Experimental study and finite element modelling of Japanese “Nuki” joints — Part two: Racking resistance subjected to different wedge configurations

The “Nuki” joint is a common timber connection in Japan, not only for historic buildings, but also for modern domestic houses. Its racking performance is dependent upon a number of factors, such as dimensions of the column and the beam, material properties of the joint members, and wedge configurations, etc. Among them, the wedge configuration, which leads to various tightnesses in the joints, may be the most influential factor on the structural behaviour during the service life. Various tightnesses introduced by wedges with different over-sizes introduce different initial stress states and stiffnesses to the joint, which have significant effects on the racking resistance of the joint. In this paper, 3D non-linear finite element models were developed to simulate racking resistance of joints tightened by different over-sized wedges. The models incorporate contact algorithms capable of modelling small slide and finite slide in different contact areas, especially large local indentations on the beam. Orthotropic elasticity was used to simulate the beam and the column in tension, whilst elasto-plasticity was used to simulate interactions in the contact zones where high contact stresses were expected. Contact stresses on both the beam and the column, also strains on the column, were studied. Finite element simulations of racking resistance of the joints with various initial conditions were compared with the corresponding experimental results. Reasonable correlation was obtained. Research on the initial stress states of “Nuki” joints was presented in Part 1 of this paper.