SEISMIC PERFORMANCE ASSESSMENT OF A MULTI-SPAN BRIDGE WITH ELASTOMERIC AND TRIPLE FRICTION PENDULUM BEARING

Trejo C.; Melchor C.; Torres M. · World Conference on Earthquake Engineering proceedings (2021)

Resumen

In the last decade, South America has experienced a substantial increase in the use of seismic isolation devices in bridge engineering projects. This increase could be explained as a result of the outstanding performance of seismically isolated bridges in the last two major earthquakes in the region: the Maule earthquake in 2010 (Chile) and the Muisne earthquake in 2016 (Ecuador). During these main seismic events, extensive damage and even collapse were observed in some non-isolated bridges, showing that these structures are still vulnerable to strong ground motions. Since the mid-2010s, key highway infrastructure has been built in high seismic hazard zones of Peru. A partial disruption of the functionality of these bridges during severe earthquakes could mean restricted access to emergency areas. Despite the reliability of seismic isolation techniques as a seismic hazard mitigation strategy, their use in key Peruvian bridges is still limited. The aim of using seismic isolators is to shift the fundamental frequency of a structure away from the predominant energy-containing frequencies of an earthquake ground motion. As a result, reduced forces are transmitted to the substructure. Seismic isolators are also capable of providing energy dissipation with the aim of reducing the transmitted accelerations to the superstructure. The most common types of seismic isolators used in South America are elastomeric isolators and sliding isolators. In this paper, elastomeric and sliding isolation techniques were applied to a critical non-isolated multi-span bridge with the aim of undertaking a deep comparative assessment of both isolation techniques. Triple Friction Pendulum Bearings (TFPB) and Lead Rubber Bearings (LRB) were selected as representative examples of elastomeric and sliding isolators, respectively. In the design of these isolation bearings, the values of isolated periods, post-yield stiffness and yield force of the TFPB system were set to be similar to that of the LRB system. This criterion was adopted for the purpose of comparing the unique effects of each type of isolator on the seismic response of the analyzed bridge. To perform the comparative assessment, a series of nonlinear dynamic analyses were carried out considering both horizontal components of seven seismic records. In the case of the LRB, a numerical model that considers the bidirectional response of the isolator was adopted. The strength degradation due to lead-core heating effects was also taken into account during the analysis. In the modeling of the TFPB, a series model that correctly describes each of the five stages of movement developed by this isolator and its bidirectional behavior was considered. To gain a fully comprehensive understanding of the behavior of these isolators, a series of benchmark tests were reproduced to validate the numerical models adopted. Upper and lower limit analyses were performed to identify the advantages and drawbacks of each isolation system. From the obtained results, it was found that the LRB system is capable of providing more uniform and lower seismic demands into the substructure; however, it induces greater isolator displacements in comparison with the TFPB system. © The 17th World Conference on Earthquake Engineering.

Instituciones: Universidad Nacional de Ingeniería