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Precompression Issue

 
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nitinengr
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Joined: 29 Sep 2008
Posts: 11
Location: Vadodara

PostPosted: Fri Jan 02, 2009 12:57 pm    Post subject: Precompression Issue Reply with quote

Can any body tell me what is the criteria of P/A  for the design of the PT slab and beam systems.

As code suggest  0.86 to 2.1 N/mm2 is the limit for the precompression.

But if i keep the precompression as 0.45 or less then what is the effect on the design.

Here i m attacing a pdf which suggest in plane compression is between 125 to 500 psi (0.85 to 3.45 N/mm2).

How can we decide P/A for the structures in which no such compression is need for the tensile stresses.

so can any one give me how it comes 125 psi.

Thanks



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gorhemant
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Joined: 27 Jun 2008
Posts: 11

PostPosted: Sun Jan 04, 2009 10:05 am    Post subject: Precompression Issue Reply with quote

Nitin,
The Technical Report 43 (TR43) specialised document on PT slab design also recommend Minimum Average Effective Prestress of 0.7MPa in clause 2.4.
It reads as follows
"Past experience shows that for the Pre-Compression to be effective it should be at least 0.7MPa in each direction"

You will agree with me that codes give some minimum main reinforcement criteria for flexure ,shear and torsion in structural elements (Slab/ Beam/Column). They have some back-ground studies or past experience and reasons. Similar to this the criteria of minimum average effective prestress from past experience only.

regards,
Hemant Gor


On Fri, Jan 2, 2009 at 4:57 PM, nitinengr <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  Can any body tell me what is the criteria of P/A for the design of the PT slab and beam systems.

As code suggest 0.86 to 2.1 N/mm2 is the limit for the precompression.

But if i keep the precompression as 0.45 or less then what is the effect on the design.

Here i m attacing a pdf which suggest in plane compression is between 125 to 500 psi (0.85 to 3.45 N/mm2).

How can we decide P/A for the structures in which no such compression is need for the tensile stresses.

so can any one give me how it comes 125 psi.

Thanks





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Structural_Engineer_2008_oct.690.pdf




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