Parametric Investigation for the Optimization of a Longitudinal Seismic Restraining System Consisting of Struts-Ties for Concrete Bridges

Abstract eng:
Seismic response of R/C bridges is an issue that has been investigated thoroughly the last decades. Many efforts have been conducted towards the enhancement of bridges seismic response and two categories of seismic design practices can be identified; seismic isolated systems and ductile systems. This paper focuses on a seismic restraining system, consisting of steel bundles, that aims on improving R/C bridges seismic response. The restraining system limits the longitudinal displacements of continuous integral concrete bridges under lateral earthquake loading. The targeted reduction of the longitudinal seismic displacements is achieved with four bundles of steel bars that act in tension and compression, as well. The steel bars of the four bundles are installed in post-tension ducts, in the superstructure of the bridge longitudinally, without bonding with the bridge’s deck concrete. The forces of the steel bundles are transferred to properly designed abutments. The study includes a parametric investigation on the area, the number and length of the steel bars for optimum results in the seismic response of a concrete bridge. A six-span concrete bridge was used as the benchmark bridge and a corresponding nonlinear finite element model was developed according to the analyses’ demands. Nonlinear analyses were performed for variable parameters, i.e. material and geometrical properties, number of spans, ground motion etc., after proper sampling. The analyses results have shown how the seismic performance of bridges varies when the area, number and length of steel bars (as restrainers) applied in each analysis case change and how the optimization for the dimensioning of the proposed system can be achieved. The parametric investigation can be the basis for a more general guideline for the design of the system. An optimized selection is found to reduce the longitudinal displacements efficiently and improve the seismic performance of bridges without introducing any structural capacity issues to the rest of the structural members of the bridge.

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