Mass timber building materials such as cross-laminated timber (CLT) have captured attention in mid- to high-rise building designs because of their potential environmental benefits. The recently updated multistory building code also enables greater utilization of these wood building materials. The cost-effectiveness of mass timber buildings is also undergoing substantial analysis. Given the relatively new presence of CLT in United States, high front-end construction costs are expected. This study presents the life-cycle cost (LCC) for a 12-story, 8,360-m2 mass timber building to be built in Portland, Oregon. The goal was to assess its total life-cycle cost (TLCC) relative to a functionally equivalent reinforced-concrete building design using our in-house-developed LCC tool. Based on commercial construction cost data from the RSMeans database, a mass timber building design is estimated to have 26 percent higher front-end costs than its concrete alternative. Front-end construction costs dominated the TLCC for both buildings. However, a decrease of 2.4 percent TLCC relative to concrete building was observed because of the estimated longer lifespan and higher end-of-life salvage value for the mass timber building. The end-of-life savings from demolition cost or salvage values in mass timber building could offset some initial construction costs. There are minimal historical construction cost data and lack of operational cost data for mass timber buildings; therefore, more studies and data are needed to make the generalization of these results. However, a solid methodology for mass timber building LCC was developed and applied to demonstrate several cost scenarios for mass timber building benefits or disadvantages.
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.
The goal of this study was to update life-cycle assessment (LCA) data associated with laminated veneer lumber (LVL) production in the Pacific Northwest (PNW) region of the United States from cradle-to-gate mill output. The authors collected primary mill data from LVL production facilities per Consortium on Research for Renewable Industrial Materials (CORRIM) Research Guidelines. Comparative assertions were not a goal of this study.
The goal of the present study was to develop life-cycle impact assessment (LCIA) data associated with gate-to-gate laminated veneer lumber (LVL) production in the southeast (SE) region of the U.S. with the ultimate aim of constructing an updated cradle-to-gate mill output life-cycle assessment (LCA). The authors collected primary (survey) mill data from LVL production facilities per Consortium on Research for Renewable Industrial Materials (CORRIM) Research Guidelines. Comparative assertions were not a goal of the present study.
Contact: C. Elizabeth Stokes, Mississippi State University, Juliet Tang, Forest Products Laboratory (United States)
Summary
Outcomes anticipated from the results of this project are biodegradation information for CLT products and an improved understanding of biodegradation differences between CLT products and comparable laminated and solid wood products. Results will benefit the emerging CLT industry and provide valuable information for market expansion into areas with high termite pressure.
The USDA Forest Products Laboratory (FPL) has, for the past two years, been assisting in removing technical barriers to the use of CLT and trying to develop interest in the United States for its utilization. Coincidentally, Promega Corporation, a leader in providing innovative solutions and technical support to the life sciences industry, is currently constructing a new facility in Fitchburg, Wisconsin, that features CLT. This is the first large-scale commercial utilization of CLT in the United States using CLT manufactured in North America. As with any new building system, it is important for the design and construction community to have information on how CLT is installed and how it performs.
The objectives of this research are twofold: (1) to document the CLT installation process with photography and video and (2) to install sensors in the CLT panels and collect data on in-service moisture and temperature conditions.
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.
Cross-laminated timber (CLT) construction has been gaining popularity in North America. However, CLT-based seismic force resisting systems are not recognized in current U.S. design codes, which is among the many challenges preventing widespread adoption of CLT in the United States. The purpose of this study was to investigate the seismic behavior of CLT-based shear wall systems and to determine seismic performance factors, namely, the response modification factor (R factor), the system overstrength factor(O), and the deflection amplification factor (Cd), using the FEMA P695 procedure. Nine index buildings including single-family dwellings, multifamily dwellings, and commercial (including mixed use) midrise buildings were developed, from which 72 archetypes were extracted. Testing performed at the component and subassembly levels included connector tests and isolated shear wall tests. A CLT shear wall design method was developed and used to design the archetypes, which were then assessed with nonlinear pushover analysis and incremental dynamic analysis. Based on the required collapse margin, an R factor of 3 is proposed for CLT shear wall systems with 2:1 or mixed aspect ratio panels up to 4:1, and an R factor of 4 is proposed for CLT shear wall systems made up of only 4:1 aspect ratio panels. Results from this study have been proposed for recognition in U.S. building codes (such as the International Building Code) through specific change proposals to update reference standards such as ASCE 7 Minimum Design Loads and Associated Criteria for Buildings and Other Structures and Special Design Provisions for Wind and Seismic.
With global urbanization trends, the demands for tall residential and mixed-use buildings in the range of 8~20 stories are increasing. One new structural system in this height range are tall wood buildings which have been built in select locations around the world using a relatively new heavy timber structural material known as cross laminated timber (CLT). With its relatively light weight, there is consensus amongst the global wood seismic research and practitioner community that tall wood buildings have a substantial potential to become a key solution to building future seismically resilient cities. This paper introduces the NHERI Tallwood Project recentely funded by the U.S. National Science Fundation to develop and validate a seismic design methodology for tall wood buildings that incorporates high-performance structural and nonstructural systems and can quantitatively account for building resilience. This will be accomplished through a series of research tasks planned over a 4-year period. These tasks will include mechanistic modeling of tall wood buildings with several variants of post-tensioned rocking CLT wall systems, fragility modeling of structural and non-structural building components that affect resilience, full-scale biaxial testing of building sub-assembly systems, development of a resilience-based seismic design (RBSD) methodology, and finally a series of full-scale shaking table tests of a 10-story CLT building specimen to validate the proposed design. The project will deliver a new tall building type capable of transforming the urban building landscape by addressing urbanization demand while enhancing resilience and sustainability.
US manufacturers are looking to expand the use of cross-laminated timber (CLT) panels into the North American market, including states located in the southeast where termites are important pests. However, there is no current assessment method for determining CLT vulnerability to the highly destructive native termites found in many states across the United States. The impact of damage by these termites is of particularly high interest in areas with suitable climate to their proliferation, such as the southeastern United States. This study evaluated durability of CLT panels and developed a laboratory assay to test susceptibility of this product to termites. Untreated CLT suffered mass losses of up to 5.8% in testing with an average visual rating of 7.2, indicating a moderate to severe attack with 10-30% of the cross section of the product affected by termite intrusion. Recommendations were developed for the inclusion of modifications presented in standardized testing protocols and will be presented to standards organizations. The proposed method may also be applied to evaluate termite resistance of other mass lumber products such as laminated veneer lumber and Glulam.
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