What is welding?
Welding is the process of joining metal parts in the molten state without the application of any mechanical pressure. Nowadays many structures are constructed with the help of steel. The steel structure is very fast to construct as compared to the concrete.
The structure made with steel should be strong enough to bear live load as well as dead load. So, all the load-bearing structural members of steel should be jointed enough by welding. Here we will learn how much should be the maximum and minimum length of the weld, the strength of the weld along with types of welding joints.
Types of welding joints
- Butt Weld
- Filled weld
- Slot Weld
- Plug weld
- Flash weld
a) Butt Weld:-
Butt welds are welds where two pieces of metal are to be joined are in the same plane. These types of welds require only some preparation and are used with thin sheet metals that can be welded with a single pass.
Common issues that can weaken a butt weld are the entrapment of slag, excessive porosity, or cracking.
b) Fillet weld:-
Fillet welding refers to the process of joining two pieces of metal together whether they be perpendicular or at an angle.
These welds are commonly referred to as Tee joints which are two pieces of metal perpendicular to each other or Lap joints which are two pieces of metal that overlap and are welded at the edges.
c) Slot weld:-
This weld is made in an elongated hole in one member of a lap joint or tees joint joining that member to the surface of the other member that is exposed through the hole.
d) Plug weld:-
This is a circular weld made through one member of a lap or tee joint joining that one member with the other. This weld is not considered for the calculation of strength.
e) Flash weld:-
This weld is made by the application of pressure over the entire area of abutting surfaces after heating them completely.
The effective length of weld
The reinforcement of the weld is neglected in strength calculation. The weld fails along the weakest plane which has the smallest cross-sectional area.
The length measured along this plane is throat thickness (t). For all strength calculation throat thickness, t is used and not the size of the weld.
At the beginning and end of the weld, the required size of the weld can’t be formed. This reduces the size of the weld which is termed a crater. At each end of the weld, a length equal to the size of the weld is subtracted from the total length to get the effective length.
How to Calculate Strength of weld?
The strength of the weld is equal to permissible stress multiplied by its throat area which is the product of throat thickness and effective length of the weld.
Permissible shear stress,
100 n/mm2 – for shop weld
80 N/mm2 – For Field weld
A) Minimum size of weld
It depends on the thickness of the thicker plate.
| tmax | Smin |
| <= 10 m | 3 mm |
| 10 to 20 m | 5 mm |
| 20 to 30 m | 6 mm |
| >30 m | 8 mm |
B) Maximum size of weld,
1) For rolled edge, Smax = ¾ t
2) For Straight edge, Smax = t – 1.5
The minimum effective length of weld
It is equal to 4 times the size of the weld or 40 mm whichever is greater.
(Left)min 4S or 40 whichever is greater
The maximum clear pitch of intermittent fillet weld
12 tmin or 200 whichever is lesser, for compression member 16 tmin or 200 mm whichever is lesser, for the tension member.
Types of welded/riveted joint
- Concentric joint
- Eccentric Joint with inplane moment
- Eccentric joint without of plane moment
I hope this article on “Types of welding joints” remains helpful for you.
Happy Learning – Civil Concept
Contributed by,
Civil Engineer – Ranjeet Sahani
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