Dependence of Dowel Joint Strength on Welding Temperature in Rotary Welding

The system for measuring the welding temperature with measuring probes has been developed for the requirements of this but also of future research (at the Faculty of Forestry and Wood Technology, University of Zagreb). The research is based on determining the welding temperature and its impact on the joint strength or the embedded force of the dowel. Based on research results, the impact of the dowel rotation frequency and temperature on the joint strength has been determined. The measured welding temperature increased as the rotation frequency increased (the rotation frequencies of 865 min-1 and 1520 min-1 were used in the research). The maximum welding temperature in pine samples welded at the rotation frequency of 1520 min-1 amounts to 217 °C, while in samples welded at the rotation frequency of 865 min-1 it amounts to 179 °C (weld penetration of 20 mm). The maximum welding temperature in beech samples welded at the rotation frequency of 865 min-1 amounts to 181 °C, and 213 °C at the rotation frequency of 1520 min-1 (weld penetration of 20 mm). The impact of the wood type on the welding temperature has not been proven. In order to avoid difficulties encountered in contact measurement of the welding temperature, a heat transfer model was developed for a more precise determination of the welding temperature.

Duration of load behaviour of a glued shear plate dowel joint

An experimental study on the duration of load effects in a glued shear plate dowel joint was conducted. The joint design features a single large diameter dowel for load transfers between members, via external steel plates, which are bonded to the timber with a low stiffness bond line. Due to the low bond line stiffness, the timber element is subjected to a close to uniform shear stress distribution over the bond area. The study comprises a total of 80 test specimens loaded in shear, both parallel and perpendicular to the grain, at three load levels in the range of 50–80% of the short-term failure load. All specimens failed within approximately 110 days in outdoor sheltered conditions during which time deformations were recorded for one specimen of each type and load level. The study found a significantly larger influence of duration of load for this dominant shear action than what is reported in the literature for bending tests. The method of ranked stress was used to determine a suggested reduction factor kmod for the shear plate dowel joint to 0.10 and 0.30 for parallel and perpendicular loading, respectively. This is a rough estimate based upon a 50-year extrapolation of 4-month data. Thus, it must be concluded that the studied shear plate dowel joint is not efficient in terms of long-duration loads in outdoor sheltered climate, and that further studies are needed in order to verify the use in other climates. It is also evident in this study that there is a lack of knowledge and empirical evidence on the duration of load effects in timber for shear loading.

Numerical Simulation Studies on Tension Behavior of Casing and Dowel Joint of Square Steel Tube

The study on tension behavior of casing and dowel joint of square steel tube was carried out by using finite element analysis software ANSYS/LS-DYNA with consideration of geometric nonlinearity, material nonlinearity and contact nonlinearity. On this basis, the effects of inside tube wall thickness, main tube wall thickness, and inserting depth on failure mode, ultimate tensile load and deformation of casing and dowel joint of square steel tube was discussed. The results show that there are three types of failure modes, i.e., bolt failure, inside tube failure and main tube failure, when the joints are subjected to axial tension force. Compare to the joint with the same wall thickness of inside tube and main tube, the reduction of wall thickness of inside tube or main tube will weaken greatly the ultimate tensile load of the joint. The ultimate tensile load of casing and dowel joints is proportional to bolt shear strength, tube wall thickness, inserting depth, and tube edge length. The fruits are useful to the design and application of casing and dowel joints of square steel tube.

Evaluation on structural performance of compressed wood as shear dowel

This study addresses the application of compressed wood (CW) made of Japanese cedar, as a substitute for high-density hardwood, to shear dowel. A double wood-to-wood shear test was performed to evaluate the mechanical shear properties of CW perpendicular to the grain, and the results were compared with those of several types of dowel material. CW with its annual ring radial to loading direction (0°) had a unique double shear performance characteristic, and showed good properties as a dowel material by virtue of its strength and rich ductility. In contrast, CW with its annual ring tangential to loading direction (90°) and maple exhibited brittle failure. While thickness of the base member was varied, the ductility of the joint became stable for diameter over 36 mm and 24 mm thickness for the main and side members, respectively. When the density of the base member increased, its stiffness, yield load, and maximum load exhibited proportional improvement with different inclinations; however, in the case of a maple dowel, the increases were small. When the density of the base member was increased, the ultimate load had positive linear tendency, whereas plastic modulus decreased. Consequently, almost constant energy absorption was observed in spite of the increased density. The optimum load-carrying capacity and ductility of a compressed wooden dowel joint could be designed by introducing an appropriate base member.