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Transcript of Bridges
Found in Earthquake fault lines
Natural wind tunnel
Nothing solid underneath (No solid bedrock)
The coasts are moving away from each other
Earthquake proof (Survived hits of 7.4 on the Richter Sale) Although the base of the pillar is stable, during an earthquake there is the possibility that the pillar topples During an earthquake the piers are allowed to move on the layer of gravel... The hundreds of cables that hold the road deck could damage the bridge by vigorous shaking caused by slow winds Liquefaction The roots of vetiver grass provides support to the soil and thus making it more stable ...In Fact The bed rock found underneath the bridge is very unstable because it is composed of sand and silt During an earthquake a phenomenon known as 'liquefaction' occurs Liquefaction describes a phenomenon whereby a saturated soil becomes a liquid under stress eg. during an earthquake Indian incense Indian incense are made from vetiver grass which have a large root system (up to 7m in length) The engineers embedded 200 hollow pipes in the bed rock to support every pier of the bridge These pipes prevent liquefaction even in an earthquake Toboggan An impossible approach This simple concept resulted into a smart solution! This occurs because the sides of the pier 'diggs' in the seabed because of weight A solution would simply by taking away the leading edge of the pier (like the toboggan) it is impossible to 'curle' the edge piers Instead of changing the the shape of the piers the engineers decided to change the surface of the seabed ...they covered the seabed with a layer of gravel The key is Particle Size! Layer of gravel Now the pier can move sideways without toppling Steel Chimney It is not gusting that makes the cables move but a phenomenon called vortex shedding Vortex Shedding Vortex Shedding Slow winds creates alternating low-pressure vortexes on the downstream side of the object. The object will tend to move toward the low-pressure zone. Different pressures result in the movement of the cables Helical Spring Shape A helical strake is attached to most of the steel chimneys The helical strake on this steel chimney reduce drastically the effect of vortex shedding Back to cables All cables that hold the deck of the bridge also have this helical shape to prevent vortex shedding Predictable Failure Is the concept that something fails at a set limit. It fails predictably Viscous Damping Viscous damping is the system used to absorb energy when the bridge is moving vigorously an thus prevent collision of the deck with the piers The engineers decided to make the deck move independently from the bridge by using the concept of a hammock The Physics behind a hammock A hammock is a kind of pendulum which moves at a steady rate. Its advantage is that it is not effected by external movement. This pendulum principle was used to make the bridge earthquake proof This makes the bridge unique in all the world Now the bridge is allowed to move freely, but if it moves to vigorously it may smash with one of the four piers.
This can destroy the bridge. The viscous dampers are only activated in extreme cases such as earthquakes. This means that the deck is free to move during high winds but during an earthquake the dampers prevent the collision with the piers. The dampers contain a fuse, when the load gets too large it fails and the viscous dampers start to work Reference Thank You http://en.wikipedia.org/wiki/Rio%E2%80%93Antirrio_bridge
http://en.wikipedia.org/wiki/Liquefaction It is found in Greece Large Root System More Stability The larger particle size (gravel) prevents the pier from 'towing in' and thus fall over. Critical Damping Helical Shape