PSI - Issue 75

Alberto Visentin et al. / Procedia Structural Integrity 75 (2025) 593–601 Alberto Visentin, Alberto Campagnolo,Vittorio Babini, Giovanni Meneghetti/ Structural Integrity Procedia (2025)

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stress acts at the weld toes due to the axial loading at the brace. After linear elastic analysis of the FE models, the PSM has been applied by exploiting the “PSM App” analysis tool. As shown in Fig. 2, the maximum equivalent peak stress is located at the saddle node “P” on the chord -side weld toe, consistently with the observed experimental crack initiation site, thereby confirming the predictive capability of the PSM. Concerning the global shell model, Table 1 summarizes the following parameters: • the length of the regions containing shell elements with increased thickness both on the brace member ( l br ) and on the chord member ( l ch ); • the FE size adopted to generate the mesh on the brace member ( d br ) and on the chord member ( d ch ); • the increased thickness applied to the shell elements on the brace tube side (t’) and on the chord tube side (T’ ) according to the empirical rules sketched in Fig. 1c-1d and discussed in previous Section 2. The following Fig. 3 provides details of the global shell model and solid submodel used in the FEA and PSM analyses. STEP 1: FE analysis of global shell model with shell thickness increased at brace-to-chord junction XY symmetry Plane: U Z = 0 ∆σ = 33.20 MPa FE size at brace d br = 5.5 mm

Shell FEs with increased thickness t’ – brace side

Brace midsurface t = 6.3 mm

Z X Y

l br ~ 11 mm

Shell FEs with increased thickness T’ – chord side

Z X Y

U X = 0 U Y = 0 U Z = 0

l ch ~ 10 mm

FE size at chord d ch = 5.0 mm

FE type: 8-node shell elements (SHELL281 of Ansys ® FE library)

Total number of FE nodes 3.90 ∙ 10 4 nodes (5 dof/node)

U X = 0 U Y = 0 U Z = 0

Chord midsurface T = 10 mm

Empirical rule proposed by (Meneghetti and Tovo 2002) T’ = T + 0.5 ∙ z = 13.2 mm t’ = t + 0.5 ∙ z = 9.50 mm

STEP 2-3: FE analysis of solid submodel

STEP 4: PSM fatigue strength analysis

FE nodes : 6.38 ∙ 10 3 nodes(3 dof/node) FE type: 10-node tetrahedral elements (SOLID187 of Ansys ® FE library)

Map displacements from global shell model to solid submodel Imported Cut Boundary Constraint [mm]

Equivalent peak stress edge-contour plot

Δσ eq,peak [ MPa ]

Cut boundaries

Global FE size d = t = 6.3 mm

t

PSMApp

D CB = 4T

D CB = 4T

Max

Z X Y

Z X Y

T

Fig. 3. Two-step finite element analysis procedure to apply the PSM to a CHS-to-SHS welded joint starting from a global shell model and a solid submodel. The represented case study is derived from the specimen “ TA1 ” (see Table 1).