31-10-2012, 04:50 PM
BRIDGES
FES Bridges Lecture.ppt (Size: 1.73 MB / Downloads: 145)
How Bridges Work?
Every passing vehicle shakes the bridge up and down, making waves that can travel at hundreds of kilometers per hour. Luckily the bridge is designed to damp them out, just as it is designed to ignore the efforts of the wind to turn it into a giant harp. A bridge is not a dead mass of metal and concrete: it has a life of its own, and understanding its movements is as important as understanding the static forces.
Buckling is what happens when the force of compression overcomes an object's ability to handle compression. A mode of failure characterized generally by an unstable lateral deflection due to compressive action on the structural element involved.
Snapping is what happens when tension overcomes an object's ability to handle tension.
To dissipate forces is to spread them out over a greater area, so that no one spot has to bear the brunt of the concentrated force.
To transfer forces is to move the forces from an area of weakness to an area of strength, an area designed to handle the forces.
Arch Bridges
The arch has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet.