Hand hole design in steel poles.

[kbarnett]

I'm looking for an analysis procedure for designing hand holes in steel poles. It must allow not only for simple shear and bending along the axis of the pole, but also allow me to consider the effects of torsion. I am concerned that a taller cutout would leave the pole more vulnerable to buckling, and I would like to know if anyone has attempted this. Rotational moment of inertia is a good place to start, but when you make the cut out, it seems to me that the edge of the hole takes the load as a beam. Has there been any testing done to determine the amount of the pole from that open edge that can be considered to be part of the beam? Any other theories would be appreciated.

 

[zestructural]

what kind of pole do you deal with communication pole or flag pole? In the communication pole, they use the ring to provide reinforcement around the hole. Pirod and valmont manufacturers are selling those rings. You can contact their engineers for specifications and calculations. Good luck.

 

[eduardotano]

Why don´t you try a FE analysis, with refined mesh around the hole? Even FE linear buckling analysis will you provide very interesting results.

 

[TpaRAF]

The mechanical engineers deal with this all the time for pressure vessel design. One method they use is "replacement area" -- keep the mom't of inertia the same at the hole as at the unchanged section.

This is done by adding a ring to the opening. The thickness can be varied to provide the equivalent I, but generally using a ring thickness the same at the upright thickness.

Use full penetration welds at the handhole ring.

 

[kbarnett]

The poles I am designing are traffic and lighting poles. I don't have access to FEA, but have been looking into them to see if there are any that might be worth my while to acquire. As far as the moment of inertia replacement, I think that is definitely the way to go for axial and bending loads, but the property doesn't seem to be appropriate for torsion. I have been thinking about this, and I believe that as the hole gets taller, torsional loads would have a pronounced effect on that opening. The twisting force at the top of the hole would run into that discontinuity, and the whole tube would quit acting like a tube and more like a beam with the stiffened edge of the hole being the flange and the tube wall being the web. Essentially, it would be like two opposing T-beams acting as cantilevers, with a load at the top and a moment connection at the bottom. In this case though, the webs curve away and a decision has to be made as to where it becomes ineffective. You could argue that the web turns into a one-sided flange. I was hoping that some reasonable assumptions could allow me to approximate this without the expense or time of learning to use an FEA program. I have the ability to test these, but I would like to predict something first. By the way, thank you to those who provided feedback.

 

[TpaRAF]

Please see thread794-119271 "Openings in cylindrical shells". Also visit

http://www.dot.state.fl.us/structures/proglib.htm

and look at the reference files for the Mastarm program. MathCAD is required, but I can send you a PDF if that would help.

My application was also for traffic and overhead sign structure uprights. While FDOT has details for handholes in smaller mastarms poles, the sign structures have much larger forces.

If the ring resisting the torsion has the same or larger value for I or J, should it matter? How large of a handhole are you considering?

Regards, RAF