Bolted Flange in Bending 1

[22west]

Anyone know where I can find a good hand calc for a bolted circular flange connection in pure bending?

I need a calc that will give me the axial force on each bolt.

 

[TGS4]

Koves' paper in JPVT from Feb 1996 includes a summary of the available methods (at the time) of dealing with external bending moments. Personally, I prefer to use EN-1591-1 (or EN-13445-3 Annex G).

I will ask a question in return - why do you need this information?

 

[22west]

I need to back up an FEA.

 

[TGS4]

How are you treating your gasket? What type of gasket do you have?

 

[22west]

There is no gasket - it is a structural flange.

 

[TGS4]

If that's the case, then a simple free-body-diagram and a little bit of static equilibrium with a healthy dose of compatibility should answer your question.

 

[22west]

I'll admit I haven't gone that far into the calc because there seems to be too many unknowns.

Imagine a round flange under bending with 12 bolts - the bolt at top dead center takes a large percentage but the others take smaller percentages decreasing to the neutral axis of the joint.

I believe these percentages are based on the general geometry..but I am not sure.

I just wanted to see if there was any literature whereby someone has already done the legwork.

 

[TGS4]

There's too many unknowns for the static equilibrium equations. That's why you also need the compatibility equations - assume that your flange is rigid (or not, in which case this will be an iterative process) and figure that the flange is rotating, pivoting around the one edge. Then, the load in each bolt will be based on the "stretch" caused by the rotation.

Unfortunately, you are going to have to get up to your elbows in the calc - no easy way around it. And, you might learn something more in the process :-O as opposed to having someone hadn you the calc.

 

[22west]

Ok, thanks alot for your input.

 

[arto]

Look in Maleev's "Machine Design" p. 125 for a rigid bracket flange.

for pipe flange w/ extermal loads & moments:
Kellogg's Piping Design book, also:

Walther J. Stikvoort's articles:
"Proper Interface Design for Pressure Vessels" in Chemical Engineering June '94 p133-4.

"Piping Reaactions on Pressure Vessel Nozzles" in Chemical Engineering, July 7, '86 pp51-3.

"Pressure Vessel Design, Nozzle Piping Reactions" in Encyclopedia of Chemical Processing & Design,Vol.42, [NY:Marcel Dekker] 1993, pp 237-44.

Also: C.J. Dekker, "External Loads on Nozzles," Int.Jnl Pres. Ves. & Piping, 53(1993) p.335-350.

 

[israelkk]

Assume that each bolt will stretch linear to its distance from the edge of the flange. Then assume the force in the closest bolt is X. Every other bolt will have a force greater or equal to X depends on its ration of its distance from edge compared to the distance of the closest bolt. Sum the products of each force and its distance from the edge and equal it to the bending moment. This will give you the force X and the force at every bolt. Now tight each bolt to a preloaded force greater than the maximum force in the bolts.

 

[JoeTank]

Assuming flange is resonablr stiff, the max bolt load is 4M/(ND)
M=moment
N= number of bolts
D=pitch circle diameter

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com