Displacement-Based Design of Continuous Concrete Bridge under Transverse Seismic Excitation

Student: Juan Camilo Ortiz Restrepo
Supervisors: Prof MJN Priestley, Prof Gian Michele Calvi

ABSTRACT

In this work a displacement-based design procedure for multi-span reinforced concrete bridge structures when subjected to seismic action in the transverse direction is presented. The procedure, initially proposed by Priestley [Priestley, 1993], is reviewed and some improvements are implemented. The design methodology is then applied to different possible bridge configurations. The accuracy of the method in terms of reaching the target displacements under the design earthquake level is then assessed using inelastic time-history analysis. Discussion of the appropriate level of damping to be considered in the inelastic time-history analysis of this type of structures is provided based in a recent a recent work developed at the ROSE School on equivalent damping for displacement-based design applications [Grant et al., 2004].

Dynamic amplification of the deck transverse moments is investigated and compared with analytical results using different variations of the modal superposition approach. What has been called the “Effective Modal Superposition,” is then proposed as an efficient method to account for higher mode effects on the deck transverse moment distributions.

A comparison of the direct displacement-based design and the force-based design, also assessed with time history analysis, is carried out for the different bridges configurations. Results in terms of pier ductility demands, displacements, deck moments and longitudinal steel reinforcement ratios are presented and discussed.

Finally, some analyses of a Rail Bridge configuration with lower deck transversal stiffness are presented to provide an idea of the scope and applicability of the design procedure under different conditions to those assumed for the initial designs.

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