The benefits of using shear connectors to join wood beams to a concrete slab in a composite floor or deck system are many. Studies throughout the world have demonstrated significantly improved strength, stiffness, and ductility properties from such connection systems as well as citing practical building advantages such as durability, sound insulation, and fire resistance. In this study, one relatively new shear connector system that originated in Germany has been experimentally investigated for use with U.S. manufactured products. The connector system consists of a continuous steel mesh of which one half is glued into a southern pine Parallam® Parallel Strand Lumber beam and the other half embedded into a concrete slab to provide minimal interlayer slip. A variety of commercial epoxies were tested for shear strength and stiffness in standard shear or “push out” tests. The various epoxies resulted in a variety of shear constitutive behaviors; however, for two glue types,shear failure occurred in the steel connector resulting in relatively high initial stiffness and ductility as well as good repeatability. Slip moduli and ultimate strength values are presented and discussed. Full-scale bending tests, using the best performing adhesive as determined from the shear tests, were also conducted. Results indicate consistent, near-full composite action system behavior.
Use of structural composite lumber products is increasing. In applications requiring a fire resistance rating, calculation procedures are used to obtain the fire resistance rating of exposed structural wood products. A critical factor in the calculation procedures is char rate for ASTM E 119 fire exposure. In this study, we tested 14 structural composite lumber products to determine char rate when subjected to the fire exposure of the standard fire resistance test. Char rate tests on 10 of the composite lumber products were also conducted in an intermediate-scale horizontal furnace. The National Design Specification/Technical Report 10 design procedure for calculating fire resistance ratings of exposed wood members can be used to predict failure times for members loaded in tension. Thirteen tests were conducted in which composite lumber products were loaded in tension as they were subjected to the standard fire exposure of ASTM E 119. Charring rates, observed failure times in tension tests, and deviations from predicted failure times of the structural composite lumber products were within expected range of results for sawn lumber and glued laminated timbers.
January 26-28, 2009, San Francisco, California, USA
Summary
Fire-resistive wood construction is achieved either by having the structural elements be part of fire-rated assemblies or by using elements of sufficient size that the elements themselves have the required fire-resistance ratings. For exposed structural wood elements, the ratings in the United States are calculated using either the T.T. Lie method or the National Design Specifications (NDS) Method. There is no widely accepted methodology in the United States to determine the fire-resistance rating of an individual structural wood element with the protective membrane directly applied to the exposed surfaces of the element. In these tests, we directly applied one or two layers of 16-mm thick fire-rated gypsum board or 13-mm thick southern pine plywood for the protective membrane to the wood element. The wood elements were Douglas-fir laminated veneer lumber (LVL) specimens and Douglas-fir gluedlaminated specimens that had previously been tested without any protective membrane. The methodology for the tension testing in the horizontal furnace was the same used in the earlier tests. The fire exposure was ASTM E 119. For the seven single-layer gypsum board specimens, the improvements ranged from 25 to 40 min. with an average value of 33 min. For the three double-layer specimens, the improvement in times ranged from 64 to 79 min. with an average value of 72 min. We concluded that times of 30 min. for a single layer of 16-mm Type X gypsum board and at least 60 min. for a double layer of 16-mm Type X gypsum board can be added to the fire rating of an unprotected structural wood element to obtain the rating of the protected element.
Summarizes information on wood as an engineering material. Presents properties of wood and wood-based products of particular concern to the architect and engineer. Includes discussion of designing with wood and wood-based products along with some pertinent uses. Keywords: wood structure, physical properties (wood), mechanical properties (wood), lumber, wood-based composites, plywood, panel products, design, fastenings, wood moisture, drying, gluing, fire resistance, finishing, decay, preservation, wood-based products, heat sterilization, sustainable use.
There is growing interest from the Canadian wood products industry to produce and use cross-laminated timber (CLT) panels in construction. Because this is a new product in North America, there is a need to demonstrate that the product meets various performance attributes such as structural resistance, sound transmission and fire resistance.
This research aims to address two primary objectives which will support the North American adoption of CLT. First, a generic calculation method for determining the fire-resistance of CLT assemblies is needed to enable producers to manufacture a number of different configurations of panels without the need to run a large number of full-scale fire tests. Second, the CLT assemblies chosen for testing have been identified as the most likely configurations to be used thereby providing test data to support the claims of fire-resistance to help satisfy the authority having jurisdiction.
