2 post Lift Concrete Construction Joint

[bagsanthony]

Hi guys, forgive my ignorance, I’m a wrencher not a Structural Engineer- Luck would have it that my garage floor has construction joints spaced 130 inches apart. This would put my 2 post lifts over the joints… this is a no-no correct? Is the solution to cut out a 3ft x3ft and set the columns on this? Thanks guys

 

[wssix99]

Correct. Its a NO-GO situation. If you have to put the columns there, then you would need to follow the manufacturer's repair slab instructions. (They will have specific instructions. Probably more involved than simple 3X3 squares. The repair slabs will probably need to be deeper than the old slab and keyed into it. Some lifts require a single pad with reinforcing spanning between the two columns.)

The reason this is a problem is because the crack reduces the pull-out resistance to the anchors that go through the plate into the concrete. The concrete resists pull-out in a conical zone around the anchor, and when the crack or joint crosses these stress cones, the whole thing is weakened.

 

[AC-WC]

Correct. Its a NO-GO situation. If you have to put the columns there, then you would need to follow the manufacturer's repair slab instructions. (They will have specific instructions. Probably more involved than simple 3X3 squares. The repair slabs will probably need to be deeper than the old slab and keyed into it. Some lifts require a single pad with reinforcing spanning between the two columns.)

The reason this is a problem is because the crack reduces the pull-out resistance to the anchors that go through the plate into the concrete. The concrete resists pull-out in a conical zone around the anchor, and when the crack or joint crosses these stress cones, the whole thing is weakened.

Hit the nail on the head!
Follow the Bendpak guidelines and you won't have any problems regardless of which lift you choose. I ended up doing a 4'X12' because of all my stress joints. Went down 14", 2" compacted stone, 2 layers of fiberglass rebar, pinned to surrounding concrete. 2 1/2 years now and no problems.
If you need pictures let me know.

Concrete Floor Requirements - 2-Post and 4-Post Lifts - BendPak

Minimum floor requirements for pre-existing concrete floors and new concrete slabs when installing BendPak two-post lift and four-post lift models.

www.bendpak.com

 

[bagsanthony]

Thanks gentlemen! Really helps! I suppose I could put the lift on an angle but would prefer to go straight on!
Yes, AC- if you have pics I would appreciate it! Thanks again

 

[AC-WC]

Sorry for the late reply had a work dinner tonight
Pic 1 is digging down 14" after cutting out the concrete
Pic 2 is 2" of crushed stone tamped down
Pic 3 is fiberglass rebar per Bendpak spacing 1st layer (chairs in pic 2-very important)
Pic 4 is fiberglass rebar 2nd layer (not specified by Bendpak) with cutouts on the top layer where the columns will set. Note pinning into surrounding area. Bendpak recommends to pin to existing concrete OR key under existing (dig out 4-6" around perimeter of hole).
Pic 5 is one column showing how far the bolts are from the expansion joints.
I paid a concrete guy to come in and do this, all I helped with was tamping the corners and actual pour. Two of them and myself. Cost was around $3500. Done in 2 days-it would have taken me weeks to do this by myself. They had the concrete saw, jack hammer, bobcat to get rid of excess, stone and used the bobcat to get the concrete in the garage. They earned their pay for sure.
I highly recommend if you end up doing this to be onsite when they work. I had a hard time getting anyone to quote, he did not have experience with 'technical pours' like this. He normally did sidewalks, driveways. He wasn't going to use rebar, did not have a ******** (to settle the concrete). Had I not been there that very important stuff would not have been done. Not blaming him because he was out of his wheel house of knowledge. I really need to get him back and do some other pours so happy with the work he did. I have only done concrete once before like 30 years ago on a driveway so I'm not an 'expert' by any means but I can do research and follow the real experts recommendations.
Because of where your lines are it may be best for you to do something similar instead of 2 separate pads. The 4X12 is definitely stronger than 2- 3X3 pads.

 

[C-S-H]

Pic 4 is fiberglass rebar 2nd layer (not specified by Bendpak) with cutouts on the top layer where the columns will set.

I'm not a fan of removing the rebar from the area where they will do the most good. It is too easy to get the geometry right. The bars they specified look to be just temperature/shrinkage reinforcement in any case. I would have bars running each way through the anchor bolt group, top and bottom, if I were adding bars to their design.

 

[bagsanthony]

Thank you so much for the excellent info AC!

Sorry for the late reply had a work dinner tonight
Pic 1 is digging down 14" after cutting out the concrete
Pic 2 is 2" of crushed stone tamped down
Pic 3 is fiberglass rebar per Bendpak spacing 1st layer (chairs in pic 2-very important)
Pic 4 is fiberglass rebar 2nd layer (not specified by Bendpak) with cutouts on the top layer where the columns will set. Note pinning into surrounding area. Bendpak recommends to pin to existing concrete OR key under existing (dig out 4-6" around perimeter of hole).
Pic 5 is one column showing how far the bolts are from the expansion joints.
I paid a concrete guy to come in and do this, all I helped with was tamping the corners and actual pour. Two of them and myself. Cost was around $3500. Done in 2 days-it would have taken me weeks to do this by myself. They had the concrete saw, jack hammer, bobcat to get rid of excess, stone and used the bobcat to get the concrete in the garage. They earned their pay for sure.
I highly recommend if you end up doing this to be onsite when they work. I had a hard time getting anyone to quote, he did not have experience with 'technical pours' like this. He normally did sidewalks, driveways. He wasn't going to use rebar, did not have a ******** (to settle the concrete). Had I not been there that very important stuff would not have been done. Not blaming him because he was out of his wheel house of knowledge. I really need to get him back and do some other pours so happy with the work he did. I have only done concrete once before like 30 years ago on a driveway so I'm not an 'expert' by any means but I can do research and follow the real experts recommendations.
Because of where your lines are it may be best for you to do something similar instead of 2 separate pads. The 4X12 is definitely stronger than 2- 3X3 pads

 

[bagsanthony]

I will update as soon as I make up my mind/ get a concrete guy! Thanks again!

