The fatigue strength of structures made of rectangular (RHS) and circular hollow sections (CHS) is characterized by inhomogeneous stiffness distributions in the connection areas of braces and chord, which lead to high stress concentration factors (SCF). Using these SCFs in conjunction with structural SN-curves, the fatigue life can be estimated.
In the preceding research project FOSTA P1132, K-joints made of CHS used a special weld design resulting in a local reinforcement of the gap area. The fatigue tests showed an increase in fatigue strength compared to conventional CHS K-joints.
Based on this, in the research project FOSTA P1442, numerical and experimental fatigue investigations were carried out on K-joints with shape-optimized gusset plates.
The use of gusset plates was intended to increase the fatigue strength of K-joints by relocating the position of the hot spot to areas with lower stresses or by reducing the stresses at the hot spot.
For this purpose, three different gusset geometries were investigated for five RHS- respectively three CHS-geometries. Variant 1 (shortened, slotted braces and gusset plate attached to the chord), variant 2 (slotted braces also attached to the chord) and variant 3 (like V2, gusset plate additionnally passed through the underside of the chord). All components are circumferentially welded.
The SCF of the three gusset plate geometries are compared with the SCF of conventional K-joints. In addition, the SCF are compared with the required fabrication effort for the geometries under investigation. Finally, on this basis, a manufacturing recommendation for practical use is presented.