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AbstractIn the recent past, numerical and experimental investigations on full-scale isolators have led to extensive improvements in seismic isolation techniques for bridge structures. Significant advances in dynamic testing techniques have been made at both software and hardware levels, and the response of an isolated bridge can be realistically simulated. In general, the response of an isolated bridge structure is strongly affected by the valley topography; therefore, high piers may not need isolation devices, since they are flexible enough to accommodate the design displacement in the elastic range. On the other hand, at those locations no hysteretic damping is provided and higher displacements can be achieved, compared to the maximum displacement allowance. In this work, a simplified procedure is proposed for the optimization of isolation systems for bridge structures. The seismic response of a designed case study structure is investigated through nonlinear time history analyses, and the effective contributions of both the nonlinear hysteretic behaviour of isolators and the elastic response of piers are considered. Regarding displacement and force responses in particular, the results show a very good agreement between mean and single-event peak responses, and the corresponding values returned by the proposed design procedure.

Abstract: This paper presents a synthesis of the activities carried out in the framework of the European project EFAST (design study of a European Facility for Advanced Seismic Testing) to determine the general characteristics of a new European world-class facility for earthquake testing of structures. To this end the demands for the necessary testing to support the modern seismic engineering research have been investigated and compared to the actual capabilities of European laboratories. The outcome is the determination of performance objectives and requirements in the gross. On the basis of the needs assessment carried out during the first phase of the project and taking into account the technological advances in both experimental techniques and equipment (hardware and software) for seismic testing, a modern facility for experimental seismic research should be composed, mainly, of a high performance shaking tables array and a large reaction structure where both traditional (pseudo-static/dynamic) and innovative testing techniques (e.g. real time hybrid testing) can be applied and combined. A tentative layout of the facility is also proposed and issues related to the best utilization of such a laboratory are discussed.

Appropriate seismic assessment of reinforced concrete bridges is an important challenge in structural engineering in consideration of the number and relevance of bridges built without applying advanced codes of practice and of the strategic role of transportation networks in modern economy. This paper focuses on some relevant aspects of the damage development and collapse modes of hollow piers, as commonly designed in the past. The following aspects have been considered: absence of confinement, inadequate shear strength, shifting of the critical section, insufficient length of lap splices. A series of experimental tests has been designed and performed; the capacity of predicting appropriate results of formulations recommended in codes of practice or proposed in recent research documents has been checked comparing experimental and analytical results.

In the first part of this paper the objectives of an isolation system for a bridge structure are discussed, in relation to modelling options and modification of the traditional capacity design principles. A displacement-based design approach is then presented, using a linear equivalent single degree-of-freedom model. The preliminary design of an isolation system for existing bridges is based on the definition of a "structure regularity" which allows the estimation of whether the response of the real structure will be similar to that predicted in the preliminary design phase. The efficiency of the approach is shown in designing the isolation system for a highly irregular bridge.