This article presents a test method that was developed to screen adhesive formulations for finger-jointed lumber. The goal was to develop a small-scale test that could be used to predict whether an adhesive would pass a full-scale ASTM E119 wall assembly test. The method involved loading a 38-mm square finger-jointed sample in a four-point bending test inside of an oven with a target sample temperature of 204°C. The deformation (creep) was examined as a function of time. It was found that samples fingerjointed with melamine formaldehyde and phenol resorcinol formaldehyde adhesives had the same creep behavior as solid wood. One-component polyurethane and polyvinyl acetate adhesives could not maintain the load at the target temperature measured middepth of the sample, and several different types of creep behavior were observed before failure. This method showed that the creep performance of the onecomponent adhesives may be quite different than the performance from short-term load deformation curves collected at high temperatures. The importance of creep performance of adhesives in the fire resistance of engineered wood is discussed.
Five full-scale fire experiments were conducted to observe the performance of a two-level apartment-style structure constructed of mass timber. Each level consisted of a one bedroom apartment, an L-shaped corridor, and a stairwell connecting the two levels. One of the primary variables considered in this test series was the amount and location of exposed mass timber. The amount of mass timber surface area protected by gypsum wallboard ranged from 100% to no protection. For each experiment, the fuel load was identical and the fire was initiated in a base cabinet in the kitchen. In the first three experiments, the fire reached flashover conditions, and subsequently underwent a cooling phase as the fuel load from combustible contents was consumed. The first three experiments were carried out for a duration of up to 4 h. In the fourth experiment, automatic fire sprinklers were installed. Sprinklers suppressed the fire automatically. In the fifth experiment, the activation of the automatic fire sprinklers was delayed by approximately 20 minutes beyond the sprinkler activation time in the fourth experiment to simulate responding fire service charging a failed sprinkler water system. A variety of instrumentation was used during the experiments, including thermocouples, bidirectional probes, optical density meters, heat flux transducers, directional flame thermometers, gas analyzers, a fire products collector, and residential smoke alarms. In addition, the experiments were documented with digital still photography, video cameras, and a thermal imaging camera. The experiments were conducted in the large burn room of the Bureau of Alcohol, Tobacco, Firearms and Explosives Fire Research Laboratory located in Beltsville, Maryland, USA. This report provides details on how each experiment was set up, how the experiments were conducted, and the instrumentation used to collect the data. A brief summary of the test results is also included. Detailed results and full data for each test are included in separate appendices.
There is a current trend towards mid- and high-rise mass timber buildings. With this trend, there is a research need to develop a comparison between mass timber compartment fires and non-combustible compartment fires. In an effort to address the knowledge gaps in the fire performance of cross-laminated timber compartments, a full-scale fire test series was developed. The fire test series included five tests with varying levels of exposed cross-laminated timber on a two story cross-laminated timber structure. Here we present a detailed summary of the fire test series, instrumentation plan, and an overview of the results.
There is a current trend towards mid- and high-rise mass timber buildings. With this trend, there is a research need to develop a comparison between mass timber compartment fires and non-combustible compartment fires. In an effort to address the knowledge gaps in the fire performance of cross-laminated timber compartments, a full-scale fire test series was developed. The fire test series included five tests with varying levels of exposed cross-laminated timber on a two story cross-laminated timber structure. Here we present a detailed summary of the fire test series, instrumentation plan, and an overview of the results.
