Design of joint 6-7 (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; X₁ = 80 mm; X₂ = 220 mm; Z₁ = 180 mm and h₆ = 60 mm; the moments at the centre of the square section are:

M_X7 = F_Y (L_c + Z₁) = 75000 Nmm,

M_Y7 = F_X (L_c + Z₁) + F_Z (X₁ + h₆/2) = 302000 Nmm,

M_Z7 = F_Y (X₁ + h₆/2) = 33000 Nmm.

Dimensional constraints: the upper column body 6 is welded to the lower tie rod 7, with sizes h₆ = 60 mm, h₇ = 50 mm and wall thicknesses t₆ = 5 mm, t₇ = 5 mm.

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

Design constraints: weldable materials for elements 6 and 7.

Materials and properties

Elements 6 and 7 were designed in weldable S235 steel according to SR EN 10025-2 (STAS 500/2).

Material properties

Sizing

From the sizing relation obtained from the shear strength condition of the weld, with F_Xs = 700 N, F_Ys = 1500 N, F_Zs = 300 N, M_Xs = 33000 Nmm, M_Ys = 75000 Nmm, M_Zs = 302000 Nmm; h = h₇ = 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 = 1.7 mm; a = 3 mm is adopted.

Constructive-technological shape