studenthelp10 said:
So the chain of events was the wind -> rocked the cables -> tension to no tension at all then back (zero) as said above = twist of bridge (b/c weight of bridge is light- b/c little tension in cables as bridge was light)-> bridge twists up and down-> the wind added to the twisty motion by splitting up when it hit the bridge some on top and some underneath making it twist more dangerously-> twisting adds compression and tension force to cement-> cement can handle compression but is very bad at tension so cement brike apart-> roadway collapses into river underneath the bridge. ?
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i need to find a way to link the chain of events together i.e. this ccaused this->... which caused this which made the bridge fail
the chain of events does not start with the cables, the wind doesn't rock the cables, the cables merely
respond to what the roadway is doing
the cables, basically, are springs, each one will adjust to whatever load is pulling it down
when a heavy vehicle goes onto the roadway, the roadway changes shape slightly, and the tension in the nearest cables reacts to that
the wind vortices are behaving like heavy vehicles, except that they can also
reduce the load
they're a bit like the air pockets (of reduced pressure) that an aircraft sometimes flies through
studenthelp10 said:
What I think is happening is that the wind force blowing from left to right on the diagram and traveling above and below the circle. Then curving back inward and spiralling. I am not sure but i think that the wind is pushing from boths sides i.e. direction right and from the spirals going the opposite way (looking like compression horizontally)- opposite forces pushing object inward. I think this then squeezes the circle together and when the sides are squeezed in the top and bottom of the circle expand (looks like tension) forces pulling object outward in opposite direction to stretch
it isn't left and right, it's up and down alternately, causing the roadway to twist
see this image, showing the vortices rolling off the roadway, alternately above and below, from http://saba.kntu.ac.ir/eecd/Ecourses/instrumentation/projects/reports/Flowmeter/vortex_files/vortex10.gif …
http://saba.kntu.ac.ir/eecd/Ecourses/instrumentation/projects/reports/Flowmeter/vortex_files/vortex10.gif
(the word "alternative" should of course be "alternate"!
)
the accompanying text explains … (http://saba.kntu.ac.ir/eecd/Ecourses/instrumentation/projects/reports/Flowmeter/vortex.htm)
On the side of the bluff body where the vortex is being formed, the fluid velocity is higher and the pressure is lower. As the vortex moves downstream, it grows in strength and size, and eventually detaches or sheds itself. This is followed by a vortex's being formed on the other side of the bluff body . The alternating vortices are spaced at equal distances.
The vortex-shedding phenomenon can be observed as wind is shed from a flagpole (which acts as a bluff body); this is what causes the regular rippling one sees in a flag. Vortices are also shed from bridge piers, pilings, offshore drilling platform supports, and tall buildings. The forces caused by the vortex-shedding phenomenon must be taken into account when designing these structures. In a closed piping system, the vortex effect is dissipated within a few pipe diameters downstream of the bluff body and causes no harm.