The shear plate dowel joint : Research on a novel connection for heavy timber structures

Sammanfattning: An increased use of wood can reduce the environmental footprint of the building sector. In order to improve the competitiveness of heavy timber structures, the thesis presents a novel type of timber connection with a high degree of prefabrication. The connection includes a resilient bond line, meaning an elastic bond line with low stiffness yet high fracture energy.It has previously been shown that a large glued joint with a conventional stiff adhesive bond line acting in shear can be made stronger by using a resilient bond line, e.g. by introducing an intermediate rubber foil. The scientific contribution of the thesis starts by comparing such resilient bond lines to conventional non-resilient bond lines. It is shown by numerical analyses that the short-term strength of glued lap joints can be increased by 40-80% by introducing a resilient bond line. Unlike other types of connections, a resilient bond line also enables the possibility to design the stiffness by varying the hardness and thickness of the intermediate bond layer.The proposed shear plate dowel joint uses a single dowel to transfer load between members. The load transfer from the dowel to the timber element is realised by externally bonded metal plates. The plates are bonded to the element using a resilient bond line, which ensures that the loading is applied to the timber member in uniform shear. Large scale experimental testing has shown an average shear stress over the plate area at failure of 3.1 MPa, while small scale specimens have reached 5.8 MPa. The structural response of the connection for different dowel materials and designs are investigated both numerically and experimentally, and it is shown that increased ductility can be obtained using tubular dowels.However, the long-term behaviour of the shear plate dowel joint has been found inadequate. A reduction factor of 0.1-0.3 was found for open sheltered climate 50-year period reference, which weakens the benefit of increased load-carrying capacity of the design proposal compared to other contemporary connections. It should be noted that this is an estimate based on 4-month small-scale data extrapolated to 50 years. However, further studies of the duration of load characteristics as well as fire resistance should be conducted prior to structural application.