During the 17 August 1999 Kocaeli earthquake in Turkey, some of the viaducts and overpasses located on the Trans European Motorway (TEM) incurred various types of damage. The Mustafa Inan (M. Inan) viaduct, which consists of 10 equally spaced, 40-m-long, simply supported cell box girders, was damaged at seismic buffer stops located at the second longest pier in the central span.

The objective of this work is to assess the performance of the M. Inan viaduct in the Kocaeli earthquake by conducting both experimental and numerical studies. The epicenter of the earthquake was 5 km south of the site, and the nearest available ground-motion record was at a distance of 2 km. The records inherit typically near-fault characteristics with a displacement offset in the fault-parallel direction and an enhanced low-frequency velocity in the fault-normal direction. Ambient vibration tests were conducted before the earthquake to measure the dynamic characteristics of the structure and calibrate the finite-element (FE) model.

The measurements indicated that the viaduct exhibits three different dynamic behaviors in three different frequency bands. In the low-frequency band of 0-1 Hz, the structural response of the piers was of major concern, and its influence was seen at the base moment and shear forces of the piers. In the intermediate frequency band of 1-2 Hz, the girders demonstrated pull-off and drop-collapse problems due to the out-of-phase movement of the central and side piers. In the high-frequency band of 3-5 Hz, the vibratory response of the elastomeric bearings appears to be more critical.

The earthquake response of the bridge was modeled using a verified FE software, LUSAS version 13.2. The linear FE analysis revealed that shorter side piers sustain larger moment and shear forces than the longer middle piers. The snap-through behavior of the longer piers increases the second-order effects, whose influence was investigated using geometric nonlinear analysis. The results show a significant increase in forces of the longer middle piers in comparison with those of linear analysis.

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