OUT OF PLANE REFURBISHMENT TECHNIQUES OF EXISTING TIMBER FLOORS BY MEANS OF TIMBER TO TIMBER COMPOSITE STRUCTURES

摘要

Old timber floors often need strengthening and stiffening as they were designed to bear moderate loads and may suffer from excessive deflections with respect to current requirements. In the past, the stiffening and strengthening of wooden floors has been often achieved by using a reinforced concrete slab over the timber decking with a steel mesh connected to the timber joists. The aforementioned technique has some shortcomings concerning mainly the increase of dead load and the need for an additional structural depth over the existing decking. Moreover, it does not meet the requirement of "reversibility", coming from the heritage administration agencies. Therefore, recently the interest in "dry", "reversible" strengthening techniques (where the existing timber beams are coupled with thick timber planks, connected with different kinds of connection systems) has been aroused . A series of experimental bending tests on timber to timber composite floors have been carried out at the Laboratory of the Department of Mechanical and Structural Engineering (DIMS) of the University of Trento. The main purpose of this campaign is to study four different configurations of connection system (all by means of screws). Experimental data have been compared with theoretical values obtained through the "theory of composite beams with incomplete interaction" (Newmark et al. 1951). A specific model has been calibrated in order to take into account both the real load distribution and the connectors spacing. Parametric analyses have been performed to investigate the influence of these parameters on the global behaviour. With regards to the Serviceability Limit State, particular attention has been paid to the midspan deflection of the tested floors.