Extracting mode shapes from drive-by measurements to detect global and local damage in bridges

Abstract

This article uses extracted bridge mode shapes to detect bridge damage, including both local damage such as that due to a bridge strike and global damage such as that due to foundation scour. Typically, only one accelerometer is required, which is mounted on an instrumented vehicle passing over the test bridge. This concept is referred to as ‘drive-by’ bridge health monitoring. For a simple vehicle/bridge interaction (VBI) model, where the vehicle is represented as a moving sprung mass, a closed-form solution for the bridge mode shape is derived from the acceleration response of the instrumented vehicle. The validity of the proposed algorithm is numerically verified using a VBI model. In addition, it is shown that the extracted mode shape can be used to assess the bridge condition. A damage index based on the extracted mode shape is proposed to detect bridge damage and to provide an indication of the damage level. In the numerical study, the factors that affect the accuracy of the proposed algorithm are investigated, including the vehicle speed and measurement noise. Two laboratory experiments are conducted to validate the mode shape extraction and bridge damage detection processes for cases of both local and global damage.