Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Kopp, Gregory A.

2nd Supervisor

El Ansary, Ayman

Co-Supervisor

Abstract

Wood-frame structures are a popular choice for construction in North America. Due to their sensitivity to severe wind events, the design of these structures under wind loading is of particular importance. One of the issues with wind loading on cladding elements like roof sheathing is the determination of the “effective wind area” to use in design since the design pressure coefficients decrease logarithmically with area. The current design approach for cladding uses a geometric tributary area approach to calculate the wind loads and determine adequate fastening schedules. This fails to include load sharing and design pressure coefficients may be excessively cautious. The objective of the current work is to determine the effective wind area of a roof sheathing panel under three fastening schedules: 6 in by 12 in, 6 in by 6 in, and 3 in by 3 in. It was found that the effective wind area of a 7/16 in oriented strand board sheathing panel was about 24 sq ft regardless of fastening schedule. This value contrasts with the tributary areas of 2 sq ft, 1 sq ft, and 0.5 sq ft, respectively for the three schedules. However, using the full sheathing panel area of 32 sq ft would be slightly unconservative.

Summary for Lay Audience

In North America wood-frame construction is a popular choice for homes. These structures are vulnerable to extreme windstorms such as hurricanes and tornadoes due to their light weight. Roofs of these structures are particularly high risk due to the large suction loads from these storms. Losing roof sheathing can cause severe water damage and cause further structural failure. To ensure roof sheathing remains attached during these storms it is important for design to be accurate. Current design practices use geometry and capacity of individual fasteners (nails) to determine overall sheathing panel capacity. This practice does not consider any load being shared between fasteners despite the proximity of these connections through the sheathing panel. This thesis looks to quantify the load sharing by determining an effective wind area, the area associated with the failure of the panel. Using finite element modelling software, a model of a single sheathing panel system was constructed. The system included 2 x 4 trusses, fasteners, and a 7/16 in oriented strand board (OSB) sheathing panel. The model had 3 different fastener orientations a 6 in by 12 in, 6 in by 6 in, and 3 in by 3 in spacing for exterior trusses and interior trusses, respectively. It was tested under 3 load cases including a uniform ramp load, a point ramp load, and a spatially-varying ramp load. Of the 3 tests it was hypothesized that the spatially-varying ramp load would produce the most accurate results for the effective wind area. The effective wind area was calculated based on the total force acting on the panel at initial failure and how many fasteners were engaged at this time for all load cases and fastener orientations. Effective wind area of a sheathing panel was found to be about 24 sq ft.

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