An integrated diagnostic approach for the assessment of historic masonry structures

Knowledge of the structural behaviour of existing masonry requires a multi-level approach, with the proper application of diagnostic and assessment methodologies. The structural performance of masonry wall structures can be understood provided that the history of their construction, their geometry, the characteristics of their masonry texture, and the characteristics of the masonry as a composite material are known. In order to obtain all these data, an effective on-site testing program, which can involve the application of different test methodologies as a combination of destructive tests (DT), minor destructive tests (MDT) and non-destructive tests (NDT), needs to be performed. Furthermore, the effectiveness of applied methodologies for the assessment of historical masonry structures strongly depends on the type of investigated structure, as well as on the appropriate numerical model for the analysis. However, the unclear aspects of any testing programme remain the same – how efficient is a particular testing technique, and how can it be assessed? Following the results of recently carried out EU and national research projects, a comprehensive set of data regarding the effectiveness of different testing methods, depending on the type of problem, have been collected and analyzed. Within this framework, several masonry heritage structures from Slovenia, which differ both from the historical and structural point of view (Pišece Castle, the Carthusian Monastery at Žiče, and a typical stone-masonry house from the Soča Valley region), have been investigated by means of different techniques, and numerically analyzed. For this purpose, two different models were used: a push-over model based, on the structural element method, and FEM analysis. It was concluded that the effectiveness of any particular diagnostic technique for the investigation of masonry structures, and for the planning of their restoration, depends on numerous factors. An attempt to determine which of the techniques could be appropriate, depending on the problem, was made. No single test is self-sufficient for the solving of a particular problem, so a combination of different NDT, MDT and DT should be performed. Summarizing all the results, it can be said that, in the process of assessing the state of a structure, even a simple investigation technique is better than none. The effort will always be repaid - if not already in the planning stage of the restoration and retrofitting actions, then certainly in the execution stage of the revitalization works, on site.