Project contact is Keri Ryan at University of Nevada, Reno
A landmark shake table test of a 10-story mass timber building will be conducted in late 2020. The test program, funded by other sources, will help accelerate the adoption of economically competitive tall timber buildings by validating the seismic performance of a resilient cross-laminated timber (CLT) rocking wall system. In this project, we leverage and extend the test program by including critical nonstructural components and systems (NCS). Including NCSs, which are most vulnerable to rocking induced deformations of the CLT core, allows investigation of the ramification of this emerging structural type on building resiliency. Quantifying interactions amongst vertically and horizontally spanning NCSs during earthquake shaking will allow designers to develop rational design strategies for future installation of such systems. The expected research outcomes are to expand knowledge of rocking wall system interactions with various NCS, identify NCS vulnerabilities in tall timber buildings, and develop solutions to address these vulnerabilities. Moreover, this effort will greatly increase visibility of the test program. The results of this research will be widely disseminated to timber design and NCS communities through conference presentations, online webinars, and distribution to publicly accessible research repositories.
The development of cross-laminated timber (CLT) panel technology has opened up new opportunities for wood in tall buildings. Several characteristics including seismic performance and speed of construction have raised interest among designers. As CLT gains acceptance in the industry, alternative structural solutions need to be investigated to improve performance of CLT as a building material. The first study presented is an assessment of the viability of hybrid poplar for use in CLT panels. Hybrid poplar is a low density species, which is not typically considered for structural applications. Low density species have the potential to improve the structural efficiency of CLT panels. The tests conducted are based on the qualification of panels outlined in the ANSI/APA PRG-320: Standard for Performance-Rated Cross-Laminated Timber to determine the structural viability of the CLT panels. The second study presented is an investigation of a new alternative energy dissipation solution to be used with cross-laminated timber rocking walls for seismic design. The energy dissipators are designed as a structural fuse which can be easily replaced after failure following a large seismic event. The results of this study give insight to alternative solutions for CLT to improve upon current applications.
New Zealand Society for Earthquake Engineering Conference
April 27-29, 2017, Wellington, New Zealand
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.
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.
This report is prepared for Softwood Lumber Board (SLB) by the NHERI TallWood Project team in order to provide a brief and timely update on the progress and preliminary research findings from the NHERI TallWood Project. This report is focused on the full-scale shake table test of a two-story mass timber building conducted during the summer of 2017 at NHERI@UC San Diego outdoor shake table.
The shake table test described in this report was conducted during a three-month period from June to August 2017. As the research team is still working on processing and analyzing the data obtained from the experiments, this report only discusses preliminary findings in a qualitative manner. The research team is expected to produce additional reports and publications based on the test results in the near future.
This paper presents results of an experimental study of commonly used angle bracket and hold-down connections in Cross Laminated Timber (CLT) wall systems under bi-directional loading. Monotonic and cyclic tests of the connections were carried out in one direction, while different levels of constant force were simultaneously applied in a perpendicular direction. The experiment aims to consider the combined and coupling effect of loads for connections in a rocking CLT shear wall system. Key mechanical characteristics of those connections were calculated, evaluated and discussed. The results show that shear and tension actions for hold-downs are quite independent but strongly coupled for angle brackets. The study gives a better understanding of hysteretic behaviour of CLT connections, and provides reliable data for future numerical analysis of CLT structures.
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.