Help need for weight ditribution assessment

[evilstuie]

Hi All,

I'm hoping someone might be able to give me some advice on a shed project.
I have a 9m x 6m shed with a 32MPA concrete slab that is 100mm deep.
I had pierings of 400x 400x400mm for each column of the shed, as well as 2 additional pierings for a future installation of a car hoist.

Unfortunately the height of the hoist doesn't allow me to put it in those poisitions so I am no wleft with 2 options. The first is to cut out the concrete and dig the whole area out (4mx2m has been recommended) and then fill with new concrete, all of whch seems like a big job.

The other option is to use base extension plates to distribute the load across a larger surface area. There were some options available but they looked like they weren't quite up to the job, and none of the car hoist companies would give me anything in writing to say this would suffice.

I've asked a metal fabrication shop to make me some 800mm x 800mm x 16mm thick steel plates drilled to the current hoist column bolt pattern which I'm hoping will make up for the lack of concrete depth which is recommended at 150mm.

The hoist is a 4 tonne 2 post car hoist (Model TPB140) but I'll be using it for cars no heavier than 1.8tonne. Do you think these plates will distribute the weight enough to compensate?

 

[evilstuie]

Anyone?

 

[jayrod12]

You likely won't get someone telling you this is fine. Are you an engineer? If so, the design aspect is easy and we can certainly point you in the right direction. If not, hire an engineer.

 

[evilstuie]

Hi Jayrod,

Thanks for the reply. I should have expanded, this is just for my home shed.
The original base plate for the hoist columns is 430mm x 250mm and the new plate I've had made is 800mm x 800mm
The plates are secured with M19 x 100mm dynabolts.

I'm just trying to find if there's an equation or calculator I can use to determine the effective weight dispersion/distribution on the estneded base plates to determine if this will reduce the stress on the concrete and securing bolts enough to safely sustain 2000kg of car weight

 

[evilstuie]

FYI plate design

 

[bIockhead]

Best of luck, but I don't think you're going to find anyone here who's looking to give you technical advice. This forum is meant for engineers to bounce around questions and ideas with those within their profession.

 

[Tex.Eng]

No simple equation or calculator exists to give you the answer you are looking for.

It sounds like someone (engineer? contractor? manufacturer?) already gave you the solution.

2000 kg is significant weight. It's not something I would attempt to lift without proper assurance that the support is acceptable. I hope that no one is planning to be under the vehicle while it's suspended...

 

[evilstuie]

The hoist itself is rated for 4000kg with the 430mm column base going into 150mm concrete base.
I'm halving the weight and quadrupling the surface area to account for 25-50mm concrete depth deficit.

I found 2 options for reinforcing the hoists to account for less than recommended concrete depth, the first was a box frame that runs perpendicular to the hoist columns which is about 800mm long and 50mm wide/high which provides additional anchor points along it for both balance and stability, and uses to bolts to connect to the column bases.
The other option was a HAPP design and was a 700mm x 700mm base plate which I used for my design.
I used the same 16mm thickness and extended the base by another 100mm each way to give a greater area.

The issue was that these were designed specifically for their anchor bolt locations and I'd need to redrill to suit my hoist, and it seemed a better idea to have somethign designed to match exactly.

I was just hoping there was a formula that could be used without knowing the current shear forces but to calculate the percentage of force that would be reduced with the increase of base surface and additional anchor points at the edges of these.

 

[Tomfh]

It might work but it needs an engineering assessment. There's no simple formula. Hoists do fall over from time to time, so you need to do it right.

 

[jhnblgr]

Cut out floor and follow the manufacturer recommendations. If you can’t do it right don’t do it at all.