Is a square sign post stronger than a round one?

Question

Which is stronger, a round sign post or a square-cross-section sign post?

I will be using one or the other to hold the top corner of a shade sail. I tried an aluminum pipe but a strong wind on the sail bent the pipe. I am about to buy a 10-foot-long sign post because they look stronger than the pipe. I found online a 2 by 2 inch square-cross-section post with a lot of holes in it. The steel is 14 gauge (0.0781 in) thick. I also found a 2 inch diameter cylindrical post with no holes in it. The steel is 16 gauge (.065 in) thick. Which one should I buy?

Answer 1

Round is strongest because it has no weak side. It disperses energy equally around the whole post.

This is why race cars use tubular frames and suspension 

Answer 2

If the cross-section AREA is the same, round is stronger. A sign post is NOT strong enough for a sail.

Answer 3

Most sign posts are made of circular hollow sections so that ought to give you a clue. The material would have been the issue with the aluminium post, rather than the geometry. The only real reason for choosing a square hollow section is to simplify the fixings.

Answer 4

A square post is stronger than a round one. See if a pipe will fit and buy a nominal 1-1/2" or 2", schedule 40 galvanized pipe. It has thicker wall and made of steel/iron, and is stronger than what you are looking at.  Look up the outside diameter of the pipe to see if it will fit the shade.   There are efficient structural shapes made for lateral loads, the most common one being the wide flange.  You can find that shape at the metal building supply houses.  It is commonly used in patio covers and car ports.  Galvanized steel WF.