Examples

As stated in 4.3, to be able to verify the ultimate and serviceability limit states, each design effect has to be checked and for each effect the largest value caused by the relevant combination of actions must be used.

However, to ensure attention is primarily focussed on the EC5 design rules for the timber or wood product being used, only the design load case producing the largest design effect has generally been given or evaluated in the following examples.

Example 9.7.1 To enable a solid timber column 6 m long to withstand a design axial compression load of 100 kN, it is laterally braced about its weaker axis at mid-height as shown in Figure E9.7.1. What is the minimum stiffness to be provided by the bracing member and also the stabilising force in the member?

Column

Bracing member

1. Geometric properties

Column: Length of the column, L

Bay length for bracing analysis, a (Figure 9.3b (EC5, Figure 9.9))

2. Actions

Column - ultimate limit state (ULS) Design axial load on the column, Nd

3. Modification factors

Modification factor for bracing stiffness, ks (equation (9.4) (UKNA to EC5, Table NA.6)) Modification factor, kf 1 (equation (9.6a) (UKNA to EC5, Table NA.6))

4. Stiffness of the bracing member Minimum stiffness to be provided by the bracing member, C

5. Stabilising force in the bracing member

Stabilising axial force to be provided by the bracing member, Fd

Nd = 100kN

Example 9.7.2 A 50 mm wide by 300 mm deep sawn timber beam is laterally braced against lateral torsional buckling at the positions shown in Figure E.9.7.2. The beam supports a characteristic permanent action of 2.25 kN and a characteristic variable medium-duration action of 3.35 kN at mid-span and has an effective span of 3.9 m. It is of strength class C22 to BS EN 338:2003 and functions in service class 2 conditions. The bracing members are 38 mm by 100 mm deep, 1.8 m long, of strength class C16 to BS EN 338:2003 and pin jointed at each end.

Carry out a design check to confirm that the bracing members will meet the requirements of EC5, assuming that the axial stiffness of each end connection on each bracing member is equivalent to 50% of the axial stiffness of the member.

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