Plastic design of fillet welds under in-plane eccentric loads

The main purpose of this study is to provide a simple and efficient method for calculating the capacity of fillet welds subjected to in-plane eccentric loads. Various methods have been proposed to determine the capacity of fillet welds under such circumstances over time. The existing design methods, such as the conventional elastic method, are very conservative and do not match the test results well due to neglecting of ductility and strain compatibility of the weld group. On the other hand, the instantaneous center of rotation method (IC) considers the above parameters but requires complex calculations. Therefore, in the present study, a method for the design of the fillet welds is introduced which considers the inelastic properties of the welds in a simple manner, while provides a very good prediction of the weld group capacity. The proposed method is much more accurate than the conventional elastic method in the design of fillet welds and is much simpler than the IC method which has limitations in use and complexity in calculations. In this method, considering the ductility for welds, it is assumed that the stress distribution in welds is uniform when the weld reaches its maximum bearable deformation.
The performance of the proposed method which is called Plastic Design Method has been compared and evaluated in comparison with the prequalified IC method. To this end, 8 different configurations of weld groups from the AISC Manual were selected and their capacities were calculated for different amount of load eccentricity. Accordingly, despite the fact that the new method has almost the same computational cost of the elastic design method, it offers more accurate strength predictions of the weld groups. For all considered cases, the ultimate loads obtained from the proposed plastic method are just slightly different from those of the IC method and they are mainly on the safe side. To be more precise, the accuracy of the results calculated by the proposed method is within 90% of those of the IC method.
In accordance with the authors’ parametric studies on the factors affecting the results of the plastic design method (e.g., the angle of loading (θ), the weld length (l), the weld throat thickness (d), the secondary parameter (k) and the tensile strength of the welded metal), it was found that the angle of loading has the most profound effect. Therefore, the influence of loading angle on the predicted results was included. Accordingly, three different loading angles (i.e., zero, 45 and 75 degrees) were chosen and the weld groups capacities were calculated in each case. The corresponding results showed that as the loading angle increases, the accuracy of the results decreases and the most accurate predictions are obtained for the case of zero angle loading as compared with those of the IC method. Nevertheless, the predictions are still in an acceptable range for non-zero angles. It is also worth mentioning that irrespective of the loading angle, the new plastic method strength predictions are always far better than those of the conventional elastic design method.