This paper describes a series of three full-scale furnace tests on post-tensioned LVL box beams loaded with vertical loads, and presents a proposed fire design method for post-tensioned timber members. The design method is adapted from the calculation methods given in Eurocode 5 and NZS:3603 which includes the effects of changing geometry and several failure mechanisms specific to post-tensioned timber. The design procedures include an estimation of the heating of the tendons within the timber cavities, and relaxation of post-tensioning forces. Additionally, comparisons of the designs and assumptions used in the proposed fire design method and the results of the full-scale furnace tests are made. The experimental investigation and development of a design method have shown several areas which need to be addressed. It is important to calculate shear stresses in the timber section, as shear is much more likely to govern compared to solid timber. The investigation has shown that whilst tensile failures are less likely to govern the fire design of post-tensioned timber members, due to the axial compression of the post-tensioning, tensile stresses must still be calculated due to the changing centroid of the members as the fire progresses. Research has also highlighted the importance of monitoring additional deflections and moments caused by the high level of axial loads.
Cross Laminated Timber (CLT), which is made by laminating dimension lumber at right angles, is an innovative high-performance building material that offers many positive attributes including renewability, high structural stability, storage of carbon during the building life, good fire resistance, possibility of material recycling and reuse. It is conceptually a sustainable and cost effective structural timber solution that can compete with concrete in non-residential and multi-family mid-rise building market. Therefore, there is a need to understand and quantify the environmental attribute of this building system in the context of North American resources, manufacturing technology, energy constraints, building types, and construction practice. This study is to compare energy consumption of two building designs using different materials, i.e. CLT and concrete.
The designs were based on a five-storey office building, Discovery Place-Building 12, which is located in Burnaby, British Columbia, at 4200 Canada Way. The existing building was built with reinforced concrete. Embodied energy was calculated based on the total amount of material required for each of the building systems. Operational energy was calculated using eQUEST, an energy usage modeling software tool. The environmental impacts of the buildings were evaluated by comparing the total energy consumption through the building life.
CLT has lower non-renewable energy consumption compared to concrete in terms of material acquisition, manufacturing and transportation. Previous studies shew that operational energy accounts for the main amount of total energy use in buildings during their service life. Hence, the importance of embodied energy increases by reducing operational energy consumption. CLT has lower embodied energy compared to concrete. Therefore, the advantage of using CLT as a construction material is becoming greater by designing low energy or passive buildings.
Wood-frame is the most common construction type for residential buildings in North America. However, there is a limit to the height of the building using a traditional wood-frame structure. Cross-laminated timber (CLT) provides possible solutions to mid-rise and high-rise wood buildings. CLT offers many advantages such as improved dimensional stability, a quicker erection time and good performance in case of fire. In order to introduce the cross-laminated timber products to the North American market, it is important to gain a comprehensive understanding of its structural properties. This paper focuses on the seismic performance of CLT connections. Over the last few years FPInnovations of Canada has conducted a test program to determine the structural properties of CLT panels and its application in shear walls. The test program comprised of more than 100 connection tests which followed the loading procedures of CUREE and ISO test protocols as specified in ASTM Standards ASTM E 2126-09 (2009). These tests were performed parallel and perpendicular to the grain of the outer layer, respectively. The impact of different connections on the seismic performance of CLT walls was investigated in a second phase on full size shearwall. CLT panels are relatively stiff and thus energy dissipation must be accomplished through the ductile behaviour of connections between different shear wall elements and the connections to the story below. A literature review on previous research work related to damage prediction and assessment for wood frame structures was performed. Different approaches for damage indices were compared and discussed. This paper describes how the energy-based cumulative damage assessment model was calibrated to the CLT connection and shear wall test data in order to investigate the damage under monotonic and cyclic loading. Comparison of different wall setup provided a deeper insight into the damage estimation of CLT shear walls and determination of the key parameters in the damage formulation. This represents a first published attempt to apply the damage indices to estimate the seismic behaviour of CLT shear walls.
Cross-laminated timber panel buildings are gaining a growing interest of the scientific community due to significant technical advantages, such as the material sustainability, the high fire resistance and quickness of erection. Nevertheless, it is well known that timber panels themselves are not able to dissipate a significant amount of energy during an earthquake. In fact, in this system the seismic design is carried out in order to dissipate the energy by means of inelasticity of connections. Generally, the elements devoted to withstand plastic deformations are the panel-panel and panel-foundation joints and, therefore, their ability to sustain repeated excursion in plastic range governs the building inelastic response. The paper here presented aims to propose an advanced approach for designing cross laminated timber panel buildings. In particular, it is proposed to substitute the classical hold-downs, which usually exhibit a limited dissipation capacity, with an innovative type of dissipative angle bracket. The new connections, called dissipative L-stub, apply the concept usually adopted for designing the hysteretic metallic dampers ADAS (Added Damping and Stiffness). In particular, their tapered shape allows a better spread of lasticization resulting in a high dissipation capacity. Within this framework, in order to characterize the force-displacement response under cyclic loads of L-stubs an experimental campaign is carried out. Afterwards, the effectiveness of the proposed approach is proved by analysing the non-linear response under seismic loads of a three-storey building alternatively equipped with hold-downs or L-stub. Finally, the response of classical and innovative system is compared in terms of behaviour factor.
