Design of beams in structural steel

Basic beam behaviour

Beam analysis is generally based on simplifying assumptions.

Beam stiffness

Beams deflect when loaded and this must be limited to avoid damage and distress.

Beam strength

Beams must be sufficiently strong to carry the applied bending moments and shear forces.

Cross-section geometry

The performance of any beam is dependent upon the cross-sectional geometry, not only on the physical dimensions, but also the shape. Steel beams are available in a variety of cross-sectional shapes.

Estimating sizes

Simplified procedures can be used to estimate the required size of beam section.

Factors affecting beam strength

Bending strength may be limited by material strength, lateral-torsional buckling or local buckling.

Factors affecting the design

The objective of the engineering design of beams is to make a choice of a beam for a particular purpose then test by established numerical procedures whether:

Introduction

Beams are an important class of structural element, and are normally horizontal.

Summary

Support conditions

The type of support influences the distribution of bending moments and shear forces. For simple span beams the supports may be pinned, fixed or free.

Use of BS 5950 - Part 1

The current code of practice called "Structural Use of Steelwork in Building" is BS 5950 Part 1. This code gives specific guidance on the strength and stiffness of steel structures for buildings to allow numerical calculations to be made.

What is a beam?

Beams support mainly vertical loads, and are small in cross-section compared with their span. Engineering diagrams adopt simple conventions to represent beams, supports and loads.