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Old Concrete Repair Question

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Ron,

ACI 318-56 specifies the minimum reinforcing as:

"Wherever at any section positive reinforcement is indicated by analysis, the 
amount provided shall be not less than 0.005b'd except in slabs of uniform 
thickness."  b' is the width of the web in T and I flexural members, or the 
width of rectangular flexural members.

IIRC, the major revision in ACI 318-56 from the previous edition was a change 
in increasing the shear reinforcing requirements as a result of the 
Wright-Patterson AFB hanger problems (caused by a "we know more than all 
those old guys so we can make drastic changes in the Code and use less 
reinforcing" mindset).

Concrete strengths were typically 2,000 and 2,500 psi.  fsubc was .45f'subc.

Allowable stresses in reinforcing were:

   20,000 psi for intermediate and hard grade
   18,000 psi for structural grade

Intermediate grade was the common grade, IIRC.

ACI 318-56 told you everything that you needed to know about concrete design 
in 67 pages (5 X 9, not 8.5 X 11).

Hope this helps.

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

Ron Martin wrote:

>>I have a project with an older building (built in 50s I think) that has 
some of the concrete spalling off .  The building is a concrete beam/column 
system with about 6" concrete walls and concrete roof.  To date, all I see is 
the clear cover spalling off the main beams and some roof purlins/joists.  I 
do not see any major damage to the section other than this spalling.  It is 
spalling back to the tension reinforcing/stirrups.  

Any good suggestions for providing protection of the steel?.  The inside of 
the building has fairly high humidity.  Water is used in their process.  

Also, does anyone have an idea what was "considered" minimum reinforcing back 
in the 50s.  We do not know what reinforcing was used during the original 
construction. I was wanting to estimate the beam strength based on current 
code requirements.<<