new and existing pad footings to existing structure

[selr]

hi, structural modifications have to be done to accomodate 3 new floors above an existing 5 storey building. I am unfamiliar with working with existing strucures and a few queries as to the best options of work method, replacement and connection etc. suitable for the situation.

-the placement of new pad footings 1.8x1.8.0.7 to new columns, founded 1.5m below ground slab level.

-some existing pad footings 2.4x2.4x0.9 founded at 1.5m have to take additional loads. Suitable increased bearing capacity is at a depth of 2.1m or increase in pad size to 3.6x3.6.

-how the columns can be connected to the underside of existing beams and if they should be reinforced concrete or composite. (the existing building is steel framed and encased in concrete for fire protection )

- How the exsiting columns can be best removed.

 

[jdonville]

Selr,

First, get your geotech to help you out.

Based on your description of the problem(s) it seems that you want to
1)add new columns and square footings below an existing slab.
2)modify the foundations for existing columns.
3)connect the new columns to existing beams - presumably these beams support the existing floors above the slab grade.

1)Without knowing the exact situation, you will probably need to demo portions or all of the floor slab to excavate for the new foundations.

2)For modified foundations, you have some opportunities and some problems. First, you need to decide if you can safely support the column loads while you are mucking about with the column's foundation.

If not, you may want to look at using micropiles to bolster the foundation capacity without having to remove the existing foundation. There are a number of micropile contractors out there that will be able to tell you what is going to be involved in the process (Hayward-Baker, Nicholson).

If you can support the column temporarily, then you need to decide if you want to go to the trouble of shoring the excavation, (possibly) demolishing the existing foundation and constructing the new one. Depending on the number of colums that will need to have modified foundations, this could be a little tedious.

3)Is outside my realm of professional experience.

Good luck!

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com