Car lift pad help

[JacobM03]

So I am planning on pouring concrete floor with radiant floor heating and a car lift for my shop with a footing this summer and I just wanted to get some opinions and help on this setup:

Shop is 32’wx30’ long with existing perimeter footing and a center run footing down the length.

This setup is for one half of my shop where the lift will reside.

Bendpak 10AP-168 2 post lift

Rebar reinforced existing Footings are 20” wide, 8” thick.

Inbetween existing footing
26.5 ft long
13.5 ft wide

Lift 145” wide

Lift base plates is going to be 7 inch away from side footings and it’ll be centered in the 26.5’ length.

I will be running radiant heat lines ontop of 2.5” 16psi grid foam (hydropex) under the slab with 4.5” thick concrete and not running any on the 4’x13.5’ section the lift will be on that will be 7” thick concrete as the absence of foam under that pad.

For rebar in the lift pad is 0.5” rebar in a 1 foot grid the size of the lift pad good? And should I run more rebar down the length of the slab too?

Also thinking of tying the new pour into the existing footing with rebar, what would be the best way for this? (Depth of tie in, how much to stick out into new pour, how many feet interval)

Also is keying in under the existing footing necessary? Bendpak says to do so when cuting out a section of old concrete to pour a base for the lift but im just thinking as my base is pretty narrow but a long slab is it neccessary in my case?

Thanks for any help and suggestions!

 

[kaymccampbell]

Your rebar should go throughout the floor as well as the lift footer. It should be one big interlocking mat. To spread the tipping load over the whole slab.

You shouldn't have to undermine the existing footer, but you probably should epoxy some rebar into it where the lift footer joins it. I'd drill about 6" deep, clean the hole, and use one of the Sika Anchor Fix products.

I'd also epoxy the lift anchor bolts. I'd get a recommendation for that from the lift manufacturer.

 

[mike93lx]

1/2" rebar on 12" centers? Holy ****, why?

 

[JacobM03]

1/2" rebar on 12" centers? Holy ****, why?

For the base of the lift? Thats what bendpak recommends for pouring a base in a cutout in existing concrete so I just thought maybe it would be a good idea to lay out a 12” center grid on the 13.5’x4’ lift section

 

[mike93lx]

For the base of the lift? Thats what bendpak recommends for pouring a base in a cutout in existing concrete so I just thought maybe it would be a good idea to lay out a 12” center grid on the 13.5’x4’ lift section

A repair slab is a different animal. No need to thicken or increase rebar on a properly spec'd slab

 

[ConCretin]

I agree with mike93ix, there is no need for that amount of reinforcing and certainly no need to add more for the lift. If you are meeting the lift manufacturer's concrete depth requirement, you are good to go. I'd add an inch to that number to make sure normal variations in base and top of slab elevation don't conspire to locate a thin spot where you are drilling for a lift anchor.

If I understand correctly, your slab and insulation will pass over the top of the footings? I wouldn't connect the slab to the footings in any way. I think it's fine for the center section to bear on the footing but generally you want the slab to be able to contract freely when curing to avoid unnecessary shrinkage cracks. A slab on grade just needs uniform support from the soils below to function properly.

Take a look at my Guide to Floor Slabs in the link below for some additional thoughts on slab construction.

 

[JacobM03]

I agree with mike93ix, there is no need for that amount of reinforcing and certainly no need to add more for the lift. If you are meeting the lift manufacturer's concrete depth requirement, you are good to go. I'd add an inch to that number to make sure normal variations in base and top of slab elevation don't conspire to locate a thin spot where you are drilling for a lift anchor.

If I understand correctly, your slab and insulation will pass over the top of the footings? I wouldn't connect the slab to the footings in any way. I think it's fine for the center section to bear on the footing but generally you want the slab to be able to contract freely when curing to avoid unnecessary shrinkage cracks. A slab on grade just needs uniform support from the soils below to function properly.

Take a look at my Guide to Floor Slabs in the link below for some additional thoughts on slab construction.

Shop is 32’wx30’ long with existing perimeter footing and a center run footing down the length that seperates the shop in half. This footing is 20” wide, I would be putting the insulation and the slab between the current perimeter footing and the center run. Hard to explain abit but heres a picture of when I was building the shop, the new pour would be on both sides in the open squares that the footing surrounds flush to the existing and not on top.

 

[firebirdparts]

Do whatever concretin tells you. I was wondering if wire mesh might be better for the whole floor.. That’s what is in my shop floor. Pinning to that center foundation would be nice but it’s extra work.

A couple sticks of rebar going from post to post is not bad in my mostly ignorant opinion. In other words a one foot grid is only two sticks.

 

[mike93lx]

I agree with mike93ix

Quoting for posteirity.

Can't wait to tell my kids!

