Has anyone seen this roof assembly before?

[Echo26]

A mechanical unit is being added over an existing roof structure. I went to site and found that the roof structure consisted of a 4" slab of concrete-like material (a little less dense) with what looks like a wire mesh at 6" spacing. The steel joists consisted of what looked like a single angle oriented as a "V" as a top chord. I was not able to confirm if there is a plate welded on top of the "V" nor was not able to see if there's some sort of connection between the slab and the existing roof slab. I also was not able to measure the thickness of the angle. The bottom chord is a plate with the web members as a rod. There was no steel deck found and the building is built in the 1950s. The existing joists are 18" DP at 4'-0" spacing.

Has anyone came across this type of structure in the past? What type of joists are these?
I would assume the top chord has some sort of connection to the concrete slab and is acting composite. Can anyone confirm this is the case for this type of joists?
Does anyone have an idea what type of material the slab is?

 

[JoshPlumSE]

Hmmm.... It kind of reminds me of a "composite joist" system I got a pamphlet on 15 years ago or so. This was before SJI had any guidance in their joist catalog.

If I recall correctly, there were a couple of different companies. One relied on "friction" between the top joist and the slab. But, the top chord may have been partially embedded in the concrete slab.

The other one had a "deformed" top chord. Where they would bend up portions of the double angle up into the slab to get their shear transfer. I want to say the company name started with a V. But, that's all I remember. I never ended up using the product for anything.

Not saying that this is what we're seeing in your pictures. But, conceptually it sounds similar. Maybe a one-off project where they were trying to do something like that.

 

[DBronson]

Echo26:

The deck looks similar to the Tectum system. Link I'm not familiar with the joist system, but the Tectum product has been around for nearly 70 years so it may be a legacy system.

Regards,

DB

 

[hokie66]

Not Tectum. That comes in boards. This was cast in place, either gypsum or some other lightweight concrete material.

 

[Aesur]

Hambro? Link

 

[JedClampett]

Could it be some kind of Rube Goldberg poured gypsum system? The statement "a little less dense" is a clue to me.

 

[JoshPlumSE]

Aesur -

Hambro is one of the two composite joist systems I was thinking of. Though my member was imperfect about how it worked. The other one, I think, started with a "V". But, i think the other one relied on friction.