PSI - Issue 57

Philipp Ladendorf et al. / Procedia Structural Integrity 57 (2024) 589–597 Ladendorf, Herion, Winkler, Dürr / Structural Integrity Procedia 00 (2019) 000 – 000

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In the preceding research project FOSTA P1132 (Herion et al. 2020), 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. Moreover, in a numerical study of RHS-K-joints with gusset-plates and open brace ends (Herion et al. 2014, 2017) it could be shown that the fatigue resistance could be improved in theory com pared to conventional RHS-K-Joints by reducing the SCF. Based on this, in the research project FOSTA P1442 (Herion et al. 2023), 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. 2. 2 Scope of the investigations 2.1. General remarks To take different industrial applications and manufacturing depths into consideration, three gusset geometries were investigated for five RHS- respectively three CHS-geometries, cp. Fig. 1. For the experiments, all components are cir cumferentially welded using fillet welds. The manufacturing effort and the stiffness arise from variant 1 to variant 3. The numerical investigations neglect the weld seams and compare the conventional K-joints with 45°-brace-angles to the geometrically optimized gusset-plate variants by using the structural hot spot stress concept according to CIDECT Design Guide 8 (DG8, Zhao et al. 2002). While the research project FOSTA P1442 covers the three load-cases axial brace-load, chord-load and in-plane-bending, the present paper mainly describes the findings of the first load-case axial brace-load.

Fig. 1: Experimentally investigated joint and gusset plate configurations a) variant 1 – gusset plate with short, slotted braces, b) variant 2 – gus set-plate with slotted, extended braces, c) variant 3 – through-chord gusset plate with slotted, extended braces

The SCF of the three gusset-plate geometries are compared with the conventional K-joints. In addition, the SCF are compared with the required fabrication effort for the geometries under investigation. Finally, on this basis, a man ufacturing recommendation for practical use is presented.

2.2. Investigated geometries

2.2.1. Profile cross-sections The cross-section geometries of the numerically investigated hollow sections are displayed in Table 1. The corre sponding geometries of the most important gusset-plate parameters are shown in Table 2. The five RHS-geometries cover brace- to chord-width-ratios between 0. 40 ≤ β ≤ 1 .00; width- to wall-thickness- ratios between 15 ≤ 2γ ≤ 25 and chord- to brace-wall-thickness-ratios between 0. 50 ≤ τ ≤ 1 .00. The eccentricities of the RHS are chosen to lie within the limits of the current design specifications (DG8, Zhao et al. 2002). For the three CHS-geometries, the investigated parameters lie between 0. 59 ≤ β ≤ 0 .75; 15 ≤ 2γ ≤ 25 and 0. 63 ≤ τ ≤ 1 .00. Although the parameters lie not within the permissible limits of DG8, for the sake of comparability, the geometric variants of the conventional and the gusset plate-K-joints share the same joint-parameters as in P1132 (Herion et al. 2020). In practice, the gusset-variant 1 could also be fabricated with an eccentricity of zero. To show the potential of the gusset-plates, it is paramount to keep the same geometric boundary conditions, so that secondary effects are the same for all investigated geometries.