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# Seismic Provision for Post Tensioned beams2

## Seismic Provision for Post Tensioned beams

(OP)

Helo, for the seismic provision above may i know if i interpreted the code correctly:

So, for example in my structural frame analysis i got an Ultimate moment, Mu = 1800 kNm at a particular support in an SMRF beam,
therefore 3/4 of 1,800kNm = 1,350 kNm. so the flexural capacity neglecting 1/4 of prestressing steel should be 1,350 kNm or at this section,
the moment capacity of the reinforcing bar(gr 276 or 414mpa) and concrete at that section should be greater than 1,350 kNm.

Did i get it right?

### RE: Seismic Provision for Post Tensioned beams

I read it as only providing a maximum of 1/4 of the strength by PT. This is quite different to arbitrarily limiting an excess of PT strength to 1/4 of that required.

### RE: Seismic Provision for Post Tensioned beams

I agree with above. It clears my doubt too.

### RE: Seismic Provision for Post Tensioned beams

The wording is a bit confusing, but the statement:

#### Quote:

the moment capacity of the reinforcing bar(gr 276 or 414mpa) and concrete at that section should be greater than 1,350 kNm
seems consistent with:

#### Quote:

only providing a maximum of 1/4 of the strength by PT

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

### RE: Seismic Provision for Post Tensioned beams

The wording seems to be saying that 3/4 of the strength provided must be by normal reinforcing.

Not that reinforcement must be supplied to provide a capacity equal to 3/4 of the applied moment.

So min your example it is not related to the 1800KNm applied. It is related to the total capacity actually provided.

Which of those two the code writers actually meant is another matter.

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