The results of an experimental programme on the structural behaviour, fire behaviour, and fire resistance of CLT rib panels are presented. The floor system consists of cross-laminated timber (CLT) plates rigidly bonded to glued-laminated timber ribs by means of screw-press gluing.
The experimental programme comprised ultimate-load tests at normal temperature as reference tests and full-scale fire resistance tests on four cross-sections. In addition to the reference tests, shear tests of the glue line between CLT plate and glued-laminated timber rib were performed for analysis of the cross-sections’ composite action.
The results of the reference tests show good agreement with results based on the simplified method according to EN 1995-1-1  and its final draft of CLT design . The importance of the glue line’s quality was confirmed. The fire resistance tests show results on the safe side compared to predictions of the fire behaviour according to EN 1995-1-2  and its actual draft . However, the fire resistance was underestimated due to conservative assumptions about the composite cross-section’s structural behaviour.
The experimental programme addressed the fire behaviour and fire resistance of CLT rib panels currently not covered in standards. The project’s overall aim is the development of design rules in fire for EN 1995-1-2.
The fire resistance of a structural building member includes its ability to survive a specified fire without loss of its loadbearing function. For glue laminated timber columns, fire resistance is determined by either subjecting a structural member to a standard fire test or by using one of two accepted calculation methods. For wood structural members, the calculation methods rely on char rates obtained from numerous standard fire tests. The existing calculation methods are limited under United States building codes to calculating fire resistance ratings of 120 minutes or less. However, over the past decade there has been a push towards tall wood buildings and designers desire more exposed wood to be permitted in buildings. This desire, coupled with the recent adoption of code language that permits tall wood buildings up to 18 stories, has resulted in the need to determine char rates for glue laminated timber to use in the fire resistance calculations up to 180 minutes. Here we present the experimental method and initial char rate results of glue laminated columns exposed to the standard fire.
The objective of this research is to address a knowledge gap related to fire performance of midply shear walls. Testing has already been done to establish the structural performance of these assemblies. To ensure their safe implementation and their broad acceptance, this project will establish fire resistance ratings for midply shear walls. Fire tests will provide information for the development of design considerations for midply shear walls and confirm that they can achieve at least 1-hour fire-resistance ratings that are required for use in mid-rise buildings.
This research will support greater adoption of mid-rise residential and non-residential wood-frame construction and improve competition with similar buildings of noncombustible construction. This work will also support the development of the APA system report for midply walls, which will be a design guideline for using midply walls in North America.
When a new engineered wood adhesive is developed for use in a fire-rated assembly, it must first pass a full-scale fire test, for example, a test in accordance with ASTM E119 in the United States. Although full-scale tests serve as the necessary entry to the marketplace, they are extremely costly and reflect the performance of the entire assembly and not just the adhesive. As a result, it is difficult to quantify differences in adhesive performance under elevated temperatures or fire conditions with these tests. Here, we present the results from a new test method developed at the USDA Forest Service, Forest Products Laboratory, to examine adhesive wood performance in glulam beams. The test is part of a larger research program for examining different adhesive formulations. The goals of the intermediate-scale test were to understand differences between adhesive formulations and to provide guidance regarding the performance for full-scale adhesive tests.
Most of the previous work focused on fire behavior of non-combustible construction. However, few investigations have systematically addressed fire development and window ejected flame based on large-scale light timber frame construction (LTFC). This paper conducted a large-scale natural fire experiment to explore the fire development of wooden buildings and the ejected flame behavior by a two-layer light timber frame construction (LTFC). The experimental LTFC included two compartments, with four façade walls consisted of external and internal linings, within 5.1 m height, 3.6 m long and 2.4 m width, and weight of 1480.1 kg. The room temperature, mass variation in burning, radical temperature profiles outside the openings-façade wall, and ejected flame dimension were measured and analyzed. The results were summarized as follows: In LTFC, the room temperature and heat release rate (HRR) would show a second rapid rise, as if “twice flashover” occurred in fully burning stage. This phenomenon is obviously different from the traditional compartment fire development of buildings. Besides, after flashover, the ejected flame height continuously increased until the fire turned into decay stage, whereas the horizontal ejection distance would maintain a steady stage and increased as the openings broken extremely. Furthermore, the region outside the openings façade wall could be divided into three regions, ejected flame region (including continuous and intermittent flame) (Tr > 180 °C), buoyant plume region(150 °C > Tr > 60 °C) and heated air region(60 °C > Tr > T8). A modified function was proposed to predict the temperature profile at different heights for the openings-ejected flame. The data of this paper will enhance the comprehension for fire development of timber buildings and provide some useful information to assess the thermal behavior of window-ejected flame of façade wall.
