Design the welded connection:

Two ISA 90 × 60 × 10 angles form a tie member of a truss and is subjected to an axial pull of 200 kN. They are linked to both sides of a 10 mm gusset plate as display in Figure. Design the welded connection.

Solution

Figure

Maximum size of the fillet weld = 3/4 × toe thickness of angle

= 3/4 × 10 = 7.5 mm.

Assuming 6 mm size fillet welds on both sides of gusset plate to each angle axial force in each angle = 200000/2 = 100000 N which is assumed to act through the CG line of the angle. There are two runs of fillet welds of length L₁ and L₂ are applied to each angle one at the top edge corner and the other at the bottom tip of the leg as shown in Figure 17.

Throat thickness of weld = 0.7 × Size of weld = 0.7 × 6 = 4.2 mm

Permissible shear stress in weld = 110 N/mm²

∴ Strength of weld per mm length = 110 × 4.2 = 462 N.

Taking moment of forces about the bottom weld line (L₂), we should have

462 × L₁ × 90 = 100000 × 59.6;

giving L₁  = (100000 × 59.6 /462 × 90) = 144 mm.

Similarly, taking moments about the top weld line (L₁)

462 × L₂ × 90 = 100000 × 30.4;

giving L₂ =(100000 × 30.4/462 × 90) = 74 mm .

 ∴ Gives 145 mm long weld at top corner and 75 mm at bottom tip with return welds of length 2 × 6 = 12 mm each as shown in Figure.