Theory of Built-up Sections

  • A built-up beam is also known as compound beam.
  • The built-up beams are used when the span, load and corresponding bending moment are of such magnitudes that rolled steel beam section becomes inadequate to provide required section modulus.
  • Built-up beams are also used when rolled steel beams are inadequate for limited depth.
  • In building construction, the depth of beam is limited by a space provided by the architect.
  • Drawing beam of small depth do not provide required section modulus. Therefore, plates are attached to the beams.
  • The strength of rolled steel beams is increased by adding plates to its flange which is one of the method forming built-in section.
  • The other method is to compound a number of rolled steel sections themselves.

Built-up Section

The built-up sections shown in figure’ A’ and ‘B’ are used for heavy loads and small spans.

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