An arch bridge

An arch bridge

ZIMSEC O Level Combined Science Notes: Arch bridges

  • In an arch bridge the arch acts to support a load by converting the downward force into sideways thrust
  • Arches can make structures last longer for example old buildings and structures in European countries have lasted as long as they have due to arches
  • These structures avoid tension which was turned into compression forces
  • The load pushes the units down together
  • The thrust runs around the ring of the arch and is then transferred to abutments
Flat lintel vs an arch

Flat lintel vs an arch

  • The arches can be made using various materials:
An arch bridge built using trellis

An arch bridge built using trellis

  • If it is made of steel it can be built using a trellis like framework
  • This ¬†greatly reduces the weight of the structure and decreases the thrust on the abutments
  • It enables engineers to build flatter arches with cheaper foundations
  • An arch bridge differs structurally from a beam/pier bridge
  • An arch is entirely in compression while the underside of a beam is in tension
  • A beam bridge is cheaper if material can be found that can carry tensile forces reliably
A modern through arc bridge.

A modern through arc bridge.

  • In a modern through arc bridge
  • the road hangs from two parallel arches
  • The load is carried in compression arches
  • The suspended road is free of compression and tension forces
  • However the thrust on the abutments is very large
  • Therefore very reliable foundations have to be built on solid rock

Old arch bridge

Old arch bridge

  • The ancient Romans discovered the principle of the arch
  • A flat lintel such as shown above can collapse under its own weight
  • However when stones/bricks/other material is made into an arch they can carry a load
  • The load pushes the masonry down and together
  • So that the arch is stable and strong

To access more topics go to the Combined Science Notes page