关键词: 榫卯节点, 直榫, 正交层板, 预增强, 木结构

Abstract:

Objective: Based on the fact that the local compression deformation of straight tenon and mortise joints under bending is relatively large and the bending stiffness and load bearing capacity are low, the concept of "cross-laminated timber" was referenced to develop suitable pre-reinforcing methods for straight tenon and mortise joints. This study was carried out to investigate the effects of locally cross-laminating on the structural performance of straight tenon and mortise joints, and put forward a reasonable pre-reinforcement methods and relevant parameters in order to provide theoretical and practical supports for the application of traditional tenon and mortise joints in modern timber structure projects. Method: 18 straight mortise and tenon joints were manufactured with glulam of No.1 Douglas fir (Pseudotsuga menziesii) lamination, of which some were treated with 4 different reinforcing methods. All of the joints were tested under monotonic loading. The failure modes and working curves were observed, and the moment carrying capacity and initial stiffness were obtained. The constitutive model of wood under complex stress state was developed and finite element(FE) model was developed. The tests were simulated by FE methods and the model was verified by comparing the predicted deformation modes, load-displacement curves, moment and stiffness with the test results. Then parametric study was conducted to investigate the effects of locally cross laminating on the structural performance of the straight tenon and mortise joints. Result: It was observed that compression deformation perpendicular to grain at the upper surface near the tenon end and the lower surface near the beam was the most critical for the untreated tenons. By locally cross laminating, the compression deformation perpendicular to gain could be effectively reduced. It was found that the initial stiffness of the joints increased from 14.0% to 36.9% for different reinforcing configurations, and the moment carrying capacity of some specimens increased while some specimens decreased. The predicted results from FE model were correlated well with the test results. With the increase of width of the cross-laminations, the stiffness of the joints firstly increased and then decreased, however, the moment presented an opposite trend. With the increase of thickness of the cross-laminations, the stiffness of the joints increased while the moment decreased. For the tenon and mortise in this study, it was recommended to take a rate of thickness of cross-lamination to the tenon width of 0.25 and a width of 210 mm as the optimum solution, respectively. Conclusion: The rotational stiffness of straight tenon and mortis joints could be improved by the locally cross laminating. By choosing appropriate parameters, the ultimate moment could also be increased. The structural performances of the straight tenon and mortise joints could be further improved by using materials like bamboo scrimber and steel plates, which might have a higher strength and ductility, instead of wood laminations.

Key words: tenon and mortise joint, straight tenon and mortise joint, cross-lamination, pre-reinforcing, timber structure