Pipe supports Allowable loads 1

[Johnrem]

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

 

[Johnrem]

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]

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]

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]

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:

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]

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]

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=axia...-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