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Existing concrete beam stirrup callout
2

Existing concrete beam stirrup callout

Existing concrete beam stirrup callout

(OP)
I have an mid 70's existing concrete beam that we have to modify (partial demo and amend/terminate some PT etc) and I have the following callout on the existing drawings:



The beam section is 24" x 24". I have assumed the call out of "DOUBLE" to refer to 2 sets of 2 legs for a total of 4 legs.

OR, does "DOUBLE" refer to 2 legs only?

There are no sections of the beam to verify what the original engineer meant.

Thoughts?

RE: Existing concrete beam stirrup callout

I think 4 legs is the correct interpretation.

RE: Existing concrete beam stirrup callout

(OP)
Thanks, hokie66.

RE: Existing concrete beam stirrup callout

Ditto. In my estimation, the conventional definition of a single stirrup in a beam of meaningful width is a thing with at least three sides, two of the them being vertical. Confidence level = 97%.

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.

RE: Existing concrete beam stirrup callout

(OP)
Thanks, KootK...and I like your confidence rating. We will know definitively after we do some site work!

Follow up question:

The PT called up in a segmnet of beam is as follows:



The "Fe=223.3k" (RED cloud) seems to have a looped tag (BLUE arrow) that is inclusive of the "Fe=74.4k" of added end-span tendons, so I therefore only have only Fe=148.8k to the internal spans.

Thoughts?

RE: Existing concrete beam stirrup callout

Quote (Ingenuity)

Thoughts?

- sloppy and ambiguous expression of design intent here I feel.

- I feel that, hopefully, the use of two different symbols is meaningful and indicative that your interpretation is the correct one.

- Your interpretation means an ext/int span increase of 50% in PT. The alternate means a 33% increase. Based on the interior span length and loading, which seems more probable?

- Is there another instance of this someplace where the meaning is more certain?

Confidence level = 88%

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.

RE: Existing concrete beam stirrup callout

(OP)
Agree, sloppy...the other end of the beam is even more ambiguous:



It graphically shows added tendons, but no call out? Sheesh!

Fortunately, we plan on some site investigation to be undertaken so we can verify before we demo, but if it anything like the last project we did like this, where we terminated tendons whilst 'live' (no temporary de-stress and re-stress), it will be 'fun'.

RE: Existing concrete beam stirrup callout

I would have thought the continuous PT is 223, and the added is 74. So if my interpretation is correct, you would have 297 in the end spans, and 223 in the middle span. But my confidence level is only about 50%, as the loop is poor drafting.

RE: Existing concrete beam stirrup callout

(OP)
hokie66, Your interpretation is my typical interpretation too, but the loop tag is indeed confusing.

I think I can get the beam to work with just 6 tendons (148.8k) internally, after we demolish the left spans, and re-configure new live-end anchorage locations.

RE: Existing concrete beam stirrup callout

Seeing they have not shown how/where the short tendon at the right terminates either, it looks like they have not completed the drawing.

Also unusual to terminate from both ends in the same span. Not worth the effort or the cost of the extra anchorages!

I will place my bet on 223.3 for the continuous tendons!

Wonder if the designer actually checked it on site to make sure what they built matches what he wanted to show on the drawings.

RE: Existing concrete beam stirrup callout

(OP)

Quote (rapt)

Seeing they have not shown how/where the short tendon at the right terminates either

Yes, I noticed that too. Sloppy on all counts.

I have run two cases of 6 and 9 tendons (148 and 223 kips) - it is tough having to provide new anchorages to 9 tendon terminations in a beam at the face of a column, especially if the tendons are grouped in bundles of 4 or 5 each! We are asking for a concrete cantilevered 'knuckle' past the column face to splay the tendons and terminate with new live-ends, but awaiting on the architects input.

RE: Existing concrete beam stirrup callout

2
(OP)
By way of follow-up. We did some site probing, and confirmed #4 stirrups are 4 legs, and the PT is 9 continuous + 3 added tendons.

Unfortunately, all 12 tendons are bunched in one group, of which we have to splay and terminate with new anchorages.


RE: Existing concrete beam stirrup callout

NICE. I wish everyone followed up. A star for your trouble.

RE: Existing concrete beam stirrup callout

(OP)
==> Additional follow-up: 2/23/2017

It was decided by EoR to permanently terminate/sever the PT and provide new concrete walls below selected beam spans and/or FRP to other remaining spans, due to the loss of all prestress.

We were therefore engaged by the GC to sever the PT, as follows:

12 x 1/2" dia UNbonded strand tendons to two beams were de-stressed via a cutting with an 5" angle grinder. Tendons were approx 90' long.

Temporary wood boards were secured to beam perimeter as the top of concrete demo had exposed long-lengths of the tendons:




'Bird-caging' of strand wires upon release of prestress:




Video LINK of cutting.

No strand exited from the live-end anchorages. No spalling to beam faces due to release of prestress.

RE: Existing concrete beam stirrup callout

I'm eager to see the video but the link appears to be bunk.

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.

RE: Existing concrete beam stirrup callout

(OP)
Dang...Google Photo does not seem to support video.

Here is a YouTube link: YouTube Link

Not the greatest video...only 16 sec.

This video shows the last 10 of 12 being cut. We cut 2 strand initially, then stopped and checked if any exited the anchorages, before proceeding with the remaining 10.

RE: Existing concrete beam stirrup callout

Better. Do you actually get to do real, plysical things like that at work?

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.

RE: Existing concrete beam stirrup callout

To me, it doesn't look like there was much elongation in those strands.

RE: Existing concrete beam stirrup callout

(OP)

Quote (KootK)

Do you actually get to do real, plysical things like that at work?

I do. Typically 25%, or so, is getting my hands dirty - real dirty - especially when having to remove and re-grease old strands etc. I was the one that severed the tendons in this video. Not one to instruct another to do something unless I am willing to do it myself smile

Quote (hokie66)

To me, it doesn't look like there was much elongation in those strands.

Very observant. Measured about half of expected elongation recovery. When the 12 tendons were placed in one bundle, they were interweaved/twisted around each other. Coupled that with old mid-70's PT grease that typically dries out and hardens, cause significant 'loss' of recovered elongation. There were no observed intermediate CJ's along the beams length, which often is the first indicator of less elongation recovery.

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