Farhad Ansari

The method proposed in this article pertains to developing a technique for structural health monitoring of cable-stayed bridges based on the inverse finite element method (iFEM). This approach is built on distributed monitoring of strains by using a Brillouin scattering-based distributed optical fiber sensor. Using this method, both the deflections and changes in cable forces are computed to assess the structural health of bridges. In contrast to the existing distributed strain-based techniques, the computation of cable forces does not require prior knowledge of loads and their locations. This provides the opportunity for use under operational conditions of the bridge, where the bridge is subjected to moving vehicular loads. The capability of the proposed technique was evaluated in laboratory experiments by a scaled model of a cable-stayed bridge. The experiments involved static and dynamic loads and the acquisition of distributed strains by a PPP-BOTDA optical fiber interrogation unit. Other sensor types, such as LVDT and FBG sensors, were employed in the experiments to validate the results of the proposed computational approach. In addition, the differences between the proposed approach and previous techniques are compared in terms of the computational approach, their attributes, and percentage errors in the computation of cable force variations.

Deflection monitoring plays a key role in bridge Structural Health Monitoring, as deflection data may offer valuable insights into potential structural issues, such as cracks and corrosion. However, monitoring bridge deflections under operative loads presents challenges, particularly in scenarios where establishing a fixed reference point for displacement sensors is impractical, such as when a bridge spans a waterway or the sensors may be vulnerable to vandalism. In recent years, the inverse Finite Element Method (iFEM) has emerged as a possible solution. This method provides a load- and material-independent means of computing structural displacements from strain measurements, in real time at a minimal computational cost. Additionally, the iFEM can serve as a virtual sensing approach to monitor strains at locations lacking sensors, enabling the assessment of the fatigue life consumption at virtually any point in the structure. Despite its potential, applications of the iFEM in the civil engineering field are very limited, with no validation on full scale bridges has been performed to date. This study addresses this gap by investingating the application of the iFEM for bridge deflection monitoring through distributed strain measurements. The proposed approach is tested on experimental case studies, involving cross-validatiion of reference-free deflections inferred by the iFEM with those obtained from displacement sensors. This work contributes to the advancements of structural health monitoring methodologies in civil engineering, demonstrating the practicality and reliability of iFEM in bridge applications.

The development of a generalized machine learning approach based on distributed detection and quantification of cracks by optical fibers is described in this article. A Brillouin scattering optical fiber sensor system was employed to develop, test, and verify the method. The main components of the approach described herein consist of an unsupervised crack identification module based on the iForest algorithm and a crack quantification component by the one-dimensional convolutional neural network method. The main attribute of this model is the versatility for application in various types of structures. The proposed method does not require further application-dependent training or calibration as long as the structural applications employ the same optical fiber type and installation adhesives. The effectiveness of the proposed method was verified by two experiments involving a 15-m steel beam in the laboratory and monitoring a twin set of 332-m-long, five-span continuous box girder concrete bridges. Regarding crack detection capabilities, it was possible to detect 107 out of 112 cracks in the laboratory beam and 20 out of the 21 in the bridges. The resolution of crack opening displacements for the steel beam and concrete bridges were 20.6 and 21.7 µm, respectively. The verification experiments further indicated the generality of the approach in applications to various types of structures and materials.