Design of joints 12-13, 12′-13′ (welded joints) — example

Design data

External forces: F_X = 1500 N, F_Y = 300 N, F_Z = 700 N act at distances L_c = 70 mm, X₁ = 80 mm, X₂ = 220 mm, X₃ = 150 mm, Y₁ = 550 mm, Z₁ = 180 mm; the forces and moments at the centre of the welded joint 12-13 are:

F_Xs = F_Xd = F_X/2 = 750 N,

F_Ys = F_Yd = F_Y/2 = 150 N,

F_Zs = F_Zd = F_Z/2 = 350 N;

M_X13 = F_Y (L_c + Z₁)/2 = 37500 Nmm,

M_Y13 = F_X (L_c + Z₁)/2 + F_Z (X₁ + X₂)/2 = 292500 Nmm,

M_Z13 = F_X Y₁/2 + F_Y (X₁ + X₂)/2 = 457500 Nmm.

Dimensional constraints: tube 12 is welded to tie rod 13, with h₁₂ = 50 mm, t₁₂ = 5 mm and g₁₃ = 15 mm.

Operating constraints: temperature T = (−30…40) °C; outdoor working environment with high humidity.

Design constraints: weldable materials.

Materials and heat treatments

For elements 12 (12′) and 13 (13′), the weldable steel S235 according to SR EN 10025-2 (STAS 500/2) was adopted.

Material properties

Sizing

From the sizing relation obtained from the shear strength condition of the weld, with F_X = 750 N, F_Y = 350 N, F_Z = 150 N, M_X = M_X13 = 37500 Nmm, M_Y = M_Z13 = 457500 Nmm, M_Z = M_Y13 = 292500 Nmm; h = h₁₂ = 50 mm; σ_at = 235/(2…3) = (78.33…117.5) MPa, σ_at = 100 MPa adopted; τ_afs = (0.6…0.7)σ_at = (60…70) MPa, τ_afs = 60 MPa adopted; the weld throat thickness is a^nec = 3.45 mm; a = 4 mm is adopted.

Constructive-technological shape