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Mass timber products are gaining popularity in North America as an alternative to traditional construction materials as part of both the gravity and lateral force-resisting system. However, several knowledge gaps still exist in terms of their expected seismic performance and plausible hybridizations with other materials, e.g. steel energy dissipators. This research explores the potential use of wall spine systems consisting of mass ply panels (MPP) and steel buckling-restrained braces (BRBs) as energy dissipators. The proposed BRB-MPP spine assembly makes up the lateral force-resisting system of a three-story mass-timber building segment that will be tested under cyclic quasi-static loading at Oregon State University. The proposed design methodology follows displacement-based design principles to determine the minimum required stiffness to limit inelastic story drift ratios at the design earthquake level. The MPP spine and BRB-to-MPP connections were capacity designed to resist forces transferred by the BRBs at roof drift ratios beyond the risk-targeted Maximum Considered Earthquake (MCER). This design solution provides an interesting alternative for the design of modern mass timber buildings. The results obtained in the experimental campaign will be used to validate the design methodology and the behavior of the innovative structural system.
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Numerical Modelling of a Three-Story Building Using a Hybrid of Mass Timber Walls with Buckling-Restrained Braces
Mass timber buildings are gaining popularity in North America as a sustainable and aesthetic alternative to traditional construction systems. However, several knowledge gaps still exist in terms of their expected seismic performance and plausible hybridizations with other materials, e.g. steel energy dissipators. This research explores the potential use of mass plywood wall panels (MPP) in spine systems using steel buckling-restrained braces (BRBs) as energy dissipators. The proposed BRB-MPP spine assembly makes up the lateral load-resisting system of a three-story mass-timber building segment that will be tested under cyclic quasi-static loading at Oregon State University. The specimen geometry and material properties result in BRBs that are shorter and of smaller core area than in most common steel structural applications. Small BRBs are prone to exhibit a hardened compressive response and fracture due to ultra-low-cycle fatigue when subjected to repeated cycles of large strain amplitude. These issues, along with the limited availability of test data, make small BRBs difficult to model. To support the experimental testing program, a material model with combined kinematic and isotropic hardening is calibrated against the available experimental data for three BRB specimens to estimate the behavior of BRBs of short length (≤3,500 mm [138 in]) and small core area (≤2,600 mm2 [4 in2]), similar to the ones designed for the test specimen. The calibrated model is used to predict the behavior of the BRB-MPP spine experiment.
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- Award ID(s):
- 2120683
- PAR ID:
- 10631685
- Publisher / Repository:
- Springer International Publishing
- Date Published:
- Page Range / eLocation ID:
- 440 to 448
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Mass timber panels are emerging as an innovative alternative for the design of elastic spines due to their high stiffness- and strength-to-weight ratio, among other factors. Recent research has shown that mass timber panels used in conjunction with steel energy dissipators are promising solutions for enhanced seismic performance. However, the available experimental data at the building scale is still minimal, which limits the understanding, adoption, and development of effective seismic design guidelines for these systems. This research addresses this gap through full-scale quasi-static cyclic testing of a three-story mass timber building. Lateral loads are transferred through Mass Ply Panel (MPP) diaphragms to an MPP spine with vertically-oriented unbonded steel buckling-restrained braces (BRBs) as energy dissipating boundary elements in the first story. The only elements designed to dissipate energy in the inelastic range are the BRBs. The building specimen achieved low-structural damage and enhanced-performance goals, being able to reach a 4% roof drift ratio with little loss of strength and stiffness. The proposed pivoting detail was effective in mitigating compressive damage at the wall toe. To support the experimental campaign and future design procedures, a high-fidelity numerical model of the building was developed using OpenSees.more » « less
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Steel energy dissipators can be combined with mass timber in integrated seismic lateral force–resisting systems to achieve designs with enhanced seismic performance and sustainability benefits. Examples of such integration include the use of mass timber post-tensioned rocking walls equipped with steel energy dissipation devices. This study proposes a solution using buckling-restrained boundary elements (BRBs) with mass timber walls detailed to pivot about a pinned base. This design allows the walls to rotate with minimal flexural restraint, distributing drift demands more uniformly with building height and reducing crushing damage at the wall base. Experimental quasi-static cyclic tests and numerical simulations were used to characterize the first- and higher-mode behavior of a full-scale three-story building featuring a mass timber gravity system and the proposed mass timber-BRB system. Under first-mode loading, the specimen reached 4% roof drift ratio with stable hysteretic behavior and a nearly uniform story drift profile. While residual drifts were nonnegligible due to the lack of self-centering, analytical estimates indicate realignment is likely feasible at the design earthquake level. Under second-mode loading, the specimen exhibited near-linear behavior with high stiffness. Experimental results were corroborated with numerical simulations for the isolated gravity frame, first-mode-like, and second-mode-like loading protocols. It is expected that results from this study will facilitate greater use of mass timber seismic lateral force–resisting systems.more » « less
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To address functional recovery after earthquakes, there is growing interest in developing enhancedperformance seismic-resisting systems. Rocking walls, featuring a base gap-opening mechanism and designed to remain essentially elastic above the base, have demonstrated their potential in various construction materials, including mass timber. If combined with steel energy dissipators, the resulting hybrid steel-mass timber rocking walls have emerged as a promising seismic-resisting system. This study focuses on Post-Tensioned Mass Timber Rocking Walls supplemented with Buckling-Restrained Brace (BRB) boundary elements and builds upon findings from experimental programs funded by the National Science Foundation (NSF) and the United States Department of Agriculture (USDA). The rocking mechanism, controlled by the BRBs and the Post-Tensioned (PT) rods, provides self-centering behaviour, reducing the potential for residual drifts and improving post-earthquake repairability. An estimating method for higher-mode loading profiles is proposed and applied to a six-story archetype, which was tested at the Large High Performance Outdoor Shake Table (LHPOST) at the University of California San Diego (UCSD) in January 2024 as part of the NHERI Converging Design Project. The estimating method is practically formulated to facilitate the implementation in design procedures.more » « less
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A full-scale, six-story, mass timber building including Mass Ply Panel (MPP) self-centering rocking walls with Buckling-Restrained Boundary Elements (BRBs) was tested at the Large High-Performance Outdoor Shake Table (LHPOST6) at the University of California, San Diego (UCSD). Measured sensor and derived data included global responses, such as floor displacements and accelerations, along with local responses, such as post-tensioning (PT) forces and uplift displacements, among others. The three-dimensional shake table testing program included 23 ground motion records with intensities of shaking ranging from Service (SLE) up to Risk-Targeted Maximum Considered Earthquake (MCER) levels. Results highlighted that: [i] the drift response was near uniform along the height of the building, [ii] the acceleration response included large contributions from the higher modes, [iii] the PT rods remained elastic and had stable post-tensioning force throughout the test program, and [iv] the self-centering system resulted in negligible residual drifts. Qualitative observations from construction and testing were also cataloged to further support the feasibility of implementation in practice. By combining steel BRBs and post-tensioning rods with MPP rocking elements, the system was able to meet the enhanced seismic performance goals targeted for the project. Future work will seek to define both resilience and sustainability targets for designs incorporating multiple performance objectives.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Book Chapter:
- https://doi.org/10.1007/978-3-031-03811-2_45
