Page 385 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

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LATERAL-FORCE DESIGN

LATERAL-FORCE DESIGN 8.39

FIGURE 8.20 Sidesway of a two-story frame subjected to horizontal and vertical loads. (a) Position of deflected
structure for drift ∆. (b) Curves show relationship of horizontal force and drift with and without the P−∆ effects.

Rehabilitation of Buildings,” Federal Emergency Management Agency, Washington, D.C., 2002)
focuses on this design concept, and recognizes two nonlinear analysis methods for evaluation of seis-
mic performance of buildings. These are the nonlinear static procedure (NSP) and the nonlinear
dynamic procedure (NDP). The NSP is commonly known as a pushover analysis, in which a given
load pattern is applied to the structure, and the sequence of yielding and deterioration is simulated by
increasing the structural deflections and changing the stiffness and resistance, while retaining the
shape of the lateral load distribution. Linear elastic and nonlinear analysis computer programs may be
employed for the NSP method. Local deformation demands are determined from the local pushover-
analysis deformation associated with a global deflection level, which is correlated to the predicted
deformation demand from a simplified response-spectrum analysis. Multiple-load patterns are usually
employed because a single-load pattern may shield a critical element from inelastic deformation.

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