Identification of structural properties of the Incirli Pedestrian Bridge and structural response analysis

Abstract

Incirli Pedestrian bridge links the Bakirköy and Bahçelievler districts of Istanbul by crossing over the D100 highway and being exposed to heavy pedestrian traffic in peak-hours, since it is the only way to reach the Metrobus line for the people live in the neighboring area. The D100 is a state road with a total of 1852 km length, which extends from Kapıkule border crossing in Western Turkey to the Gürbulak border crossing point at Eastern Turkey. The highway has particular importance to Istanbul since it is one of the largest and busiest highways in the city. In the case of an emergency, D100 will be one of the most used alternatives to run efficient logistics operations in the city. Thus, studying the structural safety of pedestrian bridges over the D100 highway during earthquakes is very important, and this is the objective of this study. Towards this objective, the seismic safety of one of such bridges, the Incirli pedestrian bridge is studied by using vibration measurements, field inspections, a measurement-calibrated analytical model, and a site-specific design-spectra based analysis. The transfer matrix formulation is used to derive the properties of an equivalent SDOF structure. The elastic design spectra used is based on the latest Turkish seismic design code for the location, the TSC2018. Using the measured natural frequency of the structure and the elastic design spectra, the earthquake forces that are expected under several scenario earthquakes with different return periods are calculated, and the stress levels at the most critical sections of vertical structural elements are evaluated. It is determined that, under the expected large Istanbul earthquake, the bridge is unsafe in its longitudinal direction, but safe in its transverse direction.