 

[finn]

Don’t tie a slab to the existing non insulated footings, and insulate under the entire slab or you’ll end up with problems because of the different expansion rates in the insulated vs non insulated portions, which will induce thermal stresses and potential cracking.

Non insulated slabs should have a thermal break where they adjoin insulated slabs. At least that’s what my inspector told me.

 

[ConCretin]

Shop is 32’wx30’ long with existing perimeter footing and a center run footing down the length that seperates the shop in half. This footing is 20” wide, I would be putting the insulation and the slab between the current perimeter footing and the center run. Hard to explain abit but heres a picture of when I was building the shop, the new pour would be on both sides in the open squares that the footing surrounds flush to the existing and not on top.

Got it. We're probably over thinking this but we usually don't let that stop us.

The advantage to doweling the slabs to the footings would be to keep the tops aligned if you happened to get some differential movement. The risk would be shrinkage cracks because the slab is restrained although I highly doubt it would be an issue In slabs that size. You could install a control joint to hide any potential shrinkage cracks if it would bug you to look at it.

You could use smooth dowels to get the best of both worlds. Just carefully align them square to the edge. it they end up crooked, they'll bind and defeat the purpose. You probably do want a thermal break around the perimeter but that wouldn't preclude the use of dowels too.

 

[wssix99]

Thanks for the clarifications.

Inbetween existing footing
26.5 ft long
13.5 ft wide

You are essentially pouring 2 slabs in that shop. You have some key things to watch out for.

The lift requires that "Anchor Bolts must be more than 6 inches from cracks and expansion joints in the concrete or from a wall." This means that your lift posts need to be at least 6" away from your footers. (The joints at those footers count as a "crack".) This lift comes in two configurations. In the narrow configuration, you would need 12' 3" between the footers and then just over 13' in the wide configuration. Are you sure you have 13.5" between the footers? (The picture looks like less. I would make sure before going further.)

I will be running radiant heat lines ontop of 2.5” 16psi grid foam (hydropex) under the slab with 4.5” thick concrete and not running any on the 4’x13.5’ section the lift will be on that will be 7” thick concrete as the absence of foam under that pad.

You don't need to omit the foam under the posts! The downward pressures the lifts put on the concrete are roughly the same as a car or truck simply parked on the slab. Cracking is your enemy here. Keeping the slab consistent across its full cross section will eliminate avenues for cracks.

Good plan to avoid the pex from the lift but you only need to run it around the areas where the posts and anchor bolts will be. When I did mine, we put a layer of mesh down on top of the foam so we could securely zip tie the pex to the grid and be 100% sure it wouldn't move during the pour. You'll want your pex in the middle of the posts - otherwise, you'll be lift with a big cold spot/heat sink in the middle of the room.

You will not find anything about putting in a thickened section under the posts in BendPak's instructions. For a new slab they recommend a consistent slab of uniform thickness. Cracking is your enemy here. Keeping the slab consistent across its full cross section will eliminate avenues for cracks. There is no reason to put in a thickened section. 2 post lifts are not designed for "footers" and don't need them. They get strength from the slab acting as a plate sitting on the solid ground. You will get strength and quality by following ConCretin's guide - make sure you have a well graded, compact base, a quality placement, make sure your contractor pours your full depth and gives you proper saw cut joints. (Saw cuts avoiding the areas where your columns will be!)

For rebar in the lift pad is 0.5” rebar in a 1 foot grid the size of the lift pad good? And should I run more rebar down the length of the slab too?

Cracking is your enemy here. Keeping the slab consistent across its full cross section will eliminate avenues for cracks. As pointed out above, you can run rebar through the section under your posts, but it is a little harder to bolt through. (You will need a rebar-cutting bit and some patience.)

Rebar is insurance against cracking, but with the size of your slabs - if you do a good job with the placement and put a saw cut joint down the middle of the long dimension, you shouldn't have any issues.

Also thinking of tying the new pour into the existing footing with rebar, what would be the best way for this? (Depth of tie in, how much to stick out into new pour, how many feet interval)

You will want to keep the slab level for proper lift operation. If one side is pinned, the slab will go off-level as the ground heaves. As mentioned above, the concrete's strength comes from the slab acting like a plate and being in contact with the ground. If you pin it, voids can form under the slab, which is waeakness.

Best to have a floating slab here and let the whole thing heave with the ground. (Since you are going to heat the slab, the ground below will likely not freeze and your slab will probably stay put, even when it is cold outside.

Also is keying in under the existing footing necessary? Bendpak says to do so when cuting out a section of old concrete to pour a base for the lift but im just thinking as my base is pretty narrow but a long slab is it neccessary in my case?

No keying. This instruction is only for repair slabs made to existing slabs that don't meet spec. (The repair keying is also slab-to-slab and not slab-to-footer.) For new construction, you will have a proper floating slab.