A structure may be totally destroyed due to a fire, but often it is only partially damaged and parts of it may still be salvaged and reused. For buildings with significant historic and cultural value, it is of utmost importance that these elements, which were only partially damaged, can still be recovered as to preserve the authenticity of the structure. In the case of timber elements after a fire, it is common to find damage on the cross-section exterior part, whereas the inner part presents still a non-damaged section. Therefore, the element is often found with an exterior irregular shape, either due to its original shape prior decay or due to the exposure to fire, that does not coincide with the inner residual cross-section. Moreover, it is essential to perform a preliminary safety analysis to verify which elements can be preserved and to what extent interventions could be needed. The objective of this work is to apply a methodology that allows to calculate the residual cross-section of partially burnt timber elements structures as to calculate the resistant and apparent sections for geometry assessment and to implement that information in three-dimensional structural models. For this purpose, this work proposes a methodology based on a combination of drilling resistance tests together with laser scanner measurements. The methodology was first tested and calibrated within a controlled laboratory environment and then validated onsite using elements from a building exposed to a past fire. The Casa de Sarmento (Sarmento's House) in Guimarães (Portugal) was used as case study, where various structural damages due to a past fire were found.
Utility pole failures are a known cause of wildland fires. Over the past 15 years in the U.S. Department of Interior, Bureau of Land Management (BLM) Idaho Boise District, 299 wildland fires have been related to electric utility powerline structure failures, an average of 20 wildland fires per year. Routine inspection and maintenance would likely reduce the number of wildland fires caused by utility pole failures. The sheer number of poles and the great distances over which electrical lines span in the BLM Idaho Boise District are factors that complicate regular inspections. BLM recognizes the need for a robust inspection protocol that can be performed quickly and easily in the field. To that end, BLM, the USDA Forest Service, Forest Products Laboratory, and Mississippi State University are working jointly to develop an inspection procedure that is comprehensive, fast, and portable. This report summarizes background information on common engineering properties of wood and deterioration mechanisms that affect wood structural performance and describes current state-of-the-art techniques used for field inspection of wood structures.
Engineered timber is an innovative and sustainable construction material, but its uptake has been hindered by concerns about its performance in fire. Current building regulations measure the fire performance of timber using fire resistance tests. In these tests, the charring rate is measured under a series of heat exposures (design fires) and from this the structural performance is deduced. Charring rates are currently only properly understood for the heat exposure of a standard fire, not for other exposures, which restricts the use of performance-based design. This paper studies the charring rates under a range of design fires. We used a multiscale charring model at the microscale (mg-samples), mesoscale (g-samples), and macroscale (kg-samples) for several wood species exposed to different heating regimes and boundary conditions. At the macroscale, the model blindly predicts in-depth temperatures and char depths during standard and parametric fires with an error between 5% and 22%. Comparing simulations of charring under travelling fires, parametric fires, and the standard fire revealed two findings. Firstly, their charring rates significantly differ, with maximum char depths of 42 mm (travelling), 46 mm (parametric), and 59 mm (standard fire), and one (standard fire) to four (travelling fire) charring stages (no charring, slow growth, fast growth, steady-state). Secondly, we observed zero-strength layers (depth between the 200 °C and 300 °C isotherm) of 7 to 12 mm from the exposed surface in travelling fires compared to 5 to 11 mm in parametric fires, and 7 mm in the standard fire. Both traditional design fires and travelling fires, therefore, need to be considered in structural calculations. These results help engineers to move towards performance-based design by allowing the calculation of charring rates for a wide range of design fires. In turn, this will help engineers to build more sustainable and safe structures with timber.
