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Johnrem (Petroleum) (OP)
2 Mar 10 6:56
Hi every specialist;

Our stress group gave me loads on a support.The support is fixed stool at elbow type. Elevation is 1.2m from BOP (bottom of pipe), pipe stool is 4" SCH 40.
Do someone have any idea how to calculate allowable loads of such kind of supports?

Thanks

 
JedClampett (Structural)
2 Mar 10 15:16
You could go into the AISC Manual for Steel Contruction and get allowable bending moment and axial load for a 4 inch pipe column.  
Or you could ask someone in your office who's done this before how they did it.  
The second method will give you more confidence in your design.
weab (Structural)
2 Mar 10 21:04
I don't understand your question - a sketch would be helpful.
Johnrem (Petroleum) (OP)
3 Mar 10 2:01
Many thanks;

I attach this time a drawing showing two cases of using pipe stool support. Case where stool will be welded to steel structure and case where stool needs a fondation.
My question is as follows: What will be the allowable loads (horizontal, vertical and moments if any) that this type of support can sustain in both cases ?
Pipe stool= 4" Sch 40, Elevation H=1.2m  

Let us start from case of weleded stool to structure.
Bagman2524 (Structural)
3 Mar 10 15:52
Just design it as a cantilever and use your basic P/A and Mc/I formulas.
westheimer1234 (Structural)
3 Mar 10 19:02
Your question seem too basic.
Are you in Piping department or Structural department?
If you are in Piping, give that loads to the structural department for them to design the stanchion, base plate and foundation.
Dont forget the windload of the pipe.


 
weab (Structural)
3 Mar 10 21:23
That's what our office might call a "dummy leg".

I agree with West.  With regard to moment, axial, and shear, if you add some of one you can add less of another.  If you can't intuitively know that this will work, a structural engineer should look at this, especially with the shape of the weld.
Johnrem (Petroleum) (OP)
4 Mar 10 2:02
West;
Can you provide the basic formula?
westheimer1234 (Structural)
4 Mar 10 4:04
P/A + Mc/I

Ask a favor from Structural Department since they will design the stanchion anyway. It will only take them less than 5 mins to design the "dummmy leg".

Piping Department usually has a standard for pipe supports.  
Johnrem (Petroleum) (OP)
4 Mar 10 4:45
Do you have any sample  of this kind of piping support with its allowable loads calculation sheet?

We dont have structural department, I have to fixe this issue by my self.
westheimer1234 (Structural)
4 Mar 10 5:16
0.6 Fy > P/A + M/Sx

P= vertical load
A= area of pipe
M = moment equals horizontal load x height of support
Sx = section modulus of pipe
Fy = yield stress of pipe
westheimer1234 (Structural)
4 Mar 10 6:02
oopps
it should be

fa/Fa + fb/Fb < 1.0

maybe experts can comment if 0.6Fy was conservative
as Fa for your case.
Johnrem (Petroleum) (OP)
4 Mar 10 7:19
what are fa, fb, Fa abd Fb in you last explanation?
Ussuri (Civil/Environmental)
4 Mar 10 7:34
Allowable and actual axial and bending stresses
Johnrem (Petroleum) (OP)
4 Mar 10 7:39
not clear, can you explain one by one:
fa is......
fb is......
Fa is ......
Fb is .......

thank u
Helpful Member!  BAretired (Structural)
4 Mar 10 11:50
fa is axial stress = P/A
fb is bending stress = M/S
Fa is allowable axial stress (varies according to height)
Fb is allowable bending stress = 0.6 Fy

Pipe produced in accordance with ASTM A53 comes in two grades with a yield strength of 205 MPa (30,000 psi) and 240 MPa (35,000 psi) respectively.  Unless you know differently, use the lesser of these values.

Will the supported pipe be in an exterior environment?  If so there will be wind loads and temperature effects to consider.  The axial capacity of the stanchion varies according to its height.

