Seismic Analysis and Parametric Study for a Continuous Seven Spans Post-Tensioned Bridge in Quito, Ecuador

A continuous post-tensioned bridge over seven spans, 27m each, was recently designed and is currently under construction in Quito, Ecuador. Located in one of the most active seismic/volcanic regions of South America, several challenges were faced during the bridge design. In addition to the limits on the deck horizontal displacement because of the adjacent buildings, a substructure system of circular columns without pier-caps or framing connections into the deck was adopted to satisfy the required vertical clearance. Consequently, the post-yield behaviour of pier reinforcement could not be allowed as a hysteretic energy dissipation system since the formation of plastic hinges at such piers impairs not only the control over deck displacement but also the stability of the bridge deck. A response spectrum analysis was first conducted on a three dimensional finite element model (3D-FEM) in order to study the relationship between superstructure, bearings, substructure and foundations as well as to obtain a preliminary design of bridge components. Thereafter, a non-linear time history analysis accompanied by a parametric study was carried out considering different types of base isolation bearings. The study emphasized that the interaction between the superstructure and substructure through the bearings is a major key to achieve the target level of energy dissipation, base shear, and deformations. Herein, the FEM, seismic analysis, as well as the part of the conducted parametric study for a flat sliding friction/spring type of bearings are presented.