Modeling System Effects and Structural Load Paths in a Wood-Framed Structure

Abstract

The objective of this project was to evaluate system effects and further define load paths within a light-frame wood structure under extreme wind events. The three-dimensional 30- by 40-ft (9.1- by 12.2-m) building, designed to be representative of typical light-frame wood construction in the southeastern coastal region of the United States, was modeled using SAP2000. Wall and roof sheathing was modeled using SAP’s built-in thick shell element. The effect of edge nail spacing of the wall sheathing was incorporated by way of a novel correlation procedure, which eliminated the need to represent each nail individually. The computer model was validated against both two- and three-dimensional experimental studies (in plane and out of plane). Uniform uplift pressure, worst-case simulated hurricane, and ASCE 7-05 pressures were applied to the roof, and vertical foundation reactions were evaluated. The ASCE 7-05 uplift pressures were found to adequately encompass the range of uplift reactions that can be expected from a severe wind event such as a hurricane. Consequently, it was observed that ASCE 7-05 “component and cladding” pressures satisfactorily captured the building’s uplift response at the foundation level without the use of “main wind force-resisting system” loads. Additionally, the manner in which the walls of the structure distribute roof-level loads to the foundation depends on the edge nailing of the wall sheathing. It was also revealed that an opening in any wall results in a loss of load-carrying capacity for the entire wall. Moreover, the wall opposite the one with the opening can also be significantly affected depending on the orientation of the trusses. In general, it was determined that complex, three-dimensional building responses can be adequately characterized using the practical and effective modeling procedures developed in this study. The same modeling process can be readily applied in industry for similar light-framed wood structures.