Two design philosophies have long been prevalent:
Allowable Stress Design
Allowable stress design (ASD) was the principal method used from the early 1900s until the early 1960s. ?ACI 318-56 was the first standard to officially recognize and permit the use of strength design (SD). ?Starting from the 1963 edition of ACI 318, there was a rapid transition to strength design, largely because of its rational approach and provision of better safety and reliability at the strength limit state.