JOURNAL OF STRUCTURAL CONTROL J. Struct. Control 2002; 9: 189–204 (DOI: 10.1002/stc.12) Passive and semi-active seismic response control of a cable-stayed bridge Hirokazu Iemura and Mulyo Harris Pradono* ,y Department of Civil Engineering Systems, Kyoto University, Kyoto 606-8501, Japan SUMMARY Effectiveness of passive and semi-active seismic response control on a cable-stayed bridge was studied by numerical analyses. An existing cable-stayed bridge which has fixed-hinge connections between deck and towers is modeled and its connections were replaced by isolation bearings and dampers. The isolation bearings are of elastic and hysteretic type. The dampers are of linear and variable type. The variable damper uses semi-active control that incorporates a pseudo-negative stiffness algorithm. A pseudo- negative stiffness hysteretic loop produced by the variable damper, combined with a positive stiffness curve of the deck-tower connections, creates nearly rigid–perfectly plastic force–deformation characteristics with a large damping ratio. The damping ratio for the main mode of the bridge for both passive and semi-active control was also calculated. Soil-structure interaction and three-dimensional effects on structural responses were studied. Copyright # 2002 John Wiley & Sons, Ltd. KEY WORDS: cable-stayed bridge; passive and semi-active control; pseudo-negative stiffness; damping ratio; soil-structure interaction INTRODUCTION Tempozan Bridge [1], built in 1988, is a three-span continuous steel cable-stayed bridge which is situated on reclaimed land and crosses the mouth of the Aji River, Osaka, Japan. The total length of the bridge is 640 m with a center span of 350 m, and the length of the side spans are 170 and 120 m (Figure 1). The main towers are A-shaped to improve the torsional rigidity. The cable in the superstructure is two-plane fan pattern multi-cable system with nine stay cables each plane. The bridge is supported on 35m-thick soft layer and the foundation consists of cast-in- situ RC piles of 2 m diameter. The main deck is fixed at both towers to resist horizontal seismic forces. The bridge is relatively flexible with a predominant period of 3.7 s. As to the seismic design in the transverse direction, the main deck is fixed at the towers and the end piers. Owing to severe damage to many bridges caused by the Hyogo-ken Nanbu Earthquake in the Kobe area (which is close to Osaka) in 1995, very high ground motion (level II design) is now required in the new Japanese bridge design specification set in 1996, in addition to the relatively frequent earthquake motion (level I design) by which old structures were designed and Copyright # 2002 John Wiley & Sons, Ltd. Received 17 September 2002 *Correspondence to: Mulyo Harris Pradono, Structural Dynamics Laboratory, Department of Civil Engineering Systems, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto 606-8501, Japan. y E-mail: pradono@catfish.kuciv.kyoto-u.ac.jp