 

[Kaizen]

This is why i cut my joints myself after the concrete guys were done. I knew roughly how many i needed and laid out the lift dimentions to make sure i had room. I ended up cutting that "block" bigger then the rest to give another 2 feet beyond the post location. Can you move yours over so its a foot or so on the other side of that joint?
If you don't know this........merry ........if you are installing these yourself and using sleeve anchors that they come with make sure you drill all the way through the slab. This way if they fail you can push them into the dirt and use another.

 

[bagsanthony]

Kaizen - when you say ' move yours over so its a foot...' Are you referring to moving the lift column posts over so I have adequate joint clearance? Just want to be sure I understand.... It will set me slightly off-center from the garage door. However, the garage is 36 ft deep so a little offset I do not think will be the end of the world....maybe your on to something!

 

[Wiz02]

The guy that installed my 2 post lift had to offset it a few inches from being centered on the garage door center line, in order to leave enough space between the post mounting holes and a control joint.

Luckily the offset location is pretty easy to manage, as all that I need to do is pull in the garage a bit closer on the driver's side.

It will be 10 years since the installation and the mounting bolts are still at the installation torque.

If you can offset the lift to meet manufacturer's requirements and still drive in without too much trouble, you can save some $$$. It may be worth mocking up with some tape on the floor to see if it will work.

 

[bagsanthony]

Agreed! Thank you for the info Wiz! I don't think it will be the end of the world.... At 36 feet deep its a lot different than having the lift tighter to the back giving less room to swing in...I will do some mocking up for sure!

 

[Hobby_Man22]

Sorry for the late reply had a work dinner tonight
Pic 1 is digging down 14" after cutting out the concrete
Pic 2 is 2" of crushed stone tamped down
Pic 3 is fiberglass rebar per Bendpak spacing 1st layer (chairs in pic 2-very important)
Pic 4 is fiberglass rebar 2nd layer (not specified by Bendpak) with cutouts on the top layer where the columns will set. Note pinning into surrounding area. Bendpak recommends to pin to existing concrete OR key under existing (dig out 4-6" around perimeter of hole).
Pic 5 is one column showing how far the bolts are from the expansion joints.
I paid a concrete guy to come in and do this, all I helped with was tamping the corners and actual pour. Two of them and myself. Cost was around $3500. Done in 2 days-it would have taken me weeks to do this by myself. They had the concrete saw, jack hammer, bobcat to get rid of excess, stone and used the bobcat to get the concrete in the garage. They earned their pay for sure.
I highly recommend if you end up doing this to be onsite when they work. I had a hard time getting anyone to quote, he did not have experience with 'technical pours' like this. He normally did sidewalks, driveways. He wasn't going to use rebar, did not have a ******** (to settle the concrete). Had I not been there that very important stuff would not have been done. Not blaming him because he was out of his wheel house of knowledge. I really need to get him back and do some other pours so happy with the work he did. I have only done concrete once before like 30 years ago on a driveway so I'm not an 'expert' by any means but I can do research and follow the real experts recommendations.
Because of where your lines are it may be best for you to do something similar instead of 2 separate pads. The 4X12 is definitely stronger than 2- 3X3 pads.

Slab looks a good 6 or 8" thick. You're wasting your time.

 

[mike93lx]

Slab looks a good 6 or 8" thick. You're wasting your time.

There is more to it than concrete thickness

 

[firebirdparts]

This has been asked 100 times. The 3 x 3 idea is not enough. The slab holds the lift DOWN and you want a lot more than that. 3 x 3 isn’t even getting close to the load. Width, I would go all the way across from post to post. Length it’s hard to say. For an asymmetric the length needs to at least reach past the center of gravity to make me feel good.

 

[racecougar]

Slab looks a good 6 or 8" thick. You're wasting your time.

Note the location of the control joints. Not a waste of time at all.

 

[AC-WC]

Slab looks a good 6 or 8" thick. You're wasting your time.

There were 3 issues that are hard to see with these pics.
1) there was mesh at the very bottom laying on the dirt i.e. it was never pulled into the concrete. It's at least 50 yrs old and I had no idea what the psi is.
2) there were other expansion joints closer to the columns that can't be seen in the pics.
3) lots of concrete spalling from winter slush/salt. After cutting I saw how thick it really was but the expansion joints just weren't worth the risk.

 

[Hobby_Man22]

There were 3 issues that are hard to see with these pics.
1) there was mesh at the very bottom laying on the dirt i.e. it was never pulled into the concrete. It's at least 50 yrs old and I had no idea what the psi is.
2) there were other expansion joints closer to the columns that can't be seen in the pics.
3) lots of concrete spalling from winter slush/salt. After cutting I saw how thick it really was but the expansion joints just weren't worth the risk.

Concrete must have been cheap back then. I see 50 year old houses with 2ft thick pads where the ac condensor sits on top of lol.