Composite Steel beam

[connect2]

So it's 1957, not that long ago.
It's a floor beam W21x68 with 1"x1"x8" long square steel studs welded to the top flange of the steel beam, center of flange only. The concrete floor slab is 9" thick and actually the beam is completely encased in concrete. The studs are variously spaced @ 6"o.c. for the first 6 feet, then 9" for the next 3 feet and then finally 12"o.c. for the next 3 feet from each end.
Question is where can one find some information to determine what capacity the composite beam has and what was the design basis at the time?
Thanks.

 

[rb1957]

the studs run perpendicular to the beams ?
8" long ??

are they merely spacers ? contact pads ??

 

[connect2]

no the studs are 1"x1" square bar. The bars are welded to the beam flange/center line with the 8" being the height the stud projects up from the flange. It's just like a regular headed stud for a steel concrete composite beam only it's a 1"x1" bar with no head.

 

[rb1957]

ok, they stick out like (very) small towers above the web ... they're "just" a contact surface, are they good for anything ?

maybe (probably ?) i'm missing something ??

 

[MiketheEngineer]

Sounds kind of wacky.. Do you have a drawing or a pic?

 

[ishvaaag]

I don't mean the treatment was correct but the procedure was still quoted by the seventies'. This is the section dealing with the prismatic studs in

La Estructura Metálica Hoy, 2nd ed.
Ramón Arguelles
Librería Técnica Bellisco, Madrid 1975

it seems comes from DIN codes support.

attached in 2 jpgs (spanish)

 

[ishvaaag]

2nd

 

[LobstaEata]

Would seem to me that if there is not any mechanical development of the shear stud (as there is no head), then only the chemical bond between the stud and concrete would be available for the shear friction required to develop the shear strength of the stud. Not sure how headless studs would be rated under those conditions.

 

[ishvaaag]

Certainly that seems the main problem; however even if it is clear codes (usually) technically progress since inception, it would be rare that the DIN guys of the era would throw something to use without some test support. Maybe they were limiting the capacities, etc, would have to study the thing to attest.

I have another text of the era common here for composite beams, and may try to see tomorrow if the thing is treated.

 

[hokie66]

This was in the early days of composite construction, as was I. I don't remember square bars being used. The two common types were headed studs and channels, as shown in one of ishvaaag's pictures. His pictures don't actually show connect2's situation.

I wouldn't be too concerned about lack of the head, as I can't see the slab lifting off the beam, especially with the beam being encased. If the beam were encased per the Specification requirements at the time, shear connectors would not have been required at all. However, this requirement stated that the top of the steel had to be 2" above the slab soffit, and that is not the case here.

I think the only issue is how well the bars are welded to the beam. If welded competently, I think the beam would be fully composite. Partially composite was not talked about in those days, and the amount of studs quoted would be more than required today for fully composite action for most spans.

 

[racookpe1978]

If the 1x1x8 inch long block is vertical to the beam, and the concrete cover over the beam is 9 inch thick, then there is only 1 inch cover. Seems like that isn't enough.

In a sideways shear load (any direction), won't that long of a "square stud" bend - thus breaking the concrete to "square stud" joint?

 

[connect2]

I immediately assumed, there's that word, that the bar was vertical, as a stud. After reviewing ishvaags attachments, thank-you ishvaag, my assumption may have been an uninformed one. So infact hookie66, ishvaggs drawings may in fact be actually what exists, which will need to be seen, to be believed, which will happen.
I guess the next question will be has anybody seen this type of construction in a North American Code or standard from this time.
My thoughts immediately are; how can the 1"x 1" block transfer shear flow? in the face of, (pun the lowest form of humour), 3/4" aggregate, and if it can, how effective can it be? And how does one arrive at an effective concrete slab (flange) width, beff, b1? Do we actually have composite action going on here?

The new application involves putting a new cooling tower on top of these beams/floor slabs, re new concentrated point loads now along the beams length vs a udl load as it previously was a water cooling basin/pond/tank/pool, with no concentrated load demand on the composite? beam/floor slab.

I particularily enjoy working on structures of this vintage and earlier. By all applications of engineering principles and current codes, they shouldn't be standing.

 

[rb1957]

if they are flat on the flange i can't see them helping much to load up the concrete.

if they are vertical, then i think they'd be less efffective.

maybe, if they are exposed on the concrete face, they're there to show where the beam is, and as a contact pad.

 

[ishvaaag]

The same prism connectors as treated in

Estructuras Mixtas, Teoría y Práctica
Julio Martínez Calzón
Instituto Eduardo Torroja de la Construcción y del Cemento
Madrid, 1966

again in two jpg pages

 

[ishvaaag]

2nd

 

[hokie66]

Sounds like you will have to dig one out to find out how they are oriented. If they are flat, I wouldn't count on composite action. I don't believe you will find these connectors in a NA code or reference, but you will find clauses allowing for the use of alternative connectors based on testing.

rb1957,
Sounds like you need a primer on steel and concrete composite construction.

 

[rb1957]

not much call for it in my business ...

i guess the subtext is "if you don't know, don't post ..."

 

[JoshPlumSE]

I think the connectors can work fine. All you need the studs to do is transfer shear between the concrete and the steel to reduce or eliminate the slip between the two surfaces.

I've seen a number of differnt steel joist companies get into composite joist systems by relying on various non-standard ways of transferring this shear.... Friction on a roughed steel surface. Bent plate parallel to top chord. Granted, they then have to back up their calculations with test data. However, this system seems way more conventional than these other ones that are being used on modern projects.

 

[gwynn]

I agree with Josh. This is a very similar to a detail I see in older precast bridge beams, where the top of the beam is crenellated to achieve composite action with the deck. Typically the crenellations are 1" deep as well, which fits with the bars being described here (aside from the sloped edge at the base if they are fillet welded). As long as the bars and the concrete are capable of transmitting the required shear flow, I see no reason not to take this as a composite beam.