2nd Croatian Conference on Earthquake Engineering 2CroCEE

In comparison with far-field (FF) ground motions, near-fault (NF) ground motions with forward directivity or fling-step effect are characterized by large pulses. These pulse-like (PL) ground motions have pronounced coherent pulses in velocity and displacement histories. Even though these prominent pulses generally have very few cycles in a PL ground motion, the destruction they cause to structures is severe and distinctive compared with non-pulse-like (NPL) ground motions. The present study suggests power demand as an alternative engineering demand parameter for reflecting the severity of the risk posed by PL ground motions. The proposed parameter is simply a product of story shears and inter-story velocities. Through an investigation using a three-story building subjected to ensembles of PL and NPL ground motions, this study confirms that power demand satisfactorily elucidates the destructive potential of PL ground motions. In contrast, force demand, which is the cornerstone laid in building seismic design codes, cannot adequately reflect the destructive potential of PL ground motions. In addition to power, power density and normalized power density were introduced to obtain a sense of the magnitude of power demand relative to the degree of structural damage.
From the energy response histories of a three-story building, extraordinary increments of kinetic energy under a PL ground motion are closely followed by significant increments of strain energy, indicating large structural deformations. It was found that damping energy is not effectively built up at the first significant increment of strain energy. This implies that inherent or supplemental damping hardly protects building structures against the first crucial strike of PL ground motions, which usually cause the most damage to structures.