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PROCEEDINGS OF THE ELEVENTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping
The Performance Assessment of a Multi-Span, Box Girder Reinforced Concrete Bridge with and without Seismic Isolation
M. Borekci1, M. Altun2 and G. Arslan1
1Civil Engineering Department, 2Institute of Science & Technology,
M. Borekci, M. Altun, G. Arslan, "The Performance Assessment of a Multi-Span, Box Girder Reinforced Concrete Bridge with and without Seismic Isolation", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 291, 2012. doi:10.4203/ccp.99.291
Keywords: earthquake, bridge, performance assessment, seismic isolation, damage.
A destructive earthquake causes structural damage and the damage occurs because of hysteretic energy and inelastic deformations . However, some structures must remain stable and also suffer limited damage after a destructive earthquake, such as bridges. Seismic isolations are helpful in decreasing the effects of earthquake loads on structures, especially on bridges.
This paper investigates earthquake performance of a multi-span, box girder reinforced concrete bridge with and without isolation. A bridge is typically isolated immediately below the superstructure and the purpose of the isolation is to protect the elements below the isolators by reducing the inertia loads transmitted from the superstructure . Lead rubber bearings (LRB) were used as isolators and they were designed according to AASHTO . Performance assessment was applied to the bridges for determining the responses of the un-isolated and isolated bridges. Performance assessment was conducted based on linear elastic method, nonlinear static method (pushover analysis) and nonlinear time history analysis which are defined in the Turkish Earthquake Code (TEC) 2007 . According to the linear elastic method, the effect/capacity ratio (r) of the columns is the damage measure. Push-over analysis and nonlinear time history analysis were performed for both transverse and longitudinal directions.
The bridge has six 30.10 m long spans, the deck width is 30.90 m and the height of the piers is 8.60 m. The main girder is box shaped and the section of the piers is solid polygon section.
The performance level of the un-isolated bridge is collapse prevention for the linear elastic method and the nonlinear static method and it is life safety for the nonlinear time history analysis in the transverse direction. The performance level of the isolated bridge is immediate occupancy the in transverse direction. The performance level of the isolated and un-isolated bridge is immediate occupancy for all performance assessment methods in the longitudinal direction.
The period of the first mode of the un-isolated bridge is 0.80 sec and the period of first mode of the isolated bridge is 1.47 sec. Isolation is very important to reduce the damage and it is beneficial to use isolation for meeting the requirements of target performance level. Seismic isolation can reduce the inertia forces of the piers of the bridge by allowing the superstructure to displace. However, the horizontal displacement capability of the LRB should meet the displacement demand of the earthquake.
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