Hi all, I’m currently building myself a fence along our boundary, and am using 3.6 M “C-Section” steel posts. My question relates to the best way to orientate the pole in the hole to achieve maximum strength, resistance to wind etc. The posts have a profile like Imgur: The magic of the Internet and the traditional way seems to be pole with widest solid face towards the fence rail, but one supplier has told me the proper way (although rarely done) is to have the longest face on a right angle to the rail, which is then attached to the one of the 2 narrower sides of the ‘c’. Would this be correct?
He may be right, depending on what you are saying. The post will be strongest against a force in line with the long face. A channel post will bend most readily with the force at right angles to that long side because the short sides are only supported where they join the long side and can bend and twist. With the rails attached to the short side at least one short side is reinforced by the rails. T posts for wire fencing have a cross section like a U with wings. The wings reduce the twist and bend but they can still be manufactured inexpensively.
Think of an I-beam (or W). It is oriented like an I (down in the same direction as the applied load). The C is basically a beam cut in half the long way–it is strongest in the long direction in terms of bending. But what kind of winds are we talking about here? Maybe the reason the posts are rarely oriented in the right direction is because you don’t need all of that strength anyway. Is it a real channel section or is it just shaped like one?