M. Nunes^1, R. Bento² and M. Lopes²
1)  Instituto Superior Técnico, Universidade de Lisboa, Lisbon (Portugal)
Av. Rovisco Pais, 1, 1049-001 Lisbon, Portugal
e-mail: margarida.nunes@tecnico.ulisboa.pt
2)  CERIS, Instituto Superior Técnico, Universidade de Lisboa, Lisbon (Portugal)
Av. Rovisco Pais, 1, 1049-001 Lisbon, Portugal
e-mail: rita.bento@tecnico.ulisboa.pt, mario.lopes@tecnico.ulisboa.pt

Keywords: Horizontal diaphragms, Timber floor, Experimental test, In-plane stiffness, retrofit of URM buildings.

Abstract. The seismic vulnerability of unreinforced masonry (URM) buildings is strongly influenced by the characteristics of timber floors. In fact, it is well-recognized that an adequate in-plane stiffness of the floors and of the connections between the floors and the walls can improve the three-dimensional response of masonry buildings.
In this work, a steel strengthening solution is proposed to improve the in-plane stiffness of timber floors. The solution consists of placing underneath the wooden floors a steel grid of thin plates and angles at the perimeter to connect to the walls of the existing building. The connections were done with screws. The strengthening solution proposed was numerically modelled, in SAP 2000. Furthermore, to check the performance of this solution an experimental investigation was conducted.
A cyclic shear test was carried out on a real scale timber floor strengthened with the steel structure proposed. This test allowed the evaluation of the failure mode, force–displacement diagrams, and of various behavioural parameters such as floor resistance and in-plane stiffness. The experimental cyclic test, showed that the strengthened timber floor performed well. In fact, the strengthening solution improved the floor resistance and its in-plane stiffness.