Abstract
On March 11, 2011, the Great East-Japan earthquake with Mw 9.0, the largest ever recorded in Japan, shook northeastern part of Japan and was strongly felt in the Yokohama-Bay Bridge area with the JMA seismic intensity 5- (lower 5). Yokohama-Bay Bridge with the total span length of 860m is densely instrumented with vibration sensors that record seismic excitation during the main shock and several after-shocks. These series of seismic responses create the most comprehensive set of data on the response of long-span cable-stayed bridge subjected to multiple-support excitation. This paper describes investigation of seismic records by focusing on temporal and spectral analysis of the bridge accelerations, dynamic characteristics of the bridge and their changes throughout the excitation, investigation of response non-linearity during large excitation, performance evaluation of the seismic isolation device: link-bearing connection between girder and towers, and the post-earthquake field observation. Seismic response of the bridge is dominated by transverse vibration; where the girder transverse vibration reached the maximum displacement of 62cm. Investigation shows that link-bearing connection functioned properly during the earthquake to accommodate girder longitudinal movement, while on lateral direction pounding at the wind shoe may have occurred. Changes in natural frequencies were observed during large excitation followed by the change in vertical-transverse coupling behavior of the mode shape. Despite the strong shaking, there was no significant structural damage observed on the bridge since the ground motions experienced was still far below the design and seismic retrofit ground motions.
