Seismic reliability assessment of base-isolated bridges in Quebec

The aim of this work is to estimate the seismic reliability of a simple typical two-span lifeline base-isolated bridge designed to behave essentially elastic or as per the Canadian Highway Bridge Design Code, for seven localities in Quebec. Two limit states are considered for possible failure due to unacceptable damage: flexure at the pier-base and displacement within the seismic isolation systems (SIS). The main problem random variables considered and modeled are seismic hazard, temperature, pier base dimensions, and material mechanical properties. The Monte Carlo method was used to evaluate the probability of failure and the reliability of each limit state. Preliminary results reveal that notwithstanding the large temperature and seismic hazard variabilities between the seven sites in Quebec, the global bridge reliability indices are almost uniform, approximately 3.45 [+ or -] 0.02. Furthermore, the security factor (i.e., 1.25) on the SIS displacement capacity results in reliability indices for SIS displacement that are not levelled with the flexural reliability indices and requires further examination and consideration. Key words: limit states design, seismic base isolation, low temperatures, reliability-based approach, bridges. Le but de ces travaux est d'estimer la fiabilite sismique d'un simple pont a deux travees, isole a la base, concu pour se comporter essentiellement elastique ou conformement au Code canadien sur le calcul des ponts routiers, pour sept localites du Quebec. Deux etats limites sont consideres pour une defaillance possible causee par des dommages inacceptables : par flexion a la base du pilier et par deplacement a l'interieur du systeme d'isolation sismique (SIS). Les principales variables aleatoires du probleme considerees et modelisees sont: l'alea sismique, la temperature, les dimensions de la base du pilier et les proprietes mecaniques des materiaux. La methode Monte Carlo est utilisee pour evaluer la fiabilite de chaque etat limite et la probabilite de defaillance. Les resultats preliminaires revelent que malgre les grandes variations de temperature et de l'alea sismique entre les sept sites au Quebec, les indices de fiabilite globaux du pont sont presque uniformes, autour de 3,45 [+ or -] 0,02. De plus, le facteur de securite (c.-a-d. 1,25) concernant la capacite de deplacement des SIS entraine des indices de fiabilite pour le deplacement des SIS qui ne sont pas niveles par rapport aux indices de fiabilite de flexion et qui doivent faire l'objet d'un examen plus approfondi. [Traduit par la Redaction] Mots-cles: conception aux etats limites, isolation sismique de la base, basses temperatures, approche fondee sur la fiabilite, ponts.
1. Introduction The seismic isolation (SI) of bridges is an earthquake protection method that aims to reduce seismic forces by decoupling the structures of the bridge from ground accelerations during [...]