Effects of deformation differences on connections in hybrid structure

Abstract

Hybrid structures that combine timber and concrete have become an increasingly attractive solution in modern construction, making use of the benefits of both materials. Timber offers a renewable, lightweight, and environmentally friendly alternative, while concrete provides stability and stiffness. However, the differences in long-term deformations between timber and concrete creates significant challenges, especially at the connections where these materials interact. If the timber elements deform more than the concrete ones in the structure, the connection that combine these, must accommodate the displacement mismatch. Such differences can lead to an increase in stress and forces, and potential long-term issues affecting the safety and performance of the structure. The aim of this Master’s thesis is therefore to investigate how these differential long-term deformations influence the structural performance of a timber-to-concrete connection in a hybrid structure. A specific focus is placed on an embedded steel knife plate connection, commonly used for its aesthetic appeal and fire-protective properties. Understanding how these deformations develop and interact at the connection will provide valuable insights for future designs. To achieve this aim, a finite element model (FEM) was developed in ABAQUS. This model simulates the connection under imposed displacements that represent long-term deformation effects. The analysis includes the distribution of forces in bolts and screws, stress concentrations in the timber beam, and the overall moment and stiffness of the connection. Different configurations of the connection were explored to identify the most critical factors that contribute to structural performance. The results of the study demonstrate that the difference in long-term deformations between timber and concrete significantly influences the load distribution within the connection. In particular, the analysis highlights the increased stresses and forces in key areas, such as the axial forces in the screws and the stress parallel to grain in the timber beam. The findings suggest that these effects should be carefully considered in connection design, especially when using embedded steel knife plate connections in hybrid structures. Furthermore, the results indicate the potential advantages of having a pinned connection and also allow steel parts to plasticise to decrease the moment development in the connection.