Design of joint 6-7 (welded joint)

A. Loading diagram and design data

External loading diagram	Loading diagram of joint 6-7
Design data External forces: FX, FY, FZ act at distances Lc (Ex.3.1), X1, X2, Z1 (Ex.1.2.2) and h6 (Ex.4.1); the moments at the centre of the square section are calculated (Calc.0): MX7 = FY (Lc + Z1), MY7 = FX (Lc + Z1) + FZ (X1 + h6/2), MZ7 = FY (X1 + h6/2). Dimensional constraints: the upper column body 6 is welded to the lower tie rod 7, with sizes h6, h7 and wall thicknesses t6, t7 (Ex.4.1, Ex.4.3). Operating constraints: temperature T = (−30…40) °C; outdoor working environment with high humidity. Design constraints: weldable materials for elements 6 and 7.

B. Choice of material and heat treatments

Elements 6 and 7 were designed using weldable steels (Ex.4.3). These steels are not heat-treated before welding; after welding, the subassembly may undergo stress-relief annealing. For the adopted steels, the yield strengths σ₀₂ and the ultimate tensile strengths σ_r are retained for the calculations.

C. Design of the constructive shape

Constructive model

Constructive features and constraints

– the weld throat thickness a should be smaller than the wall thicknesses t₆ and t₇ of the square tubes (a < min(t₆, t₇));

– the two elements must be perpendicular;

– a fillet weld is made along the closed (square) contour.

D. Calculation model, sizing and checking

The calculation model is similar to the one in Sec.3.5.

Calculation data

– loading: F_Xs = F_Z, F_Ys = F_X, F_Zs = F_Y; M_Xs = M_Z7; M_Ys = M_X7; M_Zs = M_Y7;

– shape and dimensions: the inner contour of the weld bead is a square of side h = h₇;

– materials: σ₀₂ – the yield strength; c = 2…3 – the safety factor; σ_at = σ₀₂/c – the allowable tensile stress; τ_afs = (0.6…0.7)σ_at – the allowable shear stress of the weld.

Sizing

The weld throat thickness a^nec is determined with calculation window Calc.3.5.1; a whole value a > a^nec is adopted.

E. Design of the technological shape