Renovation & Extension of a very old 3 storey structure

[foe700]

the major problem is that the 50-year old Reinforced concrete building has no structural drawings. i have considered non destructive tests of the structural members.
the dilema is how many members need to be tested to optimise testing costs. the building was originally designed to carry 5 floors but only three floors were built. however the client does not want to be limited to the 2-extra (expected) floors. what alternatives and safety precautions can take to solve this.

 

[cvg]

if you have no as-builts, then how do you know it was properly designed for 5 floors? In addition, codes have changed and current code will need to be met if you add floors. Sounds like you need to evaluate the amount of risk you would like to take when you sign the new plans...

 

[dik]

Just some scribblings...

If it was properly designed using earlier codes, there is a good chance that it is OK for current loadings, except possibly changes due to seismic loading. If you can determine the time period and determine what materials were available at the time, it might give you a better idea. You can use cover meters and other techniques to try to determine reinforcing... even some mild exploration. Just a anecdote... I was looking at renovating a building constructed about 1920 and one of the beams I cut out had the reinforcing as stipulated on the blueprint (real blueprint) but it was still tied as a bundle, complete with metal designation tag. You might try load testing a component... using drums suspended about 2" from the supporting surface below. Proof load and also do a load deflection to get an idea of reinforcing. Concrete strength can be tested by coring, but unless shear is an issue, it has little effect on the flexural strength. You might want to do a little 'girding' at the columns to see what they are made of. This can be done at about 1/5 points (away from areas of high moment and sufficiently away from mid height to affect buckling. Often old buildings have fairly large columns and slenderness is not an issue. Can use physical sizes of beams to 'guesstimate' the shear capacity... often early buildings used 2500 psi concrete or even something else. You can find a real mix.

Dik

 

[VAD]

In addition to the advice provided so far, you should check the neighbourhood for similar buildings constructed at that time period. Perhaps you may find that there may have been a common builder and perhaps track down some drawings. Any chance of getting some info from the building permitting office. The building officers generally have good historic information in their files.

Seems like the owner wants to exceed the 5 floors. If so you need to check on the building foundations as well. You would need to drill some holes to assess the condition of the subsoil etc.

I presume that you have done a condition survey of the existing building and checked for any tell tale signs of possible serious defects etc.

Dik has provided some good advice on evaluating the structural integrity of the building elements.

Interesting problem and one that points up the need for good documentation always. Some jurisdictions are working on this aspect as a result of similar types of problems.

Is this a residential or commercial building.

The mechanical, electrical, water systems have to be addressed as well.

Have fun

 

[eriq]

lovely solutions above, let me try 'running before walking'suppose all is well with the structural interity thanks to earlier codes 'conservetivness'. lets say the five floors are in place, thanks to new codes and extensive research in concrete, but then like stated in the problem the client dose not want to be limited to those floors what solutions(design) would takecare of this problem of unlimited floors. am just thinking could one propose a mix of R.c(the old members) and steel(new members) as in besides the geotech.for example consider the columns are very critical can we have hollow steel plates welded around the old r.c column to provide extra support. just asking

 

[cvg]

steel jacketed columns could be a solution for the columns. I have seen this method used quite successfully for seismic retrofit of bridges in California.

 

[dik]

VAD's comment about trying to find drawings for a similar building in the area is one that has merit. 50 years is not really that old and it may be possible to find some drawings elsewhere. Mind you, if the same guy did the same buildings, he may only have had one set of drawings <G>.

Dik