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An Overview of CLT Research and Implementation in North America
Abstract
Although not yet seen as common practice, building with cross laminated timber (CLT) is gaining momentum in North America. Behind the scenes of the widely publicized project initiatives such as the Wood Innovation Design Centre Building in Canada and the recent U.S. Tall Wood Building Competition, substantial research, engineering, and development has been completed or is underway to enable the adoption of this innovative building system. This paper presents a brief overview of the current status of CLT building development in North America, highlighting some recent U.S. and Canadian research efforts related to CLT system performance, and identifies future CLT research directions based on the needs of the North American market. The majority of the research summarized herein is from a recent CLT research workshop in Madison, Wisconsin, USA, organized by the USDA Forest Products Laboratory. The opportunity and need for coordination in CLT research and development among the global timber engineering community are also highlighted in the conclusions of this paper.
... However, in the U.S., this material is still gaining momentum. Since the introduction of mass timber materials into North America in the mid-2000s, some advancement has been made to empower pilot building projects in the U.S. and Canada using this new material, despite a lack of comprehensive streamlined building code adoption (Pei et al., 2016). SmartLAM in one of the U.S. manufacturers that has been producing locally sourced mass timber panels since 2012. ...
... The development of a product standard is one of the first steps needed to introduce a new product (Pei et al., 2016). While CLT manufacturers in Europe adopted a proprietary approach for panel mechanical properties, the first performance-based CLT material standard for CLT in North America was developed through the collaboration of APA-The Engineered Wood Association and FPInnovations (Borjen et al., 2012). ...
... North American CLT manufacturers have been gradually adopting this standard, with Structurlam, Nordic and the DR. Johnson Lumber Company being the first North American CLT manufacturers to obtain the APA certification (Pei et al., 2016). FPInnovations have developed a handbook for the design of timber building and provided directions needed for the design of wood buildings in terms of plans and specifications (Karacabeyli and Lum, 2014). ...
Timber has been considered a promising building material because of its structural rigidity, environmental sustainability, and renewability nature. In Europe and Australia, timber materials have been used for many different types of construction such as residential, commercial, education, and industrial. However, in the U.S., familiarity with timber products is gaining momentum. The construction practitioners are still reluctant to consider mass timber as a mainstream building material. A limited number of case study projects make it difficult for industry personnel to evaluate the actual construction feasibility of mass timber. As a result, a significant knowledge gap has been created that hindering the progress of mass timber material in the U.S. construction industry. To help solve the problem, this study aims to identify the existing awareness level among the U.S. building constructors regarding mass timber building materials. It further determines some of the major construction-related difficulties of mass timber buildings and recommendations to overcome those difficulties to increase the acceptance of this material. The study performed a semi-structured questionnaire survey to carry out statistical analysis regarding mass timber building material. Analysis of descriptive statistics suggested that the level of awareness and involvement by the U.S. construction practitioners in mass timber building is still significantly low as 55% of the participants indicated no experience on mass timber building construction projects. Qualitative data analysis suggested that lack of experience in timber construction, poor coordination among the project parties, design-related difficulties, and high cost of mass timber panels are the biggest construction-related barriers to adopt this product. To overcome the existing difficulties, the study proposed an increasing number of timber building projects and manufacturing plants, effective early collaboration among the project parties, developing skilled workers, and a nation-wide promotion by the owners and the architects. The outcomes of this study will be helpful for the industry practitioners and the owners to adopt mass timber as a mainstream building material. The study will further increase the acceptance of this material in the U.S. construction industry.
... In the U.S. market, the concept of mass timber building has been progressed by demonstrating a few pilot projects, although a lack of well-defined code has always remained a key concern (Pei et al. 2016). The first performance-based standard for mass timber building in North America was developed by a shared exertion between APA-The Engineered Wood Association and FPInnovations (Borjen et al. 2012 (Karacabeyli and Lum, 2014). ...
... However, in the U.S., this material is still gaining momentum. Since the introduction of mass timber materials into North America in the mid-2000s, some advancement has been made to empower pilot building projects in the U.S. and Canada using this new material, despite a lack of comprehensive streamlined building code adoption (Pei et al., 2016). SmartLAM in one of the U.S. manufacturers that has been producing locally sourced mass timber panels since 2012. ...
... The development of a product standard is one of the first steps needed to introduce a new product (Pei et al., 2016). While CLT manufacturers in Europe adopted a proprietary approach for panel mechanical properties, the first performance-based CLT material standard for CLT in North America was developed through the collaboration of APA-The Engineered Wood Association and FPInnovations (Borjen et al. 2012 to obtain the APA certification (Pei et al., 2016). ...
Mass timber has been considered as a promising building material because of its structural rigidity, environmental sustainability, and renewability nature. In Europe and Australia, mass timber materials have been used for many different types of construction such as residential, commercial, education, and industrial. However, construction practitioners in the U.S. are still reluctant to consider mass timber as a mainstream building material. A limited number of case study projects make it difficult for industry personnel to evaluate the actual construction feasibility of mass timber. As a result, a significant knowledge gap has been created that is hindering the progress of mass timber material in the U.S. construction industry. To help solve the problem, this dissertation utilizes a range of research methodologies and data analysis techniques to evaluate the feasibility of mass timber building materials in the US construction industry. The dissertation focuses on four major objectives that will help industry practitioners to adopt mass timber as a mainstream building material. The first objective of the study is to determine the existing perception of the industry practitioners
... First developed in Europe in the 1990s, CLT has only recently been introduced in the North American building market. The first CLT manufacturers in North America started production in 2010 in Canada, followed by the U.S. in 2012 and 2015 (Pei et al., 2016). Thanks to the collaborative efforts of research entities and industry professionals (Pei et al., 2016), the first North American CLT Handbook was released in 2011 (Gagnon & Pirvu, 2011). ...
... The first CLT manufacturers in North America started production in 2010 in Canada, followed by the U.S. in 2012 and 2015 (Pei et al., 2016). Thanks to the collaborative efforts of research entities and industry professionals (Pei et al., 2016), the first North American CLT Handbook was released in 2011 (Gagnon & Pirvu, 2011). The handbook provides fundamental information and design guidelines for designers and builders working with CLT. ...
... Collaboration with researchers and academia is another component defining knowledge transfer and management mechanisms. This collaboration has been of particular relevance both for the early adoption and the evolution of mass timber and CLT construction in Europe (Schickhofer, 2011), as well as for the diffusion of this technology outside of its native context (Pei et al., 2016). ...
Mass timber construction systems, such as cross-laminated timber (CLT), which originated in Europe, are gaining acceptance within North America as a viable alternative to multi-story steel-frame or concrete structures. The purpose of this study is to analyze types of innovation in the design of the building enclosure precipitated by the introduction of CLT in the North American market. Additionally, knowledge management and transfer mechanisms supporting the use of CLT in the field are investigated through the analysis of case examples. A number of factors are identified that characterize the implementation of innovation in mass timber building enclosure, among which is the interplay of structural and enclosure design in those elements at higher risk of moisture intrusion. These system innovations required concurrent design collaboration dynamics and effective knowledge management among the different project’s stakeholders and partners. This analysis can contribute to a better understanding of the current state of practice in architectural design, as well as in the mechanisms supporting knowledge management and R&D initiative in an emerging construction market.
... Among wood products, cross-laminated timber (CLT) is gaining momentum in the global market (Pei et al., 2016). CLT is an engineered wood panel consisting of three or more odd number of plies orthogonally arranged on top of each other and glued together. ...
... It was only in the early 2000s that CLT was introduced to North America. Since then, cross-laminated timber gained some momentum in North America, but it is not a common practice yet (Pei et al., 2016). Using CLT offers architects and engineers the opportunity to construct large scale mass timber buildings (Grasser, 2015). ...
