Predicting current serviceability and residual service life of plywood roof sheathing using kinetics-based models
Winandy, J.E., Lebow, P.K. and Murphy, J.F
2002
Proceedings of the 9th Durability of Building Materials and Components Conference held 17-20, March 2002, in Brisbane, Australia
Winandy, J.E., Lebow, P.K. and Murphy, J.F, (2002), "Predicting current serviceability and residual service life of plywood roof sheathing using kinetics-based models", Proceedings of the 9th Durability of Building Materials and Components Conference held 17-20, March 2002, in Brisbane, Australia.
| Abstract: |
| Research programs throughout North America are increasingly focusing on understanding and defining the salient issues of wood durability and maintaining and extending the serviceability of existing wood structures. This report presents the findings and implications of a 10-year research program, carried out at the USDA Forest Service, Forest Products Laboratory, to develop kinetics-based service-life models for untreated and fire-retardant- (FR) treated plywood roof sheathing exposed to elevated in-service temperatures. This program was initiated because some FR-treated sheathing products were experiencing significant thermal degrade and needed to be replaced. This 10-year research program systematically identified the cause of the degradation and has resulted in new acceptance and performance standards and revisions to U.S. building codes. The strength loss was cumulatively related to FR chemistry, thermal exposure during pretreatment, treatment, and post-treatment processing, and in-service exposure. Quantitatively, a kinetics-based approach could be used to predict strength loss of plywood based on its time- temperature exposure history. The research program then developed models to assess current condition, predict future hazard based on past service life, and predict residual serviceability of untreated and FR-treated plywood used as structural roof sheathing. Findings for each of these subjects are briefly described in this report. Results of research programs like this one can be used to extend the service life of wood by providing engineers with an estimate of residual serviceability and thereby avoiding premature removal. Many of the approaches in these kinetics-based service life models for plywood roof sheathing are directly applicable to the development of predictive durability models for wood and wood composite roof and wall sheathing that has been exposed to moisture and has eventually decayed. When those models are developed, they will help building code officials, regulators, contractors, and engineers in determining replacement schedules for wood undergoing biological attack. |
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