The use of georadar to assess damage to a masonry Bell Tower in Cremona, Italy Luigia Binda * , Luigi Zanzi, Maurizio Lualdi, Paola Condoleo DIS-Department of Structural Engineering, Politecnico of Milan, Piazza Leonardo da Vinci 32, 20133 Milan, Italy Received 5 December 2003; accepted 24 March 2004 Available online 18 October 2004 Abstract Frequently, the application of NDT (non-destructive testing) to historic buildings is needed in order to search for hidden parts of the structure or for structural faults. The designer who requires the investigation is always facing the difficult situation of accepting the interpretation of the results given by the NDT experts, who in turn are usually only exceptionally expert in material and structures. Only a strict collaboration between the designer and the experts and the use of different investigation techniques, from the simplest to the more sophisticated can help in the interpretation of the results. The application of georadar to the detection of three main structural problems for the Bell Tower (Torrazzo) of Cremona is presented, together with the description of the difficulties in acquisition and data elaboration and the description of auxiliary investigations used to validate interpretation of the results. q 2004 Elsevier Ltd. All rights reserved. Keywords: Masonry structure; Diagnosis; Non-destructive techniques; Delamination; Hidden elements 1. Introduction The importance of applying different techniques of investigation and of careful elaboration of the collected data in order to solve difficult problems connected with the diagnosis of structural problems associated with historic buildings has been pointed out several times [1–3,5]. In fact, when using NDT (sonic, georadar, thermovision) to detect hidden damage, voids or inclusions, one of the greatest difficulties is the interpretation of the results, even when accurately presented. Radargrams, tomographies, etc. might contain important information, but they are usually readable only with great difficulty by the designer. Therefore, the designer who has asked for their application, has to accept the interpretation given by the NDT experts, who frequently are not experts in materials and construction techniques applied in the past. Therefore, there is a need for a better evaluation and connection of NDT results to the reality of the structure, which can be helped by a clear presentation of the results themselves. Aware of these needs the authors of this paper have been working on the application of georadar and other tests to the diagnosis of the Torrazzo of Cremona, trying to produce radar images that relate directly to structural problems representing the target of the investigation. This work was performed with close co-operation between the experts in radar technology and the experts on historic buildings involved in the diagnostic actions for the tower. A first investigation was made to find and define the extent of the detachment of the thin external leaf of the load bearing wall. The wall was surveyed with a high frequency antenna along many parallel profiles so that a 3D reconstruction of the external part of the wall was possible. The results were calibrated with local inspections and were correlated with the crack pattern to understand the causes of damage. A second investigation was made to understand the morphology of an arch where the inspection of a scaffolding hole was suggesting that the external masonry leaf hides an arch with a shape different from the shape shown by 0963-8695/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ndteint.2004.03.010 NDT&E International 38 (2005) 171–179 www.elsevier.com/locate/ndteint * Corresponding author. Tel.: C39 2 2399 4318; fax: C39 2 2399 4220. E-mail addresses: binda@stru.polimi.it (L. Binda), zanzi@stru.polimi.it (L. Zanzi), lualdi@stru.polimi.it (M. Lualdi), condoleo@stru.polimi.it (P. Condoleo).