It is not prudent to rely on an answer from this forum to use on the job.  You should obtain the advice of a structural engineer as you do not seem to have even a slight grasp of the factors involved.   

BA

par060 (Structural)
4 Mar 10 12:13
hey you guys are giving away the secret handshake....
paddingtongreen (Structural)
4 Mar 10 14:07
Sorry to throw water on this fire, but that elbow is bound to rotate, perhaps about all three axes, the piping does peculiar things when it heats and when it cools, especially when it turns corners. Piping moments could add to the moments due to the orthogonal forces on the support.

Michael.
Timing has a lot to do with the outcome of a rain dance.

Ussuri (Civil/Environmental)
5 Mar 10 3:14
Surely the loads the OP was given are as a result of a piping stress analysis?  So it is entirely possible that they loads he was presented with are in all 6DOF.

But, if his pipers are anything like our pipers he needs to be careful.  Our pipers have a way of coming up with loads that just cant be accomodated reasonably. We moan, they move the supports/change the conditions and everyone is happy.
paddingtongreen (Structural)
5 Mar 10 7:28
6DOF was my thinking too. Given that the OP had to ask the question, that would make the advice given, dangerous.
"A little knowledge can be a dangerous thing"

Michael.
Timing has a lot to do with the outcome of a rain dance.

Johnrem (Petroleum) (OP)
7 Mar 10 14:21
Thank you BAretired;
Your answer is almost what I need.But in your answer you added 04 more parameters that I am not able to identify: What are P, M,S and A referong to?
In mu case, pipe support matrial is API 5L Gr B.
Vertical load= 1945N
Horziontal foce= 806N
Mx=My=0 N.M
Mz= overturing moment= 8043 N.M
Pipe elevation= 1.2M BOP.

Using these data , can you advice what will be the parameters given by you previously (I mean:
 fa is axial stress = P/A
fb is bending stress = M/S
Fa is allowable axial stress (varies according to height)
Fb is allowable bending stress = 0.6 Fy)

Thank alot

can you
BAretired (Structural)
7 Mar 10 15:40
Looks like pretty small loads.

P is the applied axial load = 1945N = 1.95kN
M is the applied moment = .806kN* 1.2m = 1.0kN-m
A is cross sectional area = 2050mm^2
S is Section Modulus = 52.7e3 mm^3
r is Radius of Gyration = 38.3mm

fa = P/A = 0.95MPa (say 1.0MPa)
fb = 1.0e6/52.7e3 = 19MPa

kL/r = 2*1200/38.3 = 62.7
Fy = Yield Stress = 35,000psi = 240MPa
Cr/A = 162MPa (Limit States Design) so Fa = 162/1.5 = 108MPa
Fb = 0.6*240 = 144MPa

fa/Fa + fb/Fb =  1/108 + 19/144 = 0.15 << 1.0

I would say it looks adequate.



 

BA

Johnrem (Petroleum) (OP)
7 Mar 10 16:08
Many thanks BAretired for your answer, however I have two additional easy questions for you:
 1) you wrote kL/r = 2*1200/38.3 = 62.7, can you explain what is K ? Is is always equal to 2?
2) You wote also Cr/A = 162MPa (Limit States Design), can you explain what is C?

3) Why didn't you consider the overturning moment Mz=8043 N.M in your calculation?
I inform that the support will be welded to pipe and to platform, that's why there is a moment.

Thanks again
BAretired (Structural)
7 Mar 10 17:20
1)  k is a factor applied to the actual length to produce effective length.  When a column is hinged at each end, k = 1.0.  When each end is fixed, theoretically, k = 0.5 but 0.65 is the recommended value.  When one end is fixed and the other is free, it is a cantilever and k = 2.0.  That is the case I assumed for your pipe support, fixed at the base and free at the top which I took to be BOP.

2)  In Canada, we use Limit States Design (LSD).  We used to used Working Stress Design (WSD), but the powers that be decided LSD was better.  With LSD, we factor dead loads by 1.25 and live loads by 1.5, then design the structure to fail under factored loads (with a few other fudge factors thrown in).  In your case I made the conservative assumption that all loads were live load, so divided Cr by 1.5 to get P. Cr is the factored compressive resistance of a column.  P is the maximum allowable working load.

