The objective of this paper was to quantify and compare the environmental impacts associated with alternative designs of typical North American low and mid-rise buildings. Two scenarios were considered: a traditional structural steel frame or an all-wood mass timber design, utilizing engineered wood products for both gravity and lateral load resistance. The boundary of the quantitative analysis was cradle-to-grave with considerations taken to discuss end-of-life and material reuse scenarios. The TRACI methodology was followed to conduct a Life Cycle Impact Assessment (LCIA) analysis that translates building quantities to environmental impact indicators using the Athena Impact Estimator for Buildings Life Cycle analysis software tool and Athena’s Life Cycle Inventory database. The results of the analysis show that mass timber buildings have an advantage with respect to several environmental impact categories, including eutrophication potential, human health particulate, and global warming potential where a 31% to 41% reduction was found from mass timber to steel designs, neglecting potential carbon sequestration benefits from the timber products. However, it was also found that the steel buildings have a lower impact with respect to the environmental impact categories of smog potential, acidification potential, and ozone depletion potential, where a 48% to 58% reduction was found from the steel to the mass timber building designs.
Through collaboration with the NHERI TallWood Project funded by the National Science Foundation,an alternative non-prestressed cross-laminated timber rocking wall system with replaceable fuse components was developed by Katerra engineers and tested at the outdoor shake table at the University of California San Diego. The objective of this specific design and testing is to prove a concept for a new high performance seismic lateral system that is easy to modularize and install, and can be rapidly repaired after major earthquakes. This paper presents the results from a total of thirteen tests conducted on the proposed system, including several repairs after major shaking. The test results showed that the structural system was damage-free under service level ground motions, and experienced repairable damage at designated connection locations for design basis earthquakes and maximum considered earthquakes. Overall the system was able to limit residual drift to an acceptable level and provide a high load displacement capacity for the building system.
The objective of this research was to develop an inter-panel connector capable of sustaining reverse cyclic loads. The prescribed use for the connector was for cross-laminated timber rocking walls. Cross-laminated timber has few current lateral systems. From this need two shear plate inter-panel connectors were designed: A and B. These connectors had high initial stiffness and displacement capacity. The end goal was shake table testing the connectors on a two-story structure. First, finite element modeling was conducted to ensure connectors were sufficient for design. Panels were tested on two scales at Washington State. The first was a single connector level, which had some errors in boundary condition, which limited the output. Second, a rocking wall test, isolating the connectors. This test produced higher quality results, though some errors at high drifts occurred. Stiffness of A and B were 4 and 32 k/in, respectively. Both had equivalent viscous damping for isolated connectors in the range of 20%, however B was dropping to a lower converging value. Due to the buckling behavior of the fuses and connection details, an augmented Fuse A was the sole fuse on the shake table structure. Shake table testing was conducted on a full-scale two-story building at University of California, San Diego. 13 motions were run, ranging in scale from service level earthquakes to scaling higher than a maximum considered earthquake. Four separate records were used to ensure a wide range of frequencies and amplitudes. The connectors experienced less visible residual deformation than in the small tests and the test displacements were lower. The beginnings of lateral torsional buckling began after the last test, scaled above maximum considered earthquake. The period was high for a two-story structure, at approximately one second. The building underwent approximately four percent roof drift and the structure alone had an equivalent viscous damping of approximately 14%. From these two separate scaled tests, the next step was to determine a preliminary design process. This process involves selection of connectors for certain purposes and utilizing modeling and performance based design to ensure the connector is proper for the given lateral system.
16th European Conference on Earthquake Engineering
The NHERI TallWood project is a U.S. National Science Foundation-funded four-year research project focusing on the development of a resilient tall wood building design philosophy. One of the first major tasks within the project was to test a full-scale two-story mass timber building at the largest shake table in the U.S., the NHERI at UCSD’s outdoor shake table facility, to study the dynamic behaviour of a mass timber building with a resilient rocking wall system. The specimen consisted of two coupled two-story tall post-tensioned cross laminated timber rocking walls surrounded by mass timber gravity frames simulating a realistic portion of a building floor plan at full scale. Diaphragms consisted of bare CLT at the first floor level and concrete-topped, composite CLT at the roof. The specimen was subjected to ground motions scaled to three intensity levels representing frequent, design basis, and maximum considered earthquakes. In this paper, the design and implementation of this test program is summarized. The performance of the full building system under these different levels of seismic intensity is presented.
