Higher-mode effect on the seismic responses of buildings with viscoelastic dampers

• Published in: Earthquake Engineering and Engineering Vibration 2002-06, Vol.1 (1), p.119-129
• Main Authors: Tsai, Meng-Hao, Chang, Kuo-Chun
• Format: Article
• Language: English
• Subjects: analysis; dampers; Damping; Earthquakes; effect; higher-mode; Seismic engineering; Seismic response; Seismology; viscoelastic
• ISSN: 1671-3664; 1993-503X
• DOI: 10.1007/s11803-002-0015-z

In conventional modal analysis procedures, usually only a few dominant modes are required to describe thedynamic behavior of multi-degrees-of-freedom buildings. The number of modes needed in the dynamic analysis depends on thehigher-mode contribution to the structural response, which is called the higher-mode effect. The modal analysis approach,however, may not be directly applied to the dynamic analysis of viscoelastically damped buildings. This is because the dynamicproperties of the viscoelastic dampers depend on their vibration frequency. Therefore, the structural stiffness and dampingcontributed from those dampers would be different for each mode. In this study, the higher-mode effect is referred to as theresponse difference induced by the frequency-dependent property of viscoelastic dampers at higher modes. Modal analysisprocedures for buildings with viscoelastic dampers distributed proportionally and non-proportionally to the stiffness of thebuildings are developed to consider the higher-mode effect. Numerical studies on shear-type viscoelastically damped buildingmodels are conducted to examine the accuracy of the proposed procedures and to investigate the significance of the higher-modeeffect on their seismic response. Two damper models are used to estimate the peak damper forces in the proposed procedures.Study results reveal that the higher-mode effect is significant for long-period viscoelastically damped buildings. Thehigher-mode effect on base shear is less significant than on story acceleration response. Maximum difference of the seismicresponse usually occurs at the top story. Also, the higher-mode effect may not be reduced by decreasing the damping ratioprovided by the viscoelastic dampers. For practical application, it is realized that the linear viscous damping model withoutconsidering the higher-mode effect may predict larger damper forces and hence, is on the conservative side.