A simple bridge. Image credit pinimg.com

A simple bridge. Image credit pinimg.com

ZIMSEC O Level Combined Science Notes: Introduction to bridges

  • A bridge is a structure that allows a road, path or railway line to cross a river/depression/gully/gap
  • The simplest bridge can be made using a beam lying across the gap
  • However such as bridge becomes impractical as its span(length between support beams) increases
  • The longer such a bridge becomes the weaker it becomes
  • As it’s length increases the bridge’s bending also increases
  • Increasing the thickness of such a bridge also increases its weight(self-load)
  • This results in the bridge bending more instead of reducing it
  • When designing and building bridges in the real world the following techniques are employed:
  • The span of the bridge is divided into smaller sections
  • The amount of bending is minimized
  • Ways are found to reduce the self-load/weight of the bridge
  • Decreasing the thrust on the supports/abutments
  • Minimizing the cost of construction and maintenance
  • Reinforcing the materials e.g. concrete used to make them stronger
  • Modern bridges are made of chiefly two materials:
  • steel and concrete
  • Steel is very expensive while on the other hand
  • Concrete is cheaper but more of it is required to make a strong bridge structure
  • A bridge has two main parts:
  • The deck on which traffic (including humans) move/cross
  • the abutments and piers which support the deck(s)
  • in a steel-concrete structure steel beams support a concrete slab
  • A reinforced concrete deck may span(have a length of) up to 30m
  • While a steel deck may span up to 50m
  • Ways have to be found to balance the strength and cost of the structure

To access more topics go to the Combined Science Notes page

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