Aspects behavior of bridges which use different vibration isolating systems GILBERT-RAINER GILLICH; DANIEL AMARIEI; VASILE IANCU; CAMELIA STEFANIA JURCĂU Center of Advanced Research, Design and Technology - CARDT “Eftimie Murgu” University of Resita P-ta Traian Vuia 1-4, 320085 Resita ROMANIA raini@uem.ro; dan.amariei@uem.ro; v.iancu@uem.ro; c.jurcau@uem.ro http://www.uem.ro Abstract: Vibration damping represents one, if not the most important issue in order to mitigate hazards and to enhance the structure’s reliability and performances. Earthquakes represent one of the main sources of vibration which can essentially harm the infrastructures. Thus, the paper summarizes researches regarding different types of seismic isolators and their influence on the structural performances, aiming to provide technical support for seismic risk mitigation. Key-Words: isolation systems, elastomeric bearings, friction pendulum bearings, structures, vibration 1 Introduction Infrastructure can be defined as the basic physical and organizational structures needed for the operation of a society or enterprise. The term typically refers to the technical structures that support a society, such as roads, water supply, power grids, telecommunications, and so forth. Transportation infrastructure is one of the oldest one; it includes between others bridges, destined to road, rail and pedestrian traffic. It is important ensuring that these structures are not damaged or destroyed by natural hazards. Researches are made to increase the safety and mitigate the effects of natural hazards (the paper will focus earthquakes). Specifically, this effort tries to determine how structures should be built or how they should be strengthened (retrofitted) to minimize the effects of natural hazards. For dynamical loads produced by earthquakes, the solution is seismic isolation. It is achieved by inserting flexible isolator elements into the structure that shift the vibration period and increase energy dissipation or by use of sliding seismic isolation. The behavior of this kind of structures is not well- known, in part due to the lack of adequate models that can account for the complex behavior of the isolators. The paper, based on the state of the art and developed analytical models, present the basics of seismic isolation, together with a comparative study regarding seismic isolators’ behavior. The influence of bearings on the structural performance is also presented. 2 Problem Formulation How presented above, structures like bridges are sensitive to vibrations while their behavior during earthquakes is important for a sustainable functioning of the community. Before the seventies of the last century a large number bridges has been constructed worldwide; little or no consideration was given to seismic resistance [1]. Collapses during earthquake exposes have signaled this deficiency, a series of revisions to the design guidelines were accompanied by the launching of substantial retrofitting programs. The first bridge retrofitting techniques, for instance, only incorporated individualized strengthening schemes such as [2]: - steel jacketing of columns, - casting of in-fill walls between columns, - strengthening of footings and bearing elements, - widening of the pier caps and abutments, - use of restraining cables. These seismic design methodologies where orientated on an elastic approach; structures where designed to undergo elastic deformation when subjected to seismic forces. The structural stiffness resulting from the elastic design methodology resulted in low levels of ductility, conducting to small amounts of dissipated energy. Stiffness also facilitates the transmission of ground motion, effect being increased accelerations, which correlated to additional mass conduct to higher shear forces. The consequences of the elastic design approach resulted in severely underestimated seismic deflections [3]. These design inadequacies resulted in the collapse Proceedings of the 10th WSEAS International Conference on AUTOMATION & INFORMATION ISSN: 1790-5117 140 ISBN: 978-960-474-064-2