Seismic Isolation of Bridges: Practice-Oriented Considerations

Seismic isolation is an effective method to control seismic forces, seismic displacements and to govern modal shapes on a structure or a part of it. Seismic isolation devices are widely used in the design of new bridges and retrofit of existing structures due to their effectiveness in the reduction of seismic forces and the relatively simple methods of installation. This work aims to provide practical considerations to be included when dealing with the design of new bridges equipped with seismic isolator devices and in particular the paper focuses on the study of seismic isolator stiffness variation and inclusion of soil-structure interaction. The purposes of the paper are a) to set a fast design procedure for the design of seismically isolated bridges b) to investigate how the stiffness of an equivalent system composed of foundations, piers and bearings can be affected by varying the stiffness of the individual components. Both these objectives will be described following a sort of flow chart containing the different main steps to be included for the design of seismically isolated bridges. This study can provide practical oriented considerations to the designers dealing with seismic design of isolated bridges and can help to understand how stiffness variations of the single components might affect the global behavior of the structure and thus the sizing of the structural elements.