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Author Topic: Why do bridges have expansion joints?  (Read 24105 times)

Offline uanna2341

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Why do bridges have expansion joints?
« on: 03/03/2013 08:28:24 »
Expansion joints, which act somewhat like loosely interlocking fingers, are placed in bridges. What is the function of these expansion joints? What will happen if no expansion joints are placed in bridges?
« Last Edit: 15/03/2013 06:10:11 by CliffordK »


 

Offline graham.d

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Re: Expansion joints
« Reply #1 on: 03/03/2013 10:55:58 »
Most solid materials expand when heated. If the air temperature rises or sun directly heats the material it will expand. When it gets cold it contracts. If there were no expansion joints (on a bridge say) then the ends of concrete slabs making up the surface would impact each other and buckle or, when cold, leave a gap.

 

Offline CliffordK

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Re: Expansion joints
« Reply #2 on: 04/03/2013 20:10:46 »
Thermal expansion is a quick answer for the expansion joints in bridges.  However, they may in fact be more complex than that.

Most bridges have somewhat of an arch, but they would be similar if they were flat.  When a heavy truck drives across a bridge, it will tend to flatten the bridge slightly, and thus making it slightly longer.  Or, if the bridge was flat, it would create a bow, and shorten it slightly.  Then when the truck leaves the bridge, the bridge will return to its former shape.

Wind may also move the bridge back and forth slightly, also lengthening and shortening it somewhat. 

And, of course, earthquakes move structures, and could be devastating to a bridge if there wasn't some flexibility in the structure.

Usually there will be some kind of hinge structure underneath the expansion joints.

Without the expansion joints?  Perhaps it would help the structure maintain shape with traffic, but buckling may occur, as well as wearing at the joints between the bridge and the foundations.  And, under extreme stress, uncontrolled cracks could develop, and could be devastating to the bridge.
« Last Edit: 04/03/2013 21:41:26 by CliffordK »
 

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Re: Expansion joints
« Reply #2 on: 04/03/2013 20:10:46 »

 

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