Experimental and Numerical Assessment of an Improved Plywood-Based In-Plane Retrofitting Method for Timber Floors in Highly Seismic Areas

Wood-based retrofitting techniques for seismic upgrading and architectural conservation of existing buildings have found increasing application in the last decades. With reference to the in-plane seismic strengthening of existing timber floors, a particularly efficient solution consists of an overlay of plywood panels fastened to the sheathing. This technique allows a great improvement in strength, stiffness, and energy dissipation of the floors. Yet, when adopting this strengthening solution for existing floors in highly seismic regions, the target design loads could require large values of in-plane strength and stiffness for the retrofitted diaphragms, and this could cause their beneficial, dissipative potential to be reduced. Thus, in this work, a strengthening solution is presented, able to retrieve high strength and at the same time activate large energy dissipation in the floors. The proposed technique consists of the creation of two independent shear planes by means of two different superimposed overlays of plywood panels. Previously developed analytical and numerical models describing the in-plane response of floors retrofitted with a single plywood overlay were adapted for the present case with two overlays, validating the results against an experimental test conducted on a sample representing a floor portion. Very good agreement was obtained between experimental and analytical as well as numerical results, thus the proposed approaches enable an efficient design process and an accurate simulation of the proposed retrofitting technique.