Hi there,
I'm designing a parking PT slab with PT beams in a corner panel where we have higher loads. I noticed that the amount of shear reinforcement in the beams running parallel to the distributed tendon (longitude direction) increases exponentially when I have the "Design column strip for Column + Middle strip resultants" option checked. On the other hand, the amount of shear reinforcement in the beams running in the latitude direction changes very little whether we have the option checked or not.
I can't figure out why this happens, and would also like to know if I should have the "Design column strip for Column + Middle strip resultants" option checked. To my understanding, we have that options checked for beams in one-way slabs, but what about beams running in both directions in two-way slabs?
"Design column strip for Column + Middle strip resultants" checked.
"Design column strip for Column + Middle strip resultants" unchecked.
Latitude tendons
Longitude tendons
Thanks
Yes, that's when I think it is appropriate.
Yes Seth, I'm running the distributed tendons in the N-S direction to achieve the minimum effective prestress (125 psi) required by ACI. The beams were added to improve deflections.
So you would recommend to check "Design column strip for Column + Middle strip resultants" only when we have one-way behavior?
You are running these distributed tendons in the slab to improve the deflection and reduce the moment in the slab right? You could have put all the tendons on the beam and achieved more drape, but you didn't because you also need the slab to "work" for service and strength design. Hence, if the slab should work as a post-tensioned slab I would tend to leave the middle strip alone and check it like any other 2-way PT slab.
Hi Seth, thank you for the quick reply.
What do you mean when you're saying "making the slab work for N-S span"? I ran the distributed tendons in the N-S direction because the spans are shorter. The slab was originally fully flat but we had to add beams in that area because the columns were failing in punching shear and the deflections were too high.
You're right. This is a 2-way slab.
I assume this is a 2-way slab. If you have distributed tendons in this direction that are there to make the slab work for N-S span, then I don't see why you would want the narrow column/beam strip to be designed for the total resultant. That approach is generally used where the slab is not being considered in the direction parallel to the beam, e.g. a one way slab.