Rebar development length AASHTO vs ACI 3

[Waxwing]

AASHTO uses a different equation for development length than ACI. Does anyone have any insights into why this is?

Also, AASHTO LRFD code uses different units than ACI. Is there any reason why this change was made?

 

[JAE]

Because AASHTO suffers from rectal cranial inversion syndrome?

 

[jayrod12]

HAHAHA. Pretty much JAE

 

[Waxwing]

JAE,

The question mark in your response indicates uncertainty. That's no good. I'm hoping to get definitive responses to my post from an expert that knows for sure.

 

[jayrod12]

I am by no means an expert however I think JAE's comment is fairly correct even conservative.

But in all honesty do the two equations result in drastically different development lengths? I would always go with ACI, they are called the concrete institute for a reason.

As for the unit change, maybe they've decided to finally join the rest of the world and use the metric system.

 

[JAE]

I do know that over the years AASHTO's design equations and methodology seemed to lag behind the building codes and material specifications by an edition or two.

Not sure if that is the case anymore.

 

[Waxwing]

Yes, ACI and AASHTO give significantly different development lengths.

Whatever meets specifications is the design code I use.

Current AASHTO LRFD is not in metric, but they chose to use a very odd system focused on ksi and kips, throwing out 100+ years of the customary notation, very odd indeed.

 

[bridgebuster]

Thank your for your the insight JAE. I never knew what to call it. My 1949 AASHO is 5"x8", 1/2 " thick. My 2013 LRFD is 1600 letter size pages.

Waxwing - lighten up, besides it's Friday.

On a somewhat serious note, there are some aspects of the AASHTO LRFD concrete specs that have been influenced by ACI.

 

[Archie264]

Regarding: My 1949 AASHO is 5"x8", 1/2 " thick. My 2013 LRFD is 1600 letter size pages.

I don't work with AASHTO but but this is a trend that seems to apply almost across the board to building codes, material standards, etc. In my opinion it's something that should be addressed, or at least brought to the table as a topic of discussion. Some people are comfortable with it and some of us find it frustrating and even alarming.

 

[Waxwing]

It appears to me that the new codes are not intended for practicing engineers, the codes are beginning to micromanage the design process. It is frustrating for engineers that do a wide range of work, and don't specialize in a particular area.

 

[bridgebuster]

Regarding the complexity of codes; back in 2000 I attended a 28 hour seminar on AASHTO LRFD (talk about agony). The primary instructor made a good point: "now we have computers so we can add all these requirements and checks".

 

[msquared48]

JAE has issues...

Mike McCann
MMC Engineering

 

[JAE]

I had to design bridges once. Didn't like it.

 

[bridgebuster]

How can someone not like bridge design? Think of them as buildings turned sideways.

 

[JAE]

With bridges I don't get to work with architects.

 

[bridgebuster]

Who would want to miss that experience?

Presently, I'm part of a team for a design build tender. Bad enough the piers they came up with are ugly; there's no easy way to detail the bars because of all their crazy shapes.

 

[TXStructural]

Waxwing, the difference is because reasonable engineers disagree about development length requirements. ACI is heavily influenced by university research (and the need to publish or perish), and so complexities are introduced to resolve special cases. AASHTO can ignore most special cases, since they design with stricter limits.

Some of us are actively working to remove unneeded complexity in ACI 318, and I hope that some current research, funded in part by CRSI, will help with this mission.

(I tried to avoid the obvious answer: Rebar in concrete develops differently in buildings than it does in bridges.)

 

[Waxwing]

My take on the ACI vs AASHTO LRFD code is the opposite. The AASHTO LRFD code appears to have "one upped" ACI when it comes to excessive complexity and unnecessary minutia. ACI already writes a Manual of Concrete Practice with plenty of commentary. I don't see anything new (when it comes to concrete) in the AASHTO LRFD code just rehash.

 

[bridgebuster]

Compared to the Standard specs LRFD is something of a radical departure, particularly with the serviceability requirements.

At least the wind requirements in LRFD are not as complex as ASCE 7, but give AASHTO time and they'll catch up.

 

[Archie264]

>>>Some of us are actively working to remove unneeded complexity in ACI 318, and I hope that some current research, funded in part by CRSI, will help with this mission.<<<

TXStructural,

Good for you for being involved in that endeavor. I don't miss very many opportunities to grip about this topic but it is with the hope that eventually it will be heard by people who are in positions that can address the issue. It sounds like I may have just found one of you. So, from one of the peons, I appreciate your willingness to push back a little on our behalf.