Roof Diaphragm Action

The transverse applied lateral load is carried to the roof and foundation by the wall which is assumed here to be a vertically spanning element.

Roof diaphragm action.

Defining a roof diaphragm. The roof sheets alone cannot normally act as a shear diaphragm but the purlins and bracing in the plane of the roof normally act as a diaphragm. A roof diaphragm can be constructed of steel plywood or concrete to create the rectangular plane underlying the roof panels. The maximum unit shear on the wall diaphragm is also equal to the roof reaction r divided by b.

In normal domestic construction there are standard details and rules for bracing and purlins which ensure that there is sufficient diaphragm action so that calculations are not required. Diaphragm action is an additional capacity of the panel to transfer the lateral loads to the outside edges of the panel to the eave for roof panels and to the ground for wall panels. Similar changes to 2306 3 for shear walls. Metal deck may also be used as lateral restraint to stabilise the beams against lateral torsional buckling during construction where the deck spans perpendicular to the beam and through diaphragm action to stabilise the building as a whole by transferring wind loads back to the walls or columns where designed by the structural engineer.

Gypsum board diaphragm ceilings shall be in accordance with section 2508 5. A diaphragm is a horizontal component that distributes lateral loads from wind or seismic activity to the shear walls or foundation of a structure. 2306 2 4 gypsum board diaphragm ceilings. The corresponding diaphragm chord forces are therefore equal to m divided by the diaphragm depth b.

This stiffness provides stability and replaces the need for other bracing elements. 2306 2 3 double diagonally sheathed lumber diaphragms. The maximum roof diaphragm moment m equals ww wl x l2 8. 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 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.

Diaphragm actions in a roof a typical horizontal diaphragm can have an allowable shear value. Double diagonally sheathed lumber diaphragms shall be designed and constructed in accordance with af pa sdpws. The elements marked with numbers corresponding to the behavior of the diaphragm in action due to the application of the lateral loads. Let s take a hypothetical horizontal diaphragm in service under following conditions and examine the allowable shear values.

For wood structures diaphragms are commonly constructed of wood structural panel wsp sheathing or decking applied to the upper face of regularly spaced floor or roof wood framing members such as joists trusses purlins or sub purlins. Roof diaphragm action roof diaphragm action amirzamanian structural op 23 jan 06 13 25.