UC San Diego

The two studies within this dissertation aim to assess the seismic performance of both existing and new reinforced concrete (RC) bridge substructures, and to develop modeling tools and design procedures for new self-centering column systems for bridges.The first section of this dissertation outlines a recent study conducted to assess the seismic performance of piles in the Coronado Bay Bridge in San Diego. Three 7/9-scale pile specimens were tested, representing a prototypical Type-II pile in Pier 22. All bridge piles were constructed with precast, prestressed shells filled with cast-in-place concrete, sharing similar reinforcement details and diameter. Specimen 1 represented an as-built pile, Specimen 2 had unbonded strands in the shell over a length of 31.5 in. to simulate construction-induced damage, and Specimen 3, retrofitted with a high-strength bar, aimed to evaluate a seismic retrofit method. The study aimed to determine whether a pile with or without simulated damage could perform satisfactorily in a design earthquake event and to develop an effective seismic retrofit method if needed. Testing involved fully-reversed lateral displacement cycles up to a maximum drift ratio of 2.5%, while the drift ratio corresponding to the design earthquake response was 1.8%. The maximum net axial tension and compression applied to the piles was 575 kips during positive displacement and 910 kips during negative displacement respectively. These forces correspond to 11% and 48% of the uniaxial compressive and tensile capacity, respectively, of Specimen 1. These values were based on seismic analysis of the bridge structure performed by Caltrans. Specimen 2 revealed tension failure due to prestressing strand loss, while Specimen 3 demonstrated the effectiveness of the retrofit method in restoring performance and enhancing ductility. Recommendations for retrofit evaluations and design in the bridge are provided based on experimental data. Additionally, interaction diagrams were created to aid in the evaluation of the capacity of the piles, and understanding of how the materials within the piles behave under combined axial load and bending moment. The second section of this dissertation focuses on the design, and modeling of a novel self-centering column design for use in seismically resistant bridge structures. Two specimens were tested. The first represented an initial design created by a team at Caltrans while the second was a modified design aimed at reducing early damage induced by cyclic loading, and allowing for potential rehabilitation without the need for complete column replacement. Both specimens were constructed with cast-in-place, post-tensioned concrete, sharing similar reinforcement and column geometries. The study aimed to achieve a design for self-centering columns which would allow drifts up to 10% during a seismic event with minimal column damage. Testing involved fully-reversed lateral displacement cycles up to 10% drift, with Specimen 1 showing rebar fracture at low drift levels, whereas Specimen 2 showed that the modifications to the design allowed for the longitudinal reinforcement to assist in lateral load resistance and energy dissipation through the +10% drift cycles. Furthermore, a fiber-section model was developed to simulate the behavior of these self-centering column designs during a seismic event, and a displacement-based design methodology was developed for industry engineers to use in the design and implementation of these self-centering columns for seismically resistant bridge structures.