Development Length

It's not 37% decrease in material because you haven't counted the rest of the bar length. You would also be limited by bar spacing (I presume) in the within-column case.

It is sometimes worthwhile refining things like this. I would say that would be the case if you can reduce column size rather than due to the steel saving directly. Also consider at what point you'd be comfortable telling a contractor to delay pour to fix inadequate length. If your specified length was trimmed to the bone and they were 3" short, would you accept? Technically it's their problem, but the client wants the building built on time and now it's you who's the problem.

Thanks for the response steveh49! In this case I am the client and I am reviewing the design drawings and rebar fabrication drawings before they are IFC. You're right that the percentage is based on the total bar length so the total decrease in material will not be 37%. Although, in some cases we will see reductions in bar length close to that percentage. I was hoping to get a better understanding on if my thinking is flawed and why Im incorrect in my assessment that the clear cover shouldn't be determined at the beam but at location the bar is being developed. Using my development length example 2 figure, my (cb+ktr)/db value would max out at 2.5 instead of 1.6 for a 2" clear cover, reducing the bar length by 28" on each side. If the trench is 1' wide this would save quite a bit of money on material cost when you have 20,000+ tons of rebar and numerous occasions where this occurs across the entire project. Also, the rebar install rate for labor is based on tons of steel, so reducing it will save on labor costs as well.

The value you use for cb should be based on the location where the bar is being developed since that is where splitting would occur. That means that if the bar is fully developed within the column (Example 1) or beyond the trench (Example 2), then you can use your value from "Clear 1". cb will likely be controlled by the bar spacing, instead of cover dimensions, though.

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It's based on cover or 1/2 bar clearance over the length of development as you're saying. For the column joint, there's more to it than just development so don't get tunnel vision. Your example seems a bit odd too. Are they really 7' columns at 4ksi?

Don't forget you probably also have 2" side cover in and out of the page, so your 75 and 47" cover is basically non-sensical.

The top clear cover governs the design so spacing and side cover are not a factor. Any other case would make (cb+ktr)/db = 2.5. We don't really have the beam to column case on our project so no 7' columns. I added that example because any example problem or document I found while researching online used the development at the beam and not at the development location into the column. The EOR is stating the clear cover should be 2". What I found through my online research supported this, but did not line up with my understanding of the theory on development length. Thanks for all of your responses, they were a big help!

You have to be mindful that bar development doesn't always equate to anchorage (or a valid load path to other members). Just sticking it into another member Ld doesn't always mean it will transfer the forces effectively.

For example in your trench example, to transfer the forces effectively around the trench cutout, you're likely to need far more length (and other reinforcement) than just having the development length of a bar beyond the cutout (even as an offset lap).

For one, you need to ensure you have sufficient moment coverage (which implies a load path around the discontinuity) and greater lengths for the development of the tension reinforcement than just Ld, and secondly a valid strut and tie model for load transfer, which implies greater lengths and development past the point where you no longer need the bar (which isn't the edge of the cutout). Both of these aspects potentially mean far greater lemgths than absolute minimum length past a critical location.

As steveh49 noted, development length is one aspect, but its important not to get too focused on it as there are many other load path related aspects to anchorage and transfer of the terminated bars that need to be addressed.

This is good information to have. Thanks!