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.