Modular construction is being touted as one solution to address project delays and cost overruns in the construction industry. Modular construction is a delivery method wherein building components are prefabricated off-site and then transported to the job site for assembly. Thus, prefabrication is a significant element of modular construction that enables work to happen in parallel to accelerate project schedules, enhance safety, and reduce physical work on-site. Timber is becoming a primary material for prefabricating elements since wood is a renewable material, possesses high strength-weight ratio, and sequesters carbon. The use of wood in the form of cross-laminated timber (CLT) introduces new opportunities but also logistical issues in the supply chain from forest to the manufacturing facility to the construction site. Depending on the type of CLT and the level of modularity (i.e., 2D elements or volumetric), major constraints in this process have been identified including (1) fluctuation in the supply of raw wood to manufacturing facilities, (2) limitations in the capacity to create CLT panels, (3) shipping limitations based on allowable loads, and (4) crane availability for assembly of panels on the site. This paper explores the use of simulation models to study the effect of these logistical constraints in modular construction using prefabricated CLT on the total time and hence cost of projects. Specifically, discrete event simulation (DES) will be used to model CLT logistics to identify bottlenecks and provide sensitivity analyses of variables such as lumber supply, travel times, and manufacturing plant capacity on project cost and time. A case study of modular multi-story building construction is examined to showcase the utility of the developed simulation framework. It is expected that simulating modular CLT logistics will enable the identification of optimal strategies towards their successful implementation.
... In North America there has been a recent surge of interest and investment in advancing the use of mass timber construction at the mid-to high-rise scale [1]. Although engineered wood products, such as glued laminated (glulam) and cross laminated timber (CLT) are not novel materials, the building systems, construction practices, and site contexts in which they are being employed sometimes are. ...
... Therefore, hygrothermal monitoring of different moisture-sensitive materials can be required in a building, and for each material/product the most suitable measurement technique should be selected, considering material-specific features, moisture response, and potential effects on short-and long-term performance of the structure. This paper, which focuses specifically on the early stages of implementation of a hygrothermal monitoring study of the Forest Science Complex at Oregon State University, has three primary aims: (1) to share observations of the hygrothermal performance at a few critical locations during construction; (2) to illuminate the monitoring methodology and discuss future improvements; (3) to disseminate results that are practicable to the mass timber industry. ...
There are currently no standards regulating water management for mass timber elements during construction, little knowledge of impacts of moisture exposure (wetting and drying performance, dimensional stability, checking), and few precedents serving as guidelines for monitoring moisture response of mass timber. To address these gaps, a hygrothermal monitoring study was devised to track moisture performance of U.S. made cross laminated timber (CLT) and glulam at a three-story mass timber building. This paper discusses moisture measurements that were collected during the first six months of construction at a CLT rocking shear wall and a timber floor connection. Despite the limited number of structural systems monitored during construction, the distribution and number of sensors in these elements allow to draw some important conclusions. The data confirmed that moisture distribution and wetting/drying rates varied based on local conditions and details (aspect, coatings, connections, etc.), with measurements at an uncoated, north-facing area showing the highest moisture levels (reaching fiber saturation at multiple ply depths and locations). Most locations rarely exceeded 16% moisture content for more than a few months. Certain moisture-trapping details consistently showed higher moisture levels (i.e., above 16%) and poorer drying. Some interior plies continued to show slow increases in MC even after months of drying conditions. These observations suggest preventative approaches implementable in the design (e.g., avoiding moisture trapping details), during fabrication (e.g., localized coating), and construction (e.g., sequencing installation to minimize exposure and allow drying).
... an attractive material for the sustainable construction industry. An engineered wood product, although incepted in Europe, now is also gaining momentum on the North American market [29]. The large amounts of forest in North America provide savings in the cost of mass CLT production. ...
... CLT has been considered as a sustainable material due to the renewable characteristics of timber, its major component. CLT also has the ability to turn lower value wood stocks into high-value product and foster economic development in rural communities [29]. Apart from that, there are several other aspects that has been identified as significant advantages of CLT over conventional concrete and steel structure such as high thermal insulation properties, cost effectiveness, environmental friendliness, design flexibility, and production of less waste during construction [32]. ...
... ANSI/APA PRG-320 [170] specifies requirements for lamination and adhesive materials (referring to existing adhesive standards), as well as methods of testing and quality assurance. It does not include NLT or CLT products manufactured without adhesive face bonds [194]. Following the Janssens investigation, Annex B of the 2018 version of ANSI/APA PRG-320 was developed. ...
Existing practices for the fire design of mass timber buildings based
on traditional fire resistance frameworks previously developed for
non-combustible enclosures are inadequate. The contribution of mass
timber surfaces to a fully developed enclosure fire is coupled to the
design fire such that timber charring rates determined from standard
fire resistance tests or parametric time temperature relationships may
not apply. This is particularly important when considering structural
fire performance of tall mass timber buildings.
This thesis describes a theoretical fire model for calculating the
thermal environment within enclosures constructed from fully or partially
exposed mass timber elements such as cross-laminated timber.
The fire model includes two new pyrolysis submodels to enable calculation
of the mass loss rate, energy release and char depth within
wood surfaces burning in the enclosure. Phenomena such as debonding
of lamellae in engineered wood panels is included and discussed.
The pyrolysis submodels are coupled to the two-zone fire model BRISK
enabling the fire dynamics in small mass timber enclosures to
be predicted. Model predictions for heat release rate, gas temperatures
and/or char depths are compared with data from 19 full-scale
fire experiments previously published in the literature.
The thesis also describes a submodel for predicting the enclosure
thermal enhancement and ventilation effects on the mass loss rate of
a burning fuel package. Model predictions have been evaluated with
good agreement for an inert reduced-scale enclosure based on a series
of heptane pool fires and a series of upholstered chair fires in a
full-size enclosure. The application of the submodel to mass timber
enclosures in combination with the previously developed pyrolysis
submodels is discussed however additional experiments with well
characterised fuel sources are required to more thoroughly evaluate
this feature of the model. Potential applications of the model include
generating thermal boundary conditions for a more advanced thermal/
structural finite element code and for deriving modified fire load
energy density values applicable to mass timber for use in simplified
fire severity formula.
It is concluded that where mass timber structures must be designed
to ’not collapse’ in fire then satisfying prescriptive time periods in
standard fire resistance tests is not sufficient. The fire performance
of these structures need to be specifically engineered considering the
expected fire growth, duration and decay periods. This requires a coupled
interaction between the moveable fire load and the combustible
enclosure surfaces to be considered.
... In addition, CLT also had been utilized in constructions of bridges [20]. Further discussion on the development of CLT research and its implementations are available elsewhere (e.g., [9,18,21]). (b) applied as stairs [23] In addition to laminas as raw materials, adhesive is a key factor to achieve a good quality of CLT products. ...
Cross-Laminated Timber (CLT) has been gaining interest in recent years as an attractive and environmental-friendly building material. As such, CLT has been used for structural components in building constructions such as apartments, commercial buildings, or offices. CLT predominantly uses newly harvested lumber as a raw material. In this study, however, CLT fabricated using recycled wood was explored for possible utilization in wood structures. The recycled wood was obtained from wooden boxes, wooden pallets, and scrap wood from lumber suppliers, and their mechanical properties were tested. The average tension-parallel-to-grain strength of these recycled woods was 52.2 MPa, while their average compression-perpendicular-to-grain and compression-parallel-to-grain strength were 20.6 and 4.0 MPa, respectively. Four CLT beams of 2 m-length, 100 mm-width, and 130 mm-depth glued with epoxy adhesive were tested to measure their flexural strengths. A set of two CLT beams was loaded on upright and lying positions, and their average flexural strengths were 8.1 and 7.6 MPa, respectively. The effects of lamina lap splices and adhesives on CLT beam flexural strength were studied. Apparently, adding several variations of lap-splices and adhesives has marginal impact on CLT beam flexural strength.
... The last decade has been marked with a rise in interest and use of mass timber construction in North America (Pei et al., 2016). This rise is driven by a range of innovative wooden structural products such as cross-laminated timber (CLT) (Gagnon and Popovski, 2011), mass plywood panel (MPP) (Freres, 2018), and more traditional wooden products such as glued laminated timber (GLT). ...
