O Level Revision : Integrated Science - Science in Structures and Mechanical Systems - Beams Structures

Human life is enhanced by structures. Every structure has a design that makes it best suited for its purpose and the material chosen to make the structure must have suitable properties.  Beams are used to carry loads.  A truss is made up of several beams joined together.  Different building materials have their advantages and disadvantages. There are a variety of methods of joining materials.


  • A beam is a supported bar which bears a load. A beam may also be defined as a bar of solid material which is subjected to forces along any points on its length.
  • Beams can be made of materials such as
    • metal
    • wood
    • concrete
    • plastic
  • A beam is supported at some points along its length so that it can perform its function.
  • Structures e.g. buildings, bridges and dams are made up of beams.
  • Systems making any such structure should be strong, light and cheap. Beams are put together to make the structure.

(i)   Simply supported beam

(ii)  Cantilever beam – supported at one end.


  • When beams are loaded, they develop internal forces that are referred to as stresses.
  • There are three types of these stresses namely compression, tension and shear.
  • Compression is pushing stress, represented by
  • Compressional forces cause buckling or shrinking.

  • Tension is pulling stress
  • Tensional force causes tearing, breaking or cracking.

  • Shear = twisting stress, represented by   Beam
  • Shear forces causes twisting, deformation or change of shape.
  • A beam can also be subjected to forces which tend to twist the beam.
  • In a loaded beam stress is distributed depending on how the beam is supported.

Loaded beams


  • The stresses are inside the beam but near the edges.
  • The central part is a neutral axis, there is no stress.
  • Existence of neutral axis is the reason why most beams are hollow. Removal of central material makes the beams lighter (hence increase in strength – mass ratio).

Types of beams

  1.  I-beam
  2. Hollow box beam
  3. Hollow cylindrical beam
  4. Solid beam
  5. L-beam f)    T - beam

The strength of beams

  • The strength of a hollow and solid beam can be compared by loading the beams each at a time thus determine the magnitude of the load which causes failure on the beam.
  • For accurate results the following must be ensured when carrying out the experiment:
    • beams must be of the same material.
    • beams must be of the same length.
  •  Loading must be in the same manner (hanging the masses or placing them on the beam).
  • Results will show that the beams will support the same load therefore the middle layer in a beam is redundant i.e. neutral thus can be removed with no effect on the strength of the beam.
  • Single beams are characterized by high concentration of stress. This compromises their life.
  • Several beams are jointed into frameworks called trusses.