Preliminary insights on the inelastic seismic response of structural systems under pulse-like ground motion

Near-fault pulse-like seismic events exhibit a pulse in the velocity time history that mainly occurs in the strike-normal direction at locations towards which the earthquake rupture has propagated. The large damage potential associated with such seismic events is due to high displacement and velocity demands, together with the transmission of a large amount of energy in a relatively short time. In presence of specific geological conditions, they can also reveal unusual peaks of the spectral values in the long-period range. Additionally, it is well known that the intensity level of the vertical shaking close to the causative fault can be exceptionally high. Within this framework, the present study presents a preliminary sensitivity analysis of the inelastic response of structural systems under near-fault pulse-like ground motion accounting for the vertical component through the P-Delta effect for better understanding the damage potential of such seismic events and for supporting the development of proper design guidelines. First, some seismic records have been selected and processed. The dominant pulse embedded in the selected records and the corresponding pulse period value are derived through a recent methodology based on the Variational Mode Decomposition technique. Several nonlinear dynamic analyses are then performed. Specifically, elastic and inelastic response spectra are first calculated taking into account the whole seismic signal and the dominant pulse only, without and with vertical seismic component and P-Delta effect. In doing so, acceleration, velocity, displacement and energy spectra are carried out and analyzed. The preliminary results here reported indicate that for large fundamental periods of the oscillator (e.g., larger than 3 s) the response can be significantly higher when the vertical component of the accelerogram and P-Delta effect are also taken into account. Moreover, it is found that the nonlinear behavior of the oscillator can have a beneficial or detrimental effect. The outcomes of this preliminary analysis aim at providing useful insights toward a better characterization of the seismic demand in inelastic structural systems subjected to pulse-like seismic events.