Breech analysis of aluminium pole?

[Zlmndra]

Hi all

Some time ago I posted a question regarding how analysis of a circular pole with a breech opening undergoing bending might be carried out. I was pointed towards M S Troitsky's work on the matter, and all was well and good for steel poles.

However now I am faced with the same problem, but with an aluminium pole. Unlike steel, I don't have a feel for how it behaves. Looking at the Australian Standards on steel and aluminium, there appears to be a fundamental difference in design theory.

Does anyone know of any work that has been done on analysing aluminium poles with breech openings in bending?

 

[Ron]

I'm not sure that I can be of much help, since I'm not familiar with your codes and criteria, but I can tell you how I handle such in the US....

I first look at the gross cross section reduction and analyze based on the reduced cross section. Since most of the aluminum sections I deal with are rectangular, I apply the criteria of that section type under the Aluminum Association design criteria. If the section is close to the allowable stresses, I then do an FEA on the area around the breach, treating the section as joined plates with a hole in one of the plates.

Most of the time, the gross analysis is sufficient, as the members can be easily changed to accommodate the breach if necessary. Only in rare instances is it necessary to go further than the gross analysis.

 

[Ron]

ps... I'm assuming your breach is a hole in the pole (drainage or electrical conduit access?), not a stiffening stress breach, such as a flagpole cleat or similar.

 

[Zlmndra]

Thanks Ron. Am I correct in understanding that in your initial step you are using a simple M = fy x S for your first step to determine the stress? And then going on to FEA to get a better picture if deemed necessary?

The breach is usually for electrical access, as you surmised.

 

[ishvaaag]

And when going to FEA include some initial imperfections, both bulging and inwards, analyze for material and geometrical nonlinearities (if using an elastic analysis program basically using the reduced Young modulus for the standing compression level and use P-Delta), and see how much the strength is affected.

 

[Ron]

Zlmndra...yes. Just a bending analysis of the reduced section.

ishvaaag....I'm not sure I would include deformations in the FEA model, as those would be post-failure. The limiting stress criteria should be applied before that occurs, since plastic design in aluminum is not particularly reliable.

 

[ishvaaag]

As to the question of how to perform the analysis in the presumption of the connection being considered fixed, lacking a forces' model and with no possible dedication to generate and ascertain one as correct, you can make a 3D model of the substructure items and subject it to the hypotheses 1 by 1. I most surely wouldn't forget to include initial imperfections to be augmented by any main compression field in the gusset.