Wind characteristics around and effects on a sea-crossing bridge based on monitoring data

Abstract

Wind loading is critical for a long-span and flexible bridge under operation. This paper studied the wind loading on a sea-crossing bridge, namely the Main Navigational Channel Bridge (MNCB) of Donghai Bridge at Shanghai, utilizing the field measurement data from its Structural Health Monitoring System (SHMS). Located at the typhoon prone area off the eastern coast of China, the instrumented bridge is a five-span cable-stayed bridge arranged as 73+132+420+132+73m, with a three-cell steel-concrete composite box girder. In this paper, first of all, based on the data of wind speed and direction monitored by two anemometers, one on the mid-span of girder and the other on one tower's tip, the wind environment at the bridge site during the period from January 2007 to December 2012 is summarized in terms of the 10-min mean wind speed, mean wind direction, turbulence intensities and so on. Then, the extreme wind environment during strong winds, e.g. typhoons, and the strongwind-induced structural responses, such as accelerations, are investigated by statistical analysis. Finally, the influence of strong winds on the variation of the bridge's modal frequency and damping ratio is discussed. During the high winds, modal frequencies become more scattered while damping ratios have an increasing trend. This research could serve as a field measurement basis for wind-resistance design and evaluation of long-span bridges in similar environments.