Timber composite solutions for high performance new diaphragms and structural rehabilitation of existing floors

The main aim of this research work was to deepen the understanding of the mechanical behaviour of timber-to-timber composite (TTC) floors with incomplete interaction in order to develop, design and test high performance solutions. Several types and arrangements of connections and different timber products, made from both softwood and hardwood species, were considered for the realisation of diaphragms suitable for a wide range of structural applications. An original assembly procedure, developed at the University of Trento, was adopted in the optimization process of these technical solutions. Such innovative procedure allows the designers to pre-stress and camber composite timber elements by simply relying on screw type connectors. The experimental tests presented in this thesis positively contributed to the calibration and validation of this assembly technique, confirming the method applicability. The test results were consistent with the numerical and analytical models, in terms of uplifts, stress levels and overall mechanical performance. The benefits from adopting the above-mentioned procedure appeared to be persistent over time, as the result of an experimental test where four composite specimens, 5.4 m long, were loaded out-of-plane and subjected to continuous monitoring under controlled environmental conditions for a period of two years. The research program was organized into two phases. The first phase was dedicated to the study of alternative strategies for retrofit interventions on timber diaphragms in historical heritage buildings. An extensive experimental campaign on the out-of-plane behaviour of the retrofitted diaphragms was performed in order to evaluate the effectiveness of the different techniques analysed. Specifically, hybrid solutions that coupled the reduced weight of softwood elements with the strength of hardwood components by means of different types of fasteners, were compared with “more common†timber-to-timber strengthening techniques. A large number of tests, covering fourteen configurations obtained by changing fasteners type, fastener arrangement and timber products, were performed to maximize the performance (cost/effectiveness) of the retrofit techniques. Test outcomes included characterization of stiffness, strength, static ductility and residual strength of the connection systems as well. The second phase of the program was devoted to the development of solutions for newly constructed diaphragms, either for new building applications or replacement of damaged/inadequate existing floors. The second phase research work included the design and testing of prefabricated timber-to-timber composite floor modules to be assembled by using laminated veneer lumber (LVL) made of beech wood. Full scale tests were performed on 6 m long and 10 m long modules, respectively designed for residential areas and offices. In addition to the full-scale testing of the modules, the connection system optimization was performed by referring to different types of test protocols, including both push-out and pull-out testing.