Column Brace For Additional Loading 4

[mountaineers19]

I am trying to find alternatives to increasing the capacity of this crane without messing with the foundation if I do not have to. I know the foundation is good for the current loading and according to my model this brace would handle the additional load and help disperse it on a larger effective area on the foundation. Does this seem like a logical fix or would the load just go straight down regardless?

 

[mountaineers19]

@mountaineers19 : some questions that may allow us to better serve you.

1) Is your foundation issue one of punching shear?

2) Are we talking about a discrete, pad footing? Or a raft?

Passes punching shear and is a spread footer. But someone did raise the point of this being an older construction that it has had 20+ years of soil consolidation which does help. One of my main concerns was the soil bearing pressure due to this not having a large effective area.

 

[KootK]

So your only concern is settlement? Unless I misunderstand the situation, I'd be inclined to not sweat that. Or, at worst, to react to it if/after it takes place.

 

[mountaineers19]

So your only concern is settlement? Unless I misunderstand the situation, I'd be inclined to not sweat that. Or, at worst, to react to it if/after it takes place.

Correct, the concrete came back with a much higher compressive strength than anticipated and passed punching shear so i was more curious about the effects of the limited effective area I have on the soil bearing capacity with the 25% weight increase.

 

[KootK]

i was more curious about the effects of the limited effective area

Can you clarify what you mean by the limited effective area? I think that get the idea but I'm not used to worrying about that explicitly.

Minor thing: the transitory nature of your crane loads may help.

 

[mountaineers19]

Can you clarify what you mean by the limited effective area? I think that get the idea but I'm not used to worrying about that explicitly.

Minor thing: the transitory nature of your crane loads may help.

Wouldn't my effective area when checking the bearing pressure on the soil below be limited to the area of the baseplate plus the 45 degree projection from bottom of baseplate to the soil?

 

[KootK]

Wouldn't my effective area when checking the bearing pressure on the soil below be limited to the area of the baseplate plus the 45 degree projection from bottom of baseplate to the soil?

I've never seen it done that way. Normally one assume the entire area of the footing to be effective so long as the footing is designed consistently with that premise.

Soil stresses will, of course, not be uniform over the entire footing area. So, in regard to that, I believe that we generally concern ourselves with the average.

 

[mountaineers19]

I've never seen it done that way. Normally one assume the entire area of the footing to be effective so long as the footing is designed consistently with that premise.

Soil stresses will, of course, not be uniform over the entire footing area. So, in regard to that, I believe that we generally concern ourselves with the average.

Gotcha, so in this case there are areas where they have a heavy duty slab acting as a spread footer would this still be the case?

 

[KootK]

Gotcha, so in this case there are areas where they have a heavy duty slab acting as a spread footer would this still be the case?

I expect so but I feel as though I would need to see something of the plans / details to be able to comment reliably.

 

[mountaineers19]

I expect so but I feel as though I would need to see something of the plans / details to be able to comment reliably.

Slab details are thickness ranging from 6-14 inches depending on the area with 66-44 WWF reinforcement. Compressive strength from samples has been anywhere from 5000 psi in the 14" section to 7000 in the thinner areas. Soil bearing capacity was stated at 4000 psf minimum in the 70s and the crane was originally installed around 20 years ago.

 

[KootK]

If the foundation of interest is a thickening that appears local to the load being considered, I would expect that you would be good to go.

 

[mountaineers19]

If the foundation of interest is a thickening that appears local to the load being considered, I would expect that you would be good to go.

Thank you very much for the input!