Efficacy Assessment of Timber Based In-Plane Strengthening of Wooden Floors on the Seismic Response of Masonry Structures by means of DEM Analyses

Masonry buildings are highly vulnerable to seismic loading, and their dynamic response is strongly influenced by the timber floor in-plane deformability and by the quality of the wall-to-floor connections. Understanding the behavior of timber floors and roofs and their interaction with the masonry walls is therefore important for the protection of historical buildings. In a previous research project, different timber-based dry-connected floor strengthening solutions were tested under in-plane loads. The experimental results show a significant increase in shear strength and stiffness. Discrete Element Method is here used to evaluate the effectiveness of the strengthening solutions in avoiding the triggering of the out-of-plane collapse of masonry walls, first on a simple masonry cell, and then on a heritage listed masonry building. A detailed cyclic model of the floor behavior was implemented: the unreinforced and reinforced floors were described by beams connected with nonlinear springs, reproducing the experimental hysteretic response. Both the case studies highlight the effectiveness of the strengthening solutions in reducing the out-of-plane displacements of masonry walls, confirmed also by a comparison with the ideal rigid diaphragm case. The reinforced floor is able to transfer the seismic forces to the shear-resistant walls. The out-of-plane displacements are compatible with the wall capacity, and the reinforced floor hysteretic cycles contribute to dissipate part of the input energy. Moreover, a proper connection design can also cap the transferred seismic forces to an acceptable level for shear-resistant walls.