Horizontal Cold Joint in a PT transfer Beam? 2

[eamonnc]

I am looking into the shoring scheme of a 10’ deep PT transfer beam. The concrete contractor wants to break it into two 5’ lifts.

The end anchorages are equally placed on each side of the hozintal joint.

The contractor assures me that the natural smooth drape of the tendons will not be compromised by having two pours.

Beyond additional stirrups for shear flow (f=VQ/I), does a PT beam care that there is a horizontal cold joint?

 

[civilperson]

The stirrups for shear are sufficient and no additional stirrups are required. The design of reinforced concrete assumes that a crack can form anywhere, (including the location of a possible cold joint).

 

[eamonnc]

Design of composite concrete flexural members are spelled out in ACI 318 Section 17.5...

If the horizontal shear exceeds the nominal horizontal shear strength (Vu > Phi Vnh), additional stirrups shall be designed in accordance to section 11.7.4 (shear friction) and are to be distributed to reflect the distribution of shear forces in the member.

 

[structuresguy]

One concern I would have is that even though the end anchorages are equally distributed each side of joint, the "uplift" force of the PT would not be. At some point, the PT drape could be causing tension to occur at the joint, and try to put the two halves apart.

Also, if some slippage along the joint occured, would the PT force be properly distributed between the two halves? I could see a reduction in net P/A in one half

How would you arrange staged stressing, if you are doing staged stressing? Stress some in each half, at each stage level?

Sorry I don't have any answers, as I have never dealt with this issue. But it does make me concerned somewhat. I would definitely be looking to add steel at teh joint (both stirrups and horizontals), and also would be using an epoxy bonding agent and roughened surface. I might even consider forcing them to cast shear keys along the interface.