What is the minimum fillet weld size when welding a 1.25" thick ASTM A36 plate to a 3/4" ASTM A992 column flange?

To determine the minimum fillet weld size for welding a 1.25" thick ASTM A36 plate to a 3/4" ASTM A992 column flange, one must refer to the applicable sections of the AWS D1.1 code, particularly those that relate to weld sizes for joint configurations.

Fillet weld size is generally determined by the thickness of the thicker member of the parts being joined. In this case, the thicker component is the 1.25" ASTM A36 plate. According to AWS D1.1, the minimum effective throat thickness of a fillet weld is often a function of the thickness of the base metal.

For structural applications, it is common practice to use a minimum weld size that is typically equal to the thickness of the thinner member or a set proportion of the thicker member based on the design requirements. In this case, if you refer to the code, the minimum weld size for plates can be calculated based on the thickness of the base plate and should not be less than 1/4" under normal circumstances. However, it is also important to consider other factors including the weld access and potential stress conditions, leading to a recommendation for a size that better accommodates these factors such as a 5/16