horizontal cold joint in one-way slab/joist construction?

[Lion06]

I have a situation in one-way concrete joist construction where the final (5) trucks were held up and ended up being poured after the rest of the concrete had set. This has created a horizontal cold joint in at least one girder, and several joists as well as a vertical cold joint in several joists at the end of the span where the shear is highest.
I am trying to find information about how this is handled and to verify capacities for shear flow across this joint using in-place reinforcement for shear friction calculations.
Any guidance or references that anyone could provide would be greatly appreciated!!

 

[Lion06]

17.5.4 says that as an ALTERNATIVE to 17.5.3, you can use any segment length you choose and then they specify Vu as horizontal shear.
I think the fact that they are distinguishing this Vu in 17.5.4 from the Vu in 17.5.3 means that Vu in 17.5.3 MUST be the vertical shear, not horizontal. If the Vu in 17.5.3 were a horizontal shear, there would be no need for 17.5.3 because it would be covered by 17.5.4.

 

[swivel63]

which year are you looking at? i'm looking at '02.

17.5.3 states
(17.5.4 in ACI - 05)

"as an alternative to 17.5.2, horizontal shear shall be permitted to be determined by computer the actual change in compressive or tensile force in any segment, and provisions shall be made to transfer the force as horizontal shar to the supporting element."

i took that section of the PCA Notes out of the '05 edition. but nonetheless...the '02 edition is the same:

"section 17.5.1 requires full tranfer of horizontal shear forces by friction at the contact surface, properly anchored ties, or both. Unless calculated in accordance with 17.5.3, the factored applied HORIZONTAL shear force Vu < phi x Vnh, where phi x Vnh is the horizontal shear strength."

seems pretty cut and dry to me. don't let the "alternative" fool you, just because it's referenced in two different locations as well as two different analysis it doesn't mean that they're not the same. if it doesn't explicitly say that it's a horizontal (like the PCA notes state) or vertical shear, one shouldn't make assumptions of it being so.

plus there's also basic mechanics theorems that state the relationship between horizontal and vertical shear stress. that might help out in this discussion.

 

[Lion06]

I am looking at '05.

Is the following quote of yours from ACI or the PCA notes?
"section 17.5.1 requires full tranfer of horizontal shear forces by friction at the contact surface, properly anchored ties, or both. Unless calculated in accordance with 17.5.3, the factored applied HORIZONTAL shear force Vu < phi x Vnh, where phi x Vnh is the horizontal shear strength."

Either way, 17.5.3 just says, "Unless calculated in accordance with 17.5.4, design of cross sections subject t horizontal shear shall be based on Vu<phiVnh where Vnh is the nominal horizontal shear strength is accordance with 17.5.3.1 through 17.5.3.4"

All of that typed, they are clearly making a distinction between 17.5.3 and 17.5.4. 17.5.3 says as typed above. 17.5.4 is the section where it allows you to arbitrarily select a length of beam to calc out your shear flow and apply that horizontal Vu.
They wouldn't make two sections for the exact same provision.
Also, I understand the basics mechanics relating vertical to horizontal shear stresses, but unless you arbitrarily select a length of beam to apply it to you can not get a horizontal shear FORCE.
If, in 17.5.3, they meant for you to select a length of beam and calc the shear flow to get a horizontal shear that would be exactly the same as they are allowing in 17.5.4. The fact that these two sections are seperated and reference each other as alternatives leaves no doubt in my mind that they are not implying the same method or procedure.

 

[swivel63]

one of them is from the ACI code and the other is from the PCI notes. the one you're referencing is the PCA notes page 12-10.

in both editions, the quote is verbatim to each other (previous editions). the PCA notes clearly say that it's a horizontal shear force and not a vertical shear force.

i ran into this exact same question a year ago in "what's the length to use to calculate the Vu from qu calculation."

17.5.4 states

"as an alternative to 17.5.3, horizontal shear shall be permitted to be determined by computing the actual change in compressive or tensile force in any segment, and provisions shall be made to transfer the force as horizontal shar to the supporting element."

but as i've said before, just because there are two different sections it doesn't mean one is for vertical shear and one is for horizontal shear. in fact, PCA clearly states that it is a horizontal shear.

 

[Lion06]

Then what was the outcome of the discussion?
What is the length to use with qu?

 

[swivel63]

LOL, he looked up into the sky and said use "d" or something like that. this coming from a man who was on the 318-99 and 02 voting commitees.

seriously, lol.

but i checked one of my concrete books.....horizontal shear stress and vertical shear stress are the same.

essentially, it said to use your vertical shear and resolve it into a unit stress. that would be the same as your horizontal shear stress. then compare that to the code strenght equations.

 

[Lion06]

well, I guess that settles that...
Do you use a cracked I of 0.35 Ig when calculating qu?

 

[swivel63]

i've always used full Ig.