Abstract :
Changes in the 2005 edition of the National building code of Canada resulted in an increase in earthquake hazard for some regions in Canada. This project studied the impact of this increase on a selected highway bridge. A seismic retrofit scheme, using carbon-fiber-reinforced polymers (CFRPs), was developed and applied to the selected highway bridge bent. The retrofitting technique is based on specific performance criteria under which the retrofitted structure must meet prescribed ductility levels corresponding to selected seismic events, and its design includes a new confinement model for reinforced-concrete columns wrapped with CFRP. Using this performance-based approach, the amount of required composite materials to achieve the specified criteria was found to be much more economical when compared with the ductility requirements in the 2000 edition of the Canadian highway bridge design code. The performance of the retrofitting technique was evaluated by pseudo-dynamic tests carried out on a 1:3 scale model of one of the bridge bents. Using the substructuring approach, the remainder of the structure was modeled, and the bridge bent was subjected to increasing levels of seismic loading, corresponding to various limit states of the bridge. The measured response of the test specimen compared well with the predictions of a three-dimensional (3D) nonlinear finite-element model calibrated with dynamic properties obtained from on-site ambient vibration tests. During the highest intensity test corresponding to a return period of 2500 years for a region of high seismieity, the CFRP retrofit showed no sign of distress, and the strain values measured on the fibers were very low, indicating that the performance-based design procedure is conservative. Key words: highway bridge, reinforced concrete, seismic retrofit, performance objectives, damage criteria, fiber- reinforced polymer, large-scale test, pseudo-dynamic test, substructuring test, nonlinear modeling. Les changements apportes dans la derniere edition du Code National du Bdiimem ont entralne une augmentation de l'alea sismique considere pour plusieurs regions. Une methode de di mens ion nement de rehabilitation sismique a l'aide de polymeres renforces de fibres de carbone (PRFC) a ete optimisee afin d'etudier l'impact de cette augmentation sur les appuis d'un pont d'etagement typique. La methode de rehabilitation est basee sur des criteres de performance specifiant les niveaux de ductilites correspondant a differents niveaux d'intensites sismiques. La methode inclut un nouveau modele de confinement des sections en beton arme a l'aide de PFRC. La quantite de PRFC calculee a l'aide de cette approche a la performance est beaucoup plus economique que la quantite qui serait requise afin de rencontrer le taux de confinement requis dans la zone de rotule plastique tel que present dans le Code canadien de calcul des ponts routiers, 2000. La rehabilitation a l'aide de PRFC a ete validee par la realisation d'essais pseudo-dynamiques par sous-structures sur un modele a echelle 1/3 du viaduc choisi. Selon l'approche par sous-structures, la superstructure a ete modelisee et un modele a echelle 1/3 de l'appui du pom a ete constant en laboraloire. L'ensemble a ete soumis a des niveaux croissants de chargemeni sismique, correspondant a differents etats-limiles du pont. La reponse mesuree du specimen a ele comparee aux previsions d'un modele 3D par elements finis non-lineaire lequel a ete prealablement calibre avec les proprietes dynamiques obtenues a partir d'essais dynamiques sous vibrations ambiantes realises in situ. Pendant l'essai d'intensite sismique la plus elevee correspondanl a une periode de retour de 2500 ans pour la region d'activite sismique elevee, le PRFC n'a montre aucun signe d'endommagement et les valeurs de deformations mesurees sur les fibres etaient tres basses, indiquant que la methode de rehabilitation des poteaux a l'aide de PRFC proposee est conservatrice. Mots-cles: viaduc, beton arme, refection parasismique, objectifs de performance, criteres d'endommagement, polymeres renforces de fibres, essais a grande echelle, essais pseudo-dynamiques, essais par sous-structures, modelisation nonlineaire.