STRUCTURAL CONTROL AND HEALTH MONITORING Struct. Control Health Monit. 2006; 13:775–791 Published online 16 November 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/stc.111 Negative stiffness friction damping for seismically isolated structures Hirokazu Iemura, Akira Igarashi, Mulyo Harris Pradono and Afshin Kalantari* ,y Department of Urban Management, Kyoto University, Kyoto 606-8501, Japan SUMMARY Research shown in this paper is focused on the development of an autonomous semi-active control laws as simplified semi-active control algorithms for seismic response reduction. The strategy of the methods is to produce desirable hysteretic loops to absorb as much energy as possible by semi-active devices. The control method requires information only on the device’s displacement and velocity. The hysteretic loops produced by the semi-active control herein provide energy absorption capacity similar to those by friction dampers, while minimizing the disadvantages of the friction dampers, such as residual displacement after strong earthquakes and the generation of high-frequency in the damping forces. The structure used for numerical simulation is the benchmark problem for control of base-isolated buildings. The results show that the simplified control strategy is effective for a variety of ground motions. Copyright # 2005 John Wiley & Sons, Ltd. KEY WORDS: simple semi-active control; hysteretic loops; isolated structures; friction-type damper INTRODUCTION Owing to recent developments of sensing and digital control techniques, active and semi-active control methods for reduction of the dynamic response of structures are emerging and some are being implemented in buildings and bridges. In particular, semi-active control is a promising approach for seismic response reduction in which the control offers the adaptability of active control without requiring the associated large power sources [1–10], since the external energy is used to modify only the dynamic properties (e.g. stiffness, damping, and friction level) of the semi-active device during an earthquake. Therefore, the semi-active control devices can be considered as controllable passive devices. The problem lies in what algorithm should control this device so that the structural response is favorable under earthquake excitation. In ensuring proper seismic performance of structures, the earthquake input energy absorption capability of structural components described by hysteretic loops plays the key role. Members Received 15 December 2004 Revised 28 March 2005 Accepted 28 May 2005 Copyright # 2005 John Wiley & Sons, Ltd. y E-mail: aphsheen@catfish.kuciv.kyoto-u.ac.jp *Correspondence to: Afshin Kalantari, Structural Dynamics Laboratory, Department of Urban Management, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto 606-8501, Japan.