footings 1

[simplebm]

Any ideas on how to strengthen an existing spread footing and pedestal for increased column load?
Present bearing 4 ksf; new bearing 9 ksf. Footing is 3.5ft x 3.5 ft x 1.0 thick. Footing is 5 ft below grade. No problem with owner suing.

 

[oldestguy]

Yes, but what size and depth now, soil conditions, actual bearing pressure now, how much increase, added settlement tolerance, owner's tendency to sue, etc.

 

[KootK]

In what ways does the existing footing fail? Flexure? Punching shear? Soil bearing stress? I've commonly seen engineers extend footings with dowelled in rebar or cast a ring of new concrete around and underneath the existing footing. Both solutions require careful attention to detailing. And neither improves punching shear.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

Is this footing already loaded by structure above? If not, rip it out and start over. If it is, prop the structure and underpin the footing. It is too small to consider enlarging by casting a ring around the footing.

 

[KootK]

Two other options:

1) If you can use that 5' space you could pour new footings either side of the existing footing and pour bridging beams either side of the pier that dowel into the pier to pick it up and take the load out to the new footings.

2) Soils permitting, you could install screw piles adjacent to the footings to pick it up.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[simplebm]

Thanks to all for your thoughts.

 

[dcarr82775]

I was going to suggest Koot's #1

 

[Leftwow]

What do you think of making squares of grade beams ringed around the footing that look like stair cases tied with multiple cables on each level into the footing structure?