adequate fire resistance, using passive and active fire protection measures. This article contains the results of mechanical and fire experimental tests of both normal and innovative hollow glued laminated timber beams. A total of 10 timber beams were tested at ambient temperature, and 3 timber beams in fire conditions, which differed in cross-section type but also in the applied fire protection. The first beam was a normal GL beam without fire protection, the second a hollow beam covered by intumescent paint, while the third was also hollow, additionally protected by mineral wool infill inside the holes. The load-carrying capacity of the hollow beam in ambient conditions was estimated at 65% of the load-carrying capacity of a normal GL beam. Fire tests indicated that hollow timber beams with both intumescent paint and mineral wool infill failed at a similar time as a normal GL beam without fire protection. One-dimensional ß0 and notional charring rates ßn were obtained. Time to the protective material failure was 17 min. The main cause of failure of hollow beams was the appearance of delamination due to the reduction of the lamella bonding surface.
Products derived from trees have been used by mankind for thousands of years, where timber has a long tradition as an ecological construction material. There is currently an increasing trend in multi-storey timber buildings, because of the projected growth in the demand for housing in urban areas between now and 2050, along with the urgent need for a more sustainable and productive construction industry. The construction of these buildings is now possible thanks to the new advances in architecture, engineering, and construction (AEC) and the new technological developments around timber construction. Its industrialization requirements imply a paradigm shift for the construction industry, which requires, among other aspects, the early and collaborative integration of stakeholders in its design and construction process. According to this, the objective of this review article is to determine the main advances and limitations related to the design and construction of multi-storey timber buildings, categorizing them in aspects such as sustainability, engineering and construction sciences, and collaborative design. The methodology of this article was based on the review of 266 articles published in Web of Science (WoS), as indexed scientific journals, between 2017 and mid-2022, performing a comparative and cooccurrence analysis of the contents. The results evidenced that 73% of the articles showed advances and limitations corresponding to the engineering and construction sciences category, 23% to sustainability, and the remaining 4% to collaborative design. The main advances in the development of multi-storey timber buildings are related to seismic analysis, connections design, fire performance, and fire design. While the main limitations are related to social sustainability, the results are not conclusive due to the low number of publications that support them.
The construction industry is one of the largest producers of greenhouse gases, accounting for 38% of global carbon emissions. Recently, interest in mass timber construction has grown, due to its potential benefits in reducing environmental impact compared to traditional construction methods that use steel and concrete, and in promoting global sustainability and climate agendas, such as the Sustainable Development Goals (SDGs) and global net-zero emissions by 2050. Despite the slow adoption of mass timber construction (MTC) in Australia, some innovative and iconic projects and initiatives have been realised. The research intends to identify critical challenges and potential for broader adoption of MTC in Australia. The study reviewed selected MTC projects, followed by a perception survey and interviews of the relevant industry stakeholders in Australia to understand the key barriers and enablers for the widespread application of MTC in Australia. Significant challenges identified in the research include a lack of understanding of fire safety, regulations, performance, inherent application, and local manufacturers and suppliers, which are yet to be improved. In addition, it was found that prior experience built confidence in the application of MTC. Furthering widespread adoption of MTC technology in Australia beyond cost competitiveness requires the Australian construction industry to work towards developing suitable regulatory and insurance policies, financing, incentivising clients, and a skilled workforce. The study focuses on an investigation in the context of industry perceptions of MTC in Australia. Based on the analysis of the critical characteristics of MTC projects, and using the empirical data, the study identifies key challenges and opportunities in the widespread application of MTC in Australia.
This InfoNote summarizes the verification and validation that the current design requirements of Annex B of CSA O86 can also be applied to small framing members used in unprotected and protected lightweight wood-frame assemblies, e.g., walls and floors. With minor editorial changes, the scope of application of Annex B of CSA O86 could include all wood and wood-based products listed in CSA O86, regardless of their original and residual dimensions.
Wood is commonly used in construction, but often perceived as being less safe than structures made from non-combustible materials. With the advancement of wood products and treatment, construction techniques, and protective systems, this may not be the case any longer. Using retrospective data from fire departments across Canada, this study aimed to determine whether the type of construction material (combustible or non-combustible) affected the fire severity outcome of a one to six storey apartment building fire, after accounting for protective systems (smoke alarms and sprinklers). The study found that, after adjusting for the presence of smoke alarms and sprinklers, structures constructed from non-combustible construction materials did not perform better in terms of injuries, requiring extinguishment by fire department, or the fire spreading beyond the room of origin. The presence of working smoke alarms and sprinklers played a central role in reducing the severity outcome of a fire. Smoke alarms and sprinklers both reduced the odds of extinguishment by the fire department and the fire spreading beyond the room of origin. Sprinklers also reduced the injury rate. Overall, this study highlighted the importance of protective systems in reducing fire severity outcomes.