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3D HBIM Model and Full Contactless GPR Tomography: An Experimental Application on the Historic Walls That Support Giotto’s Mural Paintings, Santa Croce Basilica, Florence—Italy

GPR (Ground Penetrating Radar) is a technology widely applied today in the field of non-destructive investigations. From its first applications, the field of use has involved environmental and archaeological contexts and, only recently, non-destructive investigations for the diagnostics of existing buildings, including historical ones. In the latter, the GPR is, in particular, addressed to the NDT diagnostics of walls, which often support paintings of considerable value. In this study, GPR technology was used to investigate the walls of the Bardi Chapel in the Santa Croce Basilica in Florence, which features Giotto’s frescoes. The GPR acquisition was performed with a three-antenna module that, through multiple scans, allowed to reconstruct the full 3D tomography of the three main walls of the chapel. The development of a customized system made it possible to extend the investigation area to almost the entire wall and to avoid contact between the instrument and the wall paint, thus safeguarding its integrity. The collected data, once inserted in a unified framework of the HBIM model, geo-referenced, and equipped with the information content, allowed us to evaluate the masonry structure and to generate masonry data for subsequent seismic vulnerability assessments.