Cross-laminated timber (CLT) is a type of mass timber panel used in floor, wall, and roof assemblies. An important consideration in design and construction of timber buildings is moisture durability. This study characterized the hygrothermal performance of CLT panels with laboratory measurements at multiple scales, field measurements, and modeling. The CLT panels consisted of five layers, four with spruce-pine-fir lumber and one with Douglas-fir lumber. Laboratory characterization involved measurements on small specimens that included material from only one or two layers and large specimens that included all five layers of the CLT panel. Water absorption was measured with panel specimens partially immersed in water, and a new method was developed where panels were exposed to ponded water on the top surface. This configuration gave a higher rate of water uptake than the partial immersion test. The rate of drying was much slower when the wetted surface was covered with an impermeable membrane. Measured hygrothermal properties were implemented in a one-dimensional transient hygrothermal model. Simulation of water uptake indicated that vapor diffusion had a significant contribution in parallel with liquid transport. A simple approximation for liquid transport coefficients, with identical coefficients for suction and redistribution, was adequate for simulating panel-scale wetting and drying. Finally, hygrothermal simulation of a CLT roof assembly that had been monitored in a companion field study showed agreement in most cases within the sensor uncertainty. Although the hygrothermal properties are particular to the wood species and CLT panels investigated here, the modeling approach is broadly applicable.
The use of mass timber structural products in tall building applications (6–20 stories) is becoming more common around the world including North America. A potential concern is the environmental wetting of mass timber products during construction because such products may dry out more slowly than light-frame structural lumber, and wood, as an organic material, is susceptible to deterioration at elevated moisture contents. In order to better understand the moisture conditions present in high rise timber constructions, a long-term moisture monitoring program was implemented on an eight story, mixed-use, mass timber framed building in Portland, Oregon. The building was monitored with an array of moisture meters to track moisture content throughout the building’s construction and operation. This paper presents data covering a period just over one year starting from the manufacture of crosslaminated timber (CLT) panels. Hygrothermal properties of CLT samples of the same type used in the building were measured in the laboratory, and wetting and drying experiments on representative CLT samples were conducted. Simulated moisture contents using a one-dimensional hygrothermal model compared reasonably well with laboratory experiments and building site measurements.
International Conference on New Horizons in Green Civil Engineering
Research Status
Complete
Notes
April 25-27,2018. Victoria, Canada
Summary
This paper presents preliminary findings from an ongoing research program instrumenting CLT buildings to measure wood moisture content. An overview of the research program is presented along with data from first year of moisture monitoring in an 8-story building in Portland, Oregon. This project measures the wood moisture content throughout the construction cycle, including the fabrication, shipping, staging, and erection of the panels. These preliminary field measurements can help characterize moisture changes in CLT during construction and guide the construction of future CLT buildings.
The increasing use of cross laminated timber (CLT) panels in large multi-story buildings has highlighted the structural performance of CLT in fire as a critical issue concerning life safety and serviceability. It is well-known that wood material strength decreases when exposed to elevated temperature for an extended period of time. For CLT panels, another level of complexity lies in the mechanical properties of the glued interface under high temperature. In this study, the tensile strength of typical North American wood species and shear strength of the glued interface of commonly used adhesives in CLT production were evaluated at different levels of elevated temperatures. The researchers systematically tested glue interface and wood samples in a controlled temperature chamber and obtained the load-deformation curves of the specimens until failure was observed. A total of five temperature levels were tested, with three wood species and four wood adhesive types. The glued interface strength was also compared to wood material strength itself under different temperatures. For each test, multiple samples were tested to ensure statistical significance of the results. The ultimate objective of this study is to develop a mechanistic model for CLT panels that can take into account the effect of temperature. In this paper, only the design, execution, and results from the elevated temperature tests are presented.
The 2nd Mass Timber Research Needs Assessment was held on November 13–14, 2018, at the USDA Forest Service, Forest Products Laboratory (FPL). The workshop was co-sponsored by FPL, WoodWorks, and the U.S. Endowment for Forestry and Communities. The purpose of the workshop was to gather a diverse group of people with expertise in mass timber, in particular cross-laminated timber, to discuss and prioritize research needed to move the mass timber industry forward in North America. The workshop was attended by more than 100 design professionals, researchers, manufacturers, industry leaders, and government employees. The meeting resulted in a list of 117 research needs. Following the meeting, the list of research needs was prioritized through an online survey. This report presents the prioritized research needs of the mass timber industry in North America. Also included in the appendixes are the formal minutes of the workshop, a list of participants, and the original scribe notes.
