one-way PT slab or beam can be designed over 12vfcÆ?
one-way PT slab or beam can be designed over 12vfcÆ?
(OP)
I know two-way PT slab need to be designed <7.5√fc’ per ACI 318 18.3.3. But no specific requirement limit you design even larger than 12√fc’ as long as you consider some requirement in other parts of the chapter 18: like using cracked section for deflection calculation per table R18.3.3.
Is my understanding right: if by engineer judgement and accept cracked structure and consider all other requirement, you can design PT structures up to or even larger than 12√fc’ theratically?
Is my understanding right: if by engineer judgement and accept cracked structure and consider all other requirement, you can design PT structures up to or even larger than 12√fc’ theratically?






RE: one-way PT slab or beam can be designed over 12vfcÆ?
I think the short answer is yes, it would be permissible. But in practice it would become more difficult to meet other requirement when you're getting out in that range. "Ie" would be dropping like a stone and it would become difficult to meet extreme fiber compression limits and/or find places to anchor all the tendons. It's probably some place you don't want to go unless you've been in the neighborhood before and had success.
regards,
Michel
RE: one-way PT slab or beam can be designed over 12vfcÆ?
regards,
Michel
RE: one-way PT slab or beam can be designed over 12vfcÆ?
RE: one-way PT slab or beam can be designed over 12vfcÆ?
regards,
mk
RE: one-way PT slab or beam can be designed over 12vfcÆ?
RE: one-way PT slab or beam can be designed over 12vfcÆ?
You are right. Even I knew it, I still typed wrong.
RE: one-way PT slab or beam can be designed over 12vfcÆ?
Using the ACI 2way slab design approach, it is not permissable under any circumstances to allow a stress greater than the 6√fc’ limit, no matter how much extra untensioned reinforcement is added. This is an absolute limit. Other clauses in ACI that allow partial prestressed design cannot be used to override this limit.
The reason for this is that the stresses being used in the calculation are average stresses over the full width of the slab panel. They do not allow for stress concentrations around columns and at midspan so do not represent the true stress condition in the slab.
Design codes/methods used in other parts of the world do not have this limit, but they do not use the ACI 2way slab design approach. They use a column/middle strip approach similar to that used for RC slabs in ACI. Because they are allowing for the actual stresses rather than the average values, the limitations of the ACI design approach do not apply and partial prestressed design is possible and is allowed.