Historical joist designation? 1

[OldBldgGuy]

Can anyone tell me what 82@23 / slab - 1" or 103@22 / slab - 1" might mean? They appear to indicate joists but I have not been able to open up the ceiling yet to see what's there. It's a residence at a private school, built in 1931, and the school is doing some interior alterations. I will get the ceiling opened eventually, but if anyone can tell me ahead of time that would be great. A snip from the plan is attached; the notes are in green ovals. The spans are much too short for the designations to be inches or pounds for depth or weight.

 

[Ron247]

This is purely a guess but it could be a design with joists that were "tabled" and numbered as 1 to say 200. They may be saying use #82 and #103. Again, just a guess based on the magnitude of the numbers.

 

[JAE]

I believe that 82 and 103 represent steel joists.

See attached.

Not sure what the slab -1" means - other than perhaps the joists are set 1" below the slab elevation - but a 1" slab doesn't make sense.



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[JAE]

The 23 is most likely the spacing in inches.

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[Ron247]

I have never seen that reference. Good to know. I agree, the 22 and 23 are most likely spacings. Slab-1" may mean subtract 1" from the slab thickness. I have seen some older projects where they used what looked like wire fence with a heavy paper for the "form deck" and it would sag about 1" when the concrete was poured on it.

 

[JAE]

That image I posted came from the SJI Historical Joist catalog. A very good reference to have in your office.

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[OldBldgGuy]

Thanks JAE, I think you've got it, your 1929 catalogue date is perfect for this project and the 22 & 23 are probably spacings. 8" & 10" are more logical depths for joists with these spans; funny that 82 & 103 mean 8"-#2 and 10"-#3 if you know what you're looking at. Like Ron247, I too have seen wire mesh and expanded metal instead of decking with concrete that is more like plaster applied to it; I did assume that the -1" meant the top of joists is 1" below top of floor.

Thank you for the input, I will let you know what I find when we actually open things up.

 

[JAE]

I think Ron247 has it right that the -1" means that the floor is dropped for some tile or something.

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[OldBldgGuy]

The joists are 8" deep and 10" deep just as indicated in JAE's catalogue, and the concrete slab is about 2" thick between the joists, less than 1 1/2" at the joists; essentially cement plaster trowelled onto expanded metal lath. You might think this thin slab can't possibly work and the floor may look odd from below, but it is in perfectly good condition. One room being worked on has a relatively new drywall ceiling which we cut a hole in, and the remaining area has the original plaster ceiling on metal lath wired to the joists. It's very similar to a 1926 hospital building that I worked on a few years ago, converting it to apartments, but I haven't seen these joist designations before. A photo of the ceiling space is attached.

 

[Ron247]

OldBldgGuy: This is another picture of a similar construction and concrete deck. Heavy paper on a "hog-wire" looking wire. As with yours, the floor slab was in very good condition for the age.

 

[SlideRuleEra]

Just realized the complete specs for Macomber SJ 82 and SJ 103 are in the 1934 Carnegie Pocket Companion, page 385, on my website.

http://www.SlideRuleEra.net

 

[OldBldgGuy]

Perfect! Thanks