Investigation of Live Load Defl ection Limit for Steel Cable Stayed and Suspension Bridges

Long span bridges such as steel cable stayed and suspension bridges are usually more fl exible than short to medium span bridges and expected to have large deformations. Defl ections due to live load for long span bridges are important since it controls the overall heights of the bridge for securing the clearance under the bridge and serviceability for securing the comfort of passengers or pedestrians. In case of sea-crossing bridges, the clearance of 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 defl ection. In the design of bridges, live load defl ection is limited to a certain value to minimize the vibrations. However, there are not much studies that consider the live load defl ection and its eff ects for long span bridges. The purpose of this study is to investigate the suitability of live load defl ection limit and its actual eff ects on serviceability of bridges for steel cable-stayed and suspension bridges. Analytical study is performed to calculate the natural frequencies and defl ections by design live load. Results are compared with various design limits and related studies by Barker et al. (2011) and Saadeghvaziri et al. (2012). Two long span bridges are selected for the case study, Yi Sun-Sin grand bridge (suspension bridge, main span length = 1545 m) and Young-Hung grand bridge (cable stayed bridge, main span length = 240 m). Long-term measured defl ection data by GNSS system are collected from Yi Sun-Sin grand bridge and compared with the theoretical values. Probability of exceedance against various defl ection limits are calculated from probability distribution of 10-min maximum defl ection. The results of the study on the limitation of live load defl ection are expected to be useful reference for the design, the proper planning and defl ection review of the long span bridges around the world. KCI Citation Count: 0