 Hello friends, Myself Sanjubi and I, working as assistant professor in Department of Mechanical Engineering, Walsh and Stoke Technology, Swalapur. In this video, I am explaining the design of welded joints. At the end of the session, students will be able to design fillet welded joints and design of butt welded joints. So let us consider the example of fillet weld between these two plates which is a triangular in section which is shown over here and this fillet weld has got two dimensions. One is H called as weld size or leg size and another is a minimum thickness or cross section that is T that is a throat size. The failure of this joint if at all occurs, it occurs at the minimum cross-sectional area and that is why it occurs at the throat size. Naturally, the value of T is h cos 45 and that is why T is equal to 0.707 times h. So this is the way two dimensions of the weld can be specified. One is either leg size or weld size h or a throat size. So we consider a design of parallel fillet weld as shown in the figure. So these are the two plates which are connected by two parallel fillets provided at both sides like this having their length l. So when the load applied is of joint, it will fail along this shear plane. So there will be shearing failure of parallel fillet weld and that is going to occur at this plane. So resisting area is a throat area and that is why it is a T into l. So this is a resisting area and the stress induced is shear stress. So if at all load resisting capacity or strength of the weld is concerned, the load P resisting is equal to resisting area into stress. So when we consider this stress to be allowable limit, then we can call this load that it can have a capacity to carry this much load without failure and that we call the strength of single fillet weld. So strength of single fillet weld is given against shear failure in case of this parallel fillet as 0.707h into l into tau. In this figure we have got two fillet welds parallel and that is why the total strength of this joint, weld joint will be P is equal to 2 times 0.707h into l into tau. So this is the way we can design the parallel fillet weld. Many unknown in this we can find out by the equation. We consider example of transverse fillet weld. As we know that the transverse fillet weld is a fillet weld section perpendicular to the load. So this is the case of transverse fillet weld having length l once again. So now when the load is applied on the joint as shown, it is subjected to tensile failure. So the failure in transverse fillet weld is a tensile failure and that is been obtained as a failure area or resisting area once again t into l. So it is 0.707h into l whereas the stress induced is a tensile and that is why the resisting load is P is equal to 0.707hl into sigma t. If I consider the sigma t as allowable stress then this becomes value of P that this joint can sustain without failure and that is called the strength of single fillet weld. So strength of single transverse fillet weld is obtained as P is equal to 0.707h into l into sigma t. As there are such two fillets, it is a double transverse fillet weld shown over here and that is why the total strength of this fillet joint, transverse fillet joint will be P is equal to 2 times 0.707hl into sigma t. So this is the way we can design the transverse fillet weld. Now think over here if the fillet weld is provided in this fashion that is a combination of transverse and parallel how to design it. So let us take an example of combined transverse and parallel fillet weld as shown in the figure. So these are two parallel fillet welds whereas this is a transverse fillet weld and it is subjected to a load as shown over here. So now we have to consider these two fillet welds separately that is the strength of parallel fillet weld considered as a P1 and strength of transverse fillet weld as a P2 and we know that the transverse fillet welds parallel fillet welds are subjected to shear stress and that is why the strength of parallel fillet welds which are 2 here. So we find P1 is equal to 2 times 0.707hl1 into tau because the length of that parallel fillet weld is l1 whereas the length of the transverse fillet is l2 and we know that the transverse fillet weld is subjected to tensile failure. So considering that we find out the strength P2 of transverse fillet weld as 0.707h into l2 into sigma t. So however the total strength of the joint is combination of P1 plus P2 as we have seen over here and that is why the strength of such combined transverse and parallel fillet weld subjected to axial load can be calculated as P is equal to 2 into 0.707hl1 into tau plus 0.707hl2 into sigma t. So this is the design equation which we can use for design of combined transverse and parallel fillet weld which is subjected to axial load. Now design of butt weld so we have seen the design of fillet weld now we see the design of butt weld. In case of design of butt weld we know that the butt weld is produced between 2 parts which are in the same plane and it is shown over here. The dimension of this weld is h and l. So this is the resisting area or failure area of the weld so it is h into l. So the load resisting capacity of this weld is calculated as P is equal to hl and failure is a tensile. So here the failure is a tensile failure and that is why P is equal to hl into sigma t. So if I consider this sigma t is allowable limit then definitely this becomes a strength of this butt weld which is P is equal to hl into sigma t. These butt joints are very popularly used in pressure vessels in which additional safety has to be considered so strength of the butt weld is reduced by using another term called the efficiency of the joint and considering the efficiency of the joint the strength of the butt weld used in pressure vessels is calculated as P is equal to hl sigma t into efficiency. So far we have seen all the cases in which the load is acting axially and the weld section is symmetrical about the axis but now we consider the load is acting axially but unsymmetrical weld joints are there. Particularly when we are joining the angles in structural construction l angle is connected to the beam as shown over here and load is passing through the CG. So we get the welds which are being used over here is a parallel weld one weld is l1 having length l1 and the weld 2 is having length l2 and these are parallel fillet welds and the load is passing at the center of gravity of this section over here. So this is the way the load resisting capacity of this weld section if I want to design then let P1 is the load resisting capacity of weld 1 and P2 is the load resisting capacity of P weld 2 and this must be equal to applied load on the joint P. So that is why P must be equal to P1 and P2 of a parallel fillet welds which we can calculate like this P1 is 0.707 hl1 into tau P2 is 0.707 hl2 into tau because it is a shearing failure and total load P is P1 plus P2. So this gives an equation E as a summation of force balance is there. However as these are asymmetrical having a distance from CG different they produce a moment so we have to get a moment equation also about CG of the forces P1 and P2 which can be obtained like this one P1 y1 must be equal to P2 y2. So this is a summation of moment equation we have to use as a law of statics. By using this we substitute expressions for P1 and P2 already we have derived so that we obtain just the expression l1 y1 is equal to l2 y2 and then if we assume the total length of the weld as l which is equal to l1 plus l2 we can calculate any thing of the length l1 or length l2 or total length or the size of the weld any parameter unknown which we can design by using the equation A B and C. So this is the way we can calculate or we can design the unsymmetrical welded section. These are my references thank you. Thank you.