The study of near-field effects has been ongoing since the 1971 San Fernando earthquake in California. However, not until the 1994 Northridge earthquake in the Los Angeles area and the 1995 Kobe earthquake in Japan, where fault ruptures occurred near high-density urban settings, did structural engineers take an interest in how large velocity pulses affect structures. The large velocity pulse is a characteristic of near-field motion, which is described as the cumulative effect of almost all of the seismic radiation concentrated in one location.
To study the effects of the large velocity pulse, three 22% scale bridge columns were tested at UC San Diego, each column having dimensions of 1830 mm (72 in.) in height and 410 mm (16 in.) in diameter. The bridge columns were subjected to a velocity pulse followed by a cyclic loading history. Two out of the three test specimens were loaded dynamically and the third statically.
By comparing the results of the three tests, it was observed that the high strain rate increased the strength of the bridge column by 10% to 15%. Another finding was that a plastic hinge length equal to the radius of the bridge column produced a better conversion from curvature to displacement. Finally, the velocity pulse had minimal effect on the overall performance of the bridge column.
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