What is the minimum size requirement for a fillet weld in cyclically loaded structures?

The minimum size requirement for a fillet weld in cyclically loaded structures is 3/16 inch. This specific size is established to ensure that the weld has sufficient strength and ductility to withstand the repeated loading and unloading conditions typically encountered in these structures. Cyclic loads often lead to fatigue failure if the components aren't adequately joined, hence, the code prescribes a minimum weld size to mitigate this risk.

The 3/16 inch dimension provides a balance between ensuring enough weld area to avoid excessive stress concentrations and keeping fabrication practical. This size helps to distribute stress more evenly across the weld and the base metals, which contributes to the overall structural integrity and longevity in service.

Selecting a smaller weld size, such as 1/8 inch, may not offer adequate strength to endure the cyclic nature of certain loads. Conversely, excessively large welds could lead to inefficiencies and unnecessary material costs. Therefore, the 3/16 inch requirement is specifically chosen based on extensive research and testing related to the performance of welded joints under cyclic loading conditions.