New PEER Report 2020/01: "Modeling Viscous Damping in Nonlinear Response History Analysis of Steel Moment-Frame Buildings: Design-Plus Ground Motions"

June 11, 2020

PEER has just published Report No. 2020/01: "Modeling Viscous Damping in Nonlinear Response History Analysis of Steel Moment-Frame Buildings: Design-Plus Ground Motions." It was authored by Xin Qian, John A. Martin and Associates; Anil K. Chopra and Frank McKenna, University of California, Berkeley.

Visit the PEER publications page to download a free color pdf of the document.


Summary

This report investigates the question: can seismic demands on steel moment-frame buildings due to Maximum Considered Earthquake (MCER) design-level ground motions [2% probability of exceedance (PE) in 50 years] be estimated satisfactorily using linear viscous damping models or is a nonlinear model, such as capped damping, necessary? This investigation employs two models of a 20-story steel moment-frame building: a simple model and an enhanced model with several complex features. Considered are two linear viscous damping models: Rayleigh damping and constant modal damping; and one nonlinear model where damping forces are not allowed to exceed a pre-defined bound.

Presented are seismic demands on the building due to two sets of ground motions (GMs): MCER design-level GMs (2% PE in 50 years) and rarer excitations (1% PE in 50 years); and even more intense GMs. Based on these results, we do not recommend Rayleigh damping for use in nonlinear response history analysis (RHA) of buildings. Recommended instead is constant modal damping, which also is available in commercial computer codes. Although satisfactory for estimating seismic demands for MCER design-level motions and even more intense GMs, this damping model may not be appropriate for extreme motions that deform the structure close to collapse.