Digital photogrammetry, GPR and computational analysis of structural damages in a mediaeval bridge

Abstract

Traditional architectonic heritage elements are fragile and irreplaceable resources, signs of the ancient ways of life and the history of the modern societies, and essential valuable elements of the own landscape of a region. Accurate updated documentation might be the basis for any conservation or restoration intervention over architectonic heritage in order to ensure the conservation in its original appearance and in a collapse risk-free state, with the minimum intervention. This paper shows a multidisciplinary approach to heritage documentation involving close range photogrammetry and ground penetrating radar techniques, as well as the development of finite elements based structural models. Specifically this study is focused on the documentation of a mediaeval bridge concerning the geometric shape, the building material and the current damages and its causes. The usefulness of close range photogrammetry techniques in the accurate 3D modelling, cracks detection and mapping and exterior material characterization is analyzed. Further, a non-destructive test through GPR is employed for the interior material and zones description. For both techniques, the methodology followed for data collection and data processing aimed at minimisation of time consuming and optimisation of results is described in detail. Advantages and limitations of these techniques are displayed and the accuracy of the obtained results is also estimated. Resulting information related to the whole bridge geometry is taken as basis to develop a numerical analysis using the finite elements methods (FEM). Linear finite analysis provides useful information for diagnosis although non-linear methods should be used when the properties and geometry of the internal and external elements are well known. Photogrammetry provides the exact geometry needed to perform the FEM pre-process. Radar data provide approximate information about the different internal zones of the bridge. Finally, the FEM analysis leads to obtain a stress distribution compatible with the detected damages, allowing identifying its possible causes. Close range photogrammetry, ground penetrating radar techniques and the FEM analysis are proposed to perform a complete survey of the stability of the bridge and its accurate geometry.