Coperture scatolari antisismiche

A wooden roof strengthening technique aimed at transforming the roof pitches into anti-seismic shear resisting diaphragms is presented in this paper. Shear diaphragms gather and transfer the seismic loads to the shear resisting walls. The roof box structure forms a sort of “cover” of the masonry building, which avoids the overturning of the walls undergoing out-of-plane loads, and which allows triggering a global box structure behavior. Plywood diaphragms are built on top of the existing structures without significantly modifying the roof overall layout. The proposed strengthening technique is lightweight, mainly reversible, minimally impairing of the building integrity, and can be easily applied for the construction of anti-seismic wooden roofs in new buildings. A simplified design approach, which allows identifying the static role of each structural element, is presented in this paper. The approach can be adopted to validate the results obtained by means of advanced analytical methods, such as the finite element method. An analytical method for the estimate of the box structure displacements, as well as a short digression on the displacement control requirements are also illustrated. The diaphragm technique was recently applied for the anti-seismic retrofit of some monumental buildings in Italy. A case study, as well as the basic design criteria for applying this technique are presented in this paper.