Evaluation of Iterative Displacement Based Design and Evaluation Methodologies for Bridges Using Simplified Models

Abstract eng:
In this paper, the aims and limitations of current seismic evaluation and design practice and the tendencies of the displacement-based seismic evaluation/design of bridges are discussed. From it, two evaluation/design methods consistent with the performance based seismic design philosophy are proposed. The most effective widely used approaches for the Displacement Based Design of bridges are based on the use of secant stiffness and equivalent viscous damping for the piers, both evaluated at maximum pier displacement, in this paper the stiffness and energy dissipation characteristics, necessary to estimate these parameters, are obtained for reinforced concrete hollow rectangular bridge piers. This work involves the use, first of a continuous non-linear behaviour section model and then a pier model based on the plastic hinge approach and on the results obtained by the section model of the previous step. The first method proposed closely follows current linear displacement based procedures with improvements in the way the equivalent viscous damping and stiffness of the pier sections of a bridge are evaluated. This method takes into consideration the contribution of higher modes of vibration by using for the calculation of performance the complete substitute structure instead of an equivalent single degree of freedom system. The other method, evolution of a previously developed method based on the capacity curve, considers in a direct way the non-linear behaviour of the piers by calculating the nonlinear capacity curve of the structure and deriving from it, the response curve of a reference SDOF from which the overall performance of the structure is determined. It is shown that in both methods proposed the design approach follows in an inverse manner the evaluation approach. To illustrate the application of the DBE/D methods is carried out by applying the evaluation/design approach to four typical reinforced concrete multi-span bridge structures designed in accordance with the Eurocode 8. For comparison purposes, results of non-linear step by step analyses of the chosen examples are also presented.

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