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RE: concrete of forty years old

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Marino,

You are doing very well with your English.

Concrete used for engineered construction in the U.S. 40 years ago was very
good and should not have deteriorated with age.  Common 28-day concrete
strengths were 2500 psi (17 MPa), 3000 psi (21 MPa), and occasionally 3500
psi (24 MPa).  Reinforcing steel had a yield strength of either 33,000 psi
(227 MPa) or 40,000 psi (276 MPa).  Design was being transitioned from
working stress design to ultimate strength design, however, column design,
even under working stress design, was based on the ultimate strength of the
column and reduced by a safety factor.  For flexure, the maximum allowable
concrete stress was .45f'c.

If you have the original design calculations, you should be able to determine
how the building was originally designed.

HTH

By the way, I have taken the liberty of indicating in your post how I
understood your question with the word(s) included in parentheses replaced
with the words in brackets.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Marino wrote:

Excuse but my English is not good.

I will  to clarify the idea.

It is wanted to a structure of reinforcement concrete had built for forty
years to make him an (amplification) [addition]. that which (generates)
[creates] (that the solicitation) [load] increases on the structural
elements. My question is this (that) [what] properties [would] have
deteriorated or (as) [changed] considering the age of the concrete in the
calculations.

I believe that   columns you (necessary) [would need] to reinforce because the
requirements 40 years ago are not the same ones that the current. Also as
aditional information for you the construction is in a region classified
with a Z=0.4

I (wait) [hope] to have clarified the idea

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