Unusual steel joist

[ChaosMuppetPE]

I've ran across a manufactured joist that I've never seen before and it has me slightly confused.

I've tried to back out an allowable loading using both A7 and A36 steel as this transition occurred while poured gypcrete roofing was being used, however, neither steel designation gives me anything close to what I anticipate the design loading should be. I've checked and double checked the section properties and the chord shapes appear to be formed from one piece. I've incorporated a sketch for reference.

If you've seen anything like this before, please tell me what you can about it. Preferably, I'd like to know the manufacturer of joists of this type. I suspect the structure was built in the early 60's in the Atlanta area.

 

[ThrustIssues]

Not sure if you've solved this yet but looks like it could be a Macomber joist? There's some old catalogs/info on them on this site: http://www.slideruleera.net/contributions.html

 

[tj_PE]

Not sure if you've solved this yet but looks like it could be a Macomber joist? There's some old catalogs/info on them on this site: http://www.slideruleera.net/contributions.html

agree it looks like a macomber!

 

[tj_PE]

@ChaosMuppetPE

 

[ChaosMuppetPE]

Not sure if you've solved this yet but looks like it could be a Macomber joist? There's some old catalogs/info on them on this site: http://www.slideruleera.net/contributions.html

@tj_PE

I appreciate the input. I did eventually find Macomber and it does "favor" one, but it appears to be a competitor as the profile I have doesn't match anything in their manual.

It's just one of those situations where I'm stuck. I've calculated all the section properties for the joists and backed out the loading from this. The closest section to my joists in the Macomber manual gives an allowable loading of roughly 134plf and the joist I have back calculated to 140plf so I have a feeling I at least have the material designation right. The issue I have is that dead load alone is almost this high. It appears these joists were actually only designed for dead load unless there is some kind of composite action I am not aware of with the gypsum tees. Either way, it's the first time I've encountered this.

 

[RBHeadge PE]

I can write everything I know about structural engineering on the back of a postcard - with lots of space left over -  so I'm ignorant but curious. Wouldn't it be a bit reckless to design something only for the dead load? Surely the environmental and live loads can't be neglected?

 

[tj_PE]

I can write everything I know about structural engineering on the back of a postcard - with lots of space left over -  so I'm ignorant but curious. Wouldn't it be a bit reckless to design something only for the dead load? Surely the environmental and live loads can't be neglected?

yeah, that's why chaos is perplexed. it's an existing building so likely trying to analyze what the original capacity was so he can check it for new use/loads etc. 

@ChaosMuppetPE I feel like maybe it was considered composite, otherwise why would they put concrete on the roof? is there deck under it or just a structural slab? 

are there spiders? maybe just burn it down? 

 

[DoctorWho-PE]

@tj_PE Are we calling gyp deck concrete these days?  

@ChaosMuppetPE 

Note: I have a deep dislike of gypsum as a roofing material, particularly in the cold, wet, midwest where snow sits and seeps through any holes in the the roofing material.  I'm sure it could be an acceptable material if it is kept dry and in pristine conditions, otherwise might as well put mashed potatoes on the roof.  

 

[DoctorWho-PE]

Depending on the timeline of the project (if it is anything like mine tend to be, it is due yesterday) you could try sending in a joist identification form.

https://steeljoist.org/joist-investigation-form/

 

[tj_PE]

@tj_PE Are we calling gyp deck concrete these days?  

my sincerest apologies; gypcrete*

 

[DoctorWho-PE]

my sincerest apologies; gypcrete*

I really, really hate it.  

 

[DoctorWho-PE]

An approach from the 1960's (abstract):

https://cedb.asce.org/CEDBsearch/record.jsp?dockey=0014415

 

[tj_PE]

I really, really hate it.  

I've never had it used in new buildings, so that's a plus. 

we use it for topping slabs sometimes, but it is very often swapped in/out with "real" concrete topping 

 

[DoctorWho-PE]

I've never had it used in new buildings, so that's a plus. 

we use it for topping slabs sometimes, but it is very often swapped in/out with "real" concrete topping 

I have 4 projects right now that are renos of old buildings that have gyp roof.   ugh.  

 

[ChaosMuppetPE]

yeah, that's why chaos is perplexed. it's an existing building so likely trying to analyze what the original capacity was so he can check it for new use/loads etc. 

@ChaosMuppetPE I feel like maybe it was considered composite, otherwise why would they put concrete on the roof? is there deck under it or just a structural slab? 

are there spiders? maybe just burn it down? 

I definitely like the spiders/burn it down idea. Design it for whatever, get paid, and light a fire. No liability/no problem.

 

[ChaosMuppetPE]

@vhab49_PE@tj_PE

I'm sure it has to be composite. It's the only feasible explanation. I mean, I am ********, but I am able to calculate section properties. Without doing destructive demo, I don't have  a solution for anticipating the gypcrete compressive strength, the tee attachments, or even the tee size. I am just going to reinforce the bajeebus out of it with steel bar stock or require the owner to perform destructive testing. For (10) 50' span joists, I'm not sure what would be cheaper.

 

[tj_PE]

@vhab49_PE@tj_PE

I'm sure it has to be composite. It's the only feasible explanation. I mean, I am ********, but I am able to calculate section properties. Without doing destructive demo, I don't have  a solution for anticipating the gypcrete compressive strength, the tee attachments, or even the tee size. I am just going to reinforce the bajeebus out of it with steel bar stock or require the owner to perform destructive testing. For (10) 50' span joists, I'm not sure what would be cheaper.

is there any option to just sister joists in there? if you're reinforcing the joists piece by piece maybe it's more cost effective. would be a ***** to get them in the building and put up there but maybe you can splice them somewhere or if the shear capacity is OK on existing you could just put a new one in for the bending critical and connect to existing somehow? actually maybe just easier to reinforce.

or a channel? steel plate?  just thinking hypothetically. I haven't done much joist reinforcement so not sure how much labor work is involved. 

 

[Audi Driver P.E.]

I've ran across a manufactured joist that I've never seen before and it has me slightly confused.

I've tried to back out an allowable loading using both A7 and A36 steel as this transition occurred while poured gypcrete roofing was being used, however, neither steel designation gives me anything close to what I anticipate the design loading should be. I've checked and double checked the section properties and the chord shapes appear to be formed from one piece. I've incorporated a sketch for reference.

If you've seen anything like this before, please tell me what you can about it. Preferably, I'd like to know the manufacturer of joists of this type. I suspect the structure was built in the early 60's in the Atlanta area.

View attachment 13596View attachment 13597

Did you consider AISI 1018 or AISI 1020? Both were pretty common in those days from what I can gather.