Elastic stability slenderness limits

The CIRIA Guide Simple Rules assume no reduction of capacity due to the slenderness of the section or to lack of adequate restraint. This is valid if every panel can be defined as braced and not slender.

In the examination of this condition, the CIRIA Guide states that the effective height of each panel is taken to be 1.2 x the shortest distance between centres of parallel lateral restraints (where there are effective lateral restraints at all four edges of the panel) or as 1.5 x the distance between the centres of the parallel lateral restraints (where one or two opposite edges of the panel are free). When both rotational and lateral movements are restrained the effective height may be taken as the clear distance between restraints.

In EC2 the demonstration is not quite as straightforward.

The floors are assumed to be held in position horizontally by an adequate bracing system and are 'braced' in accordance with EC2.

The floor slabs are monolithic with the wall so the effective height, I, is

calculated from the relevant clauses in EC2 referring to columns. However the Eqn 4.60

design example does not give any information on the adjacent structure so k Figure 4.27 cannot be calculated but /3 = III , cannot exceed 1.0 and therefore o col lo < 1.0 x 3540 = 3540 mm

The wall is considered slender if X exceeds the greater of 25 or 15/JV^

/' = radius of gyration = 300/f\2 = 86 mm X = IJi = 3540/86 = 41.2

N' say in lower storey (bottom loads not considered)

57.6 x 3 x 1.35 + 44 x 3 x 1.5 + 2 x 475 x 1.35/5.75

654 kN/m

654 x 103

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