Abstract

This paper revisits the 12 November 1999 earthquake in Düzce, Turkey, and attempts to derive realistic estimates of ground motions experienced near the edge of the fault‐rupture outcrop where the 2.5‐km long Bolu twin viaduct failed. The nearest accelerographic stations, in Bolu and Düzce, being neither sufficiently close to the fault nor in similar orientation with respect to the seismogenic fault, could hardly explain the observed damage when used as excitation at the exact location of the viaduct. The novelty of the research lies on the fact that the proposed ground motions are chosen on the basis of their ability to reproduce the observed rocking response of two sets of precast concrete girders temporarily stored along the highway axis at the time of the event—a case study that has hitherto received scarce attention in literature. Although lying in literally adjacent locations, all girders of the first set toppled, whereas most girders of the second set, with a different orientation than the first, remained standing. Scenarios of hybrid ground motions that account for likely near‐fault effects are devised and calibrated with nonlinear finite‐element analyses. The most likely motions identified that can simultaneously provoke toppling of the first‐site girders and not toppling of the neighboring site, are those combining a sufficiently strong forward‐rupture directivity pulse, with fault‐normal Vmax on the order of 100  cm/s, with a quite intense fault‐parallel direction fling‐step pulse that is compatible with a dislocation exceeding 60 cm.

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