Wind-induced load on wire
Wind-induced load on wire
(OP)
Hi,
Let's say we have a long steel wire in tension that is rigidly supported by its endpoints. The wire is slightly curved due to a transversal gravity load.
Will the longitudinal load in the wire be significantly increased by a wind load?
I understand that this information is very limited, but I need to know whether wind-induced loads of this type are normally considered when designing large bridge-like structures.
/hpon
Let's say we have a long steel wire in tension that is rigidly supported by its endpoints. The wire is slightly curved due to a transversal gravity load.
Will the longitudinal load in the wire be significantly increased by a wind load?
I understand that this information is very limited, but I need to know whether wind-induced loads of this type are normally considered when designing large bridge-like structures.
/hpon
Regards,
hpon





RE: Wind-induced load on wire
The question should be:
Could the longitudinal load in the wire be significantly increased by a transversal wind load on the wire itself?
/hpon
Regards,
hpon
RE: Wind-induced load on wire
RE: Wind-induced load on wire
That is what I thought (so long as the geometry is approximately identical). I appreciate the reassurance!
/hpon
Regards,
hpon
RE: Wind-induced load on wire
RE: Wind-induced load on wire
Calculate the natural frequency of your cable in it's loaded state. Then calculate the eddy shedding frequency of the von karman vortex street for a range of credible wind speeds. If the frequencies are similar, you MAY have a problem with resonance.
I say MAY rather than WILL because there can be a lot of aerodynamic damping in a cable which is vibrating a lot and it is often not a big deal - power and phone lines don't often seem to come down because of resonance. (someone will say that they do)
RE: Wind-induced load on wire
Ok, I will :)
Actually, I will just comment that we live in an area subject to occasional high wind storms. The power company presumably makes a calculation on how much they should spend to mitigate wind damage to power lines, and I think they err too much on the side of not spending for my taste (it sucks to be w/o power).
Gwolf mentions eddy vortex shedding, but even just the transients due to gusting of winds can cause trouble if not designed for. Similarly, icing during cold weather (and ice shedding as the weather warms) cause transient effects.
Some more info on how power lines can/are designed for wind loading:
http://en.wikipedia.org/wiki/Stockbridge_damper
http://en.wikipedia.org/wiki/Aeolian_vibration
http://en.wikipedia.org/wiki/Conductor_gallop
I've seen lines with these installed, I'll bet others have too, whether they knew what they were for or not:
ht
The above should give you a veritable plethora of search terms you can use on Google.
RE: Wind-induced load on wire