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Arch Bridges - Design Technology





Arch bridges

Arch bridges are one of the oldest types of bridges and have been aroundd for thousands of years. Arch bridges have great natural strength.

They were originally built of stone or brick but these days are built of reinforced concrete or steel. The introduction of these new materials allow arch bridges to be longer with lower spans.

Instead of pushing straight down, the load of an arch bridge is carried outward along the curve of the arch to the supports at each end. The weight is transferred to the supports at either end.

These supports, called the abutments, carry the load and keep the ends of the bridge from spreading out.

 


The load at the top of the key stone makes each stone on the arch of the bridge press on the one next to it. This happens until the push is applied to the end supports or abutments, which are enbedded in the ground.






The ground around the abutments is squeezed and pushes back on the abutments.




For every action there is an equal and opposite reaction. The ground which pushes back on the abutments creates a resistance which is passed from stone to stone, until it is eventually pushing on the key stone which is supporting the load.

Example of an arch bridge spanning a large gap.


Task
Using the following table state whether the object is a structure, a mechanism or a combination of the two?


umbrella structure mechanism both
folding ironing board structure mechanism both
tent structure mechanism both
spiders web structure mechanism both
bicycle structure mechanism both
rotary clothes line structure mechanism both
human skeleton structure mechanism both
deck chair structure mechanism both