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D10.B.2 Limit States Design Fundamentals

The primary objective of the Limit States Design Specification is to provide a uniform reliability for all steel structures under various loading conditions.

The Limit States Design Method uses separate factors for each load and resistance. Because the different factors reflect the degree of uncertainty of different loads and combinations of loads and of the accuracy of predicted strength, a more uniform reliability is possible.

The method may be summarized by the inequality

Yi Qi ≤ Rn FR

On the left side of the inequality, the required strength is the summation of the various load effects, Qi, multiplied by their respective load factors, Yi. The design strength, on the right side, is the nominal strength or resistance, Rn, multiplied by a resistance factor, FR.

In the STAAD implementation of the Mexican Standards, it is assumed that the user will use appropriate load factors and create the load combinations necessary for analysis. The design portion of the program will take into consideration the load effects (forces and moments) obtained from analysis. In calculation of resistances of various elements (beams, columns etc.), resistance (nominal strength) and applicable resistance factor will be automatically considered.