Masonry assessment for the seismic risk evaluation of historic structures

The preservation of historical and architectural heritage against exceptional events such as earthquakes is one of the most important challenges in Europe. The structural analysis for the seismic risk assessment is generally based on the use of computational methods and requires, as a prerequisite, a good knowledge of the existing structure with regard to the shape, the types of masonry, the mechanical properties, the state conservation and the presence of defects and damage. Semi-destructive methods are available, based on sampling, but their use is to be avoided or minimized on historic structures. A procedure is proposed in this paper, which is based on the implementation of extensive non-destructive surveys accompanied by limited minimally-destructive testing. As an application, a survey campaign recently carried out on the Ghirlandina Bell Tower in Modena, Italy, is presented. The non-destructive campaign was based on sonic tests. Being aware of the construction phases of the tower and of its various construction materials, the procedure was aimed at identifying uniform areas and portions in which to evaluate the mechanical properties. Furthermore, the tests had the purpose of identifying possible gaps, voids, layering, defects, cracks, detachments and damage. Complete information was obtained concerning the variability of the mechanical properties along the height and the different structural elements. Based on signal velocity values resulting from the non-destructive tests, some locations for semi-destructive testing were chosen. From cores bored on masonry, samples of brick and mortar were obtained. Laboratory tests and data processing were carried out with the aim of obtaining overall information on the mechanical properties of masonry in the tower.