High Performance glued-in rod connections for Cross-Laminated Timber (CLT) structures

Abstract

In timber structures, connections determine the stiffness and strength of the structures. Glued-in rod connections are one of the frequently used connections in timber engineering due to their large load capacity, good fire and corrosion performance (because of the concealed rods), and aesthetically pleasing appearance. Glued-in rods are mostly used with glulam, and to some extent, with LVL members. Although there have been many successful implementations in practice, there is still no consensus on a standard for glued-in rods and still design guides and technical notes are applied for their design. This shows the complexity of strength estimation under the influence of the hybrid structural behaviour of glued-in rods. The introduction of new engineered products, such as cross-laminated timber (CLT) that are different in terms of layer arrangement and structure, necessitates a thorough evaluation of the effectiveness of glued-in rods in such products. The current study investigates the strength of multiple glued-in rod connections embedded in CLT. For this purpose, full-scale experimental monotonic and cyclic tests were conducted, where the glued-in rods were embedded parallel, perpendicular, and on the boundary of two cross-wised layers in different embedment lengths on the edge of CLT panels. Moreover, numerical simulations and parametric studies of glued-in rods in CLT are being studied. The simulations are based on 3D finite element analysis, using a cohesive surface model for the bondlines along the rods. The parametric studies are investigating the influence of the glued-in rods length, the rod diameter, and the rod-to-grain angle on the load-bearing capacity and stiffness of the connections. Comparisons between experimental data and the numerical results showed a high conformity in the maximum load, stiffness, and failure mode of the connections. Finally, a design equation is provided to determine the pull-out strength of the glued-in rods embedded in CLT based on the shear strength of the bondline. The results of the monotonic tests demonstrated that glued-in rod connections in CLT could only exhibit ductile behaviour and fail due to ductility under the right conditions. Furthermore, the cyclic loadings demonstrated how glued-in rod connections maintain their elastic characteristics all the way up to failure. The findings of this study showed that this connection technique could provide a trustworthy and durable connection for CLT construction.