Double Angle bending 1

[ag89]

I am trying to calculate the allowable stress for double angle beams used to support utility piping. The "stem" of the double angle is turned up, i.e. the stem is in flexural compression. I have some literature on wt shapes in this configuration, seems like a lot of derivations just to arrive at 0.6Fy for the allowable stress. Just wanted to know if anyone had come across this and how to arrive at the allowable stress relating to lateral torsional buckling.

 

[0910]

let me know you are finding allowable stress as per which country code. Please specify. and also let me know how double angle is connected ( eg. back to back )

 

[ag89]

The double angles are suspended from each end with 3/4" diam threaded rod (angles are approx 4'-6" lg. The angles are connected with 7/8" plates at the ends and at midpoint. The design will be based on AISC ASD.

 

[Hariharan]

Why do you need a double angle section for pipe support?
I can't visualise any specific advantages.
Why don't you go for a channel or I- beam section? Ligher
and easier to connect, and you don't have analysis and
design problems!

Hariharan

 

[phuduhudu]

Under the British code, BS5950 there is a fair bit of work to do to get the allowable bending stress for a double angle member because it is not often used in bending. So I wouldn't be surprised if there are a few derivations to go through to get to this figure. However I wouldn't make any assumptions about the result as it could vary a great deal depending on span and angle size.
Carl Bauer

 

[Ron]

I agree with Hariharan...why not consider another section. At the least, turn the angles over such that the leg-down is in bending, not leg-up. This makes it easier to attach the pipe, gives a larger bearing area for the pipe and negates the "stem" compressionissue.

Ron

 

[Ron]

I agree with Hariharan....change the section if you can.

Otherwise, turn the angles over such that the legs are turned down. This will make allow more bearing area for the pipe, make it easier to use "U"-bolts to secure the pipe, and negate the "stem" compression issue.

Ron

 

[ag89]

Thanks for the input, I have found the section in AISC ASD ninth edition. Starting on pg 5-309, this section covers angles in flexure.

 

[IJR]

If you can do what Ron boss and Hariharan suggested, you will have a safer system, easier connections and lesser calculations to make, and guys who galvanize or paint will thank you,as agreed by friends above.

However while at the subject you might also want to take a look at this article:

Design of single and multiple Angle columns and beams, by Cedric Marsh, Journal of Structural Engineering, July 1997 page 847-856

That is for reference. But we frequently design pipe racks and we use channels or I-beams. I assume your utility is real small.

Good luck.

 

[ag89]

This installation is for very small (< 2&quot pipe and conduit. It is for a mechanical contractor doing construction in and existing building. I believe they have a surplus of angle they purchased for their piping/conduit runs. I, too, typically use wide flange or channels in piperacks. I wouldn't even consider this a piperack.

Thanks for all the input.

Ag89

 

[Ron]

ag89...one more comment, now that I think I understand a bit more about your application.

You might consider a pre-fabricated product that is both structurally viable and contains a spun aluminum flashing flange to allow better roof penetration connection. These are known as Thaler supports (Thaler is one brand, but I believer there are others). Check their website at:

http://www.partsdome.com/thalermetal/default.asp?ShopperCurrency=USD

I have used these before and they are high quality.

Ron

 

[evelrod]

Good grief, guys!
Just use &quot;unistrut&quot; like everybody else does.
Besides , it's cheap, and comes in a variety of sizes and strengths.

Rod