Pipe stands 4

[edison123]

I hope this is the right forum. If not, please direct me to the right one. Thanks.

I want to make 4 vertical pipe stands for supporting large electrical motors weighing up to 20 tons. This is only a static load just supporting the motor on the factory floor so that the motor repairs can be done from underneath.

The pipes will be 10 mm thick seamless pipes of 150 mm OD x 130 mm ID x 2000 mm high. They will have welded top and bottom square bases of 300 mm x 300 mm x 25 mm thick for stability. By my calculation, the axial pressure on the pipe wall thickness comes to about 114 kg/sq cm for each leg for a weight of 20 tons. Is this correct?

Is this load within the safe limits of steel yield stress and the hoop stress?

Muthu

http://www.edison.co.in

 

[MFJewell]

If you have done the calculation, you can look up the yield stress for steel and see if you exceed it. However, I'm not sure the pipe you listed is a standard size. It appears you want something like 6" nps, X-stg. Also, are you assuming the load is evenly distributed among the four posts and that each post has the force acting along the axial centerline? You may want to verify that.

 

[MikeHalloran]

Compressive yield is not the only criterion that needs to be satisfied.
You also have to check the columns for buckling, even with a pebble under a corner of your base and the motor mounted eccentrically.

You might want to tie the stands to each other, for stability and so they can be moved as a group.
Maybe put spring loaded casters on so they can be moved manually when unloaded,
include lifting eyes so the loaded stand and motor assemblage can be moved with an overhead crane, and bottom connecting beams so it can be handled with a forklift.

Speaking of which, you also should include some sturdy diagonal bracing so the whole mess, stands and big motor, doesn't come crashing down on the floor, the first time the stand gets hit by a forklift or a truck. That _will_ happen.





Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

You probably want the mechanical engineering forum, but it's not a hoop stress issue, but a buckling issue when you're that slender. Maybe even try the structural engineering other topics forum or do a bit of searching on supports.

When you say "pipe stands" what do you mean? Literally just straight pipe?

Unless there is a wholly vertical load and no moment loads or risk of toppling over / swaying, it might be OK, but it's the buckling issue which you need to look at and the other loads.

Draw / sketch it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[edison123]

Thank you all.

The floor is solid reinforced concrete industrial type which is pretty much level. Yield stress of steel is stated around 2500 kg/cm2. Does this apply to seamless pipes also?

Yes, pipes are straight up vertical and the load on all 4 pipes is pretty much even.

Cross bracing is a good idea. I could weld some gusset plates to the pipes outer surface and use diagonal angle braces.

I calculate individual pipe stand weight at around 75 kgs. Spring castors is a good idea to move them around.

I am lost on hoop stress calcs.

Muthu

http://www.edison.co.in

 

[MFJewell]

You don't need hoop stress calcs. You need to use column buckling. To get critical load, use length of column, modulus of elasticity, moment of inertia for column cross section, and a K value depending on how you model the end connections to the floor (maybe a 2??).

 

[LittleInch]

Have you not read the comments above? Your design is a structural issue not hoop stress which is about internal pressure. Your internal pressure is zero.

Draw your structure and then get a structural engineer to analyse it. If it goes wrong you will kill the people under the motor. Do you want that? This is not a subject for an Internet forum to decide whether or not it is fit for purpose with suitable factors of safety.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[edison123]

Ok, I got it, no hoop stress but more of buckling. Thanks.



Muthu

http://www.edison.co.in

 

[edison123]

LittleInch

I did respond and thank the posters. Thanks for your advice anyways.

Muthu

http://www.edison.co.in

 

[MikeHalloran]

Another star for LittleInch.

Muthu, seriously, you need to work closely with or delegate the job to an actual structural engineer; this is serious stuff, and clearly a little outside your skillset.
Please don't get offended; get help.


Mike Halloran
Pembroke Pines, FL, USA

 

[edison123]

1.5 meter high pipe supports for a 400 ton generator stator. 8 such supports just standing on the floor.

I did the calc for my design and got about 13 tons for each stand.

I have had 32 years doing this with zero accidents. I will try to maintain that streak.

Muthu

http://www.edison.co.in

 

[BigInch]

Hey. One way or another it looks like YOU are the expert here. That seems to prove that experts don't have to have much of a clue as to what they are really doing.... no offense, just an observation. Glad you've had such a good run of luck.

Find what you like to do, earn a living at it, and then make your lifestyle fit your income. — Chuck Yeager

 

[LittleInch]

I'm puzzled now. Your OP at the top talks about axial pressure and hoop stress which indicated to many of us that your experience in these issues was very limited as the issues were of a structural nature (bending, buckling, rigidity), not pressure retaining.

Now all of a sudden you've been designing structural supports for 30+ years? - "I did the calc for my design " - what sort of calculation?

The picture you post is of a proper structural support with bracing and connector plates and (hopefully) a structural design showing that it meets the required factors of safety from the loads it is carrying. It might even have had a load test.

so what is it? You actually really know what you're doing with structural supports or not?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BigInch]

Looks a little vulnerable to earthquakes at the moment though.

Find what you like to do, earn a living at it, and then make your lifestyle fit your income. — Chuck Yeager