Mezzanine Support Question

[Vte]

I searched a bit on the forum and on net and could not find much good information. I am planning on building a mezzanine 18' off the back wall and spanning 21' from the side wall of our storage building. I would need to use a steel post to support the one corner and use the walls to support the other 3. The slab poured 2 years ago is stated to be 4" thick with 3/8" rebar every 2', and outside footed 12" x 12" thick. Anyway, since no on slab footings were planned in advance my question would be how big in square of say a 1/4" thick steel pad should I go to support the weight of one corner under the post. the current plans of construction are to use an lvl beam to span the 21'. The joists were going to be 2" x 12" x 18' long at 24" on center with 3/4" decking.

The mezzanine is intended to be used for seasonal stuff and other household storage. We are not planning on large heavy objects or overloading it to it's max. In other words I am designing it for light to medium use to get the small items we own off the main floor area.

 

[firebirdparts]

If you have 400 square feet and let's say 30 lb/square foot of course that is 12,000 pounds. The post has 1/4 of the load, 3000. It's not really all that heavy. If you had a 6x6 post I would feel comfortable with that size contact patch. I am just going by gut feel.

 

[meathooker]

I have a 5” pad with 4000lb fiber reinforced concrete and my structural eng buddy said he wasn’t comfortable with that.

 

[Firstram]

18' span on 2x12's 24"oc will be pretty bouncy as well. Think about TJI's 16" oc with mid span blocking, they also weigh less than dimensional lumber. 20 footers are usually available at the lumber yard and the cutoff will provide the blocking.

A 2' x 2' 1/2" or 5/8" steel plate would help spread the load not to mention provide a great trip hazard! You could build a bench/work station around the column, think grinder, vise or special storage cabinet.

The better plan would be to add a footing or a second column to the LVL.

 

[Vte]

I agree Firstram about 16" oc spacing and know I could do better, but again, the use is simple light storage so not too concerned about floor give. The reason for 24" oc is the outside walls are 2 x 6" x 24" oc, so I was planning on lapping to each with a ledger board underneath. Now I wonder how much more TJI's would be and maybe if going to 16" oc go down to 10" TJI's. Not sure if that is a stupid idea or not, but just looking for the cheapest most effective way to do this project. I was personally leaning on a 1/4" x 16" x 16" base plate for the concrete contact to spread load and minimize cracking. I only want 1 post to make a clear span from wall to corner. The stairs up will be right at that spot. Again hoping to find the cheapest most effective bang for my mezzanine buck, and doing it right the first time is always more important than cost to me. Wide open for suggestions and criticisms.

 

[Farmall450]

I honestly think that would be plenty ample, as opposed to I joists, as you seem to have a clear plan for light loading. A good rule of thumb for 2x joists is half span + 2", which a 2x12 over 18 certainly passes. I would however block them, even scissored, like many older basements.

The 2' centers are a bit concerning but again, you have good reason for that and are planning on using it accordingly. TJIs aren't cheap.

 

[theoldwizard1]

I searched a bit on the forum and on net and could not find much good information. I am planning on building a mezzanine 18' off the back wall and spanning 21' from the side wall of our storage building.

So you want two beams, each 21'. The floor area will be 18x21. The back LVL is just going to be attached to 2x4 studs 16" O.C. ??? I would be more concerned with the load placed on those studs ! My gut says, you need posts at all 4 corners. Steel or 6x6.

If the joist are going to connect to those LVL beams, you can not use conventional dimensional lumber for an 18' span, even at 16" O.C.

If you have 3 beams running the 21' length, you can get by with 2x10 24" O.C. for the joists. 6 posts. Forget using steel pad. Use PT 2x4, stacked on edge (laminate with construction adhesive and screws) to make a 12"x12" pad. With 6 posts, you probably don't even need a pad.

A good lumber yard will help you spec out the size of the LVL.

 

[firebirdparts]

So you want two beams, each 21'. The floor area will be 18x21. The back LVL is just going to be attached to 2x4 studs 16" O.C. ??? I would be more concerned with the load placed on those studs ! My gut says, you need posts at all 4”

This makes no sense at all. However, I have to assume the op knows full well that you can’t span 18 feet with dimensional lumber with a heavy load on it. You’re right about that. He didn’t ask our permission for that.

 

[Vte]

So you want two beams, each 21'. The floor area will be 18x21. The back LVL is just going to be attached to 2x4 studs 16" O.C. ??? I would be more concerned with the load placed on those studs ! My gut says, you need posts at all 4 corners. Steel or 6x6.

If the joist are going to connect to those LVL beams, you can not use conventional dimensional lumber for an 18' span, even at 16" O.C.

Nope, sorry, the building is 46' x 60', the outside walls are 2" x 6" x 15.5' high, 24" oc, every 3rd one is doubled under trusses spaced 6' apart for the roof. I own half of the building down one entire side. I want to put up a mezzanine for seasonal stuff 18' off the back wall spanning 21' on my side with a stairs up the middle of the building. I was planning on putting a shoulder stud on each of the corners and a few along the back wall under a 2 x 12 that the joists will also sit on for support. I was simply going to lap the 2 x 12's onto the back wall studs resting on the 2 x 12's.

I doubt these details will help one iota but I don't want to over think it either.

 

[Firstram]

Nope, sorry, the building is 46' x 60', the outside walls are 2" x 6" x 15.5' high, 24" oc, every 3rd one is doubled under trusses spaced 6' apart for the roof. I own half of the building down one entire side. I want to put up a mezzanine for seasonal stuff 18' off the back wall spanning 21' on my side with a stairs up the middle of the building. I was planning on putting a shoulder stud on each of the corners and a few along the back wall under a 2 x 12 that the joists will also sit on for support. I was simply going to lap the 2 x 12's onto the back wall studs resting on the 2 x 12's.

I doubt these details will help one iota but I don't want to over think it either.

Solid plan. Just don't overload the slab at that corner post, don't forget, it will also be carrying the stairs as well.