This research investigates the fire behaviour of laminated veneer lumber elements and cross-laminated timber panels. The study focused on some research questions regarding the fire resistance of unprotected and protected timber structural elements, the possibility to predict accurately the fire behaviour of timber elements through numerical modelling, and the accuracy of analytical estimations of fire resistance using simplified design methods.
Experimental tests of small and large specimens exposed to fire on one or more sides and subjected to different types and levels of load were performed. The results highlight the good performance of timber structural elements in fire conditions. The collected data were used to validate two- and three-dimensional models implemented in the general purpose finite element code Abaqus. Thermal and mechanical analyses were carried out to estimate the temperature distribution within unprotected and protected cross-sections of different sizes, the fire resistance and the displacement of timber elements loaded in-plane and out-of-plane. Further, parametric studies assuming different timber properties-temperature relationships were also performed. The proposed numerical modelling can be used to investigate the fire behaviour of timber members made of other wood-based products and subjected to different loads and fire conditions.
Experimental and numerical results were compared with analytical predictions obtained by using simplified design methods proposed by current codes of practice and recent research proposals. Numerical and analytical methods provide overall acceptable estimations of fire behaviour of timber members, especially considering the high variability that characterizes the wood material and the experimental tests, in particular the fire tests.
The focus of this research was to investigate the fire performance of post-tensioned timber beams. This was completed through a series of full-scale furnace tests, and the development of a fire resistance design method. Previous research has focused on the seismic performance and gravity frame performance of post-tensioned timber, both of which yielded promising results. There is however a commonly perceived increase in fire risk with timber building, particularly multi-storey timber buildings, and the fire performance of post-tensioned timber had not previously been investigated.
This paper describes numerical modelling to predict the fire resistance of engineered timber floor systems. The floor systems under investigation are timber composite floors (various timber joist and box floor cross sections), and timber-concrete composite floors. The paper describes 3D numerical modelling of the floor systems using finite element software, carried out as a sequential thermo-mechanical analysis. Experimental testing of these floor assemblies is also being undertaken to calibrate and validate the models, with a number of full scale tests to determine the failure mechanisms for each floor type and assess fire damage to the respective system components. The final outcome of this research will be simplified design methods for calculating the fire resistance of a wide range of engineered timber floor systems.
This paper describes a series of full-scale furnace tests on loaded post tensioned LVL beams. Each beam was designed to exhibit a specific failure mechanism when exposed to the standard ISO834 fire. In addition to the beams a number of steel anchorage protection schemes were also investigated. These included wrapping the ends in kaowool, using intumescent paint, covering the anchorage with fire rated plasterboard and covering the anchorage with timber (LVL). The results of the full-scale tests cover temperature distributions through the timber members during the tests, the temperatures reached within the cavity and those of the tendons suspended within the cavity, the relaxation of the tendons during the test, the failure mechanisms experienced, and a summary of the anchorage protection details and their effectiveness. Recommendations for the design of both post-tensioned timber beams and associated anchorages are also provided.
During this MSc thesis it has been carried out an extensive literature review on fire safety engineering, on timber behaviour on fire and on fire safety regulations in different countries. A preliminary design for a high rise cross laminated timber building (CLT) has been carried out in order to obtain a minimum thickness of the structural elements needed for the load bearing structure. This thickness has been verified according to prescriptive fire regulations. Furthermore, fire safety analyses have been performed to evaluate a more realistic fire behaviour of exposed timber structures. The finite element program SAFIR and the fire model OZone have been used in the advance calculations. Finally, it is shown that timber buildings should be designed according to advance fire safety approach and suggestions are given for developing a timber fire model.
FPInnovations is involved in a large research project regarding CLT construction. One objective of this research is the creation of a design methodology for calculating the fire-resistance of CLT assemblies/construction. This methodology will foster the design of fire-safe buildings of wood or hybrid construction. In order to establish such calculation methods, a series of experimental tests has been undertaken. A total of eight full-scale CLT fire resistance tests have been conducted at the NRC fire laboratory where the panels were subject to the standard ULC S101 [1] fire exposure. The series consisted of three wall and five floor tests. Each test was unique using panels with a different number of plies and varying thicknesses. Some of the assemblies were protected using CGC Sheetrock® FireCode® Core Type X gypsum board while others were left unprotected.
