Two Post Garage Lift anchor system

[babyjay8495]

A couple years ago i installed a 9000lb two post lift. The concrete i have is around 4" thick. I never really could get the bolts torqued like i should and recently the concrete has split resulting in the lift tilting when a car is lifted. I went ahead and removed all the fasteners and moved the lift, my plan is to cut out a 30x30 section where each post goes and use 6500 psi concrete make it about 18" deep with rebar. My question surrounds the anchoring system of the posts. I've read numerous threads and have come away more questions than answers. Obviously i don't ever want to do this again and i want to make sure this lift never moves. What's the realistic best anchor system to attach the posts to the concrete? My first thought was to put in the L shaped anchors that go in the wet concrete, seems easier to me than drilling a bunch of holes. I"ve seen threads on the epoxy system, never used it before, so unsure how well it would work. Given my history with the wedge bolts i don't have all that much confidence. Thoughts?
Thanks,

 

[NUTTSGT]

What does the manufacturer of the lift specify ? That's what I would use.



If you are redoing the concrete, you're going to have an arm& leg in ready mix for what you are actually getting. You'll need about 3/4 yard but be paying for about 3 yards minimum. Personally, I'd cut a whole width slice out of the floor and pour one large section rather than two small pads.

 

[Natty Bumppo]

Depends on your manufacture's specs I would think. A Rotary 9,000 lb. lift calls for 4.25" of 3,000 psi. and a 4'x4'x6" pad. I would assume most 9,000 lb. lifts are similar.

This summer I did exactly what you are planning. I would just go with the manufacturer's specs. 18" of 6,500 psi seems like a lot of wasted concrete.

As for the j-bolts, if one of them is just a little off, you're screwed. A lift installed properly on fully cured cement with anchor wedges should give you no problems.

Here's a link to my thread if you're interested:

https://www.garagejournal.com/forum/showthread.php?t=460869

 

[pattenp]

There is no way I'd do just a 30x30 inch square at each post. My 9000lb Challenger lift calls for 4ft X 14ft X 12" thick keyed into the existing slab. I've seen no smaller than 4' X 4' X 10" squares being required.

 

[firebirdparts]

a 30 by 30 square is nuts. Pour a connected slab all the way across. The slab under the lift is like a beam holding up two oppososing overhung cranes. I would never try to depend on something other than connection. there's just no benefit. Just cut all the way across. It's not that far.

 

[babyjay8495]

Makes sense, i might do the 4x4x12 and cut it down to 5000psi mix. I'm assuming the favorite anchor system is the wedge bolt?

 

[vision8]

This is for machine installation and heavy equipment installation . I used 3/4" diameter by 12 inch long J-Bolts in a 4 foot by 12 foot by 12 inch moat tapered into the 4" slab . When you set the anchor bolts into the concrete you wrap each bolt with a 4 inch by 4 inch styrofoam collar around the anchor bolt . If using a 12 inch long bolt a 6 inch long collar will work , Collar is level with the floor . After concrete cures , remove the collar ( burn it out ) which leaves a hole around the upper portion of the bolt . This gives room to center the top of the bolts in the existing base plate holes of the column ; install the lift legs over the anchor bolts on 3/4 inch shims . Tighten bolts after leveling the columns . Now buy anchor bolt concrete grout to bed into the holes left by the sytrofoam removal and under the column base plates and around the shim packs .

Thirty Years of Steel Mill Installation .

 

[wssix99]

+1 on consulting the manufacturer. They have the proper specs for the repair slab you need to pour. (30X30 is not going to cut it.)

They also specify proper wedge anchors.

I've read numerous threads and have come away more questions than answers.

There is some good information on this site. There is some bad information on this site. There is some deadly bad information on this site. Fortunately, your lift manufacturer has professionals with proper specifications.

J bolts have limitations and are not equivalent to the anchors that came with your lift. They can fail in multiple ways and each needs to be designed/accounted for. (ie: you may need a larger J bolt to have the equivalent holding power of a 3/4" wedge anchor - and the lift holes won't accommodate that)

Epoxy anchors are very sensitive to a clean installation. If not installed perfectly, they may torque up good, but pull out under load.

Wedge anchors are simple and provide assurance that they will hold once they torque properly. (On size fits all and safety installed - that's why they come with the lift.)

 

[matt_i]

I really think you'll be better off cutting a piece out that encompasses both posts in a single piece and repouring that 6-8" thick, edge dowel into your existing slab. I wouldn't go any further than 4000 psi/6 sack mix that you can steel-trowel and will give you time to finish it.

The L-shaped anchor bolts are plenty strong but its uber high stakes...get one out of place and the whole thing will need to be jackhammered out and start over. You also get to lift each post up and over the exposed stud.

Epoxy anchors are my personal choice, if you can rigidly follow the prep directions. Requires 24 hour cure before full torque can be applied to the nuts and so that means 2 trips for an installer.

Wedge anchors, great for people who can't follow the prep directions and are very fast to put in, require only 1 trip by an installer.

If you did redo the wedge anchors, make sure you drill thru into the subgrade that way if you get a spinny anchor bolt, you simply pound it into the soil below and now you get a 2nd shot with an epoxied stud after some cleaning and prep work.

 

[wssix99]

The L-shaped anchor bolts are plenty strong

They handle tension differently. Whereas a wedge anchor develops tension along the axis of the bolt, these bent-end bolts develop it at the bend, which is a weaker point. They need to be designed for and are not equivalent to a similarly sized wedge or epoxy anchor.

Depending on the embedment, strength of concrete, and other factors, these things can pull right out of the hole like a wet noodle under the right loading.

 

[matt_i]

If a person is worried about being able to pull out the bend, they can put a nut on a threaded rod and then a big "washer". This is a 1-1/8"-7 threaded rod.



Its still a choice fraught with extreme peril and is tough to finish the floor cleanly if something like a plywood form is used to enforce spacing.

 

[brownbagg]

if i was ding the footer set up, myself i would put a whole ten yards in that footer, just for the weight

 

[matt_i]

if i was ding the footer set up, myself i would put a whole ten yards in that footer, just for the weight

Is that to make sure nobody could ever drive a spinny wedge anchor thru to the subgrade or you'd like the self-enforced exercise program of hand digging and wheelbarrowing 10 yards of dirt out from the shop?

I have to question this because the weight helps how (?) A 2 post is a set of two non-rotating jib cranes that "bend" the concrete slab as it gets loaded up.

The numbers I see thrown around constantly are 4" minimum, if a person doubled that to 8" and put the new section of 'crete that encompassed both posts in a single pour, it would satisfy the most serious installation. At about 50 wheelbarrows less work....

 

[Zmann]

Just a comment on using embedded anchors bolts

a lot of lifts directions specify you level one column and dill and bolt then place the crossbar and then bolt level the other column and bolt

My specific lift did not have the directions written this way but others of the same brand did, my lift actually gave me hard dimensions so after I bolted both columns I noticed the crossbar despite being a bolt together and having elongated holes was 1/2 longer than the dimension they gave for the column , i had to modify the crossbar but had my directions said to leave a column unbolted this would have been a non issue ,, with embeds it would be a problem
also i am sure I would not want to lift those colums 2-3" off the ground to set them onto the protruding embeds