Existing Pad Footing Enlargement
Existing Pad Footing Enlargement
(OP)
Recently I deal with one project that need to enlarge the existing footing due to the additional loading. I have some doubt to design it.
1.Is it possible to enlarge the footing because I'm not allowed to remove the existing footing?
2.The new footing area is base on the existing footing area plus the new footing area?
3.How about the new reinforcement? Can I embed the new reinforcement from the existing footing?
4.Do I need to check the punching shear? Can I deepen the existing pad footing?
I will very appreciate if somebody can give me some concrete idea and suggestion.
Thanks.





RE: Existing Pad Footing Enlargement
It would probably be better to underpin the existing footings to carry the loads down to a more suitable stratum.
You would have all sorts of issues to consider if you widened the existing pads such as additional settlement, uneven settlement, tie in problems etc etc. Although I suppose it depends on the magnitude of the additional load and the tolerances of the structure......
Hope this helps
RE: Existing Pad Footing Enlargement
RE: Existing Pad Footing Enlargement
Otherwise underpin and cast a U shaped footing around the existing.
RE: Existing Pad Footing Enlargement
RE: Existing Pad Footing Enlargement
If existing footing and pier have sufficient structural capacity (bending, punching shear and beam shear) then it might be advisable to test whether soil is actually stronger than assumed.
You can enlarge a footing to increase bearing area but as you alluded to, you would need to check shear and bending. If one of these fails then you may need to enlarge the pier, base plate or add concrete to the overall thickness. You may run into limitation on how deep the footing can be. Make sure that you dowel the new and existing footing together sufficiently so that it functions as one monolithic footing. I do not suggest relying on bonding agents! Make sure that you can develop the reinforcing.