A candidate CLT diaphragm analysis model approach is presented and evaluated as an engineering design tool motivated by the needs of seismic design in the United States. The modeling approach consists of explicitly modeling CLT panels as discrete orthotropic shell elements with connections between panels and connections from panels to structural framing modelled as two-point springs. The modeling approach has been compared to a developed CLT diaphragm design example based on U.S. standards showing the ability to obtain matching deflection results. The sensitivity of the deflection calculations to considering CLT panel-to-panel connection gap closure is investigated using a simple diaphragm example. The proposed modeling approach is also applied to the candidate floor diaphragm design for the Framework project, one of the two U.S. Tall Wood Building Prize Competition winners, currently under design. Observations from this effort are that the proposed method, while a more refined model than typically used during building design, shows promise to meet the needs of innovative CLT seismic designs where appropriate simpler diaphragm models are not available.
A candidate cross-laminated timber (CLT) diaphragm analysis model approach is presented and evaluated as an engineering design tool motivated by the needs of seismic design in the United States. the modeling approach consists of explicitly modeling CLT panels as discrete orthotropic shell elements with connections between panels and connections from panels to structural framing modeled as two-point springs. The modeling approach has been compared to a developed CLT diapragm design example based on the US standards showing the ability to obtain matching deflection results. The sensitivity of the deflection calculations considering CLT panel-to-panel connection gap closure is investigated using a simple diaphragm example. the proposed modeling approach is also applied to the candidate floor diaphragm design for the Framework project, a winner of the US Tall Wood Building Prize Competition, currently under design. Observations from this effort are that the proposed method, while a more refined model than typically used during building design, shows promise to meet the needs of innovative CLT seismic designs where appropriate simpler diapragm models are not available.
Cross-laminated timber (CLT) has become increasingly prominent in building construction and can be seen in buildings throughout the world. Specifically, the use of CLT floor and roof panels as a primary gravity force-resisting component has become relatively commonplace. Now, with availability of the 2021 Special Design Provisions for Wind and Seismic (SDPWS 2021) from the American Wood Council (AWC), U.S. designers have a standardized path to utilize CLT floor and roof panels as a structural diaphragm. Prior to publication of this document, projects typically had to receive approval to use CLT as a structural diaphragm on a case-by-case basis from the local Authority Having Jurisdiction (AHJ).
This paper highlights important provisions of SDPWS 2021 for CLT diaphragm design and recommendations developed by the authors in the upcoming CLT Diaphragm Design Guide, based on SDPWS 2021.
New Zealand Society for Earthquake Engineering Conference
Research Status
Complete
Notes
April 27-29, 2017, Wellington, New Zealand
Summary
With global urbanization trends, the demands for tall residential and mixeduse 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, fullscale 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.
New Zealand Society for Earthquake Engineering Conference
Research Status
Complete
Notes
April 27-29, 2017, Wellington, New Zealand
Summary
Framework is a 12-story, 140ft (43m) tall mixed use building to be constructed almost entirely out of mass timber, including both the gravity and lateral forceresisting systems, in a region of high seismicity in the United States (Portland, Oregon). Utilizing performance-based seismic design and nonlinear response history analysis, the structure’s rocking/re-centering cross laminated timber walls were designed for enhanced, beyond-code-level seismic objectives. These enhanced objectives were targeted through more stringent criteria on deformation-controlled elements, design for replacement of energy dissipaters, limitations on residual drift, and a project-specific testing program completed at Oregon State University and Portland State University.
The momentum behind construction of mass timber buildings in the United States provides an opportunity to promote resilient/low-damage design which is consistent with the sustainability goals of many of these projects. This also follows naturally from the inherent rocking/re-centering behavior of mass timber walls. Furthermore, extending rocking mass timber walls to taller buildings is feasible; however, it requires an additional level of thoughtful design, explicit analysis and testing, and careful detailing, including consideration of the effective shear modulus of CLT, wall shear amplification due to higher mode effects, deformation compatibility of gravity connections, and CLT diaphragms.
16th European Conference on Earthquake Engineering
Research Status
Complete
Summary
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.
