chapter  6
28 Pages


The American Institute of Steel Construction (AISC) is a technical institute that supplies speci‡cations, codes, research, quality certi‡cation, standardization, and technical assistance to its members and the general civil engineering community. The AISC Steel Construction Manual is the general guide for steel design and construction in the United States and it is the AISC Speci‡cations for Structural Steel Buildings 360-10, which governs the design of steel members and connections. There are two design methods presented in the AISC speci‡cations. Steel design is to be

performed in accordance with either one of the provisions for these methods. The methods are (1) load resistance factor design (LRFD) and (2) allowable stress design (ASD). The required strength of structural members and their connections may be determined by elastic, inelastic, or plastics analysis for load combinations associated with LRFD or by elastic analysis for load combinations associated with ASD. In both methods, the available strength must exceed the required strength. In the ASD method, the allowable strength must equal or exceed the required strength:

R Ra n≤ Ω

where: Ra is the required strength determined by analysis for the ASD load combinations Rn is the nominal strength determined according to the AISC speci‡cations Ω is the safety factor given by the AISC speci‡cations for a speci‡c limit state

In the LRFD method, the available strength is referred to as the design strength and the provisions for LRFD are structured, so that the design strength must equal or exceed the required strength.