base isolation for bridges - long duration shaking

base isolation in bridges

1. EFFECT OF MULTI-DIRECTIONAL GROUND MOTIONS ON THE PERFORMANCE OF LEAD RUBBER ISOLATORS IN BASE-ISOLATED BRIDGES Ashritha Kedarisetti University of British Columbia, Vancouver, BC, Canada Dr Carlos E Ventura University of British Columbia, Vancouver, BC, Canada

2. Motivation Previous studies: Effect of different types of earthquake ground motions on the behaviour of isolators. Comparative studies on the performance of different isolators subjected to ground motions. Present study: Investigate the hysteresis and damping properties of lead rubber isolators in brides Study the effect of the axial force demands on the anchorage systems of the isolators.

3. Description of the Bridge Three-span highway bridge – Crossing of Trent River with Highway 19 Superstructure: a) Main span – 40 m; Side span – 33 m b) Deck consists of girders and a concrete-wearing surface Substructure: Two piers with two circular columns

4. Bridge and Isolator Modelling Seismostruct is used to model the bridge Isolators are modelled as springs using zero-length elements.

5. Bridge and Isolator Modelling Bouc –Wen model Gap Element

6. Ground Motion Selection Event Magnitude Year Station Kobe, Japan 6.9 1995 TAZ Kocaeli , Turkey 7.4 1999 YPT Duzce , Turkey 7.2 1999 487 Ecuador 7.8 2016 ACHN Mexico 8.1 1985 SCT1 Peru 8.0 2007 Parcona Chile 8.8 2010 San Pedro

7. Modal Analysis of the bridge Mode Period (s) Direction Mode 1 2.58 Longitudinal Mode 2 2.48 Transverse Mode 3 2.32 Torsion Mode 4 0.45 Vertical Mode 1 Mode 2 Mode 3 Mode 4

8. Results – Axial load demands in Compression Abut 1 Isolators Pier 1 Isolators

9. Axial load demands in Compression – Mexico City_1985 Abut 1 Isolators Pier 1 Isolators

10. Results – Axial load demands in Tension KOBE_TAZ

11. Results – Hysteresis behavior of Isolators – Mexico City_1985 Ground motion applied in one direction Ground motions applied in three directions

12. Results – Isolator Damping – Chile_2010 Longitudinal direction Transverse direction (b) F igure 11 Damping in the transverse direction: (a) Chile_2010 (b) Mexico City_1985

13. Results – Isolator Damping – Mexico City_1985 (b) Figure 11 Damping in the transverse direction: (a) Chile_2010 (b) Mexico City_1985 Longitudinal direction Transverse direction

14. Conclusions Axial force demands exceed the capacity in some analyses, but determining its impact requires further study. A distorted hysteresis indicates energy dissipation in both the directions Damping produced by the isolators is not constant.

15. Recommendations Further research needs to be conducted to understand the impact of tension on anchorage systems. The results indicate the requirement for an in-depth study to understand the energy-dissipating behaviour of isolators.