Investigation of the structural behaviors of Bosphorus suspension bridge with vertical hangers replaced by inclined hangers

Abstract

The Bosphorus Suspension Bridge, which connects the Asian and European sides, has a geopolitical importance in terms of its location, and has also been integrated with Istanbul. The bridge has a main span of 1074 m, and it had inclined hanger configuration until recently. On January 2004, a hanger-to-deck connection close to European side tower was damaged due the storm. This resulted in discussion of changing the inclined hangers with vertical ones. Inclined hangers increase the aerodynamic stability of the bridge; however some of them can remain as slack and easily swing under wind load. This occurred at the Bosphorus Suspension Bridge. On July 2015, the inclined hangers were replaced with vertical ones. This study aim to investigates changing of hanger configuration on the structural behavior of the Bosporus Suspension Bridge. When the suspensions of an inclined designed bridge are later changed vertically, the changes that occur in the other carrier elements of the bridge (tower, deck, cable, etc.) are examined and interpreted, and how the existing unchanged other carrier system of the bridge is affected by this change has been investigated. For this aim, three-dimensional finite element analyses were employed for both inclined and vertical hanger configurations. Modal, static and dynamic analyses were practiced by considering geometrical nonlinearity. At the end of the analyses, dynamic characteristics, displacements and internal forces were obtained and presented in detail. The GBZ000 component of Gebze station records of 1999 Kocaeli earthquake is utilized as a ground motion for dynamic analysis. From the analyses, it was evident that the vertical hanger configuration had a positive effect on the bridge response in terms of vertical displacement and internal forces obtained. Also, it was seen that all hangers were loaded as equal in the event of vertical configuration and this made the bridge more stable. Based on these, the vertical hanger configuration is recommended in terms of more safety.