Suitability of numerical modelling approach of an integral bridge for strengthening of RC pile foundation using SSI

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Integral Abutment Bridges (IABs) have become widely popular in the recent years due to the absence of bearings at the junction of bridge deck and bridge abutment. That leads to a reduction in the overall maintenance cost of the bridge. However, the monolithic action of deck-abutment junction changes the behaviour of the overall bridge under temperature loading and earthquake shaking. In an integral abutment bridge, bearings may be absent at the locations of the piers also. Then, the bridge is known as a fully integral bridge. In such a bridge, the behaviour of the bridge tends to follow frame-type action with all the junctions of the deck and the vertical members acting as monolithic units. Although, past studies have been carried out on behaviour under temperature variation for both the types of bridges, detailed investigations of seismic behaviour of the bridge with different modelling approaches of soil-structure interaction, have not been carried out. Also, the pile foundations below bridges have been observed to undergo failure during past earthquakes and this necessitates further investigations. All these provide the motivation for the current study.In the present study, a multi-span RC integral bridge on RC pile foundation is first modelled using an open source program, OpenSees, with stratified foundation soil. For modelling Soil-Structure Interaction (SSI), two approaches are implemented separately, namely (a) soil domain approach in which the soil is modelled as a continuum, and (b) spring-dashpot approach in which the lateral strength and stiffness of the soil are modelled considering Beam on Dynamic Winkler Foundation concept. Based on the site details (the real bridge site is located in California, USA, from which the bridge characteristics have been taken), seven ground motions are selected from a strong ground motion database by matching of mean displacement spectrum for all the ground motions with a target spectrum. Under the selected site-specific ground motions, nonlinear time history analyses are carried out for different models with changes in boundary conditions at the bottom of the piers, presence or absence of backfill soil and the two different SSI modelling approaches.
Supervisor: Kaustubh Dasgupta