any civil engineers out there?

TillEulenspiegel

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Most of the maths and applications I have to deal with in electronics I can look up in a book or use my faltering memory.
The question I have is for bridge construction. I remember a little about static wind load on ridged structures, but how do you figure out the load on an aerodynamically devised structure, like a bridge? The question comes to mind as I live in Tampa and there are currently high winds on the skyway bridge. Which is kind of funny( and topical ) because there is a bridge being built in Clearwater Fla, that was subject to non balanced loading on bearing members during it's construction and all the pylons have massive cracks.
Do you just use finite element analysis of the structures and subject it to dynamic computer modeling or what?
......Signed, nervous going over bridges.

Oh and how do you calculate the harmonic of the structure and determine how to decouple it? ( the cables can be thought of as a string on a harp or guitar). Matbe the fundamental is just too low to be affected by wind?
 
It's done in an empirical way. Lots of 'rule of thumb' and fudge factors. Scale models are placed in wind tunnels. Computer models are used too, but turbulent flow is still notoriously difficult to model computationally.

When a bridge falls down, develops cracks, or sways unacceptably, the designers learn something ready for the next bridge.
 
Cheebus just had another bridge in the area collapse,man that's not helping my faith in bridge design...........
 
ceptimus said:
It's done in an empirical way. Lots of 'rule of thumb' and fudge factors. Scale models are placed in wind tunnels. Computer models are used too, but turbulent flow is still notoriously difficult to model computationally.

When a bridge falls down, develops cracks, or sways unacceptably, the designers learn something ready for the next bridge.
Click to expand...

I KNEW it!

Engineers :rolleyes:

:p
 
Graham said:


I KNEW it!

Engineers :rolleyes:

:p
Click to expand...
Clearly us software folks have taught the bridge engineers a thing or two about proper design methodology :D
 
We were taught to analyse wind load as a side load on the structure, whether it was a bridge, or a building.

Since the Tacoma Narrows failure there was more windtunnel testing of models done to check out harmonic frequencies.

I specialized in dirt and roads, and now work in pipelines, therefore didn't have much need to follow developments in bridge construction so the above is about 16 years behind current technology.
 
We drove over the (new) Tacoma Narrows bridge last Saturday.

Seemed pretty safe to me. All those grid breaks in the floor that create spoiling effects, etc. :p

To answer the original question, I'm not an expert in the field, but most similar acoustics problems (and there are some) have to be resolved by brute-force methods if at all, and with a good "fudge factor" for protection thrown in.
 
OK Well now I'm totaly reassured..............

Reminds me of the quote of the astronaut ( paraphrased ) how would You feel sitting on top of a bomb with 876,000 parts any of which if they fail could kill you, all supplied by the lowest bidder . : )
 
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