BUR #2285 has been approved by @evazion.
create alias girder -> steel_beam
Reason: Both tags appear to be used interchangeably. I couldn't see any apparent counterexamples apart from post #2799171, but those abstract shapes probably shouldn't have been tagged girder to begin with.
The alias is to steel_beam since it's the older tag, it at least has an extremely basic wiki, and it's probably the more recognizable term.
EDIT: The bulk update request #2285 (forum #163180) has been approved by @evazion.
Updated by DanbooruBot