Design procedures for cold-formed beams


To present design methods for thin-walled flexural members.


Design methods for thin-walled flexural members are presented which take into account the different kinds of buckling acting in such members and also shear lag. In particular, the design of purlins is discussed.


Thin-walled flexural members are applied for carrying lateral loads such as gravity loads in roofs for example. Their behaviour can be affected by local buckling, shear lag, web crippling, flange curling, and lateral buckling.

The effect of local buckling is covered in design by effective widths of the cross-section based on the stress distribution produced by bending moments and axial force.

For shear lag, web crippling, and flange curling, design rules are given in Eurocode 3, Part 1.3 [1].

Lateral-torsional buckling has to be evaluated similarly to hot-rolled sections according to Eurocode 3, Part 1-1 [2] taking the effective cross-section values into account.

Thin-walled cold-formed flexural members have their most important application in wall and roof constructions as purlins and rails. The structural connection with the profiled sheets or sandwich panels provides purlins with lateral and torsional restraints at one flange. This connection gives the purlin high additional stiffness compared to that of a free purlin spanning from frame to frame. The values of torsional restraints have to be measured by testing.

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