Civil Engineering Reference
In-Depth Information
Figure 4.3
Lateral buckling
Figure 4.4
Typical deformation of steel bottom flange in
distortional lateral buckling
Near internal supports of continuous beams, the compressed bottom
flange of the steel section receives lateral support only through a flexible
web; but the slab does prevent twisting of the steel section as a whole.
The flange can only buckle if the web bends, as shown in Fig. 4.3(b).
This is known as 'distortional' lateral buckling, and is the subject of this
Section.
The buckle consists of a single half-wave each side of an internal
support, where lateral restraint is invariably provided. The half-wave
extends over most of the length of the hogging moment region. It is not
sinusoidal, as the point of maximum lateral displacement is within two or
three beam depths of the support, as shown in Fig. 4.4.
It is unlike local flange buckling, where the movement is essentially
vertical, not lateral, and where the cross-section of maximum displacement
is within one flange width of the support. There is some evidence from
tests [40] that local buckling can initiate lateral buckling, but in design
they are considered separately, and in different ways. Local buckling is
