The continuum of connection rigidity in timber structures

The use of timber in rigid frames has been hampered by the debate surrounding the rigidity of the moment connections. Joint stiffness is a function of beam flexural stiffness, as well as of the rotational stiffness of the connection. The level of joint rigidity, which is predictable from joint stiffness, significantly affects the bending moments and forces that are transferred through the connection. We used joint-test data from the literature and computer models to assess the effect of various parameters on joint stiffness. There is a continuum of joint stiffness for moment-resisting connections where the deformed shapes of the beams in beam-to-column connections are described by pinned, semi-rigid, and rigid behavior. Engineers can assess the level of joint rigidity during the design process so that the resulting connections and frames meet performance expectations. It seems unlikely that a fully rigid joint can be designed for use in timber portal frames because of stiffness orthotropy. However, moment-resisting joints that are less than 50% rigid can be used in timber frames to develop frame-like behavior.