# Strength of Schedule 40 steel pipe

Help

I manufacture and install shade sails, typically using sched 40 steel pipe as the posts on the corners. Most pipe information displays the strength from pressure from the inside, but my real world application is to take a pipe, lets say 14' long, dig a 4' x 16" hole, and bury the pipe base 4' in the ground, leaving 10' above grade. I then attach the shade sail with turnbuckles to the top of the post. In my limited understanding, it is a lateral load on lets say a 4" or 6" schedule 40 pipe, with the moment 10' away at the ground.

I can figure how much pressure I am putting on the top of the pipe, Lets say 2000# for arguments sake (considering constant tension plus variation for higher wind loading). I understand the further I get from the moment (ground level) the greater pressure I am putting at that location. 12' from the moment would be much greater than 7'. I want to responsibly determine at what point to I need to upgrade to bigger pipes. 4", 6", 8", 10" etc.

If I know what the calculation would be, I can fill in the variables of post height, post diameter, and size of the sail (AKA how much wind load I am applying). I do hire engineers to do some of my projects, but that is after I quote it, which could have me spending a lot more to upgrade the strength. I also have tubing suppliers that claim a higher strength than schedule 40 pipe due to the alloys and treatment, so I want to try to translate their claim into dimensions, and savings in time, weight, and money. Ultimately, I can over engineer anything, but I hate having my customers spend unnecessarily due to my lack of physics training.

Sorry for my wordiness
Thanks,

jim hardy
Gold Member
Dearly Missed
introduction to bending stress here
http://www.strucalc.com/normal-stress-bending-stress-shear-stress/

it's been too many years since i did one of these
but my approach was

figure the stress at outer edge of the pipe
keep stress there well below fatigue limit for your material

&^%$%$#!!! rich text editor won't un-indent !!!

MOI here https://www.engineeringtoolbox.com/steel-pipes-dimensions-d_43.html

hope that's some help

old jim