INNOVATIVE APPROACHES FOR ENCHANICING THE MECHANICAL PERFORMANCE OF TIMBER-CONCRETE COMPOSITE FLOOR BEAMS

Abstract

The use of timber-concrete composite (TCC) floor systems is a rising trend. TCC systems are made of timber beams that connected to a concrete slab with connectors. The connector used for the composite beam is the most important component as its performance defines the efficiency of the composite action. The connector should be strong enough to resist the external loads from the structure, stiff enough for a limited deflection and ductile enough to plastify to transfer internal stresses. The aim of this thesis is to further develop the mechanical performance of new applications in TCC floors. TCC floors can be implemented in two scenarios: i) in existing timber structures e.g. by adding a concrete screed on top of existing timber beams and ii) in new constructions. In both, different connections, methods and mechanical properties are necessary. This thesis is investigating solutions to further develop the mechanical performance of TCC in such applications. The solutions are first studied at the connection level, and subsequently at full scale T beam level. Experimental, analytical and numerical analysis are conducted. The aim of this thesis is to serve both researchers and practitioners where more in-depth knowledge of load transfer mechanisms are provided. In existing timber structures, the possibility to add permanent loads may be limited. For this reason, the use of a lightweight concrete can be a competitive option since an improved structural performance could be obtained while limiting the added dead load. Dowel type shear connections are the most practical solutions for on-site executions such as in renovations. In this thesis, dowel type connections are investigated with different parameters using lightweight concrete. The results showed that screw connections have performant mechanical responses when used with lightweight concrete. In addition, a solution to mitigate or reduce the effects of an interlayer, that can be often practical or even necessary for execution reasons, is developed. For new constructions, the target is obtaining longer spans. Accordingly, very strong and stiff connections are necessary. The same problem has been studied in steel concrete composites in 1980s. The goal was to develop a connector alternative to studs to target long span bridges. This event marks the application of perfobond plates among others. In this thesis, these connectors are implemented to TCC using a bonded-in connection of the perfobond plate to the timber beams. For these connections, both normal weight concrete and lightweight concretes are studied. The experimental results showed a very strong and stiff response of the connectors. Lastly, the self-weight can be reduced when lightweight concrete is again used instead of normal weight concrete, but at the expense of compromising the strength capacity of the full scale T-beams.