Equivalent Lateral Force and Modal Analysis Procedures of the 2000 NEHRP Provisions for Buildings with Damping Systems Andrew S. Whittaker, a) M.EERI, Michael C. Constantinou, b) M.EERI, Oscar M. Ramirez, c) Martin W. Johnson, d) M.EERI, and Christis Z. Chrysostomou e) Equivalent lateral force and modal analysis procedures for yielding build- ings with damping systems were developed, validated, and incorporated in the 2000 NEHRP Provisions. The technical basis for each procedure is de- scribed in the paper together with the simplifications adopted for inclusion in the Provisions. Procedures for calculating the effective damping and effective period and higher mode damping ratios for buildings equipped with yielding, viscoelastic, linear viscous, and nonlinear viscous damping devices are presented. [DOI: 10.1193/1.1622391] INTRODUCTION Guidelines for the implementation of energy dissipation or damping devices in new buildings were first proposed in 1993 by the Structural Engineers Association of North- ern California (SEAONC) to provide guidance to structural engineers, building officials, and regulators who were tasked with implementing such devices in building frames (Whittaker et al. 1993). These guidelines were prepared in response to the increased in- terest shown in damping devices following widespread damage to building frames in the 1989 Loma Prieta earthquake in Northern California and the emergence of vendors of damping hardware. The intent of the authors of that document was to direct the dissipa- tion of earthquake-induced energy into the (disposable) damping devices and away from components of the gravity load-resisting system, thereby reducing repair costs and busi- ness interruption following severe earthquake shaking. The SEAONC guidelines were developed on the basis that the primary lateral force- resisting system (that is, the lateral system exclusive of the damping devices) met the strength and drift requirements of the 1991 Uniform Building Code (ICBO 1991). Three methods of analysis were prescribed for the implementation of damping devices: a) Associate Professor, Department of Civil, Structural and Environmental Engineering, University at Buffalo, State University of NewYork, Buffalo, NY 14260 b) Professor and Chairman, Department of Civil, Structural and Environmental Engineering, University at Buf- falo, State University of NewYork, Buffalo, NY 14260 c) Professor and Director, Centro Experimental de Ingeniera, UniversidadTecnologica de Panama, Panama, Rep. de Panama d) Principal, ABS Consulting, Irvine, CA 92602 e) Lecturer, Department of Civil Engineering, Higher Technical Institute, 2152 Nicosia, Cyprus 959 Earthquake Spectra, Volume 19, No. 4, pages 959–980, November 2003; © 2003, Earthquake Engineering Research Institute