The performance and behavior of lightweight wood exposed to fire conditions

by Twomey, Brian M.

Lightweight wood construction is one of the most common forms of residential construction in the United States. Unprotected lightweight wood structural members are extremely sensitive to elevated temperatures often experienced in fire conditions. Residential fires are a commonly occurring incident across the globe and consequently make up a large percentage of residential property loss and damage. In the United States, building code provisions limit lightweight construction to particular building types. These building codes prescribe protected lightweight wood assemblies in building types for which they are allowed. Although many components of lightweight wood buildings are required to be protected in some form, there are still many parts of the building that are not necessarily required to be protected, especially in private residential structures. A fire may start in an area of a building that is protected, but may propagate into areas that are not. This leaves portions of the unprotected structure vulnerable to rapid fire damage. Lightweight wood members can quickly lose load resistance due to a loss of cross-section as a result of charring. Analytical models currently exist and are generally accepted for heavy timber elements, but the applications of these models do not extend to lightweight wood members. As a result, this thesis investigated the application of an analytical model to lightweight wood elements. In developing this model, the finite element method and finite difference models were used to investigate the phenomenon of wood char in fire conditions. Finite difference models were explored as an alternative to finite element models because finite difference formulations did not require specialty programs. Following the development of analytical char models, mechanics-based analyses were conducted to evaluate the performance of lightweight beams and columns exposed to fire conditions. i