Mass timber construction has been gaining momentum in multi-story residential and commercial construction sectors in North America. As taller mass timber buildings are being planned and constructed, in-situ dynamic tests of this type of construction can be performed to further validate their design and use. As part of this larger effort, an in-situ dynamic characterization testing campaign based on ambient vibration measurements was conducted on a recently constructed four-story mass timber building located in Portland, Oregon. The building features cross-laminated timber (CLT) floors, a glued laminated timber (GLT) framing gravity system, and light-frame shear walls and steel HSS hold-downs that compose the lateral resisting system of the building. Ambient vibration acceleration testing data were collected using 18 accelerometers that were wired to a portable data acquisition system in two experimental setups. Approximately 2 h of bi-directional horizontal acceleration data were recorded. In this paper, two operational modal analysis methods are used for estimating the modal parameters (frequency, damping, and mode shapes) based on the data collected. In addition, a multi-stage linear Finite Element (FE) model updating procedure is presented for this building type and the FE estimates of frequencies and mode shapes are compared to estimates from the collected data. The calibrated FE model provides confidence to the operational modal results and presents a comprehensive modal characterization of the building. At ambient levels of excitation, the developed FE model suggests that stiffness of the non-structural elements, such as the exterior wall cladding, and glazing affects the modal response of the building considerably. Lessons learnt on this unique and first of a kind four-story structure constructed in the United States and implications for taller mass timber buildings are summarized and provide valuable insight for the design and assessment for this building type under future dynamic excitation events.
... While large scale production of CLT was established in Europe in the early 2000s, Structurlam and Nordic Structures in Canada became the first North American manufacturers of CLT more recently in 2010 (Pei et al., 2016a). As a result, the majority of tall CLT buildings have been constructed in Europe. ...
In response to the global drive towards sustainable construction, cross-laminated timber (CLT) has emerged as a competitive alternative to other construction materials. Despite the construction of CLT buildings up to 10 storeys in areas of low seismicity, few multi-storey CLT buildings have been constructed in areas of moderate to high seismicity due to lack of knowledge regarding their performance under lateral loading. Previous experimental studies of the behaviour of CLT wall systems under lateral loading have been limited to replicating the conditions within multi-storey buildings with approximately three storeys, and most wall systems tested replicated ground floor wall systems. To develop an understanding of how taller CLT buildings would behave under lateral loading, for the first time, testing of CLT wall systems replicating conditions within buildings taller than three storeys was undertaken. In this study, wall systems representative of those within a 10 storey CLT building were experimentally tested; an above ground floor wall system was subjected to monotonic lateral load and constant vertical load, with vertical loads replicating gravity loads at storeys within a 10 storey CLT building. The results obtained suggest variable behaviour of wall systems throughout multi-storey CLT buildings, with lateral movement becoming significant at higher storeys.
... If the number of CLT is sufficiently large, the compressive strength parallel to the grain of the lamina in different layers is equal to each other as f c as shown in Formula (11). Thus, the Formula (10) can be written as Formula (12). ...
The compressive strength in the major direction of cross-laminated timber CLT is the key to supporting the building load when CLT is used as load-bearing walls in high-rise wood structures. This study mainly aims to present a model for predicting the average compressive strength of CLT and promoting the utilization of CLT made out of planted larch. The densities and compressive strengths of lamina specimens and CLT samples with widths of 89 and 178 mm were evaluated, and their relationship was analyzed to build a prediction model by using Monte Carlo simulation. The results reveal that the average density of the lamina and CLT were about equal, whereas the average compressive strength of the CLT was just about 72% of that of the lamina. Width exerted no significant effect on the average compressive strength of the CLT, but homogenization caused the wider CLT to have a smaller variation than that of the lamina. The average compressive strength of the lamina could be calculated by using the average density of lamina multiply by 103.10, and the average compressive strength of the CLT could be calculated according to the compression strength of lamina in major and minor direction, therefore, a new prediction model is determined to predict the average compression strength of CLT by using the average density of lamina or CLT, the average compression strength of CLT made in this study is about 74.23 times of the average density of the lamina. The results presented in this study can be used to predict the average compressive strength of CLT by using the average density of lamina and provide a fundamental basis for supporting the utilization of CLT as load-bearing walls.
... Currently a body of mixed research is emerging on CLT and mass timber performance that is elucidating important design parameters, including those pertaining to engineering mechanics, connection and fastener behavior, moisture adsorption/desorption, fire, and vibration performance [e.g. 1,2]. Valuable information that informs design standards and practices is gained both from laboratory testing of materials and systems, as well as from measuring asbuilt performance of structures. ...
Currently, design of tall wood buildings is generally accomplished
in the USA through the so-called alternate means process, with
requires extensive testing, engineering analysis, and a stringent
peer review process. As it pertains to cross-laminated timber (CLT),
it is critical to develop effective performance prediction models,
through laboratory testing elaborating on material behaviors (e.g.
hygrothermal, vibrational, etc.) as well as monitoring data on the
mid- to long-term performance of timber structures in situ. This
paper presents the scope and preliminary outcomes of a project
aiming to cross reference laboratory research and in-situ monitoring
to establish a holistic performance-monitoring protocol for mass
timber buildings; this protocol can later serve to define standards for
mid- to long-term monitoring as well as to develop guidelines for
the design of mass timber structures.
... Innovative materials, systems, and connectors are contributing to the resurgence of wood as a material in sectors beyond low-rise residential construction. On the material level, the most notable development has been the introduction of CLT, which is increasingly being used in the residential and commercial mid-rise building sectors [5]. The cross-layered build-up of CLT panels makes for a dimensionally stable, stiff, strong, light and multifunctional construction material, suited for supporting in-and out-of-plane loads; it can be used for the realization of walls, floors, and cores, and can be easily connected to other members or structural materials [6,7]. ...
This paper presents an experimental study to evaluate the use of spatially arranged self-tapping screws (STS) as shear connections for cross-laminated timber panels. Specifically, simple butt joints combined with crossed STS with different inclinations were investigated under quasi-static monotonic and reversed-cyclic loadings. The influence of the number and angle of insertion of screws, screws characteristics, friction and loading on the joint performance was explored. The yield load, load-carrying capacity and related slips, elastic stiffness, and ductility were evaluated considering two groups of tests performed on a total of 63 specimens of different size. Performance of connections with respect to the energy dissipation and loss of strength under cyclic loads was also investigated. It was shown that the spatial insertion angle of screws plays a key role in the performance of joints, not only because it relates to the shank to grain angle, but also because it affects the amount of wood involved in the bearing mechanism. Design models of STS connections are presented and discussed, and the test results are compared against analytical predictions. While good agreement for load-carrying capacity was obtained, the existing stiffness model seems less adequate with a consistent overestimation.
... Analytical models for mid-rise CLT buildings allowed for performing non-linear dynamic analyses to determine adequate seismic force reduction factors for CLT structures [26,27]. Based on this research, seismic design provisions for platform-type CLT construction were developed and implemented in CSA O86 [15]. ...
... More studies are necessary to evaluate the fire behavior in such structures especially in the decay phase. Code acceptance is a time-consuming process, and research and standardized design methods are still in progress in North America [70] . The Ad Hoc Committee on Tall Wood Buildings (AH-TWB) started in late 2015 to address concerns regarding the mass timber construction, and proposed changes to the next version of IBC to be published in 2021. ...
The Society of Fire Protection Engineers (SFPE) provided a case study specification for a performance-based design of a high-rise building using cross-laminated timber (CLT), which will be presented in the 12th International Conference on Performance-Based Codes and Fire Safety Design Methods in Honolulu, Oahu, Hawaii on April 23-27, 2018.
The performance-based analysis include the building description, performance criteria, floor plans, trial designs, and final design document. The prescriptive building and fire codes governing this project include the 2015 International Building Code (IBC) and 2015 National Fire Protection Association (NFPA) 101 Life Safety Code. The structural design for the CLT wood framing members is in accordance with the American Wood Council (AWC) 2018 National Design Specification for Wood Construction (NDS). The SFPE Engineering Guide to Performance-Based Fire Protection was also used for the framework of the final report.
