Steel joist designation from early 1920's 2

[archeng59]

I am working on renovations to a church constructed in the early 1920's. The attached floor plan shows an unfamiliar joist designation.

Looking at the joists through a small hole in the ceiling, the joists appear very similar to two cold-formed metal cee-shapes back-to-back. The existing joists are not accessible without demolishing more of the existing ceiling, which the church is reluctant to do.

Is anyone familiar with this designation? I have not found anything on the internet so far. The 9x7 junior beams in the old AISC manuals are not what was used in the church construction.

Thanks in advance for the help.

 

[SlideRuleEra]

What you are describing are National I-Joists, also known as steel lumber:

Engineering information from a 1921 Sweet's Catalog for all seven of the available sizes, including the 9" version, is attached.

 

[archeng59]

thank you!