Concrete slab for outdoor 2 post lift

[onthefence777]

Ok guys, it seems like I am getting much closer to lift install time. I thought it would be a good idea to run everything by the pros here, in case I am missing something. I'll try to make it clear and short here.

I have a 2 post lift. I want it installed in the backyard behind the garage. I am just about done with all the necessary excavation. This new pad will be level and **** up against an existing 3" slab. Where the slabs join, the new pad will be 14' wide, and extend 12' away from the house. The new pour will be 6" deep, so I excavated 10" deep to allow for a 4" layer of gravel beneath the pad. I am also considering digging a few inches deeper directly where each post will be to allow for stronger footings in those two spots.

Concrete spec per contractor will be 3500psi, with added fiber mesh and rebar installed on 2' square, but might be spaced slightly farther near where posts will be installed so that the installers don't hit the rebar when they drill to anchor the posts.

Instead of centered and squared on the slab, The lift will be installed at a 45 degree angle on the pad for vehicle access, since a slight turn around the corner of the garage must be made. Using pythagorean's theorem, the 45 degree line where opposite corners of the slab meet makes a line that is approx 18.439' long, and rough measurement verifies. Since the lift footprint is approximately 128" long, the post should have close to 4' + from outer edge of post to the outer edge of the slab. Is this an adequate distance from edge of the slab?

For the power to the lift, my idea is to install conduit before the pour that will extrude from the ground right at the outside edge of the post closest to the garage. Will the conduit in the concrete compromise the structural rigidity neccessary near the post? If conduit closeby is a no no, how can I bring power to the lift? If this isn't an issue, I also thought of running an air line through the pad also to allow a quick disconnect on the side of the post.

I am going to let the pad cure for about a month before the lift is installed.

The 6" might be a bit excessive depth, and concrete contractor says gravel is a good idea but not really necessary because of the soil here, but I want this pad to last for many decades and would rather overdo it than not go far enough. And I do not want to worry about having the lift fail with me under it.

I would appreciate insight and advice on anything I may have overlooked...Does my plan sound adequate?

 

[pattenp]

My only comment is to not put any of the lift anchor bolts any closer than 6-8 inches to where the conduit exits the concrete. No science to that suggestion, just my thought based on life experience.

 

[onthefence777]

Thanks for that reply. Any other input on subgrade base or concrete specs?

Also, I was thinking, since the one post wont be too far away from the house... could I just run a conduit from the bottom of the eave across and attach directly to the post and then go down to the motor?

 

[wssix99]

Instead of centered and squared on the slab, The lift will be installed at a 45 degree angle on the pad for vehicle access, since a slight turn around the corner of the garage must be made. Using pythagorean's theorem, the 45 degree line where opposite corners of the slab meet makes a line that is approx 18.439' long, and rough measurement verifies. Since the lift footprint is approximately 128" long, the post should have close to 4' + from outer edge of post to the outer edge of the slab. Is this an adequate distance from edge of the slab?

Maybe not... The manufacturer will give you a spec for the minimum pad size under each post. That pad size will be rectangular. You need to also rotate that virtual rectangular pad with the post leg and make sure that the rotated pads under each post fit within your larger slab. (You can't just rotate the leg on a rectangular pad. That minimum pad has to rotate with it.) If not, the slab may not resist bending properly.

For the power to the lift, my idea is to install conduit before the pour that will extrude from the ground right at the outside edge of the post closest to the garage. Will the conduit in the concrete compromise the structural rigidity neccessary near the post?

Not if you get it near the center of the slab. (For a two post lift, the top and bottom of the slab take all of the loading from the bending forces.) Going to 6" also helps tremendously.

I am going to let the pad cure for about a month before the lift is installed.

Since its outside, are you going to put in control joints to handle any cracking that might come along?