Openings in cylindrical shells 1

[TpaRAF]

I am a structural engineer, and am seeking advice on the design of a handhole opening in a round steel column used to support an overhead sign. This is not a pressure vessel. Biaxial bending, axial compression and torsional forces are applied.

The client wants a 6" x 8" handhole placed in an 18" upright, near the column base. The 6" dimension is along the circumference, and the 8" dimen is along the axis. The hole will be capsule shaped (i.e., 3" radii)

I've seen other details where the edge is reinforced using a metal plate, full pen welded all around.

Any ideas where I can find a good reference or design example for this problem?

Thanks for your valued assistance!

 

[JoeTank]

I suggest that you follow the same area replacement rules applied by the tank, vessel and piping folks. In your case I would guess that the 6" dimension would govern, assuming that longitudinal forces are governing the column design.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[jte]

TpaRAF-

What you're describing is known to us more commonly as a skirt accesway or piping penetration on a vertical vessel support skirt. These are typically reinforced by placing a plate collar perpendicular to the skirt in the cut. This plate is usually centered on the skirt, and of equal thickness and width equal to half the horizontal dimension of the cut.

The essence of the theory is that by replacing the cross sectional area of the steel which you are cutting out you are maintaining the moment of inertia of the column. This, of course, presumes that the Ad^2 term in the I calc governs the calc. This is less true for smaller diameter vessels as the location of the cut tends to have a reduced arm to the neutral axis. By placing the reinforcement perpendicular to the plate which is being cut you are providing local stiffening which will mitigate local geometrical concerns.

So... in your specific design, I'd reccomend that a plate 28" long by 3" wide and as thick as your column be formed (rolled the easy way) to fit the cutout. A full thickness double fillet should be adequate for attaching it to the shell (your column).

jt

 

[unclesyd]

There are standard sizes of handhole as you can buy a welded ring in the form of an elispse or oval.
I've seen them advertised but the source is lost in wind farm.
There are specific requirements for location of the handhole in respect to the base. It varies with the end use.

If you need a quantity give these people a call.

http://www.laboiler.com/handholes5.html

 

[TpaRAF]

Thanks to everyone for your advice & comments!

JT, you hit the nail on the head -- that describes what I've seen elsewhere. I can use parallel-axis theorm to check that 'I' is maintained or increased. I figure the collar should be about 23" though (6"·pi + 2·2").

The hole will be placed on the column side, perpendicular to direction with the greatest bending force.

Regards, RAF

 

[arto]

Look in Troitsky's "Tubular Steel Structures" available from Lincoln Arc Weld Foundation for $24:

https://ssl.lincolnelectric.com/foundation/

[while you're there, get the Blodgett's "Design of Weldments" & "Design of Welded Structures," too!]

 

[GenB]

this is strictly structural but if you want to calc to Sec VIII-1 you can calc using the 8 in opening, they are made by forming seamless pipe, ussually s40 or s80 depending on the T needed,
you may not find a std 6x8 handhole ring but you can make one depending on the base pipe T, you may have to repad, the strength of the finish job can be as good as the base pipe.
ER