Effective length factors to Eurocode 3
A free standing wall standing on the top flange of a steel beam would fit the description of a destabilising load, however, free standing walls are not usually a feature of domestic buildings. Walls will usually be fixed to floors and roofs, and typically walls will have further support from buttressing walls. If the wall above the beam is not restrained, the wall will be unstable and would form a dangerous structure and therefore require repairing. It therefore is reasonable to presume that in domestic buildings, walls to be supported are not destabilising loads. Also loads from floors and roofs which are structural elements that provide resistance to lateral movement, do not constitute destabilising loads.
Effective length factors as shown in Table 13 in BS 5950-1 are not applicable to Eurocode design and designers should make reference to P360 Stability of steel beams and columns, published by the Steel Construction Institute. For most circumstances in domestic buildings the effective length may be taken as 1.0 multiplied by the beam span length, provided that the;
- End of the beam is built into a wall.
- End of the beam is fixed to a masonry wall.
- End of the beam is fixed to a column or a beam.
The designer is to ensure that the proposed detail adequately ensures that the end of steel beam is restrained.
In cases where restraint against torsion is due solely to bearing of the bottom flange of the beam on the support and there is no positive connection between the bottom flange and the support, the beam span length should be multiplied by 1.4.