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In a basement, I would like to replace an old 4x4 pine, load bearing, interior post with a square steel tubing post. The goal is to reduce the physical size as much as possible for aesthetics and usability, while maintaining equivalent or better compression strength of the 4x4 pine. The post is 77" tall. If a steel post is used, it would have a welded steel plate capping both ends and secured to the beam and concrete floor in the exact location of the current 4x4 post. The current wood post is not secured on either end and has been there at least 45 years.

Is there a generally used steel equivalent to a 4x4 pine post? Would a 2x2" 11 gauge black steel square tube (2.92# per ft) have equivalent compression strength? Would a 3x3" 3/16" thick black steel square tube (6.87# per ft) have equivalent compression strength?

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  • Can replace the 4x4 with a steel post, but it has be be label/made as a support post to be in code. You can't just use any steel post you pick up, even if it is the same size. Most steel support posts will be close to the size of the 4x4 anyway.
    – crip659
    Oct 1, 2021 at 19:43
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    A bit of sanding and some stain, that pine post would look good. Less work and less cost also.
    – crip659
    Oct 1, 2021 at 21:15
  • As isherwood said, you aren't going to make a meaningful difference in size, which makes it not worth the hassle. Your only other option that would achieve the goals would be to see if you can eliminate it entirely with a new beam, but if you only have 77" to work with you might not have enough ceiling space to put on e in. Oct 1, 2021 at 21:23
  • Great info, thanks. I'm going with a new 4x4 wood post.
    – Lunar
    Oct 4, 2021 at 22:28

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You're oversimplifying. Compression strength isn't the only critical factor. It also has to have the required stiffness. Otherwise, someone bumps a hip into it and the thing buckles. And it has to have a load test rating for safety and legal liability. Your insurance company will chuckle if you squash someone and then file a claim.

Use a rated beam column. The round ones are about 4" in diameter. Some are as small as 3", but you need to be sure your load doesn't exceed their design rating. The 3x3 you mentioned would probably work, but a custom-welded assembly won't have any sort of stamp of approval. You'll be liable for failure.

Keep in mind that you were only standing to gain 1" of space on any given side of the post centerline by dropping to a 2" post from a 4" post. That's not worth any safety risk, nor will it look right, being so spindly.

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