1974 Concrete beam and joist schedule 3

[enginerding]

I am evaluating an existing floor for the weight of a nuclear medicine scanner. The structure is concrete joists and slab with concrete beams. One bar placement and bending diagram is provided that includes both joist and beam details. The typical top bars, bottom bars, and bent bars are shown. The joist schedule refers to bottom straight bars, bent bars, and additional top bars. This all makes sense with the diagram. But the beam schedule shows bottom long, bottom short, and top bars. I cannot figure out the difference between the bottom long and bottom short bars and the details do not refer to them this way. Does this refer to the straight and bent bars? Seems weird if that is the case because the joist schedule on the same page refers to bent and straight bars by those names, matching the diagram. Is there some other interpretation of this? Can anyone help with this? I have uploaded the details as well as excerpts of the plan and schedules.

Thanks for any help you can provide!

 

[JedClampett]

I would say the bottom short bars are the bars that vary from bottom to top. I'm saying that because the other top bars are described as additional.

 

[dik]

Could the bottom short bars be approx 80% of the span to provide extra reinforcing at mid span to accommodate the larger +ve moment? CRSI used to have a manual that showed straight bars and trussed bars... but I haven't looked for this info in decades.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

1) I roll the opposite way that Jed does on this. So we shall have some fun sorting it out.

2) Even if I am right, I feel that this is still a poor way to communicate the reinforcing.

3) I see this as shown below and offer the following in support of that interpretation:

a) It seems to me that this is the only interpretation that would allow one to fully understand all of the top and bottom bars required without additional info.

b) In a way, this sort of mirrors my understanding of how the design would have proceeded. You'd design your total bottom bars, turn a percentage of them upwards, and then add in whatever extra top bars were required.

 

[enginerding]

These responses are great! I had all three of these thoughts as possibilities, and I completely agree that this is a poor way of communicating the reinforcement. I could see jed's stance in that the short bars are only on the bottom for a short length, and I can see KootK's stance that the bent bars are much longer than the straight ones. I also wondered whether there was a time where some portion of the bottom bars would stop short of the full span as dik suggests. While I was really hoping that someone would know how this would have been interpreted in the mid-70's, your answers are encouraging in that I am not crazy (at least not evidenced by this!).

What gets me the most is that the joist schedule on the same page refers to straight and bent bars, making it perfectly clear for the joists.

I'll keep watching this thread to see if anyone else chimes in, but I will probably end up checking it several ways to see what look like it makes the most sense. If we need to get further info to make any definite statements, then maybe we have to investigate further on site. Thanks all!

 

[dik]

KootK has another interpretation... back in the day, the rebar was typically referred to as straight bars and trussed bars... could be a different terminology. There's no reference to trussed bars in the schedule so KootK could be 'bang on'. I did a renovation about 50 years back that involved cutting out an existing beam... rebar was twisted square bars and they were bundled... still had the metal rebar tag attached...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

@enginerding: What you need here is advice from somebody old & local. someone who may have worked in an office when things were specified this way. Are you a member of the Structural Engineer's Association of Illinois? I'm a new inductee and they're awesomely active on social media. I'd try posting the details there and see if you hit pay dirt.

 

[Settingsun]

I wonder if the builder knew how to interpret this...

 

[HTURKAK]

If this refers bent ups, that is, long bars bent ups , short ones bottom straight , that could be named as bent ups or bent bars..

Let me guess the situation ;

- The beam and joist details are DETAIL S1-3,S1-4,S1-5 .. I suppose there are other details S1-1 and S1-2 which one of them complies with the beam rebars rather than a common detail valid for slab, joist, beam etc....

- TB-13,TB-14,TB-15 is continuous beam with 5 spans TB-13,TB-14,TB-15,TB-14,TB-13

- The spans are roughly similar and in the range of 24 ft,

- The top additional rebars 6 no 10 makes 7.62 sq-in and 7 no 9 makes 7.00 sq-in are almost double the span rebar (4 no6 + 4 no 7 )makes 4 .0 sq-in.

- The span of joists seems 25 ft.

With this set up, with a simple hand calculation, the support moment should be around 500000 lb-ft and span moment 300000 lb-ft

My opinion is, the short bars are really short ( with a length of 0.725 L ) and long rebars are long ( with a length of L+12 in).

Er. enginerding (Structural); I will suggest you to perform a similar inverse calculation and see the situation.(.you have the full dwgs and think you can ..).

The following excerpt from Structural detailing in concrete ( By BANGASH)..

 

[bones206]

One thing to consider is the order in which it is listed in the schedule. Presumably the primary reinforcement is listed first (reading left to right). The joist schedule reflects this as STRAIGHT first, then BENT. I dusted off my great-grandfather's CRSI manual (lot's of sneezing ensued), and it consistently shows STRAIGHT, then TRUSSED as the left-to-right order in all the example beam schedules. It would be unusual if your beam schedule had it reversed.

Good luck. This isn't even my project and it's annoying me...

 

[dik]

@bones... that's sort of the way I recall... but things are fuzzy.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik