RETROFITTING OF A BRIDGE FORM HISTORICAL STATION USING SEISMIC ISOLATION

Abstract

Being the first railway station as bridge form above the train track, constructed in Istanbul in 1915, Göztepe Train Station is one of the most special structures conserved in terms of both structural and architectural features till today. In the scope of Marmaray CR3 project, this historical landmark has been renovated and actively used as a train station. The original structural system was composite masonry, including brick masonry walls, steel beams to support timber roof, stone masonry walls and a volta slab to elevate the station. Since the region is seismically active, requirement for seismic strengthening was mandatory in order to maintain the station. There were two main goals during this project: Modifying the main train station building with minimum intervention while achieving target seismic performance level and satisfying the increased demand requirements. Structural system of the historical structure underneath the main station required in order to increase the number of train tracks from two to three. Masonry walls on the sides of the rail tracks have been removed and replaced with reinforced concrete shear walls. While working underneath, the existing station building was suspended until the new structural system below the superstructure is constructed. A special methodology has been developed for this purpose. This method allowed keeping the entire station building intact and preventing any risk of damage to the adjacent structures. Since masonry structures are primarily vulnerable to lateral forces, the masonry structural system is converted to reinforced concrete without modifying the exterior shell of the station. This conversion is carried out by employing in-situ concrete members where special care has been taken to maintain the original facades. Additionally, a seismic isolation system composed of nine curved surface sliding devices has been installed in order to reduce the seismic actions transmitted to the upper structure. It should be noted that seismic isolation also facilitates reduction for modifications at the upper structure. Structural models have been developed based on the characteristics of the base isolation devices, and by considering the modifications on the substructure and the superstructure. As a consequence of the implemented retrofit methodology, the historical structure has been modified at the minimum level, earthquake performance is brought to the target seismic performance level, and the structure was made suitable for functioning of the increased number of tracks.