Examination of Fillet Weld Strength

The strength of a fillet weld is influenced by many different factors. For example, the welding process, electrode type and strength, weld-metal chemistry, welder skill, weld profile, joint penetration, joint fit-up and restraint, and preheat and interpass temperatures all contribute, in some part, to the resultant weld strength. Many of these factors, such as skill of the welder, joint fit-up, and preheat and interpass temperatures, are dealt with through particular requirements and provisions of the AWS Structural Welding Code. Weld qualification tests, for instance, are required to demonstrate whether an individual has adequate skill and training to produce a particular weld with a desirable level of quality. The design methodology used to compute the strength of fillet welds does not directly reflect all of the factors that influence fillet weld strength. The design method utilized for many years to compute the strength of a fillet weld involves multiplying the effective fillet weld area—the product of the effective throat size and the weld length—times an allowable or ultimate stress, depending upon whether an allowable stress or limit states design approach is being used. The effective throat dimension of the weld is taken as the shortest distance from the root of the weld to a line that connects the top and bottom weld toes; this procedure gives an effective throat that is 71 percent of the weld leg size for welds with equal leg sizes. It should be noted that this procedure ignore the influence of the weld root penetration and the weld profile. These factors will result in a true weld throat size that is different than the theoretical effective throat utilized for design purposes. The purpose of the study reported herein was to study the influence of geometrical factors that influence the true effective throat of fillet welds. Specifically, a series of tests were conducted to evaluate the influence of weld leg size and fabrication gaps on the strength of fillet welds.