Nonlinear procedures for seismic evaluation of buildings

New static and dynamic displacement-based procedures have been developed by the Federal Emergency Management Agency (FEMA) for the seismic evaluation and design of buildings. The static procedures calculate displacements in y ielding buildings as the product of an elastic spectral displacement and co efficients C-i. Mean elastic and mean inelastic displacements are assumed t o be equal for elastic periods, T-0, greater than the characteristic site p eriod, T-g. The data presented in this paper and elsewhere support this ass umption for values of the strength ratio greater than or equal to 0.20. For T-0 less than or equal to T-g, mean inelastic displacements can substantia lly exceed mean elastic displacements for all values of the strength ratio; FEMA 273 accounts for this observation by the coefficient C-1. However, th e FEMA 273 cap on C-1 (= 1.5) is not sufficiently conservative and should b e increased to 3.0 for the analysis and design of modern construction. The effects of stiffness degradation, strength deterioration and pinching are r epresented in FEMA 273 by the coefficient C-2. The values assigned to C-2 a ppear to be most reasonable. Nonlinear dynamic analysis is being widely use d to estimate maximum deformations and displacements in buildings. The valu es calculated for the maximum deformations and displacements will be depend ent upon the means used to characterize structural damping in the building frame. Although structural damping is routinely implemented through a dampi ng constant (or matrix), such an implementation will overestimate the effec ts of structural damping in a yielding building and underestimate maximum d eformations and displacements. Structural damping should be characterized b y the target damping ratio (typically 5% of critical) at the point of maxim um displacement. Copyright (C) 1999 John Wiley & Sons, Ltd.