Near-fault ground motions are characterized by long-duration horizontal pulses and high values of the peak vertical acceleration, which can become critical for a base- solated structure. To check if current provisions of the Italian seismic code can be considered adequate for the design of base-isolated structures located in a near-fault area, the following cases are studied: five-storey r.c. framed buildings base-isolated by elastomeric bearings acting alone or combined in parallel or in series with sliding bearings; six-storey r.c. framed buildings base-isolated by friction pendulum bearings. The base-isolated structures are designed assuming the same values of the fundamental vibration period and equivalent viscous damping in the horizontal direction. The nonlinear analysis of the test structures subjected to horizontal and vertical components of near-fault ground motions is performed checking plastic conditions at the potential critical sections of the girders and columns. The response of an elastomeric bearing is simulated by a model with variable stiffness properties in the horizontal and vertical directions, depending on the axial force and lateral deformation; while the response of sliding and friction pendulum bearings is described by laws with friction variability, depending on deformation velocity and geometry.
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