The 32-story, 93-m (305-ft.) tall building, located in a financial district of Charlotte, NC, is residential with retail incorporated on the ground floor and two carpark levels below ground. The target market for the building is members of the gig economy and maximizes transient use. The building owner has requested the highest possible environmental standard of sustainability for the project and Occupant Evacuation Elevators (OEE) for emergency situations. The structural behavior of the CLT during a fire event is addressed, and there is an architectural design feature exposing parts of the CLT.
The Tower is designed as a mixed-use structure, including the following occupancy classifications: Assembly, Business, Mercantile, Storage, and Residential. The target market for the Tower is members from the gig economy – transient workers with short-term positions. In addition, the Tower incorporates a green (sustainable) design. The Leadership in Energy and Environmental Design (LEED) 2009 Green Building Rating System for New Construction is used to evaluate the environmental performance, from a whole building perspective, of the Tower.
CLT has numerous advantages over other typical construction materials; yet, public perception and current code restrictions in the United States limits the construction of buildings higher than 6 stories (75 ft.). Thus, building is designed the way that meets the fire safety goals and objectives, including:
Protecting occupants (transient, permanent, and staff) against fire incidents
Protecting firefighters while fire suppression and rescue operation
Maintaining the structure’s integrity in a fire event
Preventing fire spread to adjacent buildings in a fire event
In addition, the performance-based design for the Tower addresses the following building features:
Tall building with a structural timber system
Exposed timber features
Transient occupants
Occupant evacuation elevators
Sustainable design
A semi-quantitative fire hazard assessment for the green building initiatives is proposed for the Tower, assigning values to selected variables, based on professional judgment and experience. Parameters associated with the fire hazards of the above listed LEED categories are identified as performance concerns for the Tower and the façade. The semi-quantitative approach uses a widely recognized index method, establishing an order of magnitude, with relative rankings.
Some parts of the CLT Tower are exposed as an architectural feature. Walls are equipped with total encapsulation which provides a 3-hr. fire resistance rating. The tower is also equipped with a 2-hr. fire resistance rated stairwell, and a1-hr. fire-resistance rated smoke barrier elevator lobby. It is also equipped with a mechanical ventilation to the roof as the main smoke management strategy.
Performance Group III was determined for the CLT tower based on ICCPC, and the following tenability criteria was developed and analyzed in the trial designs:
Radiant Flux Max. 2.5-kW/m2 (793-Btu/ft.2/hr.) at Head Height (1.8-m
or 5.9-ft.)
Elevated Air Temperature 60 ºC (140 ºF) for 30-Minutes Exposure to Air
Saturated with Water Vapor
Elevated Smoke Temperature 60 ºC (140 ºF) for 30-Minutes Exposure
Visibility Distance Max. 10-m (33-ft.) to Doors and Walls
Smoke Toxicity (CO Concentration) Average of 1000-ppm for the First 20-Minutes of Exposure
Smoke Toxicity (Hydrogen Cyanide) Max. 100-ppm for the 20-Minutes of Exposure
To ensure the proper life safety in a fire event, three refuge floors (L9, L17, and L25) were design in the CLT Tower. The areas of refuge are complete encapsulated, and provide a 3-hr. fire resistance rating. Additionally, areas of refuge are designed at all of the stairway’s connection to floors with a 1-hr. fire resistance rating. The CLT Tower design prioritized the life safety of firefighters and occupants with mobility impairment.
The main egress strategy for the tower is elevator evacuation. Thus, egress analysis was performed based on two strategies: zone and total evacuation. Computer modeling using Elevator Evacuation (ELVAC) was performed to evaluate the performance criteria. The results were also compared to hand calculations of the Occupant Evacuation Elevators (OEE) strategy.
8 design fire scenarios were developed, and 4 were evaluated using the Fire Dynamics Simulator (FDS) and PyroSim. Trial designs, egress analysis, and design fire scenarios were then combined and compared to fire safety goals and objectives. Findings based on these evaluations demonstrated an adequate level of life safety for both transient and permanent occupants.
... Some key advantages of CLT are its low-carbon footprint, the use of low-grade timber, and the potential 9 for more efficient construction using CLT as the primary wall, floor, and roof elements [Moses and Gagnon 2010;10 Structural Timber Association 2014]. Considering also the increasing market supply of CLT [Pei et al. 2016], there is 11 an opportunity to adapt high-performance CLT-based structural alternatives to regions of low-to-moderate seismicity. 12 ...
Controlled rocking heavy timber walls are designed to rock on their foundations in response to earthquakes. For regions of moderate seismicity, it is proposed that this rocking behaviour can be adequately controlled using only post-tensioning, even with a large force-reduction factor and no supplemental energy dissipation. This article presents a force-based design procedure for controlled rocking cross-laminated timber walls without supplemental energy dissipation, including a method for estimating higher mode effects. Fragility analyses of three prototype walls demonstrate that the procedure can limit the probability of collapse to <10% during a maximum considered earthquake in a region of moderate seismicity.
... In the past decades, cross-laminated timber (CLT) has been widely used as load bearing components such as walls and floors due to its high stability and load capacity. Many experimental tests have been conducted on CLT structural performance (Dujic and Zarnic 2005;Dujic et al. 2006Dujic et al. , 2008Ceccotti 2006;Ceccotti and Follesa 2008;Ceccotti et al. 2013;Popovski et al. 2010Popovski et al. , 2015Pei et al. 2013Pei et al. , 2014Pei et al. , 2016Ganey 2015;van de Lindt et al. 2019). Those tests revealed that the connections anchoring CLT panels with foundations and walls are the critical elements that govern the structural response. ...
This paper presents the modeling of coupling effect of tension and shear loading on cross-laminated timber (CLT) connections using a finite-element-based algorithm called HYST developed in 2000. The model idealizes the connections as a pseudonail-elastoplastic beam elements (the nail) surrounded by compression-only spring elements (steel sheath and wood embedment). A gap size factor and an unloading stiffness degradation index of the spring elements under cyclic loading were integrated into the optimized HYST algorithm to consider the coupling effect. The model was calibrated to compare with 32 configurations of CLT angle bracket and hold-down connections tests: in tension with coexistent constant shear force, and in shear with coexistent tension force. The results showed that the optimized model can fully capture the coupling effect of typical CLT connections, considering strength degradation, unloading and reloading stiffness degradation, and pinching effect. The model provided a useful tool for nail-based timber connections and a mechanism-based explanation to understand the hysteretic behavior of CLT connections under biaxial loading.
... A new structural concept was proposed to integrate BRBs into glulam frames to form a new hybrid LFRS for multi-storey timber buildings and there is a need for innovation in connection design and the subsequent testing and research to evaluate the system performance [7]. Blomgren et al. [8] modelled multi-storey timber buildings braced by BRBs with timber casings but no detailed information on the connection design was provided. ...
Two full-scale buckling restrained braced glulam frame (BRBGF) specimens were tested under cyclic loading. Two different connections (the dowelled connections and screwed connections) were used in two specimens, respectively. The connection behaviour at two different positions (the mid-span connection linking inverted-V BRBs and the top glulam beam and the corner connection linking one BRB with the bottom glulam beam and one side column) was analysed by using particle tracking technology (PTT). The experimental results showed that the dowelled connections and screwed connections had enough strength and stiffness to engage BRBs. The energy dissipation was primarily from BRBs' yielding and no significant damage in connections was observed in the tests. The rotation stiffness of both connections was negligible and both connections can be assumed as pinned connections. The dowelled connections had lower initial stiffness than the screwed connections but became stiffer after overcoming the initial slips. For the dowelled connection, Eurocode 5 provided good strength estimation but overestimated the stiffness. For the screwed connection, Eurocode 5 underestimated the strength due to the contribution of friction; the stiffness model based on Eurocode 5 and European Technical Assessment (ETA) overestimated the stiffness significantly. The discrepancy between stiffness prediction and experimental results was discussed with alternative methods for future study.