In the design of timber structures, the mechanical resistance in fire conditions has to be ensured among others. In the European standards, Eurocodes, the reduced cross-section method is given to determine mechanical resistance of timber structural elements in fire conditions. The reduced cross-section method is based on an effective cross-section that is determined by two key parameters, namely the charring depth and the thickness of zero-strength layer where the latter accounts for the reductions of the stiffness and the strength of timber due to elevated temperatures. Although, the thickness of zero-strength layer of 7 mm is only prescribed for the ISO 834 standard fire exposure longer than 20 min in the Eurocodes, the same value is often used for non-standard fire exposures as well, which might not always be correct. Thus, in the present paper the thickness of zero-strength layer is investigated for a timber beam exposed to 44 different parametric fires by means of advanced numerical models and a simple design method. A hygro-thermal model and a mechanical model are applied to determine the temperature field over a timber beam cross-section and the mechanical resistance of the beam during fire exposure, respectively. The simple design method is based on the reduced cross-section method. The obtained results show that the thickness of zero-strength layer varies between 8.4 mm and 30.5 mm, which are substantially higher values than the value of 7 mm suggested in the Eurocodes for the standard fire exposure. The results also indicate that the thickness of zero-strength layer is not a constant value and should be written as a function of the parameters defining a parametric fire curve. Alternatively, the effective cross-section could be simply determined by finding the combined thickness of zero-strength layer and charring depth at temperature of about 90 °C.
This paper describes selected observations, measurements, and analysis from a series of large-scale experiments on cross-laminated timber (CLT) slabs that were exposed to fire from below, using four different heating scenarios, with a sustained mechanical loading of 6.3 kN m per metre width of slab. The deflection response and in-depth timber temperatures are used to compare the experimental response against a relatively simple structural fire model to assess the load bearing capacity of CLT elements in fire, including during the decay phase of natural fires. It is demonstrated that the ventilation conditions in experiments with a fixed fuel load are important in achieving burnout of the contents before structural collapse occurs. A mechanics-based structural fire model is shown to provide reasonably accurate predictions of structural failure (or lack thereof) for the experiments presented herein. The results confirm the importance of the ventilation conditions on the fire dynamics, burning duration, and the achievement of functional fire safety objectives (i.e. maintaining stability and compartmentation), in compartments with exposed CLT.
Building elements are required to provide sufficient fire resistance based on requirements set forth in the National Building Code of Canada (NBCC). Annex B of the Canadian standard for wood engineering design (CSA O86-19) provides a design methodology to calculate the structural fire-resistance of large cross-section timber elements. However, it lacks at providing design provisions for connections. The objectives of this study are to understand the fire performance of modern mass timber fasteners such as self-tapping screws, namely to evaluate their thermo-mechanical behavior and to predict their structural fire-resistance for standard fire exposure up to two hours, as would be required for tall buildings in Canada. The results present the great fire performance of using self-tapping screws under a long time exposure on connections in mass timber construction. The smaller heated area of the exposed surface has limited thermal conduction along the fastener’s shanks and maintained their temperature profiles relatively low for two hours of exposure. Based on the heat-affected area, the study presents new design principles to determine the residual length of penetration that would provide adequate load-capacity of the fastener under fire conditions. It also allows determining safe fire-resistance values for unprotected fasteners in mass timber construction exposed up to two hours of standard fire exposure.
Concealed spaces, such as those created by a dropped ceiling in a floor/ceiling assembly or by a stud wall assembly, have unique requirements in the International Building Code (IBC) to address the potential of fire spread in nonvisible areas of a building. Section 718 of the 2018 IBC includes prescriptive requirements for protection and/or compartmentalization of concealed spaces through the use of draft stopping, fire blocking, sprinklers and other means.
