A study about optimal stiffening of timber floors in URM buildings

Timber floors in traditional masonry buildings normally have limited in-plane stiffness, which may be not sufficient to avoid out-of-plane failure of walls or to transmit efficiently seismic forces among walls. Therefore, various stiffening techniques of timber floors have been developed with the aim of improving the global behaviour of the building. The evaluation of the efficiency of the stiffening intervention needs adequate numerical modelling strategy, taking into account the nonlinear in-plane behaviour of masonry piers and spandrels, the out-of-plane stiffness and strength of walls, the actual stiffness and hysteretic behaviour of timber floors. The macro-element modelling can be considered an intermediate strategy in terms of model complexity, as it requires experimental data for its calibration, but can be quite easily adapted to the building geometry. Nonlinear incremental dynamic analyses of different case-study buildings are presented, varying the type of floor, the seismic signal and the modelling criteria as the complexity and accuracy of the adopted technique, with the aim of analysing the effects of the stiffening techniques on the building response. The comparative analyses show that the seismic capacity of a traditional masonry building may decrease if a retrofitting method leading to excessive floor stiffening and/or mass increase is adopted, depending on the geometry and mechanical characteristics of walls and floors. This means that the need of increasing the in-plane stiffness of floors should be evaluated on a case-by-case basis, comparing the actual capacities of floors and walls.