Seismic Reliability of Reinforced Concrete Bridge Columns Based on Local and Global Damage Approaches

Abstract eng:
The seismic energy response of a reinforced concrete bridge column is dissipated through the initiation of plastic hinges, which represent the resulting damage in the column member. The seismic design criterion SDC that is used by many building codes employs the demand/capacity ductility principle for a performance-based design, which assumes a low damage state in the member, allowing for a better serviceability of the structure after the seismic event. The damage in the plastic hinge, according to the SDC, is limited to spalling and yielding of the longitudinal reinforcement bars, but the crack growth in the column core can lead to excessive strength degradation in the hysteresis behaviour of the structure. In this paper, a dynamic non-linear analysis using the Fibre Element Method is performed to obtain the hysteretic analysis for a designed column subjected to different loading rates. A stress-based method is used to determine the local damages in the core and cover of the reinforced column. Different damage states are obtained under different loading rates. The Discrete Element/Finite Element/ method, DE/FEM, with Rotating cracke model is used as a small-scale approach, to investigate the crack growth in the critical zones with softening strains and fractured elements across the concrete column’s core and cover. Despite its excessive computation time, the DE/FEM model provides reliable information about the local damage state of the RC column core, which enhances understanding the seismic performance of the structural member. In this RC column, designed according to the SDC of the California Department of Transportation (Caltrans 2001), a large area of the column core zone at the plastic hinge is damaged when subjected to Lexington Dam, Loma Prieta, 1989, and the column loses its integrity in the plastic zone, which affects the bar/concrete bond substantially. This could lead to total collapse especially if the reinforcement bars are quite exposed and start to buckle.

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