Concrete in Compression
It is generally accepted that the behavior of a reinforced concrete member under load depends on the stress–strain relationship of the materials, as well as the type of stress to which it is subjected.
With concrete used principally in compression, the compressive stress–strain curve is of primary interest.
The compressive strength of concrete is denoted fc′ and is assigned the units pounds per square inch (psi). For calculations, fc′ is frequently used with the units kips per square inch (ksi).
A test that has been standardized by ASTM C39 is used to determine the compressive strength ( fc′) of concrete. The test involves compression loading to failure of a specimen cylinder of concrete. The compressive strength so determined is the highest compressive stress to which the specimen is subjected. Note in Figure 1 that fc′ is not the stress that exists in the specimen at failure but that which occurs at a strain of about 0.002.
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