The document discusses different types of welded joints used in mechanical assemblies, including butt joints, fillet/lap joints, transverse fillet welds, and parallel fillet welds. It provides formulas to calculate the strength of different welded joint configurations based on factors like weld throat area, plate dimensions, and allowable tensile and shear stresses. Examples are given to demonstrate calculating the required weld lengths for specific plate joining problems based on the given stresses and loads.