Rebar Development Length Tables 2

[bookowski]

Curious how other people handle setting up development length/splice length tables on their drawings. To set up useful tables requires building in some assumptions, for example:
- Assuming you use ACI 12.2.2 simplified equations there are requirements for clear spacing, min. clear cover, and ties/no ties.
- If you are making a table for interior elevated slabs you would normally be using 0.75" cover, do you therefore build into your table a change in equations after #6 bars, i.e. when the cover of 0.75" becomes smaller than 1 db?
- Similar questions for walls: at basement walls we show the vertical reinforcing as the outer curtain, but on shearwalls we show it inside the the horizontals - do you create two tables and account for the different typical covers for those two situations and then build that into your table? There is also the issue that portions of shearwalls may be tied/confined bars while others are not, this also may impact the development length.

 

[TXStructural]

It is generally suitable to specify one lap for each size bar, based on the longest required for the various conditions for the project. It is also acceptable to have this set of defaults as "unless otherwise noted", then provide specific guidance on plans or details ONLY where doing so saves substantial weight/cost. Maintaining an array of different laps on a job site will result in errors and costs (time), in addition to a higher likelihood of delays as an inspector has to verify what lap is required where. This is in addition to your time and the time to document multiple lap lengths in CDs.

***Avoid unneeded complexity.

And NEVER refer the rebar detailer to ACI 318 - we see this all the time, where a designer says something like "lap splices shall conform to ACI 318)". Obviously, a rebar detailer has no way of knowing tension or compression, or any of the several values required to determine lap lengths.

 

[hokie66]

Amen, TX.

 

[bookowski]

I agree with the idea of repetitive design to avoid errors, but only having one table sounds overly conservative to me. Just the top bar factor alone is 30%. If we just added that 30% onto all of our bar lengths we wouldn't last long - multiply that 30% x say typical 25 stories of slabs and it's a lot of steel. As for the inspector, he should only be working from approved shop drawings anyway so if he is reasonably competent he can work out measuring a couple of different lengths.

I wasn't expecting the one table answer. We currently have only a few tables (slabs, walls, columns) with some notes about what assumptions they are based on. I recently was reviewing the drawings of another firm and saw that they have 9 different tables. At first I thought that it was excessive but after reviewing it I see that they are saving a lot of rebar by covering different conditions so I was wondering if this is typical for most firms.

 

[JedClampett]

We have a table with 4 laps for each size bar:
*Top or "other" bar
*Cover greater than two bar diameters or spacing greater than four bar diameters.
You bet it's complicated. So the fabricators almost always use the longest of the four laps. There's actually very few bars that are "other" bars (bottom bars), so it's not that extravagant.
I tried to boil it down to two lap lengths per bar on a couple projects and no one noticed, so I got lazier.

 

[AELLC]

I have inspected rebar years ago, and believe me, when you look at rebar in a high rise, you aren't referring to individual cut sheets. You are looking at the number of bars, spacing, general placement, and rebar size and strength grades.

You can only check lap lengths of rebars in slabs and walls, generally. It is the responsibility of the EOR to check cut sheets for lap lengths of beam and column rebars.

I would be very glad to see only one lap length per bar size in the walls and slabs, but some companies had innovative and easy to understand graphic methods of indicating more complex lap length schemes on the layout shop drawing.

 

[TXStructural]

ninety percent of buildings are fewer than 10 stories, and most are fewer than 5, so my answer to use only one length addresses those cases. In tall buildings, the payoff for all parties from design through construction is to minimize waste, reduce weight, and repeat everything, so being a bit more specific can be important. I can unequivocally say that nine different lap lengths is overly complicated. Using different values in horizontal and vertical members may make good sense, so two or three might be appropriate, particularly since columns and slabs/walls will be using different size bars, for the most part. In real applications, we often do not lap reinforcement in beams, rather they are designed with discontinuous reinforcement starting and stopping at cutoff points, so differentiating top vs other is probably not really going to save very much. In cases where continuous bars are required, the few instances may or may not warrant special treatment.