... The standard specifies a total of seven CLT performance grades and the testing methods to quantify and determine the grades. ANSI APA PRG 320-2019 [5] is referenced in the 2015 edition of the National Design Specifications (NDS) for Wood Construction in the U.S., and the 2014 edition of the Canadian National Standard for Engineering Design in Wood (CSAO86) [8]. This standard, as its scope explains in its first chapter, provides dimensions and tolerances, performances requirements, test methods, quality assurance, and trademarking for CLT panels [5]. ...
This is a technical report that has been published in "TimberAid.com" :
www.timberaid.com/calculator/articles/development-background-and-challenges-north-american-cross-laminated-timber-clt-design-standard/
... By taking advantages of CLT compressive strength, dimensional stability, and prefabrication, using existing designs in the precast concrete (Aaleti and Sritharan 2009;Sritharan et al. 2015;Rahman and Restrepo 2000;Restrepo and Rahman 2007) and steel industry for low-damage seismic-resilient systems, the wood engineering community is investigating the use of unbonded post-tensioning (PT) to develop a low-damage lateral load-resisting system with CLT. Pei et al. (2016) found that seismic resiliency can be achieved by using unbonded post-tensioned CLT rocking walls, which remain damage-free in moderate earthquakes and can be repaired easily after large-magnitude earthquakes. ...
Cross-laminated timber (CLT) panels with unbonded post-tensioning and a rocking mechanism can be used as a robust lateral load–resisting system (LLRS). The seismic performance of these systems can be improved further by incorporating external sacrificial energy dissipating elements. The additional damping provided by the energy dissipaters reduces the structural displacement demand during a design-level earthquake, and the unbonded post-tensioning provides recentering ability. This study developed a surface mountable, easily replaceable sacrificial oval metallic element specific to the CLT walls using aluminum was. This connector contributes to the wall system lateral load capacity. Laboratory testing of the aluminum connectors under cyclic shear loading was performed to characterize the force–displacement behavior and energy dissipating capacity. A detailed three-dimensional (3D) finite-element analysis (FEA) of aluminum connectors was carried out to replicate the observed experimental behavior. The experimental results, analytical modeling, and design equations for connector force–displacement response based on first principles are presented in this paper. The test results showed that the O-connectors can be used as an effective energy-dissipating element with equivalent damping ratio varying between 20% and 40%. The simplified design equations calculated the response within 90% of the measured values.
... In the U.S. market, the concept of mass timber building has been progressed by demonstrating a few pilot projects, although a lack of well-defined code has always remained a key concern (Pei et al. 2016). The first performance-based standard for mass timber building in North America was developed by a shared exertion between APA-The Engineered Wood Association and FPInnovations (Borjen et al. 2012). ...
Mass timber is a promising building material that provides excellent structural rigidity, a low-environmental pollution footprint, and better use of natural resources. However, the adoption of mass timber is not free from challenges. Especially in the US construction industry,
the material has not been accepted widely by practitioners due to inexperience and a lack of mass timber building construction projects. This study aims to determine the current awareness level among US construction practitioners regarding mass timber building material. It further identifies the existing challenges associated with the design, construction, and manufacturing process of this material. The results from 100 construction companies, 32 architectural firms, and 15 timber manufacturers show that US construction practitioners have a relatively low level of awareness and work experience in mass timber material. Among the respondents, 55% of building contractors and 30% of architects indicated that they have never been involved in a
mass timber building construction project. Furthermore, a significant number of participants who were involved in the mass timber project stated that their experience level is between 1 and 5 years, indicating that the concept of mass timber is still in a very rudimentary level. Lack of timber manufacturing plants, inexperience, high cost of engineered wood, and code limitation are some of the perceived drawbacks identified by the participants. The outcomes of the study will be helpful to determine the actual feasibility of mass timber in the US construction industry.
... Cross-laminated timber (CLT) can well bear the load in and out of the plane and connect with other materials or components when it is used as the wall and floor of a building [1][2][3], which promotes its wide application in mid and high-rise buildings [4]. Connections between CLT components (e.g., wall-wall, wall-floor, floor-floor) are the key aspects of its application in constructions. ...
This paper presents an experimental study on tongue-and-groove (T&G) and half-lap (HL) joints for 5-layer cross-laminated timber (CLT) connected with self-tapping screws (STS). A total of 54 monotonic and cyclic loading tests were carried out for vertically screwed T&G and HL joints, the load-carrying capacity, stiffness, ductility, strength impairment and energy dissipation of the joints have been investigated. The results showed that the load-carrying capacity, stiffness and ductile ratio of T&G joints were higher than those of HL joints. Besides, joints with 8 mm diameter STS had higher load-carrying capacity, initial stiffness and ductility than those with 6 mm diameter STS. Fully-threaded (FT) STS could improve the loading-carrying capacity of the joints compared with partially-threaded (PT) STS, however, the stiffness and ductility were not as good as the latter. Under cyclic loading, the strength impairment rate of T&G joints was lower than that of HL joint, and the energy dissipation of T&G joints was better when the displacement was small. Two prediction models presented in this paper were conservative compared with the experimental values. The results presented in this paper can provide fundamental basis for supporting the potential engineering application of CLT panels connected with T&G joints.
... Due to the high strength-to-weight ratio, fast rate of construction, and low environmental impact, cross-laminated timber (CLT) panels are becoming a popular construction product all over the world (Muszynski et al. 2017;Pei et al. 2016). These panels are used as wall and floor (diaphragm) elements that can act as part of the primary lateral force-resisting system (LFRS) in buildings. ...
Over the past decade, cross-laminated timber (CLT) panels have gained popularity worldwide. To achieve larger spans and to increase the resistance to diaphragm seismic and wind forces to be transferred through CLT floor or roof systems, CLT-concrete composite (CCC) floors have been developed as an alternative. While significant testing has been performed under gravity loading, limited experimental data exist on the in-plane performance of CCC systems. This study presents results from an experimental program designed to characterize the in-plane shear behavior of CCC diaphragm connections using different CLT to concrete screw connector orientations in a test setup that simulates the expected seismic load path in diaphragms for platform-type construction. Tested variables include concrete slab thickness, composite screw angle, and single spline connection systems consisting of nails or screws. Experimental results and observed damage progression from cyclic testing are presented and discussed. Results indicate that CCC systems achieved increased stiffness and strength values when compared to bare-CLT systems, but slab thickness did not influence the strength and stiffness of the system for the load paths simulated. Additionally, CCC floor systems with 45° composite screw connectors displayed increased strength but overall similar stiffness values when compared to the CCC systems with 90° composite screws. The results provide useful engineering parameters, such as elastic stiffness, peak load, displacement capacity, and ductility ratios that can be used in the development of codified design parameters or in performance-based designs.
... However, during this shake table test program and other previous tests, CLT platform buildings demonstrated a vulnerability from large accelerations and overturning moments. In North America, significant recent research efforts (Popovski et al. 2010(Popovski et al. , 2012Pei et al. 2013Pei et al. , 2016Amini et al. 2014) have focused on CLT buildings, including experimental testing and development of seismic performance factors. Resilient mass timber seismic research began in New Zealand in the mid2000s with the adaptation of a rocking wall concept originally used in concrete walls, applying the concept to laminated veneer lumber (LVL) and investigating different moment connections and posttensioning configurations (Palermo et al. 2006). ...
