Combining GPR, Passive Seismic, and Load Testing With Computational Models in the Assessment of Historical Bridges: The Case Study of the Comboa Bridge

Abstract

The preservation of historical bridges usually requires extensive structural evaluations for possible damage detection. Therefore, effective techniques are essential for diagnosis and, consequently, proper maintenance and rehabilitation actions. The combination of techniques provides complementary data that support decision making. A complete assessment was applied in the study of the Comboa Bridge, a medieval masonry structure in river Verdugo, in Galicia (Spain). It has three irregular arches, and the first visual inspection denotes the existence of important cracking and vegetation in the stonework. One of the most representative nondestructive testing (NDT) techniques for in situ evaluation is ground-penetrating radar (GPR) that offers detailed insights into subsurface conditions, revealing information about materials, voids, and deterioration, while loading tests and passive seismic methods provide dynamic responses that are related to type of structure and possible damage. This method was combined with loading tests to obtain deflections of the bridge deck and passive seismic for analyzing the dynamic behavior. Moreover, 3D models of the structure were set up using light detection and ranging (LiDAR), performed with terrestrial laser scanning, and unmanned aerial vehicle (UAV) surveying. By combining 3D models with NDT techniques, the results provide comprehensive information that enhances the understanding of a bridge’s condition and safety. These results are used for calibrating the dynamic computational model of the structure in order to obtain the vibration modes. Each technique used in the study presents limitations, which are addressed and discussed herein. Furthermore, the site conditions can also affect the results, as the effectiveness of these methods can vary greatly, depending on the materials and structures, which influences the electromagnetic and mechanical wave propagation. Additionally, the frequency of the waves may not effectively mark all relevant structural features or smaller damage. When used together, the NDT methods can complement each other’s strengths, but challenges remain. Overall, while these techniques are valuable tools for assessing historical bridges, awareness of their limitations is crucial for accurate interpretation and effective decision making in preservation efforts. The results obtained in the Comboa Bridge demonstrate improved accuracy in identifying structural anomalies. Additionally, recommendations to overcome some of these challenges in case of historical bridge assessment and also for the continuous monitoring and adequate maintenance actions to preserve the bridge integrity and safety are presented.