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Longspan Steel Roof Joists pre-1953

Longspan Steel Roof Joists pre-1953

Longspan Steel Roof Joists pre-1953

I looked at a project recently for some lighting equipment that is being hung from the bottom chord of existing steel open web joists. I was provided with the building drawings and I have taken some field measurements.

The drawings call for 36" Longspan Joists which are noted as "Macomber 'J' Underslung". The latest date on the drawings is April 1947. This confused me as all the info I have seen made available from SJI indicates longspan joists didn't come around until 1953 and indeed, the earliest longspan joist table I can find is also from 1953. I have searched on this site and Sliderulera's site, but can find no tables for pre-1953 longspan joists. At this point, I only have limited field measurements due to access issues above the dropped ceiling but I know that the joists installed are only 32" deep with double angles for the top and bottom chords, double angles for the vertical webbing, and flat bars for the diagonal webbing. I'm hoping someone can provide me with load tables for Macomber's longspan joists, preferably from an older table.

RE: Longspan Steel Roof Joists pre-1953

If it is all fabricated from double angles and flat bar, it would be easier for you to just analyze it yourself. The joist catalogues from those days would rarely give anything beyond allowable loads for certain spans.

I would also look at hanging it from the top chord once you've determined the appropriate reinforcement for the additional loads if any.

RE: Longspan Steel Roof Joists pre-1953

That was my initial thought as well, but I was hoping not to go that route - poor access and client budget being the biggest factors.

I did just receive a call and a document from SJI for Macomber joists from the 1940s. It appears to have the information I need, including load tables for the "J" underslung joists.

RE: Longspan Steel Roof Joists pre-1953

Feel free to post it up here for all to have. If you send it to slide rule, he'll put it on his website.

RE: Longspan Steel Roof Joists pre-1953

If you post it on here, he'll get it. Or go to his website, his email is at the bottom

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