This paper presents a new stochastic methodology for evaluating and quantifying the downtime of a structure in terms of a family of fragilities that represent the probability of exceeding prescribed times to return to functionality. This methodology integrates several existing concepts, namely, Federal Emergency Management Agency P-58 and Resilience-based Earthquake Design Initiative (REDi), to build a family of system (building) level fragility curves corresponding to the time needed to achieve different recovery levels (reoccupancy, functional recovery , and full recovery). This approach enables one to propagate uncertainty throughout the procedure so that variations in the delay time and repair schedules are accounted for in the resulting fragilities. As an illustrative example of this approach, the methodology is applied to assess the downtime of a two-story mass timber building that was originally tested at the NHERI@UCSD outdoor shake table in 2017. One unique aspect of this analysis is that it incorporates a relatively new material, cross-laminated timber (CLT), in a resilient posttension rocking wall design application. Nonstructural components representing a typical office building were selected and incorporated into the procedure for the two-story CLT rocking wall building. Time-to-functionality fragility curves are then developed for the two-story building, and potential design and resilience-focused applications are discussed.
... When this product will make a breakthrough in the North American market, this will offer a promising potential development (reTHINKWOOD, 2015). Since 2014, few multi-story buildings in CLT are builted across North America (Pei et al., 2016). Based on these findings, we have placed the CLT in the introductory phase. ...
An accounting system helps to provide information for planning and control of production. This article presents a Life Cycle Costing by using an Activity Based Costing approach of an innovative forestry company. In order to perform a cradle-to-gate assessment the study covers the forest and industrial activities of the forest product processing. The costs of each product in the portfolio are determined by the treatment activities they undergo. The inventory covers several years of activity of the company, which makes it possible to calculate the uncertainty of the average results with Monte Carlo simulation presented in the result section. Based on the results a products portfolio analysis was performed to identify the development progress phases of the mains products to support the product rollover strategy decision.
... The use of cross-laminated timber (CLT) in construction has expanded across international markets because of its structural performance, seismic behavior, and sustainability [1][2][3]. CLT was introduced in North America in the early 2000 s, and since then research have been developed to expand its use across the building construction sector. In spite of recent advances, limited methods and technologies are readily available to prolong the durability of buildings composed of such material. ...
Cross-laminated timber (CLT) market demand is on the rise in the United States. Adequate protective measures have not been extensively studied. The objective of this study was to investigate the weathering performance of exterior wood coatings. We evaluated coated CLT sample surfaces based on visual appearance, color change (CIE*L*a*b), gloss changes, and water intrusion. From the five exterior wood coatings evaluated, only two showed adequate performance after twelve months field exposure. Based on visual ratings following the ASTM procedures, coating failure occurs more quickly in Mississippi than in Wisconsin, due to its greater decay zone. Both location and coating type impacted the aging of the samples. Artificial weathering results were consistent with natural weathering indicating the two adequate coatings were the most resistant to failure, color, and gloss change. For future studies, new coatings designed for the protection of end-grain in CLT panels should be a target of research and development.
... Analytical models for mid-rise CLT buildings allowed for performing non-linear dynamic analyses to determine adequate seismic force reduction factors for CLT structures [26,27]. Based on this research, seismic design provisions for platform-type CLT construction were developed and implemented in CSA O86 [15]. ...
... As an engineered wood product, CLT and other mass timber panels have been recognized as the natural choice for buildings with enhanced sustainability goals because they are made from renewable resources and have less embodied energy (Milaj et al. 2017). With the use of CLT continuing to grow in seismic-prone regions, evaluation of the seismic performance of CLT structural systems is of increased importance (Pei et al. 2016). ...
A full-scale 2-story mass timber building was tested on the University of California San Diego Natural Hazards Engineering Research Infrastructure (UCSD-NHERI) uniaxial shake table during the period from June 2017 to September 2017. The main objective of the experimental program was to test the performance of mass timber building designs with different seismic lateral force-resisting systems. The focus of this study is on a building configuration designed using self-centering post-tensioned cross-laminated timber (CLT) rocking walls with U-shaped steel flexural plate energy dissipators. The shake-table tests were designed to subject the building to a series of earthquake ground motions of increasing intensity, ranging from a service-level earthquake to 1.20 times the maximum considered earthquake intensity. Between each ground motion, low-amplitude white-noise excitations were applied to the building, which responded as a quasilinear system. In this paper, two output-only operational modal analysis methods are used to estimate the modal parameters (frequency, damping, and mode shapes) based on acceleration data collected during the white-noise shake-table tests. The correlations of observed damage and repairs performed during the experimental program with changes in estimated modal features are reported. The modal parameters estimated from the testing program are also compared with a linear finite-element model that is used to validate the modal identification results and study the performance of the two system identification methods for CLT rocking structures.
... It is true that both CLT and glulam can be used together for different structural components; however, before CLT penetrated the market, glulam fulfilled the demand. CLT manufacturers in North America have experienced a steady growth since the product was first introduced, with no sign of a decline [47]. The general trend is driven by voluntary efforts in the construction industry to replace nonrenewables with more sustainable materials, the need to lower the carbon footprint and more speedy construction process [48]. ...
Buildings are accountable for much of the resource consumption and CO2 emissions generated from human activities. Nonetheless, the focus of building life cycle assessment (LCA) studies to evaluate the environmental footprint are more commonly adopted in an attributional approach. Nevertheless, understanding a direct and indirect consequences in larger system using consequential approach is also needed for policy-making. Rather small body of existing literature has been found on the implementation of consequential LCA and life cycle costing (LCC) in the building sector. In this study, attributional and consequential approach are performed for hybrid wood multistorey building. The results showed that with attributional approach, the phase that contributed the environmental impacts the most in climate change category is the production phase yet it became the use phase if consequential approach is used. By performing consequential LCA-LCC the possible hidden impacts can be uncovered and sufficient insights into the indirect impacts can be seen, thereby offering stakeholders the opportunity to avoid such future consequences.
... By taking advantages of CLT compressive strength, dimensional stability, and prefabrication, using existing designs in the precast concrete (Aaleti and Sritharan 2009;Sritharan et al. 2015;Rahman and Restrepo 2000;Restrepo and Rahman 2007) and steel industry for low-damage seismic-resilient systems, the wood engineering community is investigating the use of unbonded post-tensioning (PT) to develop a low-damage lateral load-resisting system with CLT. Pei et al. (2016) found that seismic resiliency can be achieved by using unbonded post-tensioned CLT rocking walls, which remain damage-free in moderate earthquakes and can be repaired easily after large-magnitude earthquakes. ...
Cross-laminated timber (CLT) panels with unbonded post-tensioning and a rocking mechanism can be used as a robust lateral load–resisting system (LLRS). The seismic performance of these systems can be improved further by incorporating external sacrificial energy dissipating elements. The additional damping provided by the energy dissipaters reduces the structural displacement demand during a design level earthquake, and the unbonded post-tensioning provides recentering ability. This study developed a surface mountable, easily replaceable sacrificial oval metallic element specific to the CLT walls using aluminum was. This connector contributes to the wall system lateral load
capacity. Laboratory testing of the aluminum connectors under cyclic shear loading was performed to characterize the force–displacement behavior and energy dissipating capacity. A detailed three-dimensional (3D) finite-element analysis (FEA) of aluminum connectors was carried out to replicate the observed experimental behavior. The experimental results, analytical modeling, and design equations for connector force–
displacement response based on first principles are presented in this paper. The test results showed that the O-connectors can be used as an effective energy-dissipating element with equivalent damping ratio varying between 20% and 40%. The simplified design equations calculated the response within 90% of the measured values.
... More specifically, to decrease buildings' impact, timber is more effective then both concrete and steel. Depending on the dimensions of the building, cross laminated timber has been used in high-rise structures (up to 53 m, 18 floors; see Pei et al. [108]) because of its high structural resistance [109]. Engineered timber can be employed in low-to mid-rise structures (up to 30 m, 6 floors; see Tollefson [110]). ...
