Investigation of live load deflection limit for steel cable stayed and suspension bridges

Sea-crossing bridges connect islands to secure the sea and road traffic in the area. For the construction of sea-crossing bridges, bridge engineers should plan to secure the safety of large ships passing under the bridge. In particular, clearance of cable-stayed bridges and suspension bridges is determined considering the height of the ship master from the surface of the water, the trim of the ship, the psychological free space, the tide height, and live load deflection. Of these, bridge engineers should calculate the deflection of bridges by live loads. The purpose of this study is to investigate the suitability of live load deflection limit for cable-stayed and suspension bridges over main span length of 200m. For the design of long span cable stayed and suspension bridges, limitations are L/400 and L/350 respectively in the Korean Bridge Design Code (2010) and Korean Bridge Design Code (LSD) (MLIT, 2015). Saadeghvaziri (2012) also suggested deflection limit based on natural frequency, acceleration limit of 0.5 m/s² and vehicle speed. In this study, the theoretical analysis of Yi Sun-Sin grand bridge (suspension bridge, main span length=1,545m) and Young-Hung grand bridge (cable stayed bridge, main span length=240m) were carried out and compared with these limits. The results of the study on the limitation of live load deflection are expected to be useful reference for the design, the proper planning and deflection review of the long span bridges around the world.