Design Stresses in Fillet Weld Connexions

Abstract

Intuition and personal opinion, rather than theoretical investigation, have often been the main guides in the determination of design stresses for fillet weld connexions. Excessive safety at the expense of accuracy and economy have resulted in weld connexions which, although they did not fail under working conditions, were not always economical.

In the case of eccentrically loaded joints the stress f_torsion under a torque T has been determined by using the polar moment of inertia J of the weld throats: f_torsion = Tr/J, where r is the distance of the extreme fibre from the centroid of the weld throat. This method, though accurate enough for closed weld arrangements, resulted in uneconomical sizes for other arrangements. This paper suggests a means of determining the working loads of eccentrically loaded fillet welded joints by working out the stresses in the plastic state prevailing immediately before failure occurs. From this calculation the value of the failing load is obtained, which is divided by a certain load factor, the result being taken as the permissible load. If the results are represented in the form of graphs the time spent on calculation is considerably reduced. Practical experiments gave results which were in close agreement with the result of these calculations.

In the second part of the paper, the two differing opinions on the best arrangement of fillet weld connexions joining rolled angle sections to gusset plates are investigated, so far as their effect upon the strength of the assembly is concerned, and no difference is found with regard to the static strength of the assembly, while stress peaks at the end of the welds may indicate a weakness of one arrangement under fatigue loading conditions. Further research in this direction is suggested.