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  • Envelope #27: Changes to the “reduction of development length” that you might not know about

Envelope #27: Changes to the “reduction of development length” that you might not know about

Good morning! This is Back of the Envelope, where I share bite-sized SE stuff I learned recently.

Today we are going to cover:

  1. Changes from ACI 318-14 to ACI 318-19 regarding “Reduction of development length for excess reinforcement” that you might not know about

  2. The “thing” that might be preventing you from learning

  3. The unwritten rules of dad jokes

Let’s go!

(Estimated reading time = 2 min 4 sec)

Reduction of development length

You probably already know this, but in case you didn’t:

ACI 318 allows you to reduce the required rebar development length using the ratio of As,required and As,provided (you still have to meet the minimum though, as noted in the code section):

(excerpt from ACI 318-19)

There is also a list of limitations where the reduction is not permitted. And the list is slightly different between ACI 318-19 and ACI 318-14:

Oooh did you catch the difference?

“Uhm ok? Item (f) is added. Big deal.”

Try again…

I’ll give you a hint:

That’s right - “hooked” is added to item (d).

So if you’ve been reducing your development length for hooked bars in the past, it is no longer allowed.

“Why is this added?” you ask.

It’s actually explained in the commentary:

“Concrete breakout due to bearing at a hook or head was considered in developing the provisions of 25.4.3 and 25.4.4. Because the anchorage strength, and in particular the concrete breakout strength of a hooked or headed bar is a function of the embedment depth to a power slightly more than 1.0 (Shao et al. 2016; Sperry et al. 2017b), a reduction in development length with the application of the excess reinforcement factor could result in a potential concrete breakout failure.”

In other words, based on recent research, reducing the development length for hooked bars could result in concrete breakout failures.

(I don’t quite follow the part about “power slightly more than 1.0” though).

Now you know 😊.

The “thing” that might be preventing you from learning

Came across this quote recently:

“Throw out your conceited opinions, for it is impossible for a person to begin to learn what he thinks he already knows.”

– Epictetus

This came from the book “The Daily Stoic” by Ryan Holiday and Stephen Hanselman (which I highly recommend).

As engineers, we are especially guilty of thinking that “we know it all” (which usually shows up in our interactions with non-engineers like architects, owners, and contractors).

The author is trying to make the point that in order to learn effectively, we have to set that “know it all” attitude aside – instead, be “humble and ready to let go of opinions you already have.”

Cool reminder.

The unwritten rules of dad jokes

(If you are new to Back of the Envelope, I usually try to end the email with a dad joke, so in case you didn’t learn anything new, you’ll at least get a laugh.)

So I’ve read countless jokes by now, and apparently, there are two important unwritten rules for dad jokes:



And that is all – thanks for reading!

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