Non-linear time history analyses of unreinforced masonry building with in-plane stiffened timber floors

The presence of unreinforced masonry buildings with timber floors in seismic areas has promoted the development of various retrofitting techniques. Among them, the increase of the in-plane stiffness of the floors is normally assumed as an improvement of the seismic behaviour of the building. However, the effectiveness of this retrofitting strategy is not easily predictable due to the difficulties in evaluating the modification of the seismic response of the building. In this work, a masonry case-study building with stiffened timber floors is analysed, simulating the actual non-linear behaviour of masonry piers and the hysteretic response of stiffened and unstiffened timber floors, calibrated according to tests available in literature. The 3D numerical model of the case-study building was implemented in the finite element software OpenSees. The model is able to simulate the in-plane hysteretic response of the floors and different types of failure of masonry walls. Results from non-linear dynamic analyses show that, in contrast to common expectations, traditional masonry buildings with timber floors may decrease their seismic performance if a retrofitting method leading to excessive in-plane floor stiffening is adopted.