building on old concrete basement foundation

huangyhg

building on old concrete basement foundation
i have a situation and would appreciate any recommendation or suggestion. my client has a large basement that was used as storage under a one story building which was recently destroyed in a fire.  the basement has a 12鈥?high headroom and the walls are 12鈥?thick.  there are also interior steel columns that appear to be in good condition. the building was built in 1930.
the client wants to build a two-story office building on top of the existing foundation and  i am considering the following:
1.    taking a few cores through the foundation walls and having them checked for strength. also to see if any damage was done due to the fire.
2.    sending a piece of the steel to the lab to check for type and strength.
3.    drilling in the basement slab to check thickness. i still haven鈥檛 figured out how to check the footing depth and sizes under the interior columns.
4.    checking with a re-bar finder to see if there is any reinforcement although i doubt.
5.    having a couple of borings done to see what kind of soil the 12鈥?foundation wall has been holding up over its 100鈥? length.
  any help is greatly appreciated.
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i would seriously consider replacing the steel.
a. it is from te 1930's and the consistancy of the steel can't be what it is today.
b. the steel survived a major fire, but exposure to the heat may have damaged the steel.
c. you will never have a better oppertunity than now to do it.
i've seen concrete from the early 1900's (ie, 30 years older than your foundation) that had old bricks and large rocks in it, had pieces of railroad rails for reinforcing, etc- there's just not much telling what you'll find in there.
if the building were constructed in 1930's, it is possible that the steel is a36. were there supporting beams for the floor over the basement?  did these sag (drape) over the columns.  there's a good chance these were undamaged.
it is unlikely that the concrete was damaged.  is it chalky, soft?
footings sizes can be determined by cutting through the existing slab and excavating.
it might be prudent for the building owner to retain an engineer to review the conditions of the superstructure and foundation walls...
dik
the steel columns probably were a9 steel and the rebar in the concrete probably was a15, most likely intermediate grade.  your tests will tell you. (do the chemical analyis too!)
a36 steel came into general use in the 1960's. a9 steel has a lot of sulphur, so you don't want to weld to it.
google this:  "a9" steel and select the aisc steel interchange option.