Innovative timber connection systems with the combination of indoor adhesive application and on-site adhesive-free assembly

In timber connections, adhesively bonded connections are, in general, cheaper, stiffer, and stronger compared to typically adopted mechanical connections. However, bond line quality is sensitive to various process-related parameters; thus, it is generally preferable to do the gluing in the factory with these parameters controlled during assembly and then transport the entire structure to the construction site. This leads to a limitation on the size of the timber structure owing to the limited transportation capacities. Another concern regarding fully glued timber-to-timber connections falls in their non-ductile behavior prior to the ultimate failure, which is crucial, especially in seismic regions. This paper focuses on the design of two innovative connection systems aimed at overcoming these two key limitations. Both systems offer the advantages of indoor adhesive application and on-site adhesive-free assembly. The first connection system involves a hybrid solution connecting prefabricated elements by means of steel rods and special ‘‘wheel-geared’’ notches of birch plywood, while the second connection system employs pure plywood notched connections during the on-site assembly. These two novel connection systems have potential for use in both moment- and force-resisting applications. In this study, they were introduced and designed in the format of a frame corner, where bending moment, axial force, and shear force are present. Analytical models predicting the capacity for each possible failure mode were developed and then validated by the test results. It can be found that the first connection system exhibits moderate ductile behavior, and its load-bearing capacity is considered to be satisfactory. The capacity can be further improved to be as strong as the fully glued connection if thicker plywood plates are utilized. The second connection system possesses lower strength and stiffness. However, it could still be applied in non-critical connection regions where no substantial external load exists.