Welding MT Strut Channel to Plate Steel

For several reasons I need to weld a steel plate to the backside (not open side) of an MT-60 channel strut to attach the strut to existing structure. What Code should I direct my personnel to for the proper welding procedure. Would this be AWS D1.1 or some other welding code? I would think it would the same code you weld back to back channels to but could not find that information.