Italian and European guidelines for seismic design of isolated bridges

In the past few years official guidelines have been issued in Europe and in Italy to regulate the design of (passively) isolated bridges. Explicity covered is the use of elastomeric and elato-plastic elements. The design philosophy aims at ensuring adequate protection with respect to two Limit-States or Perfomance Levels: the first one being the limit of fully elastic response, the second one being a state where the structure is still undamaged while the isolating elements are close to their ultimate deformation. Capcity design measures are adopted to ensure the protection of the structural parts even for larger-than-anticipated seismic events. Detailed requirements on the behaviour of the isolating elements so that they can reliably fulfil their protective role are given. Modelling, methods of analysis and verification criteria complete the content of the Guidelines. Aspects requiring improved definition are discusses in the conclusions of the paper.(AU)

Optimal design of isolated bridges and isolation systems for existing bridges

Designing new isolated bridges, the selection of optimal characteristics for strength, stiffness and displacements capacity for both piers and isolators is not at all obvious. When designing an isolation system for an existing bridge, the variable parameters are less, but it should not be assumed as a principle that all piers have to be isolated. A study on this subject has been recently presented by the same authors (1) where an optimization procedure was outlined, even if it was more an idea to be developed and verified than a reliable design tool. Since then, the idea has become a proposal for a design method, and the method has been implemented in an efficient software program and applied to a large number of cases which confirmed the soundness of the principles adopted in the design philosophy.(AU)