Additive technologies for improving the strength and deformation characteristics of plastic washer joints of wooden structures

Introduction. Modern wooden structures are mostly connected by mechanical working joints. To increase the reliability of nodal joints, various kinds of washers can be pressed, inserted, or glued into the wood of the elements, thus ensuring the transmission of forces from one element to another. Joints on glued washers can transfer significant forces on a relatively small area of mutual contact, which is due to their high loadbearing capacity. Thus, the gluing of steel washers in places of increased stress concentration during force transfer ensures a significant redistribution of buckling/cracking stresses over a larger area of the connected parts. However, steel washers are highly corrosive, so additional measures are required to protect metal parts from corrosion or to replace the material with the composites. The results of full-scale tests of the samples with glued-in plastic washers are used to consider the ways of increasing the strength and deformation characteristics of the plastic washer material by applying additive technologies. Aim. To increase the load-bearing capacity of the wooden structure joints by increasing the strength and deformation characteristics of the glued washer material. Materials and methods. A method for full-scale tests of wooden specimens with glued fiberglass washers is presented. The wooden elements are made of second grade pine, while the washers are of REC Formax and REC Friction plastics. The test was performed in compression along the fibers, with control of vertical shear deformations. The methods of increasing the strength and deformation characteristics of plastic washers by using additive technologies are considered. Results. Using the data of full-scale tests the diagrams of sample deformations on glued plastic washers are drawn, the obtained results are analyzed. The sufficiently high plasticity of washer materials is established. The ways for increasing the strength and deformation characteristics of plastic washers, particularly by reinforcing the plastic washers is suggested. Conclusions. In order to increase the load-bearing capacity of the joints on the glued fiberglass washers, the reinforcement of plastic using additive CFC printing technologies and the use of different reinforcing fiber materials is adopted.