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Seismic evaluation of an old concrete building

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Talking about flow charts...

I would like to work out a method for approaching the problem of
evaluating the seismic 'capacity' of a reinforced concrete building
built around 1950 in Quebec, Canada.
That is a high risk zone (for Canada)  Za = 4,   Zv = 3.

Actually, the context is that this building has been designed and used
as a school, and now the City wants to know if it can be recycled as a
library.  This means a higher floor live load, so I need to evaluate the
cost of the required reinforcement, in order to help make the decision
to demolish or reinforce.  Once we make major modifications like
reinforcing, we would also need to make it satisfy the current code with
regards to seismic resistance.

Of course, I have no drawings showing the existing steel reinforcement.

This is the first time I have had to do a seismic evaluation, so I have
been trying to work out how to go about it.

The building is a 2-story frame, no shear walls, floor slabs are
one-way, and there are beams on all column lines in both directions.
There is also a line of beams in the longitudinal direction mid-way
between column lines.

Step 1.  Evaluate the base and story shears according to code, assuming
a non-ductile concrete frame.
Step 2.  If I knew the reinforcement, I could check the columns and
beams for adequate strength.  But of course, I don't, so...
Step 3.  No choice but to add some sort of bracing (ductile ?) to resist
the seismic loads, assuming no contribution from the existing members.
Is that right ?

What sort of choices do I have for bracing systems in this case?  I have
searched on Intenet, as well as in my concrete books.  Nada.

If I understand the code correctly, I do not really need to provide
ductility for this building if I calculate it as a non-ductile frame.
So would diagonal steel bracing in the appropriate places be sufficient?

Any comments or guidance would be appreciated.


Kevin Below
Génécor inc., Québec



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