Shear Stud Welding: Before or After Hot-Dip Galvanizing?
OSHA's final rule on Safety Standards for Steel Erection requires installation of "Shear Studs" or "Nelson Studs" be field-installed to reduce the tendency for tripping hazards. However, there are some structure owners that allow or permit welding of studs prior to galvanizing. OSHA and the FHWA have addressed an exemption to OSHA's final rule on Safety Standards for Steel Erection, but how this works on a state by state or even project by project basis will be different based on expressed concerns over safety.
When the contract requires field installation of studs after galvanizing, stud locations are either masked to prevent galvanizing in the stud location, or the stud locations are ground to remove the galvanizing down to bare steel. In those cases, it is not common to remedy or coat the top flange after shooting the studs. The concrete is poured, and little to no moisture is expected to travel all the way down to the flange surface (although possible). For this reason and to avoid staining, it is recommended to stop masking application 1-2 inches from the edges along the top flange surface.
Currently, the AGA provides recommendations for stud welding, AASHTO/NSBA S8.3 Hot-Dip Galvanizing Specification addresses considerations for field-applied shear studs in Section 6.5, and Welding of Shear Studs to Galvanized Steel Beams from The Steel Construction Institute (SCI) summarizes the history of technical challenges regarding this process.
New research Weldability of Bridge Steel with Protective Coatings is investigating new field welding procedures for shear studs without having to remove hot-dip galvanizing and metallizing, therefore minimizing repair work in the field. Specifically, this research will help determine if acceptable welds can be produced over zinc-coated ASTM A709, Grade 50 steel using flux-cored arc welding (FCAW) and arc-stud welding (SW). This is in direct response to a 2022 update of the AASHTO/AWS D1.5M/D1.5 Bridge Welding Code allowing welders to field-weld through coatings if they prove they are qualified. See Project Overview from Transportation Research Board (TRB).
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