Structural Dynamics & Vibration Control Lab., KAIST, Korea 1 A Comparative Study on Aseismic Performances of Base Isolation Systems for Multi-span Continuous Bridge Kyu-Sik Park, Graduate Student, KAIST, Korea Sang-Won Cho, Graduate Student, KAIST, Korea In-Won Lee, Professor, KAIST, Korea The 14 th KKNN Seminar on Civil Engineering November 5 - 7, 2001, Kyoto, Japan

Structural Dynamics & Vibration Control Lab., KAIST, Korea 2 CONTENTS  Introduction  Aseismic Base Isolation Systems  Sensitivity Analysis  Conclusions

Structural Dynamics & Vibration Control Lab., KAIST, Korea 3   A comparative study on aseismic performances of various base isolation systems (BISs) for the critical design parameters has been rarely done.   Most of previous studies are focused on the building structures in spite that BISs are widely used for the bridge structures. INTRODUCTION

Structural Dynamics & Vibration Control Lab., KAIST, Korea 4   Objective A comparative study on aseismic performances of BISs for multi-span continuous bridge for critical design parameters To evaluate aseismic performances of BISs suitable earthquake-resistance design of structures

Structural Dynamics & Vibration Control Lab., KAIST, Korea 5 M ASEISMIC BASE ISOLATION SYSTEMS 1. Pure Friction (PF) System the simplest device limits a maximum acceleration transmitted from the substructure may have an excessive defection or a residual deformation may be used economically in the simple or small- scale structure

Structural Dynamics & Vibration Control Lab., KAIST, Korea 6 Aseismic Base Isolation Systems Rubber Inner steel plate Outer steel plate Protective rubber Flange M K C 2. Rubber Bearing (RB) System widely studied and used over the world consists of alternating layers of rubber and steel plate parallel action of spring and dashpot mainly shifts natural period of the isolated structure

Structural Dynamics & Vibration Control Lab., KAIST, Korea 7 3. Lead Rubber Bearing (LRB) System widely studied and used over the world additional energy dissipation by a central lead core bilinear model of characteristic curve is used Rubber Inner steel plate Outer steel plate Protective rubber Flange Central lead core M K eff C eq Aseismic Base Isolation Systems

Structural Dynamics & Vibration Control Lab., KAIST, Korea 8 4. Resilient Friction Base Isolation (R-FBI) System parallel action of resiliency of rubber and friction of Teflon coated plate has a recovering force by rubber after sliding M K C Cover plate Central rubber core Peripheral rubber core Rubber cover Connecting plate Sliding ring Aseismic Base Isolation Systems

Structural Dynamics & Vibration Control Lab., KAIST, Korea 9 5. Electiricite De France (EDF) System consists of the elastomeric bearing and the friction plate in series behaves as a RB unit during a low-intensity earthquake may have a residual deformation during a high- intensity earthquake ` M K C Reinforced neoprene pad Friction plates Stud anchor Aseismic Base Isolation Systems

Structural Dynamics & Vibration Control Lab., KAIST, Korea 10 SENSITIVIY ANALYSIS 1. Ding-Jin Bridge a continuous bridge with 15 spans constructed in the western coast expressway in Korea the span length of bridge: 725 m the width of the superstructure: m the longitudinal slope: 0.03% Rayleigh damping with structural damping ratio of 2%

Structural Dynamics & Vibration Control Lab., KAIST, Korea 11 Sensitivity Analysis Connection element BIS element Pier element H Pier No. 7

Structural Dynamics & Vibration Control Lab., KAIST, Korea 12 Sensitivity Analysis 2. Input Earthquake Records El Centro (N00W, 1940)   PGA: g, PFR: 1~4 Hz Mexico City (N90W, 1985)   PGA: g, PFR: 0~1 Hz San Fernando (S16E, 1971)   PGA: g, PFR: 1~5 Hz PGA: Peak Ground Acceleration PFR: Predominant Frequency Range

Structural Dynamics & Vibration Control Lab., KAIST, Korea 13 Time(sec) Acceleration(g) Frequency(Hz) Magnitude Sensitivity Analysis

Structural Dynamics & Vibration Control Lab., KAIST, Korea Sensitivity Analysis Numerical simulation   variations in natural period of the isolated bridge   variations in friction coefficient of the BIS   comparative study for different earthquakes with the selected design parameters Comparisons   the peak displacement of deck to check the serviceability   the peak bending moment of the lower end of pier to check the design sectional force Sensitivity Analysis