Life cycle assessment is a tool to quantify the environmental impact of products and has been widely studied in the building context. This is an important context given the building sector's substantial embodied energy and carbon. Against this backdrop, this study has two main objectives. The first objective is to create a benchmark the environmental impact of buildings. The second objective is to develop a procedural guideline that assists practitioners in decreasing the environmental impact of buildings. To achieve these objectives, a systematic review of the relevant literature was conducted to categorize and summarize relevant studies. A meta-analysis followed to synthesize the life cycle assessment results that emerged from the collected articles. The articles were categorized into two main groups: articles on construction materials and articles on entire buildings. Eight construction materials (i.e., concrete, reinforcement bars, structural steel, timber, tiles, insulation, and plaster) and three building types (i.e., concrete, timber, and steel) were identified, and related embodied energy and carbon were extracted. Subsequently, the data were analyzed through descriptive and inferential statistics. Findings from the meta-analysis informed a regression model, which in turn informed a procedural guideline for practitioners who seek to reduce buildings' environmental impact. Further, the findings of this paper shed light on previously equivocal results concerning the impact of construction materials and buildings, but also support previous findings for structural materials, showing, for example, that the use of timber structures results in substantial savings over concrete structures in terms of both embodied energy (43%) and carbon (68%).
... It has been estimated that the global annual production of CLT is growing exponentially in Europe, it was 25,000 m 3 in 1996, 340,000 m 3 in 2010, 650,000 m 3 in 2015, up to 1.2 million of m 3 in 2020 [1,2] (Figure 1). Nevertheless, an annual increase of the manufactured CLT has been also recorded in the United States, Canada, Australia, Japan and New Zealand [3][4][5]. ...
Cross-laminated timber (CLT) buildings are recognized as a robust alternative to heavyweight constructions, because beneficial for seismic resistance and environmental sustainability, more than other construction materials. The lightness of material and the satisfactory dissipative response of the mechanical connections provide an excellent seismic response to multi-story CLT buildings, in spite of permanent damage to timber panels in the connection zones. Basically, CLT constructions are highly sustainable structures from extraction of raw material, to manufacturing process, up to usage, disposal and recycling. With respect to other constructions, the potential of CLT buildings is that their environmental sustainability in the phases of disposal and/or recycling can be further enhanced if the seismic damage in structural timber components is reduced or nullified.
This paper reports a state-of-the art overview on seismic performance and sustainability aspects of CLT buildings in seismic prone regions. Technological issues and modelling approaches for traditional CLT buildings currently proposed in literature are discussed, focusing the attention on some research advancements and future trends devoted to enhance seismic performance and environmental sustainability of CLT buildings in seismic prone regions.
This paper presents the behavior of floor diaphragms of a shake-table experiment of a full-scale 2-story mass-timber building structure. The structure consists of glued-laminated timber beams and columns, and floors and walls were designed and built making use of cross-laminated timber panels. Two different floor systems were designed, where the roof consists of a topped cross-laminated timber (CLT)-concrete composite system, and the floor level consists of untopped CLT panels connected with plywood single-surface splines. The CLT floor systems were designed to remain essentially elastic over the whole series of shake-table tests, which included testing of three lateral force-resisting systems tested at three different seismic intensity levels (service level, design basis, and maximum considered earthquake) for a total of 34 shake-table earthquake tests. Results from the testing indicate that CLT diaphragms designed to remain essentially elastic based on basic principles of structural mechanics and existing test data can achieve desired seismic performance objectives. In addition, sources of overstrength in certain elements of the diaphragm need to be explicitly considered for a holistic diaphragm design.
The National Design Specification(NDS) for wood construction 2015 includes new provisions for gravity load design of Cross laminated Structures (Chapter 10). However, the Special Design Provision for Wind and Seismic(SDWPS) 2015 does not provide any technical information required for designing composite CLT floor and roof diaphragms for wind and seismic loads. Hence, the investigation of in-plane stiffness properties of CLT diaphragms is necessary in order to garner related technical information and develop a design guide for practitioners.
This study evaluates the seismic response of an advanced hybrid steel-timber structure using a nonlinear static and dynamic analyses. A three-story prototype building located in Vancouver, BC, Canada was designed first. The gravity load resisting system (GLRS) consists of cross-laminated timber (CLT) floor slabs, glulam beams, and glulam columns. The lateral load resisting system (LLRS) includes a chevron-type steel Concentrically Braced Frame. The numerical model of the structure was then developed in the OpenSees program. Nonlinear hysteresis response of steel braces and timber joints were explicitly simulated. The results of the analysis revealed that the hybrid structure possess an acceptable lateral stiffness while providing sufficient ductility to dissipate seismic energy. No unsatisfactory response was observed in the timber system.
This paper investigates the in-plane shear behavior of a full-scale 20 ft. x 20 ft. (6.1 m x 6.1 m) cantilever Cross Laminated Timber (CLT) diaphragm experimentally. The diaphragm consisted of eight 5 ft. x 10 ft. (1.5 m x 3 m) three ply CLT-panels connected to each other along the long edge by plywood surface splines with nails and connected along the short edge to glulams underneath with screws. The diaphragm was tested with a cyclic loading protocol. The ultimate capacity of the diaphragm exceeded the design capacity. Test results showed that sliding (slip along the loading direction) and rotation of CLT panels, caused by fastener deformations were the two major energy dissipation mechanisms. The strains measured on the top and bottom surfaces of CLT panels revealed a deep beam like effect, in which the edge CLT panels contributed significantly to resisting coupled tension and compression forces with little to no contribution from the CLT panels near the neutral axis. A comparison between the various contributions of diaphragm deflections computed using the latest code equation (2021 version of NDS) and that measured from the test suggested that a revision to the current diaphragm deflection equation may be necessary.
A new simplified mechanistic model was developed in this study to predict the rocking and sliding lateral response of a CLT panel wall under monotonic pushover with different boundary and gravity loading conditions based on an approximation of the principle of virtual work. Namely, for a given forced lateral displacement increment, the CLT wall will engage in a combination of rocking and sliding motion that will minimize the total work needed to go through that displacement increment. The proposed model was compared to the existing test results to illustrate its ability to capture the two types of wall behavior. Being a simplified mechanistic model, a number of material nonlinear characteristics such as the local crush of wood and the biaxial interaction of the connectors were not captured, resulting in a backbone characterization accuracy not as good as some existing well-calibrated models. However, the contribution of the study is to provide a mechanistic approach to address the switching between rocking and sliding behavior of CLT panelized walls under different boundary conditions. Using the model, a sensitivity analysis was conducted to investigate the effect of wall configurations and boundary conditions on the behavior of CLT shear walls.
The research presented in this paper analysed the stiffness of Cross-Laminated-Timber (CLT) panels
under in-plane loading. Finite element analysis (FEA) of CLT walls was conducted. The wood lamellas were modelled as an orthotropic elastic material, while the glue-line between lamellas were modelled using non-linear contact elements. The FEA was verified with test results of CLT panels under in-plane loading and proved sufficiently accurate in predicting the elastic stiffness of the CLT panels. A parametric study was performed to evaluate the change in stiffness of CLT walls with and without openings. The variables for the parametric study were the wall thickness, the aspect ratios of the walls, the size and shape of the openings, and the aspect ratios of the openings. Based on the results, an analytical model was proposed to calculate the in-plane stiffness of CLT walls with openings more accurately than previously available models from the literature.
In this paper, some of the results are presented from a series of quasi-static tests on CLT wall panels conducted at FPInnovation-Forintek in Vancouver, BC. CLT wall panels with various configurations and connection details were tested. Wall configurations included single panel walls with three different aspect ratios, multi-panel walls with step joints and different types of screws to connect them, as well as two-storey wall assemblies. Connections for securing the walls to the foundation included: off-the-shelf steel brackets with annular ring nails, spiral nails, and screws; combination of steel brackets and hold-downs; diagonally placed long screws; and custom made brackets with timber rivets. Results showed that CLT walls can have adequate seismic performance when nails or screws are used with the steel brackets. Use of hold-downs with nails on each end of the wall improves its seismic performance. Use of diagonally placed long screws to connect the CLT walls to the floor below is not recommended in high seismic zones due to less ductile wall behaviour. Use of step joints in longer walls can be an effective solution not only to reduce the wall stiffness and thus reduce the seismic input load, but also to improve the wall deformation capabilities. Timber rivets in smaller groups with custom made brackets were found to be effective connectors for CLT wall panels. Further research in this field is needed to further clarify the use of timber rivets in CLT.
