Bending stress in horizontal pressure vessel saddle base plate 1

[dannyo]

I am looking for a correct formula for the bending stress in the saddle base plate of a horizontal pressure vessel. The current formula I have has incorrect units.

fb = [(6*M)/(tb^2)] is the formula I'm using (units of lb/in instead is lb/in^2), where fb = bending stress, M = bending moment, tb = base plate thickness.

I have limited access to references so I would appreciate any formula or online reference site anyone could provide.

Also, if this is the correct formula could someone explain to me why the units are not in psi.

 

[welding1]

The formula you are using is standard engineers bending.

M/I = Sigma/y

M= bending moment
Sigma = Bending Stress
y = maximum distance from the neutral axis to the beams extreme fibres. For a flat plate beam = t/2
I = second moment of area = b.d^3 /12. For a flat plate beam of unit width b and depth d = t

Bending Stress= 6.M /(t^2) per unit width of beam

You can use any consistent units you want.

If you are designing saddle supports you should also consider the effect on the vessel, because the vessel will tend to bend between supports and also sag onto the supports, becoming oval in shape.

There is a method for designing saddle supports in British Standard PD5500 appendix G.

Good Luck

http://www.gowelding.com

 

[dannyo]

welding1:

Thank you so much for the response. Your post was extremely helpful for my understanding of the formula and its origin!