The cross section of beams

The cross section of beams

ZIMSEC O Level Combined Science Notes: Strength to Mass ratio

  • Engineers do away with materials that are under little stress so as to be able to build efficient structures in terms of weight and cost
  • The material that lies close to the neutral axis is under little stress
  • Beams used in building should have a high strength to mass ratio
  • The lower their mass the higher this ratio
  • The diagram shows the cross section of different beams
  • The hollow beams, the I and Z beams are just as strong as the solid beams
  • But they are much lighter than their solid counterparts
  • This is because unnecessary material has been removed in the hollow beams
  • This results in a high mass to strength ratio
  • In the Z and I beam the thin metal plates carries the shearing stresses.
  • It holds the top and bottom plates together
  • Also hollow box beams are used in constructions where light building materials are required
  • For example win spans of bridges
  • In I beams the middle of the beam resists vertical/shearing forces
  • The flanges at the top and bottom of the beam resist horizontal tension and compression
  • The horizontal compression and tension forces are often greater than the shear forces and are more likely to cause failure in a structure

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

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