Richard D
Well-known member
I am imbedding a 3/4" steel plate, with grade 8 nuts welded underneath, into new concrete. Also have 16" C channel, 5" wide, down under.rebar drilled into the existing concrete as well.
My Maxjax Installation
- Thread starter Richard D
- Start date
Uh....this does not look like a proper installation. Cutting two really small sections, to only a few inches depth, and rebar ties back into the existing slab is not sufficient.
DO NOT USE THIS TO LIFT CARS, IT WILL NOT HOLD.
DO NOT USE THIS TO LIFT CARS, IT WILL NOT HOLD.
Here is what Bendpak recommends for retrofit when existing slab isn't sufficient for instance:
www.bendpak.com
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.
Unless you had an engineer certify your solution, I wouldn't be trusting it over something that is published. That monolith of a slab is needed given the cantilever forces involved of a 2 post lift. The shorter lift height doesn't really change this math substantially. Keep in mind, there are forces both pulling the posts inward, but also forces of a car's potentially slightly off center of mass forward/backwards wiggling around as you wrench on things or remove components shifting that weight. The rotational force on the what looks like 24" cutouts you did, won't hold up, it will twist right out of the ground.
Also, if you go and see concrete requirements for any manufacturer (Bendpak, Rotary, Mohawk, etc.) they all have something very similar to what I linked from Bendpak. So this isn't just me suggesting something that's overkill, it's what every lift manufacturer has determined to be safe. I'm fairly certain if you contacted maxjax, they would not accept your installation.
Hard to say, really only an engineer could tell you whether what you've done is ok or not to be saved.
All I saw is a WAY smaller cutout than what is normally required for a lift retrofit.
I’m just gonna start over. I really thought, and my pretty smart yet non-engineer friends agreed, this was WAY better than five anchor bolts pounded into 60 year old concrete. I do not want to take chances. Thank you for your input I honestly appreciate it. I’m just bummed out at the moment.
The general idea of making adjustable positions isn't bad, some people have done that with extra anchor bolts at different spacings. I've also seen people embed plates into concrete for lifts too...the big issue here was just the volume of concrete needed for a slab tie in.
I totally understand and totally agree. I am a draftsman and designer with 30+ years of experience, but not in concrete. After looking at the drawings and reading your explanations, I am a believer. Doesn't make me feel any less sick about all the work we did for naught, but I am glad no one, cars or people, got hurt before my "L.E." Learning experience! Seriously, thanks for the input, it just may have saved a life.
Welcome, good luck!
dkmc
Well-known member
Incidentally I wonder what grade of fastener grade 8 nuts turn into when you weld them....
dkmc
Well-known member
Hard to say they are alloy steel. Might make them brittle.
May I suggest a recap and lesson learned? What was the initial requirement? Existing conditions understood?. The decision process.?
From what I am seeing it is going to cost bucks to fix this.
I have been that guy they all point to as the reason it all should have been done different. This is why I state the above. The wisdom comes from the experience. Make this thread positive..
Good luck,
John McA
From what I am seeing it is going to cost bucks to fix this.
I have been that guy they all point to as the reason it all should have been done different. This is why I state the above. The wisdom comes from the experience. Make this thread positive..
Good luck,
John McA
Will be about a grand for concrete. Saw is a loaner and the kid's labor is room and board. Should be a 2 weekend job. I am going at least a foot deep next time, 4 feet wide, all the way across, and underlapping a good ways behind the existing slab. Lots of steel, including a structure connecting the two plates buried in the rebar and concrete. I'll draw it all up in CAD and ask for advice, I'm still a bit too disgusted to really even go out there at the moment. I imagine I'll also wait for cooler weather.
About to get back on this project now that we are finally done with 80+ degree weather. I have the big 3/4 plate with the holes in it, I also scored a 24"x120" piece of 1/2" plate, I will weld the two together so I have steel all the way across, and weld "bell Bottom" down riggers every couple feet. Then dig, rebar, 4000 psi concrete etc. as per the drawing above.
Why not just do it the recommended way? My buddy just put up a 10’ 2 post lift in his old barn. Concrete was 2-4 inches in spots so he had it cut and new stuff poured as recommended, with rebar to 6”. The new pad is about 16x12 and tied into the old. We don’t worry about working under the lift.
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I used the epoxy anchors on mine. 4” concrete. I’m only lifting old Porsche’s that weigh about 2K on average.I just trust threaded steel more than anchors. I've always hated anchor bolts. Plus I have a couple dozen of them. The steel plate is already built. You can't tell me anchors would be stronger than this:
Talk to an engineer about your design. When my father in law was alive, I’d ask him engineering type questions and he used to explain all sorts of details that I never thought of. At the very least, it’s helpful to get an educated second opinion.
mike93lx
ALLIANCE MEMBER
Did you move on from the welded contraption? Just follow their specs
mike93lx
ALLIANCE MEMBER
What could go wrong? A guess and gut feeling over an engineered solution? Send it
At least no one would get hurt if it fails
mike93lx
ALLIANCE MEMBER
Who would produce said instructions? The manufacturers provide an engineered solution already. I would expect your are on your own and would need to get an engineer to evaluate your specific setup.
This is where I got the idea:
www.garagejournal.com
I appreciate all the advice and concerns, mine is not exactly the same as above, but similar. If I am still "off the beam", let me know; I definitely want to be safe, I honestly think the anchors are not the best way to go, but the "only" way to go in existing concrete.
MaxJax Custom Install - Porsche 993
Despite all of the warnings and concerns from some experts about my installation failing, my car has now been on my MaxJax non-stop for just over two years. Maybe it'll fail in the third year. ;)
www.garagejournal.com
I appreciate all the advice and concerns, mine is not exactly the same as above, but similar. If I am still "off the beam", let me know; I definitely want to be safe, I honestly think the anchors are not the best way to go, but the "only" way to go in existing concrete.
I don't understand the plate idea. Is the plate level with the surface? I understand your concern with pounded in anchors. There strength is from lateral forces when properly installed. the key is properly installed. If i were doing a virgin pour I would use j hooks. The thread cited is using SS tubes? That is not a good engineered soln regardless of how it worked with a little porsche on the lift. SS is not recommended for that type of use unless it is the grade of an ARP fastener. I don't those are. This is why we have engineers..........