One component PUR adhesive is widely used in engineered wood products applications, such as cross-laminated timber (CLT). However, the dramatic deterioration of PUR adhesive bond strength at elevated temperature can out tremendously threat for tall wood building, especially under fire. In this project, we are aiming to improving the bond strength of the PUR adhesive at high temperature by incorporating chemically modified halloysite to improve the poor interface between inorganic fillers and the polymer matrices. To improve the interaction with PUR (Loctite UR20 by Henkel®), the halloysite was chemically grafted with polymeric diphenylmethane diisocyanate (pMDI) (pMDI-H). The effect of adding pMDI modified halloysite to the PUR adhesives was investigated in terms of nanofiller dispersibility, thermal and mechanical properties of the pMDI-halloysite-PUR composite film, and the bonding shear strength of the glued Douglas fir and Spruce-Pine-Fir (SPF) shear blocks under different temperature.
Significant improvement of the bond shear strength can be observed with the addition of 5 and 10% of pMDI-modified PUR adhesive, and the key research findings are summarized as below,
a. pMDI can be successfully grafted onto hydroxylated halloysites to improve its dispersibility in one-component PUR adhesive;
b. Addition of pMDI-H into PUR adhesive can lead to improved glass transition temperature and storage modulus. In contrast, no significant enhancement was observed in h-H added PUR films due to the poor dispersibility;
c. Addition of up to 10% h-H and pMDI-H did not show significant change of the shear strength at 20 °C for both Douglas Fir and SPF;
d. Significant enhancement of shear strength at elevated temperature (60-100 °C) can be observed for 5% and 10% pMDI-H modified PUR adhesive, showing 17% improvement for Douglas Fir and 27-37% for SPF.
Cross-laminated timber (CLT) is well known as an interesting technical and economical product for modern wood structures. The use of CLT for modern construction industry has become increasingly popular in particular for residential timber buildings. Analyzing the CLT behavior in high thermal environment has attracted scholars’ attention. Thermal environment greatly influences the CLT properties and load bearing capacity of CLT, and the investigation can form the basis for predicting the structural response of such CLT-based structures. In the present work, the finite element method (FEM) is employed to analyze the thermal influence on the deformation of CLT. Furthermore, several factors were taken into consideration, including board layer number, hole conformation, and hole position, respectively. In order to determine the influence, several numerical models for different calculation were established. The calculation process was validated by comparing with published data. The performance is quantified by demonstrating the temperature distribution and structural deformation.
The 2021 International Building Code (IBC) introduced three new construction types—Type IV-A, IV-B and IV-C—which allow tall mass timber buildings. For details on the new types and their requirements, see the WoodWorks paper, Tall Wood Buildings in the 2021 IBC – Up to 18 Stories of Mass Timber. This paper builds on that document with an in-depth look at the requirements for shaft walls, including when and where wood can be used.
The acceptable solutions in Division B of the anticipated 2020 NBCC limit the height of Groups C and D buildings of sprinklered encapsulated mass timber construction (EMTC) to 12 storeys in building height, and a measured building height of 42m. The recently published 2021 IBC contains provisions to permit buildings of mass timber construction under the IBC Type IV construction, surpassing the NBCC provisions by maximum building height, building area, occupancy groups, and interior exposed timber. The IBC mass timber buildings are permitted to have a building height of maximum 18 storeys, depending on the occupancy group. Within Type IV construction, four subdivisions are described to have varying maximum permissible building height, area, fire resistance rating (FRR), and interior exposed timber.
Through a comparison of mass timber provisions of both Codes, relevant research reports, test reports, industry standards, this report documents the consequential and inconsequential differences and developed conclusions on whether the NBCC can adopt the IBC provisions, and with what modifications so that the new provisions may fit the NBCC context.
