Welding Tips and Tricks

Hello all,

I'm getting ready to start a stair project. I have concrete footings poured that I will bolt 1/8" or 1/4" plates to and then upright square tube will be welded to those plates to serve as legs for the stairs. The footings aren't uniform nor level on top. What I'd like to do is bolt the plates to the footings first and then plumb and square the legs and weld them to the plates in place. My concern is with having too much heat transfer to the concrete and cracking it. Thoughts?

I should mention that the current plan is to have a piece of 1/4" aluminum between the concrete and the mild steel because the footings were poured slightly recessed to the surrounding concrete and water pools there, so I'm trying to keep the steel up out of the water. Is this a bad idea?

Thanks,

j

you can't weld on concrete. the moisture in the concrete turns to steam and blows bits of concrete off.
however you could tack the bits in place, remove them and then weld out.

aluminium is no good under the steel. aluminium does corrode and especially when in contact with other metal plus water.
your best bet is probably to use concrete epoxy to raise the footing. i'm not sure if thin layer of concrete on top of the footing would be strong enough hence use epoxy. i'm assuming you cannot cut a drainage channel for the top of the footing.

edit: also epoxy your bolts/thread into the concrete. i usually use stainless thread. otherwise water can fill the holes and rust your bolts out.

Just throwing ideas, and I'm sure someone will confirm or deny but what about placing a piece of cement board down instead of aluminum plate? Would the aluminum and steel cause an area of reactivity? it would also help to maybe absorb some of the heat you're talking about. hope you get it figured out.

Thanks for the information and ideas. I don't know why I didn't just think to tack and move - great tip.

I should have mentioned that these are exterior stairs / footings. I'll have to go back to the drawing board on the water issue, but now with some additional ideas.

Usually in a situation like this you would drill and epoxy the anchor studs, and pre weld the verticals to the base plates and double nut the plates, one below and one on top. That way you can adjust the verticals to plumb with the double nuts and raise the plate as needed for drainage. then pack in a suitable grout under the plates. Check out all kinds of structures with vertical support, street lights, signs, structural steel buildings etc. The solid anchors with the expanding collar at the bottom end (not the expanding sleeve type) work well also as long as the concrete is in decent shape. Pre drill the plates and use them for templates to drill the holes before welding the verticals.

homeboy wrote:Usually in a situation like this you would drill and epoxy the anchor studs, and pre weld the verticals to the base plates and double nut the plates, one below and one on top. That way you can adjust the verticals to plumb with the double nuts and raise the plate as needed for drainage. then pack in a suitable grout under the plates. Check out all kinds of structures with vertical support, street lights, signs, structural steel buildings etc. The solid anchors with the expanding collar at the bottom end (not the expanding sleeve type) work well also as long as the concrete is in decent shape. Pre drill the plates and use them for templates to drill the holes before welding the verticals.

I once installed a basketball post using this method. The post was 6x6 with a 11 x 11 plate welded to bottom. There was a 3/4” hole on each corner of the plate. Basically, a steel plate with the same hole pattern as the plate welded to the post had four bolts installed and double nutted. Several inches of bolt stuck up and the other end had a 90* bend. That plate and bolt assembly was placed in the wet concrete. Once cured a nut is added to bolt sticking up from the plate in the concrete. Then the post is placed on those new nuts. Then other nuts secure the post. Thus allowing for leveling.

Just as Homeboy explained.

Welding on embed plates happens all the time. Concrete is sensitive to heat, but you anchors should have a significant embedded length that it won't matter.

You should weld the base plate on your posts first and then shim the middle of the underside of the base plate and rock it into plumb, tightening the anchor bolts as you go. The post could have a camber in it and or the base plate couple be welded on askew, so leveling the base plate is mostly useless. Put a shim pack in the middle with a proper height and rock the post as needed to get plumb, turning the nuts as needed to lock it in. You could also use leveling nuts (jamb nuts), but you won't likely find them since they are much thinner than regular nuts. Typically we dry-pack grout under the base plate to allow for a uniform load transfer.