Type of Weld and Economy in Structural Steel Construction.

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Type of Weld and Economy in Structural Steel Construction.

Being a fresher in the steel structures industry it’s always been a question of curiosity that how someone can achieve  economy in welding. There are number of welding processes and weld types available again there is variability in selection of length and size of the weld. Economy in welding is directly related with the certain factors. This article is all about that practices. 

TYPE OF WELD: 

It is a basic principle that fillet welds are generally used for light loads and butt welds are generally used for structures that are supposed to carry heavy loads. Again the another type of weld is plug and slot weld and it is being used in special conditions. Like in case of Limited length of weld or in case of difficulty in the geometry of the surface onto which we have to carry out the welding operation.   That’s all been  decided with the help of experience that someone can gain while working in the steel structures design industry. But we can say that these are the general thumb rules.  However there are number of factors like the availability of weld metal type of weld metal and fabricators equipment and methods. But it was found that, fillet welding of the size range of 12 to 14 mm are found to be more economical compared to grooved weld and same is represented in the figure attached below. With increase in the size of fillet weld that is specified above it will become less economical choice.

weld size and cost of weld
Image Source:Economical Structural Steel work Fifth edition – 2009. Australian steel institute

SIZE AND LENGTH OF WELD:

Economy in welding is also affected by selection of size and length of weld.  As we all are aware with the fact that the strength of a weld is largely dependent upon its size and its length . With increase in both size and length of any weld its strength increases irrespective of its economy calculations. While we consider economy we have to look at the third important parameter which is the volume of weld metal consumed. Mathematically there is a relationship in size of weld and volume of metal consumed. Roughly it can be said that with doubling in size of weld, its volume increases by four times of its original value. In other words one can consider that the volume of the metal used in welding varies with the square of the weld size.  On the other hand strength will not increases in that much amount. Hence, a justification of size and length of welding should be done to maintain the economy in the structure. so overall, yes there is an increase in the strength with the increase in size of the weld yet there is a large amount of increase in the volume of the weld metal.  In fact a shorter increase in strength values will cost us to a great increase in volumes of the weld metal and that is something you should be aware of

CONCLUDING REMARK:

Now how to deal with such problems of design? The answer lies in the fact that we have to manage the strength and size of the weld based on its length. We can reduce the size of weld to save the volume of the weld metal and so that we can achieve economy in construction but the loss of strength due to this size reduction have to be balance with increasing weld length. That’s how somebody can manage the size and the length of weld in order to achieve economy in steel structures design.

Therefore as a golden word what I can suggest  is that “small size welds of long lengths would cost less than large size weld of small weld length”.

It also offers additional advantages of accommodating complete welding in single pass, which again reduces time of construction, amount of metal required and therefore reduces the cost again.

References:

  • Economical Structural Steel work Fifth edition – 2009. Australian steel institute.
  • Design of steel structures by S. Ramamrutham.
  • Bonnet C. & Angeli A.G. 1986; INFLUENCE OF NITROGEN CONTENT ON DEPOSITED WELD METAL NOTCH TOUGHNESS, science-direct.  pp 293-303
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