Project Duration: 
2019 - 2021
 
Research Team:
Dr. Mariapaola Riggio – Oregon State University (OSU), Department of Wood Science and Engineering
Dr. André R. Barbosa – OSU, School of Civil and Construction Engineering
Dr. Lech Muszynski – OSU, Department of Wood Science and Engineering
 
Graduate Research Assistants:
Ryan P. Longman
Esther J. Baas, E.I.T.

Design Advisory Group:
Prestressed Timber Limited (PTL), KPFF Consulting Engineers

Research Advisory Group:
D.R. Johnson, Freres Lumber, University of Canterbury
 
Facilities:
A.A. “Red” Emmerson Advanced Wood Products Laboratory (OSU), Multi Chamber Modular Environmental Conditioning (MCMEC) at the Green Building Materials Laboratory (OSU)
 
Abstract:
Earthquake engineers are focusing on performance-based design solutions that minimize damage, downtime, and dollars spent on repairs by designing buildings that have no residual drift or “leaning” after an event. The development of timber post-tensioned (PT), self-centering rocking shear walls addresses this high-performance demand. The system works by inserting unbonded steel rods or tendons into timber elements that are prestressed to provide a compressive force on the timber, which will pull the structure back into place after a strong horizontal action. But, because these systems are less than fifteen years old with just four real-world applications, little information is known regarding best practices and optimal methods for engineering design, construction and/or tensioning procedures, and long-term maintenance considerations. This project intends to contribute knowledge by testing both cross-laminated timber (CLT) and mass plywood panel (MPP) walls through testing of anchorage detailing, investigating tensioning procedures for construction, determining the contributions of creep on prestress loss over time, and comparing all laboratory test data to monitoring data from three of the four buildings in which this technology has been implemented, one of which is George W. Peavy Hall at Oregon State University. This will be accomplished by testing small- and full-scale specimens in the A.A. “Red” Emmerson Advanced Wood Products Laboratory, and small-scale specimens in an environmental chamber.
 

Introduction:

Changes introduced to the 2021 International Building Code (IBC) allow for mass timber structures up to 18 stories. This change stresses the need for seismically resilient timber lateral-force resisting systems (LFRS). Even though there has been laboratory testing of post-tensioned (PT), long-term performance data is scarce because the technology is new and installed in relatively few structures to date. Models for laminated-veneer lumber (LVL) and glulam PT frame elements have been proposed but have not been tested or validated with other mass timber elements such as cross-laminated timber (CLT) or mass plywood panel (MPP) shear walls. To verify these models for new mass timber materials, the specific material properties as well as responses to creep and mechano-sorptive deformations must be experimentally determined.

Research Details:

Testing will initiate with small-scale static tests investigating optimal bearing and anchorage plate details for the shear walls. The compressive force on the timber is largely concentrated at the place of tensioning, and in real-world applications has shown concerns with compression failure, stress cracking, delamination, and buckling. In concrete applications, steel reinforcement is often used to reduce the possibility of exploding the concrete due to such large forces. This study will investigate the addition of reinforcement at this bearing area for CLT and MPP walls as well as compare new and recommended design of anchorage details. After information is known regarding the bearing details, three specimens of each wall type with optimal anchorage detailing will undergo two tensioning regimes for construction. This will assist in determining if current tensioning procedures are adequate to achieve the engineering-design specific load.

Once it is better understood the best practices for design and construction, small-scale specimens and one control of each wall type will be tested in an environmental chamber to isolate the effects of creep behavior and how it affects the prestress loss in the rods. Lastly, once more information is known regarding creep and prestress loss, two full-scale, three-story CLT and MPP walls will be designed and prestressed according to previous findings and placed in the A.A. “Red” Emmerson lab for one-year to investigate the real-world effects of anchorage detailing, tensioning procedure, and creep.

Results + Resources:
This study is currently in the design phase. Expected start of the experimental study: May of 2020.
 
Poster Presentations:
Baas E. J. “Design Validation of Cross-Laminated Timber Rocking Shear Walls,” Society of Wood Science and Technology Annual Meeting: Yosemite, CA, Poster 10-2019.

Upcoming Poster Presentations:
Longman, R. P., “In-plane Creep Behavior of CLT and MPP Panels and its Effects on Tension Losses in Post-tensioned Shear Walls.” International Mass Timber Conference: Portland, OR. 24-03-2020.

Upcoming Conference Presentations:
Longman, R. P., Baas, E. J., Riggio, M., Barbosa, A. R., Muszynski, L. “Creep Behavior of CLT and MPP PT Shear Walls.” 2020 Forest Products Society International Conference: Portland, OR. 22-06-2020.
Baas E. J., Granello, G., Barbosa, A.R., and Riggio, M. “Post-tensioned timber wall building: lessons learned from design and construction practice in New Zealand and United States.” 2020 World Conference on Timber Engineering: Santiago, Chile. 24-08-2020.

Publications in Process:
Baas E. J., Granello, G., Barbosa, A.R., and Riggio, M. “Post-tensioned timber wall building: lessons learned from design and construction practice in New Zealand and United States.” Proceedings, 2020 World Conference on Timber Engineering: Santiago, Chile.
 

Project Lead Bio + CONTACT:

Mariapaola Riggio, Architect and Ph.D. in Structural Engineering, Assistant Professor in the Department of Wood Science and Engineering (OSU) since September 2015. Dr. Riggio has an established reputation among the international scientific community, as an expert in timber buildings assessment. Her research activity is mainly devoted to the valorization of traditional and novel forest products in the built environment.

 
Funding Acknowledgements:

This study is funded under “Design, construction and maintenance of mass timber PT shear walls: data, models and recommendations” conducted through the TallWood Design Institute with funding by the U.S. Department of Agriculture’s Agricultural Research Service (USDA ARS) Agreement No. 58-0204-9-165.