PT Tendon detailing adjacent to Elevator Shearwalls

[fredPE]

I am relatively new at PT Slab design, and always am curious about how to layout Banded tendons and deformed bar reinforcing parallel to concrete shearwalls. In my mind, I think of the ends of shearwalls and the corners of intersecting shearwalls as columns, and try to detail the tendons and deformed bar reinforcing in those regions as if they were columns. However, when you actually try to get the tendons and bars in the space provided, it gives you some trouble.

For instance, I have a shearwall at my elevator core. On one side of the wall, there is an elevator opening that cuts off all access for tendons and reinforcing to go through. Then, you have your shearwall thickness, which could have two mats of verticals and horizontal steel, as well as stirrups for your boundary elements. With this layout, it seems that it is a lot more difficult to run any tendons through the wall, versus putting tendons in the space over a similar sized column. Furthermore, sometimes the contractor pours these concrete walls several floors ahead of the inframing slabs, so you are not able to put any tendons into the shearwall space. In other words, you could be stuck putting all of the banded tendons onto one side of the supporting shearwall.

For this case, do you have to satisfy the ACI Code requirement for placing banded tendons in the column band width of (3*t + Width of the column)? In the condition described above, the allowable space for my tendons becomes just 1.5*t (12" for an 8" slab). Also, do you need to put the deformed bar steel in this same space as if it were a column?

Thanks for any help you can provide.

 

[fredPE]

TTT

 

[gsmith22]

you may get better responses on the "Engineering Forums by Industry-Concrete Post-tensioned engineering" board but I will give it my best.

For walls formed ahead of floors, pockets are required to be left in the wall for the tendons (perp to wall) to be formed with the slabs and stressed later. For tendons parallel to wall, I would think you could just place those outside of the wall with the floor as there isn't any bending in that direction and these tendons are just for temp/precomp of adjacent slabs. Remember, perpendicular to walls, you have one way action and parallel to walls, you have no bending.

 

[hokie66]

There are no simple or correct answers to your questions. Tendons can be placed within a wall, provided there is adequate space. The duct is placed with the wall, then spliced when the floor is built.

But the stresses can be carried by nontensioned reinforcing also. This also applies to the tendons perpendicular to the wall when adequate access does not exist for stressing on the back face. In this case, stressing pockets are commonly used, with nontensioned reinforcement used to take the slab reaction into the wall.