Help Identifying a Floor System

[RobertHale]

My company was called in to look at rehab and renovation on a jail built in 1901. From a historic sign, I know the builder for the jail was the Pauly Jail Building Company. For a large chunk of the building, it is what you would expect from a turn of the 20th century building URM with wood joist framing over a crawlspace. However, for the "lockup" portion of the building, there is a floor framing system that I have not seen before. Essentially, it looks like S8 (or equivalent) beams spaced at roughly 36 inches in an arched corrugated form supported by the beam bottom flanges. In the larger spaces, there are steel beams (S12) that provide intermediate bearing support for the embedded beams. I did my best to use the Wayback machine to look at the information on slideruleera.net, but I didn't see any system that matched what I saw. I am wondering if anyone has run across this system before and might have some information about it. See the pictures below. I will note that some rehab appears to have occurred recently, but no one in the project seems to know what happened and when.

 

[JAE]

This is an example of an arched tile floor similar to what I think you have here.
The tile was utilized to create a level of fire protection where your jail situation may not have had the same concern, if any, for fire protection.

The floor "capacity" would be based on the steel beams supporting the arches - the floor arches probably have more strength than the beams but you'd have to investigate the thickness of the floor at the center of the arch span against punching shear resistance.
In some cases with flatter arches such as this they used a horizontal spacing of tie rods between the beams to keep the arch thrust from spreading the beams apart.

This image below came from the "Antiquated Structural Systems" articles by D. Matthew Stuart in the Structure Magazine, December 2007.

 

[hardbutmild]

but you'd have to investigate the thickness of the floor at the center of the arch span against punching shear resistance

Punching of an arch? I have never heard of that happening. How does an arch punch?

 

[Tomfh]

At the top of the arch the concrete is thin. A concentrated load at that location could punch through.

 

[hardbutmild]

I do not feel like this is possible, especially with the sheeting underneath. Is there a case of a vault failing due to punching? I'd expect it to fail by a 4 hinge mechanism under a point load.
Even if it does fail locally, it should still be fine.

 

[LittleInch]

I can't see this being a "system", more than it looked like a good way to self support the presumably concrete floor above without needing framework. What is the floor above and what sort of thickness is there?

Maybe this was the way they poured concrete floors in 1901?

Or they had some excess corrugated sheets.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JAE]

hardbutmild,
Yes - what Tomfh suggests.

Our local codes (IBC) require that floors resist not only uniform live loads but concentrated live loads over a set area (i.e. 2.5 ft. square).

If the top of the arch is thin, even with a metal deck below, there can be punching shear failures under a concentrated load - like a forklift wheel load for example.

The metal deck won't do much to resist the punching shear as the primary stiffness is the concrete (i.e. shear stiffness not flexural stiffness).

 

[JAE]

I might add I've seen this happen before - a hardware store company purchased a building whose floors were concrete metal deck slabs spanning between floor joists.
They used very heavy forklifts and when I arrived there the floor was a mess - shear fractures everywhere.

 

[hardbutmild]

concrete metal deck SLAB is not a concrete metal deck VAULT!
Imagine a vault that is extremely high… it becomes more like two colums at an angle than a plate.
Shear or flexural stiffness do not mean much to a compresion member like a vault, it’s pure axial.
It’s more like trying to punch an egg. sure, you can do it with a needle (unrealistically small area for real structures) - you have a loaded area od 1.5x1.5 ft at a span of 3 ft as OP mentions. it’s like trying to puch an egg with your finger. and eggshell is extremely thin compared to the span.
in URM vaults you also need to consider point loads, but i never heard of a vault failing due to puncing.
punching shear requires shear in an element. vault is a pure compression element.

 

[JAE]

vault is a pure compression element.

No it's not. Not if there's a 5,000 lb. wheel load pushing down on the apex of the arch where the deck is essentially horizontal.
Yes there's compression in the concrete - in one certain direction - but with a 2" x 6" area load of 6,000 lbs. you'd definitely have shear forces vertically in the thin slab.

I think you are properly suggesting that the compression increases shear capacity and I would agree with that for two of the four sides of the compression block.

Take it to a ridiculous extreme - if the arch was an eggshell and you placed that wheel load on it there would definitely be punching shear.

The OP doesn't know the thickness - I simply pointed out that a very thin floor - and old buildings from 1900 certainly have thin floors at times - could be a possible failure mechanism.

 

[hardbutmild]

Take it to a ridiculous extreme - if the arch was an eggshell and you placed that wheel load on it there would definitely be punching shear.

Nope, it would crush. That is a completely different type of failure. But surely if this type of failure is possible there should be at least one photograph of any arch/vault/dome failing by punching... or some scientific paper about it.

The OP doesn't know the thickness - I simply pointed out that a very thin floor - and old buildings from 1900 certainly have thin floors at times - could be a possible failure mechanism.

I just disagree, sorry. Look at this work (it's about masonry, but it's the same... compression only material):

https://dspace.mit.edu/bitstream/handle/1721.1/72648/808355613-MIT.pdf

Chapter 4 is concerned with point loads and nowhere in the whole document is there a mention of punching. They try to fit a thrust line inside a vault, this means it's only considering compression. Thinner the vault is, harder it is to fit a compression line inside, but it still fails by forming a mechanism and not by punching.
Please look at figure 4.11 on page 41. See how small the point load area is and still no punching? And thickness plays no role here, look up a book "EQUILIBRIUM OF SHELL STRUCTURES" by heyman... no punching is mentioned as a concern in vaults and domes even at ridiculously small thickness.

 

[bones206]

Maybe the OP from this post could help out: thread507-486083

 

[bones206]

This is a screenshot from this document:

https://pdhonline.com/courses/s212/s212content.pdf

Unfortunately not much detail offered besides the image, but it does indicate where the tension rods are likely located.