An advanced modelling tool, WoodST, has been developed for fire safety analysis of timber structures. It is demonstrated that this advanced modelling tool can predict the structural response of LVL beams, glulam bolted connections, OSB-web I-joist and wood-frame floors under forces and fire conditions with an accuracy acceptable to design practitioners (i.e., within 10% of test data). The developed modelling tool can:
Fill the gap in terms of suitable models for timber connections, which is an impediment for the design and construction of tall wood buildings;
Provide a cost-effective simulation solution compared to costly experimental solutions; and
Significantly reduce the cost and shorten the time for the development and/or optimization of new wood-based products and connections.
Shear connectors ensure effective interaction between wood beams and concrete slabs of composite beams, and their properties noticeably affect the fire resistance of timber-concrete composite beams. To investigate the shear stiffness of notched connectors in glued laminated timber (GLT)-concrete composite beams under fire conditions, 16 shear tests were conducted. The effects of fire duration and notch length on shear properties of the connectors for a given spacing were studied. The fire tests indicated that the reduction of the notch length from 200 mm to 150 mm remarkably affected the failure mode of the shear specimens, changing from compression failure of notched wood to shear failure of notched concrete. The increase in fire duration reduced effective width of the notched wood, negatively affected the shear stiffness and shear capacity of the connectors, and the shear stiffness decreased more rapidly. The notch length did not have a substantial effect on the shear stiffness of connectors. Based on the experimental results, an analytical model to estimate the shear stiffness of notched connectors in GLT-concrete beam under fire conditions was established.
This paper is intended for developers and owners seeking to purchase insurance for mass timber buildings, for design/construction teams looking to make their designs and installation processes more insurable, and for insurance industry professionals looking to alleviate their concerns about safety and performance.
For developers, owners and design/construction teams, it provides an overview of the insurance industry, including its history, what affects premiums, how risks are analyzed, and how project teams can navigate coverage for mass timber buildings. Insurance in general can seem like a mystery—what determines premium fluctuations, impacts of a strong vs. weak economy, and the varying roles of brokers, agents and underwriters. This paper will explain all of those aspects, focusing on the unique considerations of mass timber projects and steps that can be taken to make these buildings more insurable.
For insurance brokers, underwriters and others in the industry, this paper provides an introduction to mass timber, including its growing use, code recognition and common project typologies. It also covers available information on fire performance and post-fire remediation, moisture impacts on building longevity, and items to watch for when reviewing specific projects.
The development of this primer commenced shortly after the 2018 launch of the Mass Timber Institute (MTI) centered at the University of Toronto. Funding for this publication was generously provided by the Ontario Ministry of Natural Resources and Forestry. Although numerous jurisdictions have established design guides for tall mass timber buildings, architects and engineers often do not have access to the specialized building science knowledge required to deliver well performing mass timber buildings. MTI worked collaboratively with industry, design professionals, academia, researchers and code experts to develop the scope and content of this mass timber building science primer. Although provincially funded, the broader Canadian context underlying this publication was viewed as the most appropriate means of advancing Ontario’s nascent mass timber building industry. This publication also extends beyond Canada and is based on universally applicable principles of building science and how these principles may be used anywhere in all aspects of mass timber building technology. Specifically, these guidelines were developed to guide stakeholders in selecting and implementing appropriate building science practices and protocols to ensure the acceptable life cycle performance of mass timber buildings. It is essential that each representative stakeholder, developer/owner, architect/engineer, supplier, constructor, wood erector, building official, insurer, and facility manager, understand these principles and how to apply them during the design, procurement, construction and in-service phases before embarking on a mass timber building project.
When mass timber building technology has enjoyed the same degree of penetration as steel and concrete, this primer will be long outdated and its constituent concepts will have been baked into the training and education of design professionals and all those who fabricate, construct, maintain and manage mass timber buildings.
One of the most important reasons this publication was developed was to identify gaps in building science knowledge related to mass timber buildings and hopefully to address these gaps with appropriate research, development and demonstration programs. The mass timber building industry in Canada is still a collection of seedlings that continue to grow and as such they deserve the stewardship of the best available building science knowledge to sustain them until such time as they become a forest that can fend for itself.