The effect of elevated temperature on mechanical behavior of structural wood and wood-based composites Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/794081235

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  • Engineers, in practice, are often faced with the challenge of evaluating a fire-damaged structure and developing a rehabilitation and retrofit plan. In order to decide on a rehabilitation and retrofit plan, information on thermal degradation of building materials and connections are vital. A critical knowledge gap exists in terms of thermal degradation of materials and connections with respect to light-frame wood construction. Along with solid sawn lumber (SSL), various wood-based composites such as plywood, oriented strand board (OSB) and laminated veneer lumber (LVL) are also used in wood-frame construction. Characterization of the thermal degradation of strength of these structural materials will help assess the service life and strength of the damaged structure. This study addressed the thermal degradation of material strength and connection strength by conducting tests on wood, wood-based composites and connections after subjecting them to elevated temperatures, hence studying the post-fire residual strength in wood and wood composite construction. The properties evaluated in this study were bending strength (MOR), bending stiffness (MOE), lateral nail capacity, dowel bearing strength, fracture toughness and bond strength (IB) after exposing the materials to elevated temperature for various exposure times. In addition, the bending strength of OSB and plywood was studied in great detail as a function of additional temperatures and exposure times. A general trend of degrading bending properties, fracture toughness, dowel bearing strength of materials and yield strength of the connections of various configurations with high temperature and duration of exposure was observed and confirmed by statistical analysis. A statistical regression based model incorporating the effects of temperature, time of exposure and thier interaction and a model based on first-order kinetics were developed and evaluated for predicting the strength loss. The kinetics-based model was better than the regression-based approach. Using the kinetics analysis along with time-temperature superposition for OSB and plywood, a master curve was generated at a reference temperature of 150°C that can be used for residual strength estimates and failure time predictions. A reasonable prediction of connection design values was made using National Design Specifications (NDS) yield models for thermally degraded materials. Conventional tests for bond strength provided excessive scatter which renders any statistical comparison highly difficult. An alternative to IB and bond classification could be fracture testing using energy methods for wood bond strength evaluation. The various analytical models developed will help for characterizing the thermal degradation of material properties. Models specified in design codes were evaluated against the thermal degradation of materials. This knowledge of thermal degradation and the models will help engineers and architects in recommending categorical improvement, rehabilitation and retrofit of structures.
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  • description.provenance : Made available in DSpace on 2010-12-16T23:53:21Z (GMT). No. of bitstreams: 3 Arijit Sinha Dissertation.pdf: 26363301 bytes, checksum: 63b18b7063dd83d4d36c99b7310e800c (MD5) license_text: 19110 bytes, checksum: ab81fc52740b5da6c371905ae0a5e657 (MD5) license_rdf: 29876 bytes, checksum: 5c0253339ec6b06df60e340de8bf0f39 (MD5)
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  • description.provenance : Approved for entry into archive by Laura Wilson(laura.wilson@oregonstate.edu) on 2010-12-16T23:53:21Z (GMT) No. of bitstreams: 3 Arijit Sinha Dissertation.pdf: 26363301 bytes, checksum: 63b18b7063dd83d4d36c99b7310e800c (MD5) license_text: 19110 bytes, checksum: ab81fc52740b5da6c371905ae0a5e657 (MD5) license_rdf: 29876 bytes, checksum: 5c0253339ec6b06df60e340de8bf0f39 (MD5)

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