Design of joint 4-5 (welded joint) — example

Design data

External forces: F_X = 1500 N, F_Y = 300 N, F_Z = 700 N act at distances L_c = 70 mm, h₄ = 15 mm; X₁ = 80 mm; the moments at the centre of the square section (the welded joint) are:

M_X5 = F_Y (L_c + h₄) = 25500 Nmm,

M_Y5 = F_X (L_c + h₄) + F_Z X₁ = 183500 Nmm,

M_Z5 = F_Y X₁ = 24000 Nmm.

Dimensional constraints: tie rod 4, of width b₄ = 60 mm and thickness h₄ = 15 mm, is welded to the square tube 5 of side h₅ = 50 mm and wall thickness t₅ = 5 mm.

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

Design constraints: weldable materials for elements 4 and 5.

Materials and heat treatments

Elements 4 and 5 were designed in weldable S235 steel according to SR EN 10025-2 (STAS 500/2).

Material properties

For the weld bead, the allowable shear stress corresponding to weldable steels is adopted: τ_afs = (0.6…0.7)σ_at.

Sizing

From the sizing relation obtained from the shear strength condition of the weld, with F_Xs = 1500 N, F_Ys = 300 N, F_Zs = 700 N, M_Xs = M_X5 = 25500 Nmm, M_Ys = M_Y5 = 183500 Nmm, M_Zs = M_Z5 = 24000 Nmm; h = h₅ = 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 = 1.45 mm; a = 3 mm is adopted.

Constructive-technological shape