The greater the depth of a beam the more load it can support

The greater the depth of a beam the more load it can support

ZIMSEC O Level Combined Science Notes: The relationship between a beam’s strength and depth

  • A beam is stronger if it’s depth if it has greater depth
  • For example if a plank is turned on its narrow side it is stronger than when it is lying in its wider side

Beams in nature and engineering

  • Where the load is applied in any direction such as in
  • Engineering structures
  • Biological structures such as the human body
  • In such cases a hollow cylindrical beam(tube) ┬áis ideal
  • For example long bones, lamp posts, chair legs, building columns etc
  • In tubes the un-stretched material has been removed this makes them efficient and lighter
  • It would be difficult for animals such as humans to walk with solid beams
  • Tubes are equally strong in all directions including at right angles to the surface.
  • Square tubes are not as strong as tube beams in this regard.
  • A beam must be light and strong
  • Cylindrical beams achieve this by removing unstretched material
  • This increases their mass to strength ratio
  • A beam must also be thick in order to support extra weight
  • It must not be too long as this will result in it weakening the structure
  • beams in tall structure tend to be cylindrical
  • This is because tubes tend to crease rather than crack when placed under compression


  • When cylindrical tubes are placed under pressure they are likely to buckle
  • Buckling occurs when the beam is not strong enough to resist shear forces
  • This can be prevented by making the beams thicker or by increasing their cylindrical diameter

To access more topics go to the Combined Science Notes page.