IBC 2107.2.3 vs. ACI 530 2.1.8.6.1.1 Masonry Lap Length Cage Match 1

[agrant]

As I'm sure most of you masonry rebar lappers know, the IBC has some hip, neat and groovy provisions for the development lengths of rebar in comparison to our old, able-bodied friend, ACI.

Being a good, conservative engineer, I've limited my masonry wall reinforcing to #5's. This is mainly to limit the lap lengths to 48"; so my mason buddies have a chance at doing their job.

Of course we could revert to using bar couplers on heavily reinforced masonry, but this seems a bit drastic (unless you've got stock in Lenton of course).

I've been thinking about contacting the state board and seeing if we could perhaps omit the omitting IBC section, but once again - that seems a little drastic.

So I'm a little curious what the others think about it?

Forlorn with Fives

(that's a sleepless in seattle reference for all the able alliterates out there)

 

[jheidt2543]

There have been a couple of threads that address this topic over the last year or so. You might try searching the archives with "masonry lap" or "masonry rebar".

The new IBC 2000 has caused fits in the field with masons trying to install all the rebar called for and questions in design offices. I've seen some walls designed with #9 bars in grouted cores. You might as well pore molten steel in the core as try to get grout passed all that rebar.

How is it that all those masonry buildings built before the IBC 2000 are still standing?

 

[rrmiv]

Based on thread javascriptpenindex(450,350,'

http://www.tipmaster.com/includes/refinfo.cfm?w=450&h=350')

it seems many engineers lean toward ignoring the newer IBC requirements and are using tried and true ACI. Even limiting the reinforcement to #5 bars, it would be very difficult to build a wall with 48" laps. Again, does anyone know the rationale behind the changes to lap splice lengths? Has this been a failure mode?

 

[Focht3]

I'd guess that it comes from experience with the Northridge earthquake. But that's only a hunch -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[rrmiv]

Sorry, my earlier thread reference was intended to direct to thread507-37599.

 

[agrant]

Thanks for the input so far. Prior to posting, I did read thru a couple of previous threads, including rrmiv's prior thread. They had some very interesting information in them, alas my extensive thirst for knowledge has not been quenched yet.

I'm not sure that just "ignoring" the code requirements is the right way to go. I could see a validation in using engineering judgement to justify jobs already built under the IBC which do not adhere to the new IBC provisions. New construction is a different story though.

As a sidenote it could be that all the engineers out there are even totally aware of the IBC's revisions to masonry lap lengths.

My firm had taken the stance to stay with #5's and see what the IBC 2003 said - someone had told somebody of a possible revision. Unfortunately, that revision did not take place and the IBC 2003 still has the modified lap lengths.

I also agree that a 48" lap is a long way to lift a block. I'm sure the masons would agree with that.

It would be interesting what the masonry society or some other "pro-block" group would have to say about these provisions.

#9's in masonry, WOW! That would be a fun thing to spec out.

 

[jike]

I have talked with a friend on the ACI 530 committee and I have been told that they are also wrestling with this same requirement. Don't be surprised if the new ACI 530 matches the IBC. The code was changed as a result of a recent testing program.

In the meantime, I plan on staying with #5's centered in the wall.

 

[agrant]

Some further gossip on the matter:

I have heard the Masonry Society has stated the requirement in the ACI (short lap lengths) is staying the way it was written and the IBC (long lap lengths) are changing to match.

This source said that the IBC lap lengths came from ultimate design and was just modified for service design, hence the error. This seems a bit suspect to me, because lap lengths should be similar regardless if ultimate or service design is used.

Just thought I'd let you know.