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Re: Seismic evaluation of an old concrete building

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Kevin,

	You should conduct an engineering survey of the building.

	With a pacometer you can find most of the reinforcing; with a few (say
at least 12) cores you can find the concrete strength of each class of
concrete used in the building; and you can do tension tests on two sizes
of reinforcing to determine Fy for small and large bar sizes.

	An historic search may also help.  Check with the architects
association, the engineering association, and the corporate registry;
follow any leads you find.  You may find a business was sold or a
retired engineer may have some files in his basement.  Some people never
get around to throwing out old files.  We hired a retired professor of
history do this for us a project in Calgary and, among other things, we
found that our ninety year old four story building was planned for six
stories.

	In the 1950s working stress method of design and manual methods of
analysis would have been used, therefore, with good luck and an honest
contractor, you may need very little reinforcing for gravity loads if
you're careful in choosing your floor area use.

	Good luck with the project.

				Regards,

				H. Daryl Richardson

Kevin Below wrote:
> 
> 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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