Breeko Block Beams and Channel Slabs

[T_Bat]

Hey everyone,

I'm looking at some potential renovations to an existing 1950s era building. The floor system appears to be precast channel slabs (13" and 16" deep and about 3'-2" wide). In some areas they bear on CMU walls. In a few areas they bear on a line of beams made from some type of masonry block. Based on my research the beams were likely positioned in the field produced by a company called Breeko out of Nashville. I assume they also made the channel slabs. I'm not sure if it was common to pretension the channels slabs or were they just conventional reinforcement based on the era. This is in middle Tennessee, which believe it or not, was one of the first frontiers for pre/post-tensioning in this era.

Does anyone have any info on Breeko or their products? I've done a deep dive on the google machine. I've located some info in old newspapers and mentions in various old PCI documents but nothing that may help my preliminary analysis. The goal is to try to rate the floor and roof for acceptable occupancies...

If anyone has any info it would be much appreciated!

 

[T_Bat]

Some pictures... One of the floor channel slabs cut:

Breeko block beam...

Breeko block on column...

End of block beam...

Roof channel slabs...

 

[Ingenuity]

Your first photo seems to be a 'modern' precast pretensioned double or triple T - was the building modified after it original construction?

With regards to Breeko Block Beams, they were post-tensioned with two threaded bar tendons EDIT: 0.6" DIA GALVANIZED STRAND:

I am not so sure that your beams are Breeko beams. The photo you detail that shows the end of the beam seems to indicate multiple wires or rods, AND your section shape has the enlarged flange to receive the orthogonal panels.

The Channel Slab may be MidCon Channel Slabs from Wisconsin:

I have Matthew Stuart's "Antiquated Structural Systems Series" Parts 1 through 10 that I can upload if you wish, or search the subject at

http://www.structuremag.org

 

[Ingenuity]

In light of the info that follows, some of the info I posted above may not be correct/relevant.

In 1979 PCI produced a series on the beginnings of prestressed concrete in the US to celebrate the 25th year of PCI, and Ross Bryan authored a paper on prestressed concrete in Tennessee entitled: "Prestressed Concrete Innovations in Tennessee": Link and the paper is attached too.

It mentions Breeko block and channel-type slabs, and a lot of other systems too. Contrary to my statement above, Breeko used strand in their systems, by Roebling Company, who at the time were the only supplier of prestressing strand in the US.

I have not read it all, but probably worth a review by you.

Breeko plant, a pretensioning bed that was notable for two reasons. It was designed for deflecting strands, and it did not require anchorage abutments. The thrust of the strands was carried by the continuous block beams that supported the form (see Fig. 16). The first production bed was 200 ft (61 m) long and could produce 3-ft (0.9 m) wide channel slabs, up to 14 in. (356 mm) deep, which would span 50 ft (15.3 m) for roof loading. As we all know, the channel slab soon gave way to the double-tee except for heavy floor loading.

Deflected strands in precast channel slab webs in the 1950's - pretty pioneering stuff!

You may have to do some field investigation of the as-built system, including GPR scanning and maybe invasive probing, checking out strand #'s and diameters, etc. In some cases we have extracted 60" long segments of strand from pretensioned elements and had the samples lab tested for mechanical properties when proposed new loadings necessitated such.

 

[T_Bat]

Thanks! The article by Mr. Bryan was my first clue. The engineering firm he started is still around and I’ve reached out to them to see if they have info. From the info I found, Breeko made a variety of beams - though the two strand beam in the picture is the most common. Ing, thanks for the info. I’m looking to see if an existing roof can be used as a bar (100 psf). I feel it is highly unlikely but I want to do my due diligence. That being said - if I can be reasonably certain that it will not work without a bunch of testing, I’d like to save my client’s money. If based on my research it seems possible we will likely get some testing done.

 

[T_Bat]

Also if you want to upload those articles it would be greatly appreciated!

 

[JLNJ]

I would be careful about using those channel slabs. The margin for error is slim in such a small non-redundant element.

If memory serves (25+ years ago), GM had these in several of their manufacturing plants. They had a few local roof panel collapses, likely due to spalling, bar exposure, and the resulting corrosion.

 

[T_Bat]

Well after some phone calls I was able to (amazingly lucky) track down the original hand calcs performed by Mr. Bryan's firm back in the day. His firm is still around and kicking and they were gracious enough to let check out their records. They basically have notebooks from when Ross Bryan and his team developed load table for a bunch of different early manufacturers.

It was a bit like finding some original, handwritten score of a famous symphony or Beatles's lyrics on the back of an old napkin. That being said - it appears my suspicions are confirmed. There is now way these things will work at their current span for 100 psf live. I'm looking now to provide some potential options to make them work. IF these were conventionally reinforced, I would say cut the span with an intermediate support then cut the channels to make them simply supported. However, no that I know these are pretensioned, I'm concerned that the level of prestresssing, when cut to a shorter span, may lead to problems with too much prestress force.

Does that seem like I'm headed the right way?

 

[Ingenuity]

T_Bat:

See attached PDF file, as requested. With the info you have obtained from Ross Bryan Associates, I doubt the attached will be much assistance, but maybe for future projects.

That was mighty professional and courteous of Ross Bryan Associates to share the info with you. Nice.

However, now that I know these are pretensioned, I'm concerned that the level of prestresssing, when cut to a shorter span, may lead to problems with too much prestress force.

How so?

The ultimate flexural moment capacity of the section will be unchanged. For flexural stresses (P/A + M/S), after 60+ years where creep & shrinkage have all taken place, you may consider the staged-construction aspects where the DL + SW is taken by the existing span conditions, and your new LL stresses will be based upon the new half-span condition. If you cut the channels to preserves their single-span condition, then your pretensioning strand/s will slip at the cut and hence loss of force over a development length. I would not cut the channels, but would check the negative flexural moment effects over your new intermediate supports.

 

[T_Bat]

Thanks Ing - I agree, very appreciative of RBA. Nice to see the engineering community work together.

To your point about not cutting the span - I need to finish going through the info from RBA but these likely have little reinforcing other than WWF where effective for negative moment. If I attempt to cut the span from 50' to 25' (which is about what I need from the RBA tables) then the negative moment will be fairly high. Do you feel adding some external reinforcing is still better than the cut channel approach?