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This article proposes a novel method, entitled Reference-based Component Scaling (RCS) method, for estimation of bridge mode shapes using vehicle scanning methods. The proposed method uses two instrumented vehicles to measure the accelerations on the bridge. While one vehicle remains stationary on a pre-determined location, the other one travels over the bridge with a constant speed both exciting the bridge and recording its response. The accelerations recorded on both vehicles are then processed using variational mode decomposition method and Hilbert transform to obtain their modal components. Leveraging its comprehensive framework that incorporates modal components derived from both vehicles, the RCS method effectively tackles the primary challenges encountered by vehicle scanning methods. These challenges include: i) shifting and shrinking effects of bridge damping on mode shapes, ii) distortions in modal components due to incomplete elimination of the roughness effect and iii) distortions in modal components caused by acceleration peaks during the vehicle´s transition from a rigid platform to the bridge. To this end, the RCS method addresses adverse effects of bridge damping without a priori knowledge of the modal damping ratios. To assess the accuracy of the proposed method, numerical analyses were carried out on three different bridges with different number of spans and boundary conditions. The effect of crucial parameters such as road roughness, bridge damping, uncertainties in measurements, and existing traffic on the accuracy of the proposed method was investigated. The results of the numerical study show that the RCS method stands alone in providing accurate estimates of mode shapes of bridges that are seated on elastic bearings, that have realistic damping ratios and relatively high road roughness profiles. • A novel vehicle scanning method to estimate the mode shapes of bridges is proposed. • The Reference-based Component Scaling (RCS) Method uses two instrumented vehicles to measure the response of the bridge. • Through the normalization process, the RCS method tackles the challenges that current drive-by methods cannot address. • The RCS method stands alone in providing accurate estimates of mode shapes of bridges on elastic bearings that have realistic damping ratios. [ABSTRACT FROM AUTHOR]

The recent bridge collapses worldwide underscored the perilous state of the global bridge infrastructure. Structural health monitoring (SHM) methods, particularly vibration-based techniques, offer a non-destructive approach to evaluate bridge conditions. However, installing dedicated SHM systems on each of the millions of bridges worldwide is prohibitively expensive. Vehicle scanning methods (VSM) have emerged as a cost-effective alternative, leveraging vehicle-mounted sensors for bridge assessment. Previous VSM research has primarily focused on frequency and mode shape identification through accelerations derived from numerical models. A smaller subset has explored damage detection, either based on modal properties or direct analysis of vehicle accelerations. This study proposes a new damage index that distinguishes itself by establishing a physical connection between the accelerations recorded on the vehicle and the instantaneous curvature of the bridge. This analytical connection provides a straightforward and effective means for damage detection and localization in bridges using VSM, offering the advantage of efficiency and accuracy. As such, the proposed damage index avoids the use of modal properties for damage detection, which are known to be prone to several factors and are not necessarily accurate enough when used in VSM applications, and the over-fitting problems associated with data driven methods. Numerical investigations indicate that the proposed damage index is robust against the potentially adverse effects of several parameters including road roughness, measurement noise, bridge frequency, damage location, variations in boundary conditions, and vehicle speeds. • Physical connection between contact point accelerations and bridge damage is developed • Based on this connection, we propose a damage index that can detect and locate damage • The proposed damage index was shown to be robust against several parameters • The physical connection paves the way for accurate damage detection and localization. [ABSTRACT FROM AUTHOR]