Non-destructive methodologies in the assessment of the masonry arch bridge of Traba, Spain

Ground-penetrating radar (GPR) is one of the most recommended non-destructive techniques in bridge inspection. The medieval Traba bridge (NW Spain) was evaluated with GPR to analyze its state of conservation from a historical, archaeological and structural points of view. This bridge was assessed by using the 250 and 500 MHz antennas. Because the heterogeneity of historical masonry arch bridges, the analysis and interpretation of GPR data can be complex. In such circumstances, a sophisticated numerical modelling was employed to facilitate data interpretation. The GPR numerical analysis was undertaken using the finite-difference time-domain (FDTD) method and the synthetic models were created from the accurate external geometry of the bridges provided by three-dimensional laser scanning methods. The GPR numerical modelling allowed the study of the attributes of reflected signals from various targets within the bridge structure. Results revealed unknown inner details as well as a possible interior cavity in one of the piers. This information might be useful for civil engineers to verify the structural stability of the bridge.