Finger joints are commonly used to produce engineered wood products like glued laminated timber beams. Although comprehensive research has been conducted on the structural behaviour of finger joints at ambient temperature, there is very little information about the structural behaviour at elevated temperature. A comprehensive research project on the fire resistance of bonded timber elements is currently ongoing at the ETH Zurich. The aim of the research project is the development of simplified design models for the fire resistance of bonded structural timber elements taking into account the behaviour of the adhesive used at elevated temperature. The paper presents the results of a first series of tensile and bending tests on specimens with finger joints pre-heated in an oven. The tests were carried out with different adhesives that fulfil current approval criteria for the use in loadbearing timber components. The results showed substantial differences in temperature dependant strength reduction and failure between the different adhesives tested. Thus, the structural behaviour of finger joints at elevated temperature is strongly influenced by the behaviour of the adhesive used for bonding and may govern the fire design of engineered wood products like glued laminated timber beams.
Report of Testing Cross Laminated Timber Panels for Compliance with CAN/ULC-S101 Standard Methods of Fire Endurance Tests of Building Construction and Materials: Loadbearing 3-Ply CLT Wall with Attached Wood Frame Partition
Intertek Testing Services NA, Inc. (Intertek) has conducted testing for the Canadian Wood Council, on Cross-Laminated Timber Panels, to evaluate their fire resistance. Testing was conducted in accordance with the applicable requirements, and following the standard methods, of CAN/ULC-S101 Standard Methods of Fire Endurance Tests of Building Construction and Materials, fourth edition, July 2007. This evaluation took place on December 30, 2011.
Inspection, Testing, and Monitoring of Buildings and Bridges
Summary
Depending on the severity, fire damage can compromise the structural integrity of wood structures such as buildings or residences. Fire damage of wood structures can incorporate several models that address (1) the type, cause, and spread of the fire, (2) the thermal gradients and fire-resistance ratings, and (3) the residual load capacity.
The investigator should employ engineering judgment to identify those in-service members that are to be replaced, repaired, or can remain in-service as they are. Suchjudgment will likely be based on the visual inspection of damaged members, connections, and any protective membranes.
This study which involves the development of fire loads and design fires for residential and non-residential mid-rise buildings is part of NEWBuildS’ “Rationalization o f Life Safety - Code Requirements fo r Mid-rise Buildings” project. The project is focused on analysing the code requirements that relate to fire resistance and the use of automatic sprinklers for mid-rise buildings built with combustible or non-combustible construction. The ultimate goal of the project is to come up with alternative solutions and, potentially, trigger changes in the code requirements for mid-rise buildings.
A review, compilation, and analysis of fire load survey data was conducted from available literature for residential and office buildings. A web survey of floor areas was also conducted for floor areas of mid-rise buildings. Fire loads and fuel packages for midrise buildings were developed based on previous surveys as well as the web survey. The fire load data in conjunction with statistical data was used to select fire scenarios from which design fire scenarios were chosen.
The fire characteristics of the selected fuel packages, such as heat release rate, and production of toxic gases, were analyzed using the two-zone fire risk analysis model, CUrisk, in order to develop appropriate design fires for mid-rise buildings.
Recently, Vancouver architect, Michael Green, issued a report entitled Tall Wood, arguing that skyscrapers and other tall buildings should use more wood as a primary construction material. His argument is that wood is up to the task, is less polluting, and is more environmentally sustainable than the materials currently used. Green’s (2012) buildings would employ “massive timber” elements such as cross laminated timber, laminated strand lumber, and laminated veneer lumber. Green is not suggesting that these tall building be of wood only. Rather, he is arguing that mass timber be integrated with other commonly-used structural materials such as concrete and steel.
While wood and wood-mix skyscrapers capture the imagination, extending the height of buildings with the more typical lighter-frame construction is perhaps a more practical concern. Currently, light frame construction tends to be limited to buildings of four storeys and less in North America. In some jurisdictions, this limit is mandated by building codes: in others, it is simply practice. Yet, the ability to construct acceptably safe timber structures with appropriate sprinkler and other technologies led Switzerland to change its fire codes in 2005 and allow the use of structural timber in medium-rise residential buildings of up to six storeys (Frangi and Fontana, 2010). Depending upon the application, mid-sized wood frame buildings can be a less expensive and more flexible alternative to other structures.
Despite the prevalence of wood frame structures throughout North America and parts of Europe, major concerns remain over the fire safety of such structures. This paper discusses some of the issues relating to wood structures and flammability.
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