Roof Diaphragm Shear

The term diaphragm is usually applied to roofs and floors.

Roof diaphragm shear.

Shear diaphragms are commonly used in buildings as a means of transmitting lateral loads. Af pa sdpws shall be met and wood structural panel diaphragms are permitted to resist horizontal forces using the allowable shear capacities set forth in table 2306 2 1 1 or 2306 2 1 2. A shear wall however is a vertical cantilevered diaphragm. The diaphragm forces tend to be transferred to the vertical resisting elements primarily through in plane shear stress.

V n s wl 247 72 212 plf 2b 2 42 v e w wl 180 42 52 plf 2b 2 72 3. The side walls carry the load to the roof diaphragm on top and the foundation at the bottom. Since the framing will be spruce pine fir with sg 0 42 the shear values from table 2 must be adjusted according to footnote a. In building design these loads are typically caused by wind and seismic events although earth and water can exert lateral forces as well.

A similar design is required in the other orthogonal direction east west but is not illustrated here. The brackets allow the use of continuous ridge venting in blocked diaphragms by replacing the boundary nailing between the roof sheathing and the ridge board ridge beam that is lost due to the gap required for venting. The results of this study show remarkably narrow scatter in tested to calculated strength ratios. These construction systems can be used when designing a building for lateral loads such as those generated by wind or earthquakes.

While the diaphragm shear stiffness development is similar for both mca and steel deck institute s sdi diaphragm design manual the only difference is the panel edge term k. Steel deck plywood and concrete are all common materials utilized in diaphragm applications. Allowable stress design asd will be used. In structural engineering a diaphragm is a structural element that transmits lateral loads to the vertical resisting elements of a structure such as shear walls or frames.

Sheathed elements such as walls and a roof covere d with panels and tied together provide additional strength to the building. The maximum diaphragm shear in the roof diaphragm is. The allowable shear capacities in tables 2306 2 1 1 and 2306 2 1 2 are permitted to be increased 40 percent for wind design. Shear nailing of the roof diaphragm north south the diaphragm loaded in the north south direction has been selected to illustrate the design of a wood structural panel roof diaphragm.

Shear x brackets are designed to transfer in plane shear forces at the ridge line of roof diaphragms why use shear x. Diaphragms are typically horizontal but can be sloped such as in a gable roof on a wood structure or concrete ramp in a parking garage.