Near-fault fling-step ground motions: Characteristics and simulation

The presence of long-period pulses in the near-fault pulse-type ground motions increases the damage potential of such ground motions, particularly for the flexible structures like bridges. It is necessary to carry out nonlinear analyses of structural systems for ensuring their safety in the near-source regions. This study considers the simulation of fling-step motions under the assumption that a fling-step accelerogram can be decomposed into a pulse component and a component without any pulse. Fling-step pulses are extracted from a database of 20 recorded fling-step accelerograms through smoothening via the five-point moving average method and are base-line adjusted for zero velocity and permanent displacement at the end of the pulse time-window. The velocity waveform of these pulses is modelled by a mathematical function characterized by three parameters related to amplitude, duration and location of the pulse. The amplitude and duration parameters are proposed to be estimated for an anticipated motion in terms of the closest distance of site from the fault for a given magnitude and faulting mechanism, while the location parameter is proposed to be taken same as the location of peak ground acceleration in the non-pulse component. It is shown through a numerical study that the proposed method of simulation works well provided the amplitude parameter of the pulse is chosen with care.