1920s steel joist designation

[carpoolturkey]

I am working on a building in Minnesota built in 1924. The majority of the building is clay tile concrete joist construction, but there is a portion that is a steel framed roof.

The snips attached show steel joist designations that we initially thought were junior steel beams, but we are not able to find beams as light as these in any historical literature we have.

We are now wondering if they might be open web steel joists, as the sections that are attached appear to show these joists drawn intentionally different to the standard beams that are also shown.

Is anyone familiar with pre-SJI joists being noted like this? 8I@5.9# and 6I@4.9#?

We have reached out to AISC and SJI, but know there is a lot of knowledge on this forum too.

 

[carpoolturkey]

Section 1

 

[carpoolturkey]

Section 2

 

[KootK]

1) In what follows, put my level of confidence wayyyyy down at 20% or so. If anybody else sounds as though they know what they're talking about disregard my stuff.

2) I note three interesting things in the details:

a) There is mention of stabilizing the purlins with beam clips. This kind of suggests a solid web. I suppose a vertical end web would do it too.

b) There is mention of punching the "flanges" of the purlins for wood plate attachment. "Flanges" not "chords".

c) The flanges / chords are drawn with lips. I don't know of rolled chord sections that would have those lips unless one makes the chords out of channels which sounds heavy and ridiculously expensive.

3) Back to back cold formed channels? Graphically, it doesn't show a double web.