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Module 1: Weld Connections

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Video 1
Hello, I am going to discuss about the design of plug and slot weld. In last threelectures we have discussed about fillet weld and then butt welds and I have told that threetypes of welds are there fillet weld, butt weld and plug weld or slot weld, now plug weld andslot weld is nothing but a type of fillet weld. As I have told earlier that in case of plug or slotweld we are facing problem of limited distance and limited length of the joint. If the length ofthe joint is limited and if we have higher values of tension or compression force then it isdifficult to adjust the entire length on this limited length. So, in that case we have to cut someportion of the overlapping portion in terms of slot or plug to make adjust of that additionallength.
Now if we see here in case of plug or slot weld if we see here that here we have limitedlength say L right. So here we will get only this much length and if it is L1, L1 and L2 thentotal length we are getting L2 + 2L1 right.So if we get the Lw value which is more than L then it is difficult to adjust because our lengthis limited, this L1 is fixed so to adjust within a limited length we make some cut of theoverlapping position. We cut some portion in terms of slot or plug and then fill with thewelded material and this is how we increase the strength and accommodate the additionallength.
So, if we see a slot is cut in one of the overlapping member and the welding metal is filled inthe slot now what is slot and what is plug. When the slot is small and completely filled withweld metal then it is called plug weld, but if the periphery of the slot is filled with weld metalthen it is called slot weld. This is how slot weld and plug weld has a difference.
Now in IS816-1969 certain specifications are given which we need to follow for design ofplug or slot weld so what are the specifications we need to see. Say first the width or thediameter of the slot should not be less than three times the thickness of the part in which theslot is formed or 25 millimetre whichever is greater. Slot diameter means when we aremaking a slot so this diameter or this is width this slot diameter or width should not be lessthan three times the thickness of the part in which the slot is formed or 25 mm at least 25mm.So this diameter will be at least 25 mm or at least three times the thickness of the part inwhich the slot is made so this is what we have to remember and diameter of the slot has to befixed in this way. Another thing is the distance between the edge of the part and edge of theslot or plug or between the adjacent slot or plugs should not be less than three times thethickness of thinner member or 25 mm whichever is greater.
Now if we draw the things then it will be clear say suppose we have a slot here and becauseof this limited distance, we have to make some slot first point is telling that the diameter orwidth should not be less than three times the thickness of the plate in which slot has beendone at least it should be more than three times the thickness of the plate right this is onepoint. Second point is telling the distance between edge of the part and edge of slot thatmeans distance between edge of part or edge of slot or plug like this or adjacent to slotsshould not be less than three times the thickness of thinner member or 25.Then another point we have to remember corners at the enclosed ends should be rounded to aradius not less than one and a half times the thickness of the upper plate or 12 mm whicheveris greater. So corner at the enclosed end means at the enclosed end we have to make therounded corner with a radius not less than one and half times the thickness of the upper plateor 12 mm thickness whichever is greater. So these three points we have to keep in mind andthe design stress on a plug or slot weld will be same as that in fillet weld and is specified inclause 10.5.7.1.1 of IS800:2007.So as I told that design criteria will be same as we have done in case of fillet weld becausethis is nothing but a type of fillet weld only thing is because of limited distance we have tointroduce some slot so that the additional length are adjusted.
Now with this we will go through some example so that we can understand how to design aslot weld with the product provision whatever we have understood means whatever we havediscussed and then we will be designing the member.Example:An ISMC 300 @ 363 N/mm is used to transmit factored force 800 kN. The channel section isconnected to a 12mm thick gusset plate. Design a fillet weld connection if the overlap islimited to 300 mm. Use slot welds if required. Assume site welding.
Video 2
Now as we have time will through another example which I have discussed in last lecture. Incase of butt weld or in butt weld lecture we have discussed that is how to calculate theequivalent stress of the weld joint means when it is under shear and normal stress or shear orbearing and normal stress. So how to check that design strength of the joint when it issubjected to axial tension or compression bending and shear, so I will go through oneexample with this.Example:A pipe of 100 mm diameter and 8 mm thick is connected to a 16 mm thick plate with filletweld. It is subjected to a vertical factored load of 10 kN at a distance of 0.5 m from thewelded end. It is also subjected to a factored twisting moment of 3 kNm. Find the size of theweld assuming shop welding and steel of grade to be Fe410
So in this few lectures, we have discussed about the different type of connections startingfrom rivet connection to bolted connection and then finally weld connection again weldconnection, fillet and butt weld has been discussed and design criteria has been discussedhow to calculate the design strength of the fillet weld and butt weld these things we havediscussed and accordingly we have solved certain number of examples, I hope this will clearthe r designing methodology how we have done and we will be able to design different typeof joint using bolt or weld, thank you very much.