Numerical analysis of a timber-concrete composite floor system

Sammanfattning

Reinforced concrete is one of the most widely used materials for flooring systems due to itseasy availability worldwide, low price, good strength and stiffness, high durability, and itsability to be formed into any shape and size. However, to prevent the exhaustion of naturalresources and reduce the carbon footprint of cement production, it is becoming necessary toreduce the use of concrete. To pursue sustainability and implement the findings of the ParisAgreement, the construction industry is increasingly starting to use timber as an environmentallyfriendly material. In particular, the use of cross-laminated timber (CLT) has increasedin flooring systems. However, the use of CLT as a system comes with structural challenges,such as ensuring adequate vibration-related comfort, sound insulation, and fire resistance. Toaddress these performance shortcomings of CLT or reinforced concrete floors, timber-concretecomposite (TCC) has recently become an increasingly preferred alternative, offering a viablesolution for both the construction of new floor systems and the renovation of existing floors.TCC floors typically feature a thin concrete slab connected to a timber component via shearconnectors. The timber component is designed to withstand tension and is located on the bottom,while the concrete slab is designed to bear compression and is located at the top. Theconnection system transmits the shear forces between the two components. However, designingfor disassembly, reducing resource consumption and waste, and decreasing dependency onvirgin resources is crucial. To contribute to this aim, this study focused on numerical investigationsof a novel dismountable TCC floor system comprising prefabricated concrete and athree-layer CLT connected with notches and screws.To enable disassembly after the end of service life, wooden dowels were placed in the concretelayer, and screws were drilled inside the wooden dowels to connect the concrete and CLT.In this research, concrete and steel’s elastic and plastic material properties were modeled, alongwith timber-only elastic material properties. Specimens were modeled in 3D in Abaqus/Standard.The scope of the research was to analyze the proposed TCC model in the short-term SLS stage,and subsequently check the bending performance, and composite action behavior of the slabunder a four-point bending test. To achieve this, the research results were first validated andcompared with the gamma method provided in EC5, Annex B. Then, under four times largerdisplacement, the performance of the slab was tested, and a parameter study was conducted onthe fiber direction for wooden dowels, the material properties of the wooden dowels, and thedepth of the notch.Overall, the analyses carried out in the study of the TCC flooring system with connectors toensure its future demountability tentatively demonstrated the feasibility of such a solution.The calculations showed the correct composite action and therefore stiffness of the entire floorsystem so that deflections are within an acceptable range. Importantly, it is a solution that fitsin well with the requirements of a circular economy, which could be a competitive advantagein future years.