Cfq

• where Fc d is the design value of the axial load acting on the spaced column and Atot is as defined against equation (8.20).

kc is the instability factor associated with the critical axis (i.e. the axis having the maximum slenderness ratio) and is determined in accordance with 5.3.1.

In addition to checking the strength of the shafts, the strength of the packs, gusset plates and mechanical fixings (when used) must also be checked. The shear forces in the packs or gussets are derived assuming rigid body behaviour and are as shown in Figure 8.7.

From basic statics, the value of the shear force Td shown in Figure 8.7 is:

Vdii ai

where a1 is the distance between the centre lines of adjacent shafts and Vd is obtained from equation (8.27),

Fc c,d i20kc

Fc,d Xef 3600kc

Fc,d

60kc for A.ef < 30 for 30 < A.ef < 60 for Aef > 60

where the symbols are as previously defined and Fc d is the design axial load on the spaced column, kc is the instability factor associated with buckling about the y-y axes, determined in accordance with Section 5.3.1, and A.ef is the effective slenderness ratio defined in equation (8.20).

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