Experimental Demonstration of a Mode Shape-Based Scour-Monitoring Method for Multispan Bridges with Shallow Foundations

Malekjafarian, Abdollah; Kim, Chul-Woo; O'Brien, Eugene; Prendergast, Luke J.; Fitzgerald, Paul; Nakajima, Syunsuke

Abstract

A vibration-based scour monitoring approach applicable to bridges with multiple simply supported spans on shallow foundations is experimentally investigated in this paper. A monitoring strategy based on the relative changes in pier mode shape amplitudes due to scour is postulated. The first global mode shape of a bridge structure with multiple spans is extracted from acceleration measurements using an output-only approach, Frequency Domain Decomposition (FDD). The relative changes of the pier mode shape amplitudes under scour are then tracked. Here, each pier mode shape value is compared with the mean values of the remaining piers in a process that creates a Mean-Normalised Mode Shape (MNMS). The approach is demonstrated on a scaled model of a bridge with four spans, supported on sprung foundations, where scour is simulated by the replacement of springs with springs of lower stiffness corresponding to a reduction in foundation stiffness. It is shown that at a given ‘scoured’ pier, significant increases in the MNMS value occur, suggesting that the location of the scour can be identified. The magnitude of the MNMS at a given pier also increases with an increase in stiffness loss due to scour. In practice, the approach would work best by carrying out a visual inspection of the bridge to establish the initial health condition at the time of sensor installation. After this initial process, the bridge can be monitored remotely for scour on an ongoing basis.

Citation

Malekjafarian, A., Kim, C.-W., O'Brien, E., Prendergast, L. J., Fitzgerald, P., & Nakajima, S. (2020). Experimental Demonstration of a Mode Shape-Based Scour-Monitoring Method for Multispan Bridges with Shallow Foundations. Journal of Bridge Engineering, 25(8), Article 04020050. https://doi.org/10.1061/%28asce%29be.1943-5592.0001586

• Journal Article Type: Article
• Acceptance Date: Mar 13, 2020
• Publication Date: 2020-08
• Deposit Date: Mar 26, 2020
• Publicly Available Date: May 31, 2020
• Journal: Journal of Bridge Engineering
• Print ISSN: 1084-0702
• Electronic ISSN: 1943-5592
• Publisher: American Society of Civil Engineers
• Peer Reviewed: Peer Reviewed
• Volume: 25
• Issue: 8
• Article Number: 04020050
• DOI: https://doi.org/10.1061/%28asce%29be.1943-5592.0001586
• Keywords: Civil and Structural Engineering; Building and Construction
• Public URL: https://nottingham-repository.worktribe.com/output/4205536
• Publisher URL: https://ascelibrary.org/doi/10.1061/%28ASCE%29BE.1943-5592.0001586
• Additional Information: Received: 2019-03-14; Accepted: 2020-03-13; Published: 2020-05-29