Near-fault earthquakes with pulse-like horizontal and vertical seismic ground motion components: Analysis and effects on elastomeric bearings

Near-fault earthquakes have been largely studied in the last years by paying special attention to the occurrence of a pulse-like horizontal seismic ground motion, and to the related effects on structural systems. Conversely, less attention has been paid on the vertical component of the ground motion in such seismic events. Within this framework, the present study is meant at investigating a fairly overlooked special case, that is the occurrence of near-fault earthquakes exhibiting a pulse-like seismic ground motion along the horizontal direction and the vertical one. Specifically, the variational mode decomposition technique is employed to prepare and characterize two subsets of near-fault earthquake records that consist of fault-normal and vertical seismic ground motion components. One subset collects earthquake records with pulse-like waveform in both velocity components, whereas a pulse-like waveform in the fault-normal velocity component only takes place in the earthquake records of the second subset. If both fault-normal and vertical components embed a dominant pulse-like waveform, then it is found that the ratio of the corresponding pulse periods well correlates with the pulse period along the fault-normal direction, while it is uncorrelated with respect to the pulse period along the vertical direction. Next, it is investigated the displacement demand of high-damping rubber bearings for base-isolated buildings under earthquake records characterized by a horizontal impulsive ground motion together with either a pulse-like or a nonpulse-like vertical shaking, provided that the pulse period in the horizontal direction is similar and the peak ground accelerations are individually the same after scaling. Final results shows that the maximum displacement of elastomeric bearings subjected to a pulse-like horizontal ground motion is moderately amplified, on average, when the vertical excitation is also pulse-like.