Fig 3


Fig 4

Additional installation requirements for plywood bracing panels

Additional installation requirements are common to:

• Standard Bracing Solutions
• Engineered Bracing Solutions

When specifying bracing:

• Distribute the racking loads by positioning the bracing panels evenly throughout the structure.
• Space the braced walls no further apart than the ability of the ceiling to act as a diaphragm between braced sections.

Where internal walls are utilized as bracing panels :-

• The face grain of the plywood bracing panels can be either vertical or horizontal.
• All fasteners shall be driven a minimum of 7mm from the plywood edges.
• Fastener spacings for horizontal butt joints shall be the same as for the top and bottom plates.
• Unattached panel edges or 'fly joints' are not permitted.
• Braced sections shall be effectively fixed to both the ceiling or roof diaphragm, and to the sub-floor.
• Wall noggings may be eliminated except where required for fixing of non-structural linings or to support horizontal butt joints in braced sections.
• All horizontal and vertical plywood panel butt joints shall be fixed to common grounds.
• The specified fasteners and fastener spacing for panel edges shall be as detailed in Table 1 or as shown in Diagrams 8 to 12.

Bottom Plate To Sub-Floor Connection

All plywood braced wall sections shall be connected to the sub-floor by one of the following methods:-

Type A Bottom Plate Fixing

The bottom plate of Type A bracing units or of plywood braced wall sections of up to 2.25kN/m racking resistance shall be fixed as follows:

For load-bearing walls on timber framed floors

• Two nails at intersections over joists.
• One nail at a maximum of 600mm centres in parallel with the joist.

For non load-bearing walls,

• One nail at intersections over joists.
• One nail at a maximum of 600mm centres in parallel with the joist.

Nails lengths for fixing shall be:-

• 75mm long for plates up to 38mm thick.
• 90mm long for plates up to 50mm thick.

The minimum nail diameter for hardwoods and cypress pine shall be 3.15mm diameter, otherwise 3.75mm.diameter.

To Concrete Slabs, One 75mm masonry nail at a maximum of 1200mm centres.

Type B Bottom Plate Fixing

The bottom plate of Type B bracing units or of plywood braced wall sections of up to 4kN/m racking resistance shall be fixed as follows:

For bottom plates running parallel to floor joists or over concrete slabs and using one of the fixing methods below :

• To alternate floor joists or
• At a maximum of 1200mm centres.

Fixings shall :

• Commence as close as possible to the end stud of each bracing section.
• Be placed a practical minimum end distance of 7 x bolt diameter (7D) for seasoned timber plates and 8D for unseasoned timber to avoid end splitting.
• Incorporate a 38 x 38 x 2.0mm steel washer per 10mm diameter bolt fixing.

a. Timber Framed Floors

(a) One M10 bolt (b) 30mm x 0.8mm galvanised looped strap( Fig.3 )

(b) Equivalent metal fasteners

b. Concrete Slabs

One appropriately embedded M10 bolt, or equivalent

Brick Ties
Special brick ties have been developed for applications where plywood bracing is associated with brick veneer construction. These ties are usually proprietary items. Manufacturers' installation instructions must be adhered to strictly.

Fig.4 gives general installation details.

WIND UPLIFT RESISTANCE OF STRUCTURAL PLYWOOD SHEATHED WALLS

Plywood sheathed wall frames can provide roof hold-down by transferring the wind uplift loads through the rafter or trusses to the top plate, then from the top plate to the bottom plate through the plywood acting in tension. The loads are then transferred to the subfloor or floor by the appropriate connection of the bottom plate to floor joists or concrete slab. The bottom plate to subfloor fixing must be as specified for Type B bracing units to meet the required uplift. Connection of the plates to the plywood is critical. When installed as specified in Table 1 the plywood sheathed wall sections act as a continuous cyclone rod thereby avoiding stress concentrations. The uplift resistances given in Table 1 were based on prototype testing of full panels.

Table 1 - Allowable Uplift Resistance of Plywood Sheathed Wall Systems

Table 1 gives the allowable uplift resistance in kN per rafter for two plywood to top and bottom plate connection methods.

The fastener specification is as detailed in Table 1 and the uplift resistances apply to all the plywood thicknesses and stress grades given in Tables 8 to 12.

A single 900mm bracing panel can provide the specified uplift resistance for a rafter if the rafter is fixed a minimum of 300mm from either end of the plywood panel.

The design of the rafter or truss to top plate connection is critical.

The connection design can be as per the National Timber Framing Code or Framing Manuals produced by bonafide timber organisations.

Alternatively, the connection shown in fig 3 is acceptable for both uplift resistances given in Table 1.

Reference:

Plywood Association Manual

| New Search |

| Projects | Technical Data | Specification | Environment | Education | Research | Glossary |

Timber Research Unit
Department of Architecture
University of Tasmania