For wind loading, why horizontal guide spacing is higher than vertical ?

Dears,

In guide spacing charts for metallic piping, we observe that horizontal guide spacing is higher than vertical ?
For eg, for NB 6", 45PSF wind, vertical guide span is one fourth of the horizontal guide span.

Will any of our mentors give the reason behind this? Is it for prevention of buckling in vertical run of piping ? For nonmetallic piping, buckling requirement is significant. Why will buckling occur in vertical run for metallic piping - due to eccentric weight loading during wind load ?

How will we evaluate buckling in verical run during wind - is any simple formula available?

regards,

sam

Sam,

I don't see any possibility of buckling in the vertical run of pipe under the action of wind.

Let us analyze the restraints to the action of wind in the horizontal portion: We have the friction forces at the vertical restraints along with the guides/anchors contributing to this effect.This essentially makes the horizontal portion a very stable structure.

On a vertical run we generally do not have vertical load bearing supports ( of course this depends on size, riser length etc)or at least on a fewer scale than they are on the horizontal thus make them more unstable structure than the horizontal portions( there is of course this counterargument that the vertical leg is of a shorter length than horizontal leg thus contributing to lesser total magnitude of the wind force ).So it is the guides which have to make maximum contribution to take care of the wind load on a more unstable structure, hence they are more in number.

Regards

Yes always a wise idea to count on friction to restrain things... I guess there was not enough friction evident in the failures of buildings in this years round of natural disaster!

Friction is not allowed to be used as a restraint under some building codes.

As for evaluation of guide spacing simple beam element formulae will give you an idea as to what your guide spacing should be baseed upon stress or deflection.

Some people add more guides based upon the idea that vortex shedding may cause lines to vibrate... they try to raise the natural frequency to a higher number..

As for horizontal or vertical spacing criteria the lateral loads will be the same therefore I would say for lateral loads the guide spcing could be the same, but if one checks the vertical pipe for unstable column buckling you may end up with more guides to take this into account.