Substantial Openings in Double Tee 4

[KootK]

I'm seeking guidance and/or references for dealing with substantial openings in precast double tee flanges. I'd think this to be a pretty common thing but I've not yet hit the jackpot on google. Some starter thoughts:

- strut and tie as always. 2" flanges though. Not getting a lot of bar in there.

- design the stems across the opening pretending that there's no flange at all.

- even designing the member sans flanges, I still worry about the vestigial flange bits absorbing compression and buckling etc.

As with all things that get prefabbed, shipping and handling stresses inducing cracking is proabably as important as anything else.

Recommendations?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

As I said in my original reply, I've only ever been able to find generalized guidance on this topic and otherwise have had to fend for myself.

Google preview shows me this but not the page before. Looks promising save the $240 CAD sticker price for the doc...

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TehMightyEngineer]

Mmmmm, I worry it's basically $240 for a single useful page. I've never felt we got it worth the money when we bought a pricey document for a few pages (looking at you ASCE and ASTM). Still, that seems to be more guidance than I've ever found.

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[Guest262653]

I have access to this FIB report (which I can't post here for copyright reasons) but 240$ for that page only seem a bit hight, IMHO. It looks like a good document, like all FIB reports, but I haven't read it in full since precast is not my usual practice area.

The 4 lines' paragraph that relates to figure 10.21 states that "Holes in ribbed-floor elements may be formed in the positions shown in Figure 10.21". And continues stating the obvious requirement of no vertical holes in webs and the allowance for horizontal web holes above the prestressing tendons. Nothing more.

 

[KootK]

which I can't post here for copyright reasons)

Any chance you could post a snip of the page section right before the diagram? The opening width numbers appear to be similar to the US/CAN guidance: you can have holes but don't put them in the stem or stem fillet. It's the 1000 dims that give me a modicum of hope. Seems to me that, if you're going to include that, you are making assertions about what might be okay from a structural engineering perspective. Maybe.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

This is what they had to say in the '94 version of the FIB.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Retrograde]

This is the paragraph that immediately precedes the figure.

 

[Guest262653]

Retrograde beat me to it. It's really only that paragraph.

 

[KootK]

Thanks Retrograde and avscorreia! I may still pick up the pub eventually because, taken as a whole, it looks pretty great. For now though, it's nice to not have to fork out $240 for something that probably doesn't address my immediate need.

How are you guys interpreting the diagram provided? As "this is okay engineering wise" or "this is constructable but needs some checking"? As I mentioned previously, the 1000 dimension throws me off a bit. I don't see why one would include that unless the intention was to actually imply engineering acceptability. On the other end of the spectrum, it's hard to imagine that one would be able to have all three indicated openings concurrently without getting into trouble. I'm going to be investigating my openings somewhat rigorously regardless but I would very much like to understand how others are interpreting the information.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Retrograde]

I've never designed a double-tee so take my advice for what it's worth.

I would interpret the diagram as saying that you still need to design the double-tee with a reduced effective flange width due to the openings, but provided you stick to the recommended opening sizes you don't need to do any special checks on longitudinal shear etc.

 

[Agent666]

See attached, while it applies to steel composite beams its still possibly of relevance to your situation.

This gives some justification to the alpha angle describing how forces flow around openings being comparable to the rate of increase in effective width in composite design near the ends of simply supported members, this seems like a reasonable assumption.

Note in figure 4 the orthogonal forces which might require some consideration with no topping being present.

With topping I believe it could easily be argued that with the magnitude of forces I'm expecting with a typical floor configuration that these forces resolve themselves without too much thought in the whole diaphragm.