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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.
Equivalent lateral force and modal analysis procedures for yielding buildings with damping systems were developed, validated,and incorporated in
the 2000 NEHRP Provisions. The technical basis for each procedure is described 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 arepresented. [DOI: 10.1193/1.1622391]
Guidelines for the implementation of energy dissipation or damping devices in new
buildings were first proposed in 1993 by the Structural Engineers Association of Northern 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 interest 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 dissipation of earthquake-induced energy into the (disposable) dampingdevices and away from
components of the gravity load-resisting system, thereby reducing repair costs and business interruption following severe earthquake shaking.
The SEAONC guidelines were developed on the basis that the primary lateral forceresisting 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:

Associate Professor, Department of Civil, Structural and Environmental Engineering, University at Buffalo,
State University of New York, Buffalo, NY 14260
Professor and Chairman, Department of Civil, Structural and Environmental Engineering, University at Buffalo, State University of NewYork, Buffalo, NY 14260
Professor and Director, Centro Experimental de Ingeniera, Universidad Tecnologica de Panama, Panama, Rep.
de Panama
Principal, ABS Consulting, Irvine, CA 92602
Lecturer, Department of Civil Engineering, Higher Technical Institute, 2152 Nicosia, Cyprus


Earthquake Spectra, Volume 19, No. 4, pages 959–980, November 2003; © 2003, EarthquakeEngineering Research Institute



response-spectrum analysis, linear response-history analysis, and nonlinear responsehistory analysis. The linear procedures could only be used with velocity-dependent (e.g.,
viscous or viscoelastic) dampers in building frames that would remain elastic for designearthquake shaking. Nonlinear response-history analysis was mandated for theimplementation of displacement-dependent dampers or for yielding frames incorporating
velocity-dependant dampers. Detailed procedures for the prototype testing of damping
devices were also presented in the SEAONC guidelines.
In the mid 1990s, the Federal Emergency Management Agency (FEMA) funded the
development of guidelines for the seismic rehabilitation of buildings. New methods of
seismicanalysis and evaluation were presented in FEMA-273 and FEMA-274. The four
new analysis methods presented in FEMA-273 and FEMA-274 were the Linear Static
Procedure, the Linear Dynamic Procedure, the Nonlinear Static Procedure, and the Nonlinear Dynamic Procedure. All four methods were displacement based and all directly or
indirectly made use of displacement-related information for component...