Simplified methods for design of base‐isolated structures in the long‐period high‐damping range

A recent trend in the design of base-isolated structures is the extension of the natural period and the incorporation of high damping. This paper shows that the existing simplified methods perform less accurately in this field of application, mainly due to inappropriate use of spectral data and insufficiently adjusted equivalent models. The paper proposes new period-dependent concepts to reduce pseudo-acceleration spectra and to transform these values into total accelerations with respect to the viscous damping ratio. The model of equivalent damping is adjusted to reflect several period-dependent effects. The estimation of the accelerations in MDOF systems is based on additional period shifts. All modifications are derived for a simplified linear approach based on eigenforms, and a non-linear approach based on pushover and capacity spectrum analysis. To illustrate observed problems and to demonstrate the capabilities of the proposed concepts, example structures are studied in detail. Furthermore, intensive statistical tests prove the effectiveness of the modifications in a wide parameter range and show considerable improvements over traditional approaches. Copyright © 2005 John Wiley & Sons, Ltd.

[1]  Robert D. Hanson,et al.  Seismic design with supplemental energy dissipation devices , 2001 .

[2]  Julian J. Bommer,et al.  The effective number of cycles of earthquake ground motion , 2005 .

[3]  R. S. Jangid,et al.  Base isolation for near‐fault motions , 2001 .

[4]  Yu-Yuan Lin,et al.  Study on Damping Reduction Factor for Buildings under Earthquake Ground Motions , 2003 .

[5]  Anil K. Chopra,et al.  A modal pushover analysis procedure for estimating seismic demands for buildings , 2002 .

[6]  Nelson Lam,et al.  The ductility reduction factor in the seismic design of buildings , 1998 .

[7]  Kuo-Chun Chang,et al.  An improved capacity spectrum method for ATC‐40 , 2003 .

[8]  Izuru Takewaki,et al.  Frequency domain modal analysis of earthquake input energy to highly damped passive control structures , 2004 .

[9]  Farzad Naeim,et al.  Design of seismic isolated structures : from theory to practice , 1999 .

[11]  Eduardo Miranda,et al.  Site-Dependent Strength-Reduction Factors , 1993 .

[12]  Julian J. Bommer,et al.  Scaling of spectral displacement ordinates with damping ratios , 2005 .

[13]  Hui Li,et al.  Effect of non‐proportional damping on seismic isolation , 2002 .

[14]  Kazuhiko Kawashima,et al.  MODIFICATION OF EARTHQUAKE RESPONSE SPECTRA WITH RESPECT TO DAMPING , 1984 .

[15]  James M. Kelly,et al.  The role of damping in seismic isolation , 1999 .

[16]  Anil K. Chopra,et al.  A modal pushover analysis procedure to estimate seismic demands for unsymmetric‐plan buildings , 2004 .

[17]  Peter Fajfar,et al.  Consistent inelastic design spectra: Strength and displacement , 1994 .

[18]  Vinay K. Gupta,et al.  Scaling of strength reduction factors for degrading elasto-plastic oscillators , 2005 .

[19]  A. Papageorgiou,et al.  Near‐fault ground motions, and the response of elastic and inelastic single‐degree‐of‐freedom (SDOF) systems , 2004 .

[20]  P. Franchin,et al.  On the accuracy of simplified methods for the analysis of isolated bridges , 2001 .

[21]  Fahim Sadek,et al.  Linear Procedures for Structures with Velocity-Dependent Dampers , 2000 .

[22]  Kuo-Chun Chang,et al.  Evaluation of damping reduction factors for estimating elastic response of structures with high damping , 2005 .

[23]  Peng Pan,et al.  BASE-ISOLATION DESIGN PRACTICE IN JAPAN: INTRODUCTION TO THE POST-KOBE APPROACH , 2005 .