Modification of the ACI rectangular stress block for high-strength concrete

Most concrete codes do not explicitly cover concrete with strengths above 50-60 MPa (7000 to 9000 psi). Compression stress blocks from three current codes that do allow design for high-strength concrete (SC) sections are presented. Comparisons of test data from the literature to strengths calculated using the current ACI rectangular stress block indicate it is not conservative for high strength concrete column sections failing in compression. New equations for the parameters that define the ACI rectangular stress block are suggested and compared to tests.