4 Hot Spot Stress for Web-Stiffened Cruciform Joint

4.1 Applicability

4.1.2

The procedure for calculating hot spot stress at flange of web-stiffened cruciform joint is given in [4.2].

4.1.3

The procedure for calculating hot spot stress in way of the web of the web-stiffened cruciform joint is given in [4.3].

Figure 17 : Web-stiffened cruciform joints

4.2 Calculation of hot spot stress at the flange

4.2.1

For hot spot at the flange of web-stiffened cruciform joints, the surface principal stress is to be read out from a point shifted away from the intersection line between the considered member and abutting member to the position of the actual weld toe and multiplied by 1.12. The intersection line is taken at the mid-thickness of the cruciform joint assuming a median alignment.

The hot spot stress, in N/mm², is to be obtained as:

σ_HS = 1.12 σ_shift

where:

σ_shift : Surface principal stress, in N/mm², at shifted stress read out position.

The stress read out point shifted away from the intersection line is obtained as:

where:

t_1-n50 : Net plate thickness of the plate number 1, in mm, as shown in Figure 18

x_wt : Extended fillet weld leg length, in mm, as defined in Figure 18, not taken larger than t_1-n50.

4.2.2

The stress at the shifted position is derived according to the following formula and illustrated in Figure 19:

σ_shift = [σ_membrane (x_shift) + 0.60 ⋅ σ_bending (x_shift)] ⋅ β

where:

σ_surface(x_shift) : Total surface stress at x_shift position (including membrane stress and bending stress), in N/mm².

σ_membrane(x_shift): Membrane stress at x_shift position, in N/mm².

α : Angle, in deg, between the plates forming a web-stiffened cruciform joint as shown in Figure 19.

Correction factors for connections with plate angles intermediate to those given should be derived based on a linear interpolation of the above values. The calculated hot spot stress is to be used in conjunction with the hot spot S-N curve for weld toe connections according to Ch 9, Sec 3, [4.2].

Figure 18 : Geometrical parameters of web-stiffened cruciform connections

Figure 19 : Procedure for calculation of hot spot stress at web-stiffened cruciform connections

Figure 20 : Determination of stress read out points for web-stiffened cruciform connections

4.2.3

Surface principal stresses at the centre point of the two first elements on left and right side of the line A-A are averaged and taken as the surface principal stresses in way of the web position (line A-A). The surface principal stresses for load case ‘i1’ and ‘i2’ are linearly interpolated along the line A-A in order to determine hot spot principal stresses at the stress read out point located at the x_shift position as shown in Figure 20. The two principal hot spot stress ranges are determined at the stress read out point between load case ‘i1’ and ‘i2’.

4.3 Calculation of hot spot stress in the web

4.3.1

Hot spots located in way of the web as indicated in Figure 21 are to be checked with the hot spot stress defined from the maximum principal surface stress at the intersection offset by the distance x_shift from the vertical and horizontal element intersection lines as illustrated in Figure 21. The intersection line is taken at the mid thickness of the cruciform joint assuming a median alignment. The hot spot stress, in N/mm², is to be obtained as:

σ_HS = σ_shift

where:

σ_shift : Maximum principal surface stress, in N/mm², at the intersection offset by the distance x_shift.

The stress read out point at the intersection offset is obtained as:

where:

t_3-n50 : Net plate thickness of the web, in mm, as shown in Figure 21

ℓ_leg1, ℓ_leg2: Leg length, in mm, of the vertical and horizontal weld lines as shown in Figure 21.

Figure 21 : Hot spots in way of web