Structural Dynamics & Vibration Control Lab., KAIST, Korea 15 Variations in natural period of the isolated bridge Sensitivity Analysis

Structural Dynamics & Vibration Control Lab., KAIST, Korea 16 as the natural period increases, the peak displacement increases whereas the peak bending moment decreases. the peak responses of bridge subjected to Mexico City earthquake are amplified in the natural period of about 2 ~ 3 sec. the peak responses of bridge with LRB system are smaller than those with a RB unit. Sensitivity Analysis

Structural Dynamics & Vibration Control Lab., KAIST, Korea 17 Natural Period(sec) Displacement(cm) Moment X10 7 (Nm) Natural Period(sec) Displacement(cm) Moment X10 6 (Nm) R-FBI System EDF System

Structural Dynamics & Vibration Control Lab., KAIST, Korea 18 the peak responses of bridge with R-FBI system - similar to the response spectrum of each earthquake for small value of friction coefficient - as friction coefficient increases, the peak responses are not sensitive to variations in the natural period. the peak responses of bridge with EDF system - shows a similar trend to those with RB and LRB systems as friction coefficient increases - if there is no sliding in the friction plates, the responses of bridge are the same as those with a RB unit. Sensitivity Analysis

Structural Dynamics & Vibration Control Lab., KAIST, Korea 19 Variations in friction coefficient of the BIS Sensitivity Analysis

Structural Dynamics & Vibration Control Lab., KAIST, Korea 20 as the friction coefficient increases, the peak displacement decreases whereas the peak bending moment increases. the most portion of the displacement is sliding deformation and the deformation of pier is negligible. Sensitivity Analysis

Structural Dynamics & Vibration Control Lab., KAIST, Korea 21 Friction Coefficient Displacement(cm) Moment X10 7 (Nm) Friction Coefficient Displacement(cm) Moment X10 6 (Nm) R-FBI System EDF System

Structural Dynamics & Vibration Control Lab., KAIST, Korea 22 the peak responses of bridge with R-FBI system - similar to those with a PF unit as friction coefficient increases - decrease as friction coefficient increases in natural period of 2 sec for Mexico City earthquake the peak responses of bridge with EDF system - when there is no sliding in the upper plate, it behaves like RB and LRB systems. - amplified like those with RB and LRB system for Mexico City earthquake Sensitivity Analysis

Structural Dynamics & Vibration Control Lab., KAIST, Korea 23 Comparative study for different earthquakes with the selected design parameters Sensitivity Analysis the procedure of selecting design parameters - calculate the ratio of the peak responses to average value according to the natural period and friction coefficient - select the value of alpha which indicates the relative importance of displacement

Structural Dynamics & Vibration Control Lab., KAIST, Korea 24 Sensitivity Analysis M ratio D ratio M ratio D ratio M ratio D ratio M ratio D ratio

Structural Dynamics & Vibration Control Lab., KAIST, Korea 25 Sensitivity Analysis the selected design parameters

Structural Dynamics & Vibration Control Lab., KAIST, Korea 26 the peak displacement of bridge with the rubber type bearing is larger than that with the friction type bearing while bending moments is smaller. the peak responses of bridge with the friction type bearing are less sensitive to substantial variations in the frequency range and intensity of earthquake excitation. for the selected design parameters - R-FBI system has the smallest peak deck displacement - EDF system has the smallest peak bending moment Sensitivity Analysis

Structural Dynamics & Vibration Control Lab., KAIST, Korea 27 residual deformation

Structural Dynamics & Vibration Control Lab., KAIST, Korea 28 CONCLUSIONS   As natural period of the isolated bridge increases and as friction coefficient of the device decreases the peak deck displacement increases the peak bending moment decreases   It is important that suitable values determined by the sensitivity analysis, be used in the design parameters of the device instead of fixed ones.

Structural Dynamics & Vibration Control Lab., KAIST, Korea 29   For the selected design parameters R-FBI system has the smallest peak deck displacement EDF system has the smallest peak bending moment Conclusions

Structural Dynamics & Vibration Control Lab., KAIST, Korea 30 Thank you for your attention.

Structural Dynamics & Vibration Control Lab., KAIST, Korea 31 the bilinear model of characteristic curve of LRB system Appendix

Structural Dynamics & Vibration Control Lab., KAIST, Korea PF System holds as long as Stick mode: Slip mode: 2. RB System 3. LRB System 4. R-FBI System holds as long as Stick mode: Slip mode: 5. EDF System Stick mode: Slip mode: holds as long as Appendix