Im hoping in this forum of a few million people someone on here will be able to help with a Mechanical Engineering question.

Im wanting to build a sectional vertical structure about 25-30' tall out of scheduled 80 pipe. It will also have some things mounted at the top. I know that scheduled 80 pipe has a tensile strength is rated for minimum of 48,000psi and supposedly as high as 65,000psi from what ive been able to find. For every joint im going to have it internally sleeved and bolted together for easy disassembly in case i ever have to take it down for repairs. Base will be similar in design with sleeved joint. I havent decided if im going to have the base mount pole/sleeve as a plate bolted into large concrete block pad or just dig a hole, sink a longer base section of the pipe and fill the surrounding hole in with concrete. figured id decide that later.

What im mainly worried about is where it connects at the base and the stress to that joint from the main structure. Some of the other joints will most likely experience stress too but i think the base will catch the highest amount. Where im erecting the structure it can get some pretty strong sustained winds even when theres not a storm. I want to insure its not going to snap and fall over from the stress the wind will put on it.

Ive estimated weight based off the standard per foot measurements listed on steel sites that itll weight between 130-160 lbs for the length of the structure main structure (internal sleeves @ the joint included). the stuff mounted on top will be fairly light so im not so worried about figuring that in.

How can i calculate what the stress will be at the mounting joint at the base? I figure this will be where i see the greatest amount of flexing and torsion stresses.

also if possible i did not take calculus or trig in school so please try to dumb it down as best as possible.

 

What sort of things mounted to the top? Anything up there will act like a sail and increase the stress on the pole. If it is not something frequently taken down, I would put at least a trio of stabilizing cables on it, to take the horizontal stress off the pole. The vertical strength of the pole is gone if it kinks at all with too much horizontal force and it will collapse.

 

primarily itll be a flag pole.. but was thinking of mounting a weather station at the top of the pole.. them things that measure wind, direction things like that.. if i dont mount the weather station itll be a light instead to illuminate the flag at night.. i dont want to buy another one of them store kits as theyre weak and break on me after 2-3 years of being up.. ntm even here at the beach where the current one is the winds are less than they will be where ill be putting the other one up.. any time theres enough wind here i end up having to take the flag down because it whips the pole around enough to break it..

the commercial grade ones cost waaaaaaaaaaaay too much (500-2000$ range) which i really dont want to spend that.. id rather use the schedule 80 pipe thats cheaper than even the cheapest commercial poles..

 

The material and specs for sch80 and genuine flagpole material is different, pipe is not designed for lateral stresses like you are talking.

 

the biggest thing i can tell between the 2 is that the residential aluminum poles tend to have wall thicknesses in the 1/8" range.. havent found a thickness spec for the fiberglass ones.. commercial grade aluminum ones are 5/32" thick..

only other difference ive found was depending on the mfg and material the tensile strength for the store bought ones were rated on the low end of 40,000lbs-psi with some of the larger named companies claiming theirs is in the 50,000lbs-psi. in the aluminium poles.. fiberglass ones were about the same..

If i went with structural steel pipe 7/32" thick. stainless was running about the same thickness.. for the grade pipe in carbon steel im looking at has a tensile rating of 58,000lbs-psi

 

Still can't figure out what your up to Shawn, but looks like your going to need a bigger hammer.

 

you mean instead of the 16oz hammer ill have to use the 5lb sledge??