Problem with drop in anchors and thin floor

[wssix99]

A 4 post lift is a fine thing for a thin floor. Extra concrete and rear don't add "strength" to a slab-on-grade. (Rebar only provides crack control and a deeper slab only reduces the bearing pressure at the base of the slab.) As long as the lift isn't loaded to the max, no critical limits are going to be hit for the thin slab.

 

[Rusted Nut]

the pads are 10x12 which means even less load than you calculated. This was what I was trying to explain earlier. Others have made the point about shear and I agree it's at play, but I don't believe it's a significant issue here.

Why are anchoring the lift to the floor? It’s not going to flip over, but it might slide on the floor. When bolted to the floor, this sliding action is shear. When the lifts slides, it trying to shear the bolt in half. Shear is 90% of what you are dealing with on a 4 post lift.

If your patching fix doesn’t work, get some Hilti “screen tubes” and epoxy; they work very well.

 

[LopezBart]

Having lived on the Ring of Fire my whole life, I'll note that in areas where earthquakes are a thing some more analysis is required. If such are unknown in your neck of the woods - great. Otherwise, all sorts of interesting loads are possible on those anchors.

Frequency of Damaging Earthquake Shaking Around the U.S. | U.S. Geological Survey

www.usgs.gov

- Bart

 

[whateg01]

Why are anchoring the lift to the floor? ...

He's stated already that he's shimming it to make it level.

 

[Rusted Nut]

He's stated already that he's shimming it to make it level.

I get that. But shimming is not anchoring. My question referred to OP’s comment he was dealing with shear.

 

[whateg01]

I get that. But shimming is not anchoring. My question referred to OP’s comment he was dealing with shear.

I think he says that because others have pointed out that it's mostly shear forces. Anchoring does also help keep it from rocking. I don't recall the brand but one shop I visited, I was afraid to lean on the 4 post lift because it swayed so badly.

 

[wssix99]

The feet can walk a bit. Using pins with shims makes things tidy. I plasma cut shims to match the base plates of mine, bolted them all, and everything is tight and looks great. (... and doesn't move when I accidentally screw up a leg lock and have my load briefly crooked...)

 

[Jaja]

It's true the pads shift a little when it's cycled up/down but in this case it's because of the floor and the pitch.

This lift has been moved twice and in my prior 2 homes the shop floor was flat and it didn't move much as it cycled. In fact, at house #2 after it was moved it didn't need any re-adjustments. In my current home, the lift is in my attached garage which is only 24' deep and the floor is pitched to the opening so the slope has had an affect on the columns being plumb and the carriage being level.

If I left it free standing I expect the movement would eventually slide the shims out from the pads. That's why I'm "pinning it" in place.

I considered raised pads like @Dakota00 did here https://www.garagejournal.com/forum...elain-tile-install.212509/page-8#post-4841733 which is still "pinned" in place but I wanted the flexibility to move the lift around if needed. That's also why I avoided epoxy anchors or any pound in wedge style anchors.

It's been a busy week and I won't get to the anchors until Friday. Thanks for the comments. More to come.

 

[N_Jay]

Don't split loads equally, because nothing is perfect.

400 LB on 4 legs doesn't guarantee 100 LB per leg.