I'm putting up a small metal building for the first time, it is a 12 X 30. I went to my local metal building supply store, and they recommended that for my building size I can use a 4x4 14 guage square tube instead of an I-beam, with one on each corner and two in the middle. Since I'm not a welder the sales person at the metal building supply store suggested that I coat the square tubing with a rust repellent paint and stick them in the ground two feet in concrete, thereby circumventing putting in a weld plate as a well as an edge thickened slab. I've done treated wood posts like this but I just don't know how fast the square tubing can rust in the ground like this. If you have any experience or knowledge in this area, please let me know about what you think.
knowledge in this area, please let me know about what you think. ^^^^^^^^^^^^^ I have observed that when old concrete structures are demolished, the re-bar always comes out looking new and totally rust free. Does the concrete provide chemical protection? Concrete structures that are intended to last for hundreds of years are built with unpainted re-bar. Anyone able to provide an explanation?
wrote: (clip) If you have any experience or
Several inches of concrete will protect the rebar by keeping the water away. Concrete is somewhat porous but the more concrete there is, the more water has to work to get through. Building codes usually specify keeping the rebar inside the form so that 3 or 4 inches of concrete stay between the rebar and the outside. Where the contractors screw up and the rebar is exposed or very near the surface it most definitely rusts and the expansion of the rebar due to rusting will cause the concrete to spall away. If you drive near construction of new bridges or roadways, notice that most of the rebar is epoxy coated (usually green) to help with rust prevention.
I just don't know how fast the square tubing can rust in the ground like this.
Fourteen guage tube sounds light to me, for both structural purposes and the length of time that it takes to rust through. Concrete tends to retain as well as wick moisture, hence the need for treated sole plates in 2x4 studs walls. I'd feel better if the posts where galvanized, or somewhat greater wall thickness. You don't mention where this is located, climate or ground water conditions. Probably would not be an issue in the desert.
Why not do it like a house. Foundation with bolts up and on a sole plate. Bolt down on a wood plate - and on top of that a Horz tube. Then stand and weld everything on top of that.
I'll have to look at mine and maybe take a picture - mine isn't much different if any from what I said - and I have 6" reinforced floor with 4 bay doors.
Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder
Gary Brady wrote:
I looked at a house once with similar steel for the carport supports sunk in the concrete. They were rusted completely through just above the concrete after 16 years. And that was the least of the problems with that house!
This is exactly what _must_ happen! There are temperature differences and water will condense exactly above the concrete. -> rust The tube is hollow (wounder! it's a tube!) and you don't reach into for painting. But you will have the condensed water there the same. Exactly above the concrete. -> rust.
I would kick that salesperson a painted I-beam (lenght as on stock) into his <youknowwhere> until it's coming out where his brain is _supposed_ to be.
If you use a tube, it is important to drill a hole just above the base plate (you will use one) so that water can get out. You also will zink coat it, it is quite cheap.
I'd take the time to do it right the first time. You may get a few decades from casting the steel into the concrete or you may be screwed in 5, depending on where water collects and the amout of condensation. It may be an extreme example but....spill some fertilizer on a damp floor near a post and what will probably happen in a few years? What if the dog tends to pee on the outside corner near a post? Stuff like that happens all the time in most farm shops. Think of the old carports where a pipe is cast into the concrete: One seems to last forever, and the next has nothing left but rust. Why risk that any one of yours will be the one that rusts? There are just too many outside factors involved to risk it.
I'd weld a proper plate on the bottom of an I beam and do a raised grouted footing like is done on commercial buildings.
If you do go with casting directly into the concrete, I'd zinc it as was mentioned by someone else and I'd go thicker than 14 gauge.