Where does 40db come from for lap splice? 1

[YoungGunner]

I'm staring at our company's details, other engineer details/notes, and I'm seeing a consistent idea that bars should be lapped 40 times the bar diameter. But in staring at ACI for any development equations, tension or compression, I don't get that value. Any insight to this? I'm mainly trying to figure out the correct lap splice for vertical dowels into the bottom of a foundation wall (pinned-pinned, not cantilevered) where neither tension or compression are a concern, but I'm concerned I don't understand lap splices enough when I see 40db everywhere but can't come up with its origin.

 

[TLHS]

That's going to be roughly correct for ~30MPa concrete and ~400MPa steel. Take a look at the second table on page 7, in the normal range of bar sizes with a conventional amount of cover, your 40 diameters generally works out. It's not a number that's written in the code, it's an approximation of the code requirements that makes people's lives easier for practical design.

http://resources.crsi.org/index.cfm...ne&fileID=957CA25E-EA32-9673-7873C22C9661EA16

That's something you'll put on general notes or use as your starting points for details, but if you do a detailed calculation it's generally going to be less, so you can crush that down by spending some engineering effort when it's necessary.

That being said, your situation is not a lap splice. It's development into the footing unless there are some bars that are being tied directly into. Depending on what you're trying to accomplish, there are a number of ways you might evaluate it (and people have some strong opinions on footing anchorage). Maybe provide a sketch with what you're talking about?

 

[dik]

excellent link... thanks.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[YoungGunner]

Just a simple foundation wall sitting on a footing. I consider the overlap of the dowel and the vertical bars as a lap splice, not just ld or ldc. However, lap splices for most my foundations are Class B, and therefore are 1.3(ld).

 

[TLHS]

Oh yeah, that part of it is certainly a lap splice, I thought you were talking about the length into the footing. Sorry for the confusion.

Hey dik, if you're not aware the Reinforcing Steel Institute of Canada has a manual of standard practice that has a bunch of similar rebar tables calculated the CSA A23 way in the appendix, along with a bunch of dimensional recommendations for rebar details.

It's also full of documentation of typical practice. I've actually got a note that I've been using that says that certain things should be as per the RSIC manual of standard practice. Contractors don't refer to it, but when they do one of those things that just isn't great but isn't in your specifications because it's just normal practice there's often something I can point at as justification if they decide to put up a stink.

It used to be more expensive, but the digital copy is only $20 now and it's 130+ pages of reasonably useful information. I don't have the latest 2020 edition, so there may be additions.

https://rebar.org/shop/

 

[TLHS]

An example of the tables (one is for top the other for bottom bars)