EQUIVALENT VISCOUS DAMPING EQUATIONS FOR DIRECT DISPLACEMENT BASED DESIGN

Abstract

Estimation of equivalent viscous damping is an important step in the methodology of the direct displacement based design. Errors in the estimation of this parameter may lead to consequent errors in the ductility demand of the designed elements. Equivalent viscous damping estimated by Jacobsen's approach for steady-state harmonic response are compared with effective damping factors obtained from an iterative procedure using time — history analyses of single-degree-of-freedom systems. In order to separate the effects of elastic-viscous and hysteretic damping the designs and analyses were carried without elastic viscous damping. Six hysteretic models representing a wide range of hysteretic energy absorption characteristics and six artificial records were used in the analysis. It is found that in general Jacobsen's approach overestimates the values for equivalent viscous damping. Based on the analytical results, modified design equations for equivalent viscous damping are proposed.