The method of assessing fillet welds groups treating welds as lines is reasonably safe and conservative and is very convenient to use.
a) Weld subject to bending....See table below for typical unit areas and unit Moments of Inertia
1) The area of the fillet weld Au..(unit thickness) is calculated assuming the weld is one unit thick..
2) The (unit) Moment of Inertia Iu is calculated assuming the weld is one unit thick..
3) The maximum shear stress due to bending is determined...τb = M.y/Iu
4) The maximum shear stress due to direct shear is determined.. τs = P /A
5) The resultant stress τr = Sqrt (τb2 + τs2 )
6) By comparing the design stress Ss with the resultant stress τr the value of the weld throat thickness is calculated and then the weld size.i.e. if the τr /Ss = 5 then the throat thickess t = 5 units and the weld leg size h = 1,414t
a) Weld subject to torsion...See table below for typical unit areas and unit Polar moments of Inertia
A fillet weld subject to torsion is easily assessed as follows.
1) The area of the fillet weld Au (unit thickness) is calculated assuming the weld is one unit thick
2) The (unit) Polar Moment of Inertia Ju is calculated assuming the weld is one unit thick.. The polar moment of inertia J = Ixx + Iyy
3) The maximum shear stress due to torsion is determined...τt = T.r/Ju
4) The maximum shear stress due to direct shear is determined.. τs = P /A u
5) The resultant stress τr is the vector sum of τt and τs. r is chosen to give the highest value of τr
6)By comparing the design stress Ss with the resultant stress τr the value of the weld throat thickness is calculated and then the weld size.i.e. if the τr /Ss = 5 then the throat thickess t = 5 units and the weld leg size h = 1,414t
Calculation Reference
Schaum's Outline - Machine Design
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