Compression Flange of Beam or Girder


The widened portion of a beam or girder, such as the horizontal portion of the cross section of a simple-span T-beam, which is shortened by bending under a normal load is known as Compression Flange.

In a continuous floor beam under gravity loading, the laterally un-braced bottom flange is subjected to compressive stresses (Compression Flange) near the interior support(s). To prevent lateral buckling of the flange, this region must be adequately designed.

Related Question:
  • What is compression flange?
  • Why compression flange is important?
  • Which portion of beam or girder is known as Compression Flange?
  • Why compression flange must be adequately designed?

Slender Beam

Image of Beam

The Slender beam can be defined as the beams in which the spacing of the lateral support to the compression flange or face is more than 50 times the least width of the flange or face.

Since lateral support equal to a minimum of 2 percent of the total (internal) compression in the compression flange is usually considered adequate, and may often be satisfied by simple friction of separate floor materials transmitting the load to the beam, the beam slenderness problem will be encountered only rarely in routine design. It may arise in design of long span upturned roof beams or in the design of thin deep panels used as spandrel beams. Such spandrels are often precast and added to the frame as simply supported beams with a span equal to the column spacing and width of the compression flange as little as 4 inch.

When a slender beam condition arises, the simple solution is to provide lateral bracing within the spacing limits, thus eliminating the condition. Where lateral bracing is impracticable, the load capacity must be reduced.

**Hansel. William, and Winter. George, "Lateral Stability of Reinforced Concrete Beams", ACI Journal, 56(Sep.1959), 193-214.
** Sant. J., and Bletzacker. R. W., "Experimental study of Lateral Stability of Reinforced Concrete Beams", ACI Journal, 58(Dec. 1961), 713-736.
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