3)  I thought the horizontal force of 0.806kN was applied at a height of 1.2 which would cause a moment of 1.0kN-m.  If you are saying there is an additional moment of 8.043kN-m, then fb becomes 9.04e6/52.7e3 = 171.5MPa.

Then fa/Fa + fb/Fb = 1/108 + 171.5/144 =1.20 which means it is 20% overstressed.  

You stated:

Quote:

I inform that the support will be welded to pipe and to platform, that's why there is a moment.
There is no platform shown on your sketch, so I don't know what you mean.  

A 6mm fillet weld at the top of baseplate is not enough to develop the section in bending.  In Type 'A' detail, what are you welding the underside of baseplate to?  In Type 'B' detail, the anchor size is omitted.  I would not recommend hooked bars to develop a serious moment connection.

There are too many oddball things in your design.  You need to get help from a local structural engineer.  
 

BA

Johnrem (Petroleum) (OP)
8 Mar 10 15:15
Thank you BAretired;
Your answers are the most valuable that I got.
Sorry to request you additional information as follows:
1) Can you indicate book or PDF file where I can find the theory of explanation above, or at least where I can find values of Cr (factored compressive resistance of a column)?
2) My stool will be welded to HEA 200 beam. The plate "A" dimensions are 160*160mm square.
3) Why in you design verification you didn't check the thickness of the plates "C" and bolts dimensions and finally the welding sizes. I can't imagine that whatever will be the plates and bolt size, the support will sustain the given loads. Is there any procedure to check these parts of the support? (please see attached pdf file that I sent previously)
4) Is you design verification explained above applicable in case the stool will be connected to concrete foundation (not welded to steel structure)?

Best regards
 
BAretired (Structural)
8 Mar 10 17:01
1)  "Elements of Strength of Materials" by Timoshenko and MacCullough is an old but good reference.  There are many books which could be found on the same subject. You can also check on some of these sites:

http://www.google.com/search?q=axial%2C+bending+stress&hl=en-GB&;sourceid=gd&rlz=1Q1IRFA_enCA356CA356&aq=t

or use Mr. Google.

Values for Cr/A for various values of Fy came from Table 4-4 of "Handbook of Steel Construction" published by CISC. An Fy value of 240MPa is not listed, so I modified the value for 250MPa by straight ratio.

2)  If the moment is in a direction which puts torsion or overturning on your beam, that will have to be checked.

3)  I did not check the baseplates, but in a proper analysis, the plates must be checked.  The bending moment in the  baseplate depends on support conditions.  It will be different for Type 'A' and Type 'B' details.  Again, this is explained in the CISC handbook.

Weld resistance is listed in CISC Handbook. The tension on a pair of anchor bolts can be determined conservatively by dividing the moment by the distance between bolts.  The capacity of anchor bolts depends on the yield value of the steel and the anchorage detail.  Your detail for Type 'B' is a common but poor one.  I saw quite a few of those pull out of the foundation in the tornado of 1987 in Edmonton.  The bend at the bottom straightens out and the bolts pull out leaving  perfectly cylindrical holes showing where the bolts had been prior to pulling out.

A better detail, in my opinion is to use straight anchor rods with nut on top and nut with standard washer or anchor plate on the bottom.  The depth of embedment to resist pullout may be found in your concrete code.

4)  Design verification would be the same for Type 'A' and Type 'B' from top of baseplate up.  With the forces and moments you provided, the pipe selected will not suffice.  A fillet weld size needs to be 1.5 times the thickness of pipe in order to fully develop the strength of pipe in tension.

Baseplate thickness, weld on underside of plate or anchor bolt sizes need to be checked.

Also, the capacity of the steel beam or foundation supporting the pipe must be capable of carrying the combination of loads and moment.

BA

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