Limit State Design in The United States
The United States has been particularly slow to adopt Limit State design (known as Load and Resistance Factor Design in the US). Design codes and standards are issued by diverse organizations, some of which have adopted Limit States Design, and others have not.
The ACI 318 Building Code Requirements for Structural Concrete uses Limit state design.
The ANSI/AISC 360 Specification for Structural Steel Buildings, the ANSI/AISI S-100 North American Specification for the Design of Cold Formed Steel Structural Members, and The Aluminum Association's Aluminum Design Manual contain two methods of design side by side:
- Load and Resistance Factor Design (LRFD), a Limit States Design implementation, and
- Allowable Strength Design (ASD), a method where the nominal strength is divided by a safety factor to determine the allowable strength. This allowable strength is required to equal or exceed the required strength for a set of ASD load combinations. ASD is calibrated to give the same structural reliability and component size as the LRFD method with a live to dead load ratio of 3. Consequently, when structures have a live to dead load ratio that differs from 3, ASD produces designs that are either less reliable or less efficient as compared to designs resulting from the more rational LSD method.
In contrast, the ANSI/AWWA D100 Welded Carbon Steel Tanks for Water Storage and API 650 Welded Tanks for Oil Storage still use allowable stress design.
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