10.16 Strength of Transverse Fillet Welded Joints
We have already discussed that the fillet or lap joint is obtained by overlapping the plates and then welding the edges of the plates. The transverse fillet welds are designed for tensile strength. Let us consider a single and double transverse fillet welds as shown in
Fig. 10.6 (a) and (b) respectively.
Fig. 10.6. Transverse fillet welds.
In order to determine the strength of the fillet joint, it is assumed that the section of fillet is a right angled triangle ABC with hypotenuse AC making equal angles with other two sides AB and BC.
The enlarged view of the fillet is shown in Fig. 10.7. The length of each side is known as leg or size of the weld and the perpendicular distance of the hypotenuse from the intersection of legs (i.e. BD) is known as throat thickness. The minimum area of the weld is obtained at the throat BD, which is given by the product of the throat thickness and length of weld.
the product of the throat thickness and length of weld.
Let t = Throat thickness (BD),
s = Leg or size of weld,
= Thickness of plate, and
l = Length of weld,
From Fig. 10.7, we find that the throat thickness,
t = s × sin 45° = 0.707 s
∴ *Minimum area of the weld or throat area,
A = Throat thickness ×
Length of weld
= t × l = 0.707 s × l
If σt is the allowable tensile stress for the weld
metal, then the tensile strength of the joint for single fillet weld,
P = Throat area × Allowable tensile stress = 0.707 s × l × σt
and tensile strength of the joint for double fillet weld,
P = 2 × 0.707 s × l × σt = 1.414 s × l × σt
Note: Since the weld is weaker than the plate due to slag and blow holes, therefore the weld is given a reinforcement which may be taken as 10% of the plate thickness.