Investigating the Soil-Structure Interaction and dynamic behavior of historical watch towers in Malta and Gozo

The Maltese archipelago is characterized by the presence of several seventeenth century coastal watch towers. They are part of the cultural heritage of the Maltese islands and they represent an important milestone in the fortification history of the island during the Order of St John rules. They are at a constant risk due to natural processes such as coastal weathering, erosion and land movement, but above all they are more vulnerable to earthquake ground shaking and thus subjected to a possible considerable seismic risk. Historical fonts confirm that such structures have been damaged in the past by earthquakes that occurred both at local and regional distances. In this study, we present results that can be used to evaluate the seismic vulnerability of these structures. In order to do so, the dynamic characteristics of these towers as well as soil-structure interaction were investigated through an extensive geophysical campaign carried out at different locations. Measurements of ambient noise were recorded inside each tower to compute the fundamental frequency. In addition, measurements were also taken around the towers in order to determine the ground response. A digital 3-D model for each tower was constructed and ANSYS software was used to analyse the structure’s behaviour and to compare the simulated data with the experimental ones.