| Small-diameter round timber, which is a kind of forestry by-product mainly from thinning of the artificial forests, refers to juvenile timber usually with girth smaller than normal round timber. A large quantity of such timber is produced every year. Small-diameter round timber is plentiful and inexpensive, yet it is presently destined for low grade applications such as pulp for making paper, board production or even fuel in uneconomical ways. Innovative and efficient ways need to be developed to utilize the small-diameter round timber for structural members. To achieve the objective, five kinds of the composite members were developed. These included the built-up stud, the wood-steel joist, the wood-steel roof truss, the shearwall with the developed built-up stud and the diaphragm with the developed wood-steel joist. The structural performance of these members was investigated by full-scale testing, FE simulation and theoretical analysis. The methods to calcualte the load-carrying capacity of the members were presented, and the design values and design methods of these members were also developed for the purpose of engineering application. It has been found out that the developed members had good performance and can be used as substitutes of the corresponding members in the conventional light wood frame construction.The physical and mechanical properties of the small diameter round timber of China Northeast Larch (Larix gmelinii Rupr), i.e. the bending strength, the bending modulus of elasticity, the ultimate tension and compression strengths parallel to grain and the shear strength parallel to grain, were determined by conducting test on 295 small clear specimens and 61 full-sized small-diameter round timber specimens. Based on the test results, the design values of strength and modulus of elasticity of the small-diameter round timber were derived.36 built-up studs were manufactured and assembled into 12 specimens. The load-carrying capacity of the built-up stud was investigated by testing the specimens under either axial or eccentrical compression, respectively. FE model of the built-up stud was developed and used to simulate the performance of the stud. To predict the load-carrying capacity considering bulking, the equavalent slenderness ratio of the built-up stud was derived.To investigate the behaviour of the developed shearwall,15 wall segments with different configurations were manufactured and tested under cyclic lateral load. The failure modes of the wall segments were observed and the hysteresis curves obtained. The lateral resistance, elastic shear stiffness and the ductility ratio were evaluated. The hysteresis model of the sheathing-to-frame nail connection and an FE model of the shearwall were developed using ABAQUS, and the structural behaviour simulated. The design value of the shear strength of the shearwall was provided based on the test results and the analysis.The failure modes and load-displacement curves of the composite joist and the wood-steel roof truss were obtained by testing 18 full-sized wood-steel joists under bending and 6 full-sized wood-steel roof trusses under concentrated loads, respectively. The performance of the composite joist and wood-steel roof truss were further investigated with the developed FE models, and the methods to determine the design strength of the joist and roof truss were provided.The in-plane stiffness of the composite diaphragm was investigated under 3rd-point loading in the plane of the diaphragm. The sheathing-to-frame nail connections were tested to obtain the load-slip curves, and the FE model of the diaphragm was developed based on the test results. The load distribution between shearwalls due to different stiffness of the diaphragm was investigated by means of a deep beam on the spring model and suggestion was provided to determine the load-sharing factor between shearwalls in the developed light wood frame construction. |
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