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jrm2002 ...
Joined: 26 Jan 2003 Posts: 67
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Posted: Thu Dec 29, 2005 5:36 pm Post subject: Tensile Strength Of Concrete:IS 456 and IS 1343 |
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Hi all:
As per IS: 456 2000, the Indian Standard code of practice for Reinforced Concrete the flexural tensile strength of concrete is given as 0.7x square root(fck)-clause 6.2.2 page 16.
But as per IS:1343 1980,code of practice for Prestressed concrete the maximum principal tensile stress is given by 0.24 x square root(fck)- clause 22.4.1 page 46.
Why this difference, i.e. 0.7x square root(fck) for reinforced concrete and 0.24 x square root(fck) for prestressed concrete?? Plz. help!!
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ibarua General Sponsor
Joined: 26 Jan 2003 Posts: 1039
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Posted: Fri Dec 30, 2005 6:59 am Post subject: Tensile Strength Of Concrete:IS 456 and IS 1343 |
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30 December 2005
Flexural tensile stress is the allowable TENSILE stress in the concrete.
Principal stress is the RESULTANT of all the stresses in the section. For example, a section may be subjected to flexural as well as a compressive or tensile stress at the same time. The principal stress is the resultant of such stresses.
Hence the apparent difference.
Indrajit Barua.
On Thu, 29 Dec 2005 jrm2002[AT]red... wrote :
Quote: | Hi all:
As per IS: 456 2000, the Indian Standard code of practice for Reinforced Concrete the flexural tensile strength of concrete is given as 0.7x square root(fck) -clause 6.2.2 page 16.
But as per IS:1343 1980,code of practice for Prestressed concrete the maximum principal tensile stress is given by 0.24 x square root(fck)- clause 22.4.1 page 46.
Why this difference, i.e. 0.7x square root(fck) for reinforced concrete and 0.24 x square root(fck) for prestressed concrete?? Plz. help!!
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svhajare SEFI Member
Joined: 26 Jan 2003 Posts: 6
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Posted: Fri Dec 30, 2005 7:29 am Post subject: Tensile Strength Of Concrete:IS 456 and IS 1343 |
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Dear Mr. Indrajit Barua With referance to your mail , I want to clear it that the principal stress is not resultant stress it is maximum stress on which there is no shear stress , that is maximam pure tensile stress capacity hence it is 0.24 sqrt (fck) in IS 1343 not 0.7 sqrt (fck) as asper IS 456
Mr. Hajare Shriram Vijarao, MTech Structure, Software Engineer , SoftTech Enggs, Pvt. Ltd, Pune Contact me 9823466680.
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kunal at sercm.csir.re... Guest
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Posted: Fri Dec 30, 2005 11:16 am Post subject: Tensile Strength Of Concrete:IS 456 and IS 1343 |
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Dear Mr. jrm,
I suppose you need to be clear regarding the type of tensile stress (or strength) you are dealing with as mentioned by Shri Barua. Tensile strength can be obtained by two distinct ways namely (1) under bending tension (2) direct tension. Of these, the later one is difficult to obtain and its reliability is also questionable due to many reasons. It is worth noting that both the tests will give different values for same material, with bending tension being 50 to 60 percent more than the direct tension.
The IS:456 stress is the rupture strength (i.e. tensile strength in bending) and that of IS:1343 is principal tensile strength. Be also noted that the rupture tensile stress for prestressed concrete is also 0.7 times sqrt(fck) [fck in MPa] (You can refer some suitable clause of IS1343 for reference). Traditionally, we are ignoring tensile strength of concrete for flexure, while for bond and shear many a times we take them into account. If you read closely, IS:1343 will show you two seperate clauses to estimate shear strength (with and without concrete cracked in flexure). [exact clause numbers I don't remember now - it may be perhaps what you have mentioned].
Now knowing that the concerned difference is due to different types of tensile stress specifications, your original question can be re-spelled as "why principal tensile stress (and not rupture tensile stress) is specified in IS:1343 (in clause you mentioned)?" - Try it.
with pleasant regards,
Kunal Kansara
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