Long-Term Behavior of Posttensioned Wood Howe Trusses
Publication: Journal of Structural Engineering
Volume 146, Issue 7
Abstract
Two full-scale Howe trusses were instrumented and posttensioned to study their time-dependent behavior in outdoor conditions. Force, relative humidity, and temperature data were acquired for more than 2 years. In addition, a single (nominal size in inches) Douglas fir member was also instrumented, posttensioned and data were acquired for more than 5 years. The data indicated that a permanent prestress state can be achieved in Howe trusses posttensioned using current technologies. Wood viscosity caused some prestress losses, which occurred primarily in the first few months for the Douglas fir members. Linear viscoelastic analyses reliably predicted observed behavior. Because wood and steel have different coefficients of thermal expansion, there were daily and seasonal prestress force fluctuations, which can be predicted using linear elastic structural models. The data showed that extended periods of very high relative humidity did not significantly change member forces. Nevertheless, Fickian diffusion analyses were performed to predict wood moisture content within a cross-section under atmospheric equilibrium moisture content boundary conditions.
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Data Availability Statement
All data, models, and codes generated or used during the study are available from the corresponding author (long-term data files on force, temperature, and RH; MATLAB program for linear viscoelastic analysis of trusses; finite difference MATLAB program for 2D Fickian diffusion).
Acknowledgments
The following individuals and organizations made significant contributions to the research: Sheila Duwadi from the FHWA; Christopher Marston from the National Park Service; the late David Wright from the National Society for the Preservation of Covered Bridges; Jim Garvin from the New Hampshire Department of Natural and Cultural Resources; Tim Andrews from Barns and Bridges of New England; Vern Mesler from Lansing Community College; Ken Chaloupek and Scott Burgess from the Seaman Corp., manufacturer of the architectural fabric cover; the Case Alumni Association; CWRU staff members Neil Harnar, Michael Butler, and David Conger; CWRU students Vincent Marvin, Lin Wan, and Janette Siu; and John Smolen from Smolen Engineering Ltd.
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Published In
Journal of Structural Engineering
Volume 146 • Issue 7 • July 2020
Copyright
©2020 American Society of Civil Engineers.
History
Received: May 22, 2019
Accepted: Nov 20, 2019
Published online: Apr 18, 2020
Published in print: Jul 1, 2020
Discussion open until: Sep 18, 2020
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