Roof Diaphragm Bracing

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.

Roof diaphragm bracing.

The shear walls may also be known as vertical or cantilevered diaphragm s. Similar to a shear panel a horizontal diaphragm is a horizontal truss in a roof plane or solid sheet element in a floor. Diagonal rafter bracing should be approximately 45 to the rafters on plan. Bracing sometimes not required.

Bracing for larger roofs. The side walls carry the load to the roof diaphragm on top and the foundation at the bottom. The functions of roof bracing roof bracing performs three distinct functions. 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.

On a 300ft roof the latter may be significant and add to the load on the diaphragm. Expensive and inefficient diagonal bracing which might otherwise be required. Challenges of calculating shear. It is placed between vertical elements to transfer lateral loads to the vertical elements such as shear panels vertical trusses or moment frames.

The fluted deck is equivalent to the web of a horizontal beam of which the. Diaphragms are easy to build and to connect to other por tions of the structure. Usually the floor system will be sufficient to act as a diaphragm without the need for additional steel bracing. Once installed these sheets can also be used as a horizontal brace and therefore the steel deck acts as a diaphragm.

The steel deck sheets used for roofs and floors provide support for gravity loads between the joists and or beams. For truss and framed roofs roof space bracing and roof plane bracing are not required where there is sarking that meets nzs 3604 2011 clause 10 4 4 requirements or where there is a structural ceiling diaphragm complying with clause 13 5 directly attached to the rafters. See figure on the right. To roof diaphragm at top and to foundation at bottom roof horizontal diaphragm carries load to end walls.

The tops of the columns in the middle of the diaphragm will lean the amount of drift in the vertical bracing plus the midspan deflection of the diaphragm. Applicable to all trussed rafter roofs unless rigid sarking such as timber boarding or plywood is used. Sheathed elements such as walls and a roof covere d with panels and tied together provide additional strength to the building. Truss stability bracing this is permanent bracing which holds the trusses upright straight and prevents any out of plane buckling of the members.

See product data sheet no 3 for more information. In timber floors for example the floor sheeting carries the shear forces. Diaphragm action at the roof level. At roof level bracing often known as a wind girder may be required to carry the horizontal forces at the top of the columns if there is no diaphragm.

When designed correctly a roof diaphragm can reduce or eliminate the need for diagonal bracing.