Evaluating existing structure (no drawings) 2

[pwildfire]

Hi guys,

I have been asked to design an addition to a local building. This building was originally built in the 1930s and is one of the designated fallout shelters for our area, and is apparently a very strong building. Unfortunately, the owner does not have and has not been able to obtain any drawings for the building.

The addition is to add a 3rd story to the top of the existing structure. I have no issues with designing the new building, but I am not comfortable with making assumptions about the strength of the existing structure, and am not sure how to proceed without drawings. There is an unfinished cellar area in this building, so I have access to some column bases for examination.

I do some structural design at my current position but am a mechanical engineer, so I am hoping that someone with more of a structural background may have encountered this issue before.

I suppose what I really need to know is:
A) Are there practical methods to determine the nature of the existing building without making too much mess?
B) Is there any 'accepted practice' in this situation with regards to what assumptions are acceptable?

Thanks
Pat

 

[JAE]

A) Are there practical methods to determine the nature of the existing building without making too much mess?

In some cases if you can determine the load carrying capacity of various members throughout the building (various joists, beams, columns, etc.) then you can to some extent extrapolate that out to a general understanding of the overall building capacity (gravity-wise).

However, with additional stories, you now have opened a can of worms with respect to lateral wind and seismic. This is usually very problematic with additional stories.

Also, the footings may or may not be capable of supporting the added floor and roof loads that you will deliver to them.

As far a not making a mess - you probably would have to use local destructive removal of materials to really get at the make-up of the building elements.

For concrete buildings this could involve chipping into columns and beams to reveal reinforcing bars. Taking cores of concrete, samples of steel, etc. for tests would be important.

B) Is there any 'accepted practice' in this situation with regards to what assumptions are acceptable?

There are various publications out there that deal with this. The links below are just some random sites I found with an internet search:

http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc36941.pdf

http://www.asce.org/Product.aspx?id=2147485434

http://www.asce.org/Product.aspx?id=2147485463

http://www.fema.gov/library/viewRecord.do?id=1513

http://www.modernsteel.com/Uploads/Issues/February_2007/30762_steelwise_reno.pdf

http://www.bcbuildingscience.com/evaluation.html

http://books.google.com/books/about/Building_evaluation_for_adaptive_reuse_a.html?id=JKBE1Ao6XOcC

I don't know your qualifications and don't mean to question them - but if you aren't an experienced structural engineer, this type of engineering is highly specialized and takes a good deal of knowledge and awareness to do it right without creating public risk. Perhaps one of those situations where one may not know what they don't know can be very dangerous.

 

[ztengguy]

I think I would sub it out to a local PE in your area, someone that has experience with older drawingless buildings.

 

[ukengineer58]

assumption can be deadly. to be honest it sounds like you shouldn't be touching this project.

 

[MiketheEngineer]

Hire a local structural engineer - save yourself and the building

 

[SteelPE]

If you are in the US your jurisdiction probably follows a version of the IBC code. The only assumptions I make when rehabbing an existing structure are in regards to chapter 34 of this code. I follow the 5% rule for gravity members and the 10% rule for LFRS members. If I go over these numbers I usually end up rehabbing the entire structure.