Demountable and Reusable Steel-Timber Composite (STC) Beams

The construction sector significantly impacts the environment due to high resource consumption, waste production, and carbon emissions. To address these challenges, this research aligns with the European Green Deal's objective of achieving carbon neutrality by developing and studying an innovative steel-timber composite (STC) flooring system, which embodies the principles of the circular economy. The main objectives of this study were to design a demountable and reusable STC flooring system, to develop novel shear connections that enable the reuse of structural components, and to establish analytical procedures to estimate the bending capacity of STC beams.
Steel-timber composite structures represent a relatively new structural system with limited research available and no established codes or guidelines specifically addressing their design and implementation. Additionally, there is no record of shear connections for steel-timber composite structures designed for demountability and reuse. This pioneering research has made significant progress in developing and assessing an STC flooring system and its shear connections. The STC flooring system consists of downstanding I-shaped hot-rolled steel beams and timber slabs made of laminated veneer lumber (LVL). The LVL slabs are connected to the top flange of the steel beams using novel shear connectors that enable demountability and reuse of the structural components.
To achieve the objectives of this research project, experimental, numerical, and analytical investigations were conducted. Experimental tests included material characterization of LVL, push-out tests on the novel shear connections, full-scale bending tests on the STC beams, and vibration tests. Numerical models were developed using ABAQUS software to simulate the behavior of the STC beams and extend the findings of the experimental tests. Analytical procedures, including a strain-based procedure and a simplified procedure, were proposed to estimate the capacity of the STC beams. Additionally, an analytical procedure based on the γ-method was proposed to estimate their bending stiffness and elastic moment resistance.
The findings of this study indicate that the novel shear connections contributed to achieve composite action and enabled the demountability and reuse of the STC beams without compromising structural integrity when loads remained within service limits. The STC beams demonstrated significant stiffness as well as load-bearing and deformation capacities. The tested beams showed improvements in stiffness of approximately 80% and in capacity of at least 40% compared to a reference identical steel-timber beam with no composite action. The proposed analytical procedures provided accurate estimates of bending stiffness, and elastic and ultimate moment resistance. Vibration tests showed that the natural frequencies of the STC beams were above the excitation frequencies typical of walking and crowd activities, indicating a low risk of resonance.