Seismic strengthening of a theatre masonry building by using active FRP wires

Masonry buildings of the architectural heritage were often built with poor materials and according to irregular structural schemes. This occurrence is critical when forces due to earthquakes should be taken into account for the assessment of structural vulnerability. It is well known that seismic forces are able to activate failure mechanisms that constitute typical collapse schemes of masonry buildings during earthquakes, when masonry elements are not adequately connected. In the last years new materials were employed as strengthening systems for structural purposes, and composite materials are those that have found a large field of application in this context. A new technique for seismic strengthening is presented in the paper, with reference to a real application. The application will be presented with reference to a historical masonry building used as public theatre, in which four pre-tensioned Fiber Reinforced Polymer (FRP) wires were designed and applied as external strengthening ties. The paper illustrates a study of seismic vulnerability for a large building used as theatre, through linear and non linear kinematic analyses. The results of the analyses allowed to understand the possible failure mechanisms that needed to be inhibited. The use of FRP pre-tensioned wires, 40 meters long, shows itself to be an effective structural solution in terms of costs and speed of application in order to reduce the seismic vulnerability. The results of the analyses will be illustrated and discussed in the paper, also with reference to the experimental tests that were necessary for the characterization of the material properties. The results will show how the presence of the FRP system is able to prevent possible collapses of the slender walls that are present in the building. The differences between the results of linear and non linear analyses will also be shown and discussed