This study investigated the vibration serviceability of timber structures with dowel-type connections. It addressed the use of such connections in cutting-edge timber structures such as multi-storey buildings and long-span bridges, in which the light weight and flexibility of the structure make it possible that vibration induced by dynamic forces such as wind or footfall may cause discomfort to occupants or users of the structure, or otherwise impair its intended use. The nature of the oscillating force imposed on connections by this form of vibration was defined based on literature review and the use of established mathematical models. This allowed the appropriate cyclic load to be applied in experimental work on the most basic component of a dowel-type connection: a steel dowel embedding into a block of timber. A model for the stiffness of the timber in embedment under this cyclic load was developed based on an elastic stress function, which could then be used as the basis of a model for a complete connector. Nonlinear and time-dependent behaviour was also observed in embedment, and a simple rheological model incorporating elastic, viscoelastic and plastic elements was fitted to the measured response to cyclic load. Observations of the embedment response of the timber were then used to explain features of the behaviour of complete single- and multiple-dowel connections under cyclic load representative of in-service vibration. Complete portal frames and cantilever beams were tested under cyclic load, and a design method was derived for predicting the stiffness of such structures, using analytical equations based on the model for embedment behaviour. In each cyclic load test the energy dissipation in the specimen, which contributes to the damping in a complete structure, was measured. The analytical model was used to predict frictional energy dissipation in embedment, which was shown to make a significant contribution to damping in single-dowel connections. Based on the experimental results and analysis, several defining aspects of the dynamic response of the complete structures, such as a reduction of natural frequency with increased amplitude of applied load, were related to the observed and modelled embedment behaviour of the connections.
Glulam members which are manufactured with Japanese cedar plantation timber are constructed into a box type of portal frames to investigate the moment-resisting performance when subjected to a lateral load. The joints of the frame are connected using aluminium connectors and self-tapping screw fasteners, and the placement of fasteners on the connection are arranged into three patterns. The loading protocol is applied laterally in seven cyclic stages for the racking test. The maximum lateral load of 51.4 kN is attained for the portal frame fastened using self-tapping screws arranged in square pattern, followed by single circular pattern and double circular pattern. Resulted dissipated energy obtained from the portal frame with square pattern placement is 1224.2 kNmm during the cyclic loading stages, higher than the other fastener arrangement by 20%. The allowable shear strength of the box-type portal frame is decided by the load corresponding to the shear deformation of 1/120 radian.
Glulam-based post-tensioned moment-resisting portal frames were developed by a producer from British Columbia in collaboration with ASPECT Structural Engineers. These modular frames, manufactured from appearance-grade glulam, can be viable solutions for substitution of steel moment frames in predominantly wood-framed buildings. This paper presents an experimental study on the structural performance of post-tensioned glulam moment-resisting portal frames under in-plane lateral loads. A total of twelve frame specimens in four different configurations were tested under static or reversed cyclic loads. The test results show that the behaviour of post-tensioned moment-resisting portal frames was relatively similar under static and cyclic loading, in which non-linear elastic behaviour was observed due to the post-tensioning. The peak lateral loads applied to the tested post-tensioned frames was in a range of 34.1 kN to 61.7 kN and the lateral stiffness ranged from 0.53 kN/mm to 2.65 kN/mm, respectively. Depending of the frame configuration, typical failure modes identified during the testing consisted of a combination of either (i) compression perpendicular to grain failure at the columns on the side in contact with the beam; or (ii) compression perpendicular to grain failure at the beam on the side in contact with the columns; and (iii) screw failure in the column-to-base joints (if present). The tests give a valuable insight into the seismic performance of post-tensioned glulam moment-resisting portal frames.
