The photo is from a steel-framed industrial building in Brooklyn. It’s at a funny angle because I took it without seeing what I was doing, while kneeling to the left of the gyp-board partition on the far left, with my hand struck through a hole in the partition. This is the exterior wall of the building, which is framed in steel, sheathed in sheet metal backed up by wood (and the wood is supported by the steel), and has in recent years been finished on the interior with the gyp board.
What you’re seeing: the black more-or-less vertical is a small steel wide-flange that is one of the perimeter columns. The black at the top is a channel purlin, toed down, supported by the column. The brown on the right is the wood back-up for the sheet-metal facade. The fuzzy pink in front of that is modern fiberglass insulation. The shiny gray on the left is light-gage steel framing used to support the gyp board; the yellow at the bottom left is the back of the gyp board.
A few things of note:
- You can tell that the channel is a purlin and not something fancier (a piece of a vierendeel truss, for example) because you can see the end of the channel flanges stopping short while the column flanges continue up.
- The brownish-orange stain on the right side of the column is from an old leak, not active in some time. Water was obviously pooling on top of the purlin, which is why the vertical-axis rivets have rusted a bit but the horizontal-axis rivets have not. (The former are in holes that extend from the top of the purlin to below.) The spots of bright orange are the red-lead primer paint sowing thought gaps in the finish coat of black paint.
- The light-gage framing is attached by “powder-actuated fasteners” which is a fancy term for nails shot out of a gun. Note the nail end at the upper left: the fastener was driven through the steel channel, which gives you a sense of the localized force of those guns.