General Order 64-A

Section IV

Strength Requirements For All Classes Of Lines

48.3    Reinforced Concrete

The ultimate strength of materials used shall not exceed values commonly accepted as good practice.

In the absence of other data, the following ultimate strengths may be used for materials of concrete structures:

Steel.  Tension or compressions, 55,000 pounds per square inch.

Concrete mixture: 1-2-4 Portland cement.

Compression:

900 pounds per square inch in 7 days after mixing.

2,400 pounds per square inch in 30 days after mixing.

3,100 pounds per square inch in 90 days after mixing.

4,400 pounds per square inch in 6 months after mixing.