Concrete Portal 3

[dik]

Attached is an elevation of a concrete portal and I'm looking for information about the development and anchorage of the bottom reinforcing steel and where others would consider the 'beginning' of the support. In Canada, our code requires the span to be considered as the clear distance plus the minimum of (the depth of the member or the width of the support). Our CSA Code is similar to the ACI... Bar sizes are 35M (Similar to a #11 bar...

 

[rowingengineer]

I don't quite understand your question, as the joint you are describing is moment carrying, however I found figure 13 the attached paper interesting.

An expert is a man who has made all the mistakes which can be made in a very narrow field

 

[dik]

Thanks for the paper... Column (bunch of 25M's - #8) and bottom rfg (10 - 35M #11) were going to be straight bars; there is no chance for stress reversal. Top reinforcing is a standard hook (35M's) There are actually two beams side by side. No seismic issues...

The concern I have is the splicing of the reinforcing and cut-off locations (bars in this locale are 59' and 5 - 35M fit snugly in one layer with no provision for bundling). I'm looking for a rationalisation for commencing the 'start' of embedment length at or near the forward edge of the haunch.

The actual design moments are predicated on a span centre to centre of column and not the clear span at the haunch plus the depth of the beam.

Dik

 

[BAretired]

I'm not sure that you need a "rationalization" for the start of development length. Where else would it start if not the inside edge of the haunch?

BA

 

[rowingengineer]

I'm in a world on confusion, if there is no opening moment on the joint, then why do the bottom bars need to be developed? Is this is a simple dead + live load situation? If so wouldn’t you need top steel at the knee position?

While I don’t understand what is going on, the way to design this joint in my opinion is to use the strut tie method (the Canadian code is the best for the strut tie in my opinion). using this method you will get nodes, which you must develop your steel past.

An expert is a man who has made all the mistakes which can be made in a very narrow field

 

[dik]

Very high shear loads involved... 15M (#5) dble bars at 12... Our concrete code has a requirement that the bars be developed a distance beyond the support to accommodate the shear and moment.

Dik

 

[dik]

BAR...
forgot to add that I would normally use the inside edge of the haunch as the starting point with the span length equal to the clear haunch distance plus the depth of the beam at each end.

I'm trying to avoid splicing the 35M bars due to the limited length of 59' and cut-off points I can use. The loads are 'real' and high and I'm looking for some background on the approach. I can find no reference material on haunches and the effect they have on reinforcing steel at their location. I want to avoid 'adding' an additional 4' or so to the bot rfg.

Dik

 

[rowingengineer]

sorry dik, I'm still not following the grove train. I don't understand the "support" statement? The area we are discussing is a joint is it not? Thus the requirement for development of the steel at the support should be for tension steel and compression steel. Is the reo being used as compression reo or tension reo? For both of these situations you should develop past the nodal point of a strut tie model.

An expert is a man who has made all the mistakes which can be made in a very narrow field

 

[dik]

Not a joint... but the extension of the bottom reinforcing steel across the interior point of the haunch. I suspect the contractor would create a pour joint at the U/S of the beam and that the entire beam would be poured monolithically.

Dik

 

[hokie66]

For the purposes outlined by dik, and in the absence of clear code language, I would use about half way across the haunch as the face of the support.

 

[csd72]

dik,

It sounds like you need to improve your understanding of the fundamentals behind the code clauses. Once you understand this then the answers to questions like this fall into place.

This is what code commentaries were invented for.

As engineers we don't just need to know, we need to understand.

 

[dik]

csd72... that's my problem; I have a vague understanding of the principles behind it <G>... and was uncomfortable with the application of the code directly and was wondering if anyone had a better grip on things... Hokie's idea, being somewhat arbitrary, has a better comfort level, in the absence of added info.

Dik

 

[csd72]

http://download-book.net/ACI-CONCRETE-DETAILING-ppt.html

 

[dik]

Thanks csd... good link and some interesting ppt dox...

Dik

 

[csd72]

Happy to help if you have any more specific questions once you have looked at those.