Project contact is Vikram Yadama at Washington State University
The broader impact/commercial potential of this PFI project is in development of a commercially-viable process for manufacturing high-performing, durable mass strand timber panels for building construction from low-value and underutilized small-diameter softwood trees, such as from hazardous fuel thinning operations for improved forest health. The broader impacts are: (1) advancement of discovery and understanding while promoting teaching, training, and learning by including students and faculty in the research; (2) enhancement of infrastructure for research and education by establishing collaborations between interdisciplinary, yet complementary academic and industry stakeholders; (3) broadening of research dissemination to enhance understanding by involving industry and academia in the research, publishing project results in diverse media sources, and presenting research results in several formats that will benefit a wide range of forest products industry stakeholders; and (4) improved economic competitiveness of the U.S. forest products industry. In addition, if this proof-of-concept research leads to commercial applications, the benefits to society are: (1) new products with reduced environmental impacts, improved durability, and longer service-life; (2) technology that increases the U.S. forest products industry's competitiveness through creation of new jobs and increased opportunities for potential exports; and (3) increased use of wood, an environmentally-friendly, renewable, sustainable, and carbon-sequestering material.
The proposed project addresses challenges facing cross-laminated timber (CLT) panels in mass timber construction. Construction currently requires extreme care to protect CLT panels from moisture while ensuring long-term durability. Although builders take measures to reduce moisture exposure, it is inevitable that the CLT panels will take on water during their service-life. This project addresses these problems by utilizing thermal modification to produce chemical-free, mass timber panels with increased resistance to moisture and decay and improved dimensional stability. The goals are to: (1) evaluate process-performance relationships for thermal modification of small-diameter wood strands, and (2) demonstrate the feasibility of manufacturing high-performance cross-laminated strand-veneer lumber (CLSVL) mass timber panels. The objectives are to: (1) demonstrate the feasibility of utilizing thermally modified laminated strand veneer lumber for production of high-performance CLSVL panels, and (2) determine the potential environmental impacts of the new CLSVL panels. The technical results include validation of a repeatable process for thermally modifying small-diameter pine strands, validation of a method for manufacturing CLSVL panels, verification of physical and mechanical performance of the CLSVL panels, and establishment of commercially-viable process-performance relationships to enable commercial production of the CLSVL mass timber panels.
Project contact is Karl Englund at Washington State University
Cross laminated timber (CLT) has energized the wood industry, not only throughout the US but also across the globe. Potential for lower construction costs and a sustainable building material has provided proponents of CLTs the fuel for their growth. However, to obtain lower feedstock costs and provide a truly sustainable building product the use of small diameter timber (SDT) and other lower quality woods is imperative, but not yet realized. The out-of-plane (OOP) defects such as twist, cup and bow commonly found in SDTs, make processing CLTs prohibitive due to the press load requirements that are needed to “flatten” these defects out and create intimate contact at the glue line. Due to this issue, many CLT manufacturers utilize high grade lumber, while SDT and other low value woods are culled out and not used. Our proposal will characterize the OOP defects commonly found in SDT Douglas-fir (DF) and ponderosa pine (PP) from the Inland Northwest, will develop a tool to calculate anticipated forces to compress out the OOP defects and evaluate the durability performance of a full-scale CLT panel that includes commonly rejected lumber from SDT due to presence of OOP defects. The tool developed in this project will provide the CLT industry with the know-how to determine the press loads required to make a panel from SDT feedstocks and how to lower these accumulated loads through reducing or changing the laminate cross-sectional dimensions. Results of this study will promote increased utilization of SDT lumber, currently rejected, for CLT production and will contribute to healthy forests and rural economic development.
The FEMA P-58 performance-based earthquake engineering methodology was used to assess the economic losses associated with earthquake damage to nonstructural components of two prototype buildings with post-tensioned cross-laminated timber rocking walls. A suite of 22 far-field ground motions were used for nonlinear time history (NLTH) analysis. Truncated incremental dynamic analysis was used to scale the ground motions, and results of the NLTH analyses were used to develop cumulative distribution functions for inter-story drift and peak floor accelerations. The economic factors assessed in the risk analysis included the expected repair cost with respect to spectral acceleration, the probability of exceeding an expected repair cost for selected time periods, and the expected annual loss over different time periods considering various discount factors. It was determined that the ratio of nonstructural repair cost to total building cost at the design earthquake and maximum considered earthquake was lower for the low-rise building than the mid-rise building. However, the probability of nonstructural damage at the service-level earthquake was lower for the mid-rise building than the low-rise building.