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where s is the spacing of the fasteners around the perimeter of the sheets and s and so are in the same units. The maximum spacing permitted is 150 (mm) for nails and 200 (mm) for screws.

kn is the sheathing material factor and where different materials are used on the opposite faces only 50% of the strength of the weaker panel is allowed to be used. The factor is defined in equation (9.30) in EC5 as follows: For sheathing on one side, kn = 1.0 (9.23a)

For sheathing on both sides,

Fi,v,Rd,max where fi,v,Rd,max is the design racking strength of the stronger sheathing, and Rd,min is the design racking strength of the weaker sheathing.

The racking resistance is also dependent on ensuring that the wall is secured to the adjacent structure. An example is shown in Figure 9.11 where the wall/structure connection must be able to transfer a horizontal shear force of FijV,Ed at the base and also the rigid body overturning compression force, Fi>c,Ed, and tensile force,

The rigid body overturning forces on the wall are derived from simple statics and are given in EC5, equation (9.32):

bi where the terms are as previously defined. The net force at the connection points must also take into account the effect of the reaction force due to the vertical loading on the panel.

Where the wall comprises more than one wall panel, the panels must be able to transfer the minimum of the vertical shear force in the wall at the panel junction or a design force of at least 2.5 kN/m. For the example shown in Figure 9.11, the vertical shear force, F 1i Ed, between wall panel a and wall panel b to be taken by fixings between these panels will be:

where the functions are as previously defined and F 1i>q,Ed and F2i q d are the reactions at the corner wall/structure connection positions due to the vertical loading on the wall. For the vertical loading condition shown in Figure 9.11:

qibi Fi,vert,Eda

2 bi

When the lateral loading on the wall is acting in the opposite direction to that shown in Figure (9.11), although the corner reaction forces due to the vertical loading on the wall remain unaltered, the direction of the rigid body overturning forces will reverse. For this condition the vertical connection shear force, F2i Ed, to be taken by fixings between wall panel a and wall panel b will be:

Where F 1i Ed and F2i Ed are in kN, the design condition for the vertical shear force at the junction of the panels in kN units will be:

where h is the height of the wall in metres.

The vertical wall studs must also be designed for the axial forces in the wall in accordance with the requirements of Chapter 5 and where they bear onto horizontal members, compression stresses perpendicular to the grain must also be verified as described in Chapter 4.

See Example 9.7.4.

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