Roof Diaphragm Shear

In building design these loads are typically caused by wind and seismic events although earth and water can exert lateral forces as well.

Roof diaphragm shear.

The side walls carry the load to the roof diaphragm on top and the foundation at the bottom. The maximum diaphragm shear in the roof diaphragm is. 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. Allowable stress design asd will be used.

The results of this study show remarkably narrow scatter in tested to calculated strength ratios. A similar design is required in the other orthogonal direction east west but is not illustrated here. The shear walls may also be known as vertical or cantilevered diaphragm s. The roof diaphragm is oriente d horizontally and carries loads to the endwall shear wall and then to the foundation.

V n s wl 247 72 212 plf 2b 2 42 v e w wl 180 42 52 plf 2b 2 72 3. The diaphragm forces tend to be transferred to the vertical resisting elements primarily through in plane shear stress. Shear x brackets are designed to transfer in plane shear forces at the ridge line of roof diaphragms why use shear x. 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.

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. A diaphragm is a flat structural unit acting like a deep thin beam. Sheathed elements such as walls and a roof covere d with panels and tied together provide additional strength to the building. The term diaphragm is usually applied to roofs and floors.

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. 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. 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. Shear diaphragms are commonly used in buildings as a means of transmitting lateral loads.

Steel deck plywood and concrete are all common materials utilized in diaphragm applications. 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.