Study On Mechanical Behaviour Of Dowelled Steel-to-timber Joints

Because of its quick and easy construction procedure and reliable strength, dowelled steel-to-timber joints are widely used in modern timber structures. Currently, the existing researches are mostly focused on strength of joints, a few researches are concerned about stiffness and ductility of joints. In this disseration, an experimental investigation on dowelled steel-to-timber joints is carried out, which were subjected to tensile loadings at different orientations with regard to the grain direction (0°,30°,45°,60° and 90°). Each specimen in the experiment consists of two side timber members connected with a main steel plate using dowels. A series of specimens with 12mm、16mm or 20mm dowel diameter, different slenderness (wood member thickness/dowel diameter t/d= 1.5,4 and 8) and different number of dowels (n=1,2 and 4) were tested.The main influence factors on the joint load-carrying capacity were reported. The load-carrying capacity has an obvious positive correlation with dowel diameter and timber thickness. With the increase of the angle between load and timber grain, the load-carrying capacity has a decreasing trend. When the number of the dowels in joints increases, the load-carrying capacity has an obvious increasing trend. Also, the effective number of dowles in multi-dowel joint is less than the actural number of dowels, the effective number of dowles decreases as the angle between load and timber grain increases. By comparing the experimental load-carrying capacity and those calculated according to Chinese code, European code and American code, it is found that European code has the good prediction capacity and Chinese code gives a conservative prediction.For joint stiffness, the current European and American design codes showed their weak predictive ability. On the whole, joint stiffness increases as timber density, dowel diameter or number of dowels increases, and with the increase of the timber thickness (dowel slenderness), joint stiffness shows a decreasing trend. As the angle between load and timber grain equal to 30°, the joint stiffness is largest, then with the increase of the load angle, joint stiffness decreases. An empirical expression of stiffness for steel-to-timber joints with single dowel was proposed on the basis of the formula in Eurocode 5 using non-linear fitting of the experiment results.In ducitily aspect, an absolute ductility ratio is determined. The joint ductility shows a slight increasing trend as the angle between load and timber grain increases, and increases as the dowel slenderness increases. When the number of dowels in the joints increases, joint ductility decreases obviously.