The Hong Kong Bridge. Image credit

The Hong Kong Bridge. Image credit

ZIMSEC O Level Combined Science Notes: Suspension bridge

  • Old suspension bridges were usually built using rope/vegetable fibre
  • The ropes could withstand tension forces while they were new but they would quickly deteriorate
  • Suspension bridges are usually constructed for very long spans
  • An example is the Chirundu¬†bridge across Zambezi¬†river between Zimbabwe and Zambia
  • Steel cables are suspended from high towers and the road/railway is supported below the cables
  • The vertical supports reduce the span of the bridge and reduce bending
A suspension bridge

A suspension bridge

  • The cables are in tension
  • The greater the load the greater the tension
  • The pillars/towers (abutments) are in compression
  • Long spanned bridges are now possible due to the strength of modern steel cables
  • Cables are also continuous and do not need joins
  • They are made up of hundreds of wire so the failure of one wire strand will not result in the whole structure failing
  • Cables in a suspension bridge are in the form of an inverted arch
  • This best accommodates the forces that are acting on the cables and bridge
  • While in an arch bridge the arch is in compression
  • The inverted arch in the suspension bridge is entirely in tension
  • The curved cables carry these tensions

To access more topics go to the Combined Science Notes page