Cross-laminated timber, or CLT, is receiving attention for its potential application in tall building structures. As a combustible material, one of the main challenges for the construction of these buildings is the fire risk that results from its use in the structure.
Unprotected CLT can burn along with the fuel load present in a compartment. Irrespective of the structure's fire resistance rating, it is uncertain whether the structure will be totally consumed in the event of a complete burnout. If the structure would continue to burn, this could result in collapse of the building. Alternatively, the fire could decay by self-extinguishment.
Self-extinguishment of CLT was investigated with a theoretical model that describes the conditions under which it could be achieved. Two series of experiments were conducted to quantify these conditions. It was concluded that there is a potential for self-extinguishment of CLT if fall-off of charred layers is prevented by applying sufficiently thick lamellae, if the heat flux on the CLT during smouldering is below 5–6 kW/m², and if the airflow over the surface during smouldering is limited to a speed of 0.5 m/s. An exploration towards design implementation is presented.
A 2-story full-scale model of a cross-laminated timber (CLT) house was tested under quasi-static monotonic and cyclic loading. The primary objectives were to investigate 3D system performance of a CLT structure subjected to lateral loads in terms of lateral strength and deformability capacity, global behavior of the structure, frequency response of the structure before and after each test, and performance of anchoring connectors (hold-downs, brackets) and connections between CLT panels. The house was 6.0×4.8 m in plan with a height of 4.8 m. A total of five (one push-over and four cyclic) quasi-static tests were performed, one direction at a time. Parameters, such as the direction of loading, number of hold-downs, and number of screws in perpendicular wall-to-wall connections, were varied in the tests. The CLT structure performed according to the design objectives, with the ultimate resistance being almost identical in both directions. Failure mechanisms, i.e., shear failure of nails in the brackets in the first story as a result of sliding and rocking of the CLT wall panels, were similar in all tests. Even after the maximum force was reached, no global instabilities of the house were detected. Torsion effects did not compromise the integrity, stability, or the lateral resistance of the building. The outcomes of the full-scale CLT house tests will be used for further analytical and numerical analyses to help the implementation of CLT as a structural system in the North American building codes and material standards.
Cross laminated timber (CLT) is an innovative building product currently gaining popularity in countries around the world. However, there is little published information available regarding its performance in fire. The focus of this research is on a series of eight medium-scale CLT fire-resistance floor tests. Parameters such as charring rates, deflection, gypsum board protection and adhesive performance, as well as the overall fire resistance of the floors when subjected to both standard and non-standard fire exposures were evaluated. The results compare favourably to recent standard full-scale CLT floor tests and demonstrate that CLT panel assemblies can be designed to possess a fire-resistance that complies with building code requirements. The additional fire performance data provided from the results of these tests will help facilitate the incorporation of CLT into design standards and building codes.
The cross-laminated timber (CLT) is a prefabricated solid engineered wood product made of at least three orthogonally bonded layers of solid-sawn lumber or structural composite lumber that are laminated by gluing of longitudinal and transverse layers with structural adhesives to form a solid rectangular-shaped, straight, and plane timber intended for roof, floor, or wall applications. While this engineered wood product has been used in Europe for over 15 years, the production of CLT and design of CLT structural systems have just begun in North America. For the acceptance of new construction materials or systems in North America, such as CLT, a consensus-based product standard is essential to the designers and regulatory bodies. This paper describes and documents the background information and some key issues that were considered during the development of the ANSI/APA PRG 320 Standard for Performance-Rated Cross Laminated Timber. This standard is a bi-national standard between the U.S. and Canada, and was developed based on the consensus standard development process of APA-The Engineered Wood Association as a standards developer accredited by the American National Standards Institute (ANSI).
This study proposes an iterative direct displacement based design method for a novel steel-timber hybrid structure. The hybrid structure incorporates Cross Laminated Timber (CLT) shear panels as an infill in steel moment resisting frames. The proposed design method is applied to design 3-, 6-, and 9-story hybrid buildings with three bays and CLT infilled middle bay. Nonlinear time history analysis, using twenty earthquake ground motion records, is carried out to validate the performance of the design method. The results indicate that the proposed method effectively controls the displacements due to seismic excitation of the hybrid structure.
Cross-laminated Timber (CLT) has been extensively used in Europe and is now gaining momentum in North America; both Canada and more recently the U.S. Construction projects have shown that CLT can effectively be used as an alternative construction material in mid-rise structures and has significant potential in commercial and industrial buildings. In the United States, the CLT system is not currently recognized in seismic design codes and therefore a seismic design can only be performed through alternative methods specified in the codes. The FEMA P695 report published in 2009 presents a methodology to determine seismic performance factors namely the response modification factor, overstrength factor, and deflection amplification factor for a proposed seismic resisting system. The methodology consists of a number of steps to characterize system behavior and evaluate its performance under seismic loading. The additional benefit of the methodology is that it considers variability in ground motions and uncertainties in tests, design, and modeling. This paper presents an overview of the P695 methodology and more specifically the approach adopted to apply the methodology to Cross Laminated Timber (cross lam) systems in the United States. The type of tests and testing configurations conducted as part of this study and development of the CLT archetypes are discussed. Nonlinear models used to simulate CLT behavior at the connection, wall, and system levels are presented and the procedure to determine collapse margin ratio is explained.
Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.
With two producers in operation and over 20 buildings already constructed or in planning process, use of cross-laminated timber (CLT) is gaining popularity in Canada. Since CLT as a structural system is currently not included in the National Building Code of Canada (NBCC), one of the most important issues are the values for the force modification factors for seismic design of CLT structures when NBCC equivalent static force procedure is used. In this study, a test-calibrated numerical model for CLT shear walls was applied to develop the design resistances for typical CLT wall configurations. An estimation of a possible range of R d-factors was obtained by developing design variations for three multi-storey CLT apartment buildings. By specifying the desired seismic performance in terms of inter-storey drift, it is concluded that an Rd-factor of 2.0 will likely provide desirable building performance during the design earthquake level event in Vancouver, B.C.
Rolling Shear Capacity of Southern Pine Cross Laminated Timber Panels, Wood Design Focus
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Fire Resistance Of Partially Protected Cross-Laminated Timber Rooms
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Protected Cross-Laminated Timber Rooms",
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Development of lateral load resisting system. Chapter 2 of 'Application of Analysis Tools from NEWBuildS Research Network in Design if a Highrise Wood Building
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Development of lateral load resisting system.
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Corss Laminated Timber Horizontal Diaphragm Design Example
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ANSI/APA PRG 320-2012: Standard for Performance-Rated Cross-Laminated Timber " Performance Standard for Cross-Laminated Timber, APA – The Engineered Wood Association
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APA – The Engineered Wood Association, Tacoma,
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Quantification of Building Seismic Performance Factors. FEMA
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Edge Connections for CLT Plates: In-Plane Shear Tests on Half-Lapped and Single-Spline Joints
- Masoud Sadeghi
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Sadeghi, Masoud, and Ian Smith. "Edge
Connections for CLT Plates: In-Plane Shear Tests
on Half-Lapped and Single-Spline Joints." In
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Contribution of Cross Laminated Timber Panels to Room Fires
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McGregor "Contribution of Cross Laminated
Timber Panels to Room Fires", Carleton University,
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The Case for Tall Wood Buildings
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Wood Buildings" Technical Report, Canadian
Wood Council, British Columbia. http://cwc.ca/wpcontent/uploads/publications-Tall-Wood.pdf
- Dagenais Osborne
Osborne and Dagenais "Preliminary CLT Fire
Resistance Testing Report", FPInnovations, 2012
ANSI/APA PRG 320-2012: Standard for Performance-Rated Cross-Laminated Timber" Performance Standard for Cross-Laminated Timber
- Apa
APA (2012) "ANSI/APA PRG 320-2012: Standard
for Performance-Rated Cross-Laminated Timber"
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APA -The Engineered Wood Association, Tacoma,
WA.