The calculation procedure for welding size depends upon types of loading the welding is subjected to. For example, welding design calculation for pure tensile loading and welding design calculation for bending loading is different than design for torsion loading. Let’s discuss the welding design calculation for torsion loading with an example.
A Typical Example
In the above example a shaft is welded to a plate and a pure torsion load (F) is acting on the shaft.
Applied torsion load F = 100000 N
Design strength of welding Fw = 220 N/mm2
Radius of the shaft R = 50 mm
Welding throat thickness (t) and leg length (s)
Welding Size Calculation Procedure by Line Method
- The first thing you need to calculate here is torsional moment (M).
- Calculate unit throat area (Au) of the welding as below:
Au = 2*pi*R = 314 mm2
- Calculate unit polar moment of inertia (Ju) of the welding joint using the equation from standard table and putting the value of height of the fillet (a) = 1 like below:
J =2*pi*a*(r+0.5*a) 3
Ju =2*pi*(r+0.5)3 (by putting a=1)
- Calculate torsional shear stress (T) using the following equation:
- Calculate welding throat thickness (t) as below:
t = T/Fw
- Finally calculate the welding leg length of welding size (s) as below:
s = 1.414*t
= 1.97 mm (take 2mm welding size)
Welding design procedure explained in this welding design tutorial is based on BS 5950 and is called the line method. The height of the fillet weld is assumed as one for moment of inertia and area calculation in the case of the line method. Welding size calculation for torsion load can always be verified by using FEA tools.
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