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padamkr1 SEFI Member
Joined: 26 Jan 2003 Posts: 18
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Posted: Fri Sep 03, 2004 4:08 pm Post subject: Strong column and weak beam concept |
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ÜHello sefians,
Will anybody clarify ,how to ensure strong column and weak beam concept in a multistoried housing complex
Regards
Padam Kumar
DELHI
padam kumar
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sdec.in Silver Sponsor
Joined: 26 Jan 2003 Posts: 473
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Posted: Sat Sep 04, 2004 5:13 am Post subject: Strong column and weak beam concept |
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Simply by ensuring that the beams are not stiffer than columns in the stiffness matrix, their contribution to stiffness at a joint can be manually checked and compared even by simple idea of size Sangeeta
-----Original Message----- Message From padamkr@yahoo.co.in [mailto:padamkr@yahoo.co.in] Sent: Friday, September 03, 2004 9:47 PM To: sdec@bol.net.in Subject: Strong column and weak beam concept
Hello sefians,
Will anybody clarify ,how to ensure strong column and weak beam concept in a multistoried housing complex
Regards
Padam Kumar
DELHI
padam kumar
Yahoo! India Matrimony: Find your life partneronline.
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mc.upadhyay1 ...
Joined: 26 Jan 2003 Posts: 134
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Posted: Sat Sep 04, 2004 6:27 am Post subject: Strong column and weak beam concept |
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Hello One should have more moment of inertia of columns as compared to beams. So that the probability of forming hinges (during earthquake) will be in beams rather than columns; which will avoid total collapse of the building.
Regards
Mukesh Ch. Upadhyay
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Rudra Nevatia ...
Joined: 26 Jan 2003 Posts: 215
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Posted: Sat Sep 04, 2004 12:07 pm Post subject: Strong column and weak beam concept |
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As the name suggests, comparative strength rather than stiffness governs this concept. Beam may be stiffer but should not have more residual strength than the column or the beam-column interface.
A beam-column interface with less residual strength than the beam is equally disastrous. For concrete structures, insufficient bond strength of top *or* bottom bars will lead to brittle failure before a flexural hinge forms in the beam.
Rudra Nevatia
--- mc.upadhyay@jil.co.in wrote:
Quote: | Hello One should have more moment of inertia of columns as compared to beams. So that the probability of forming hinges (during earthquake) will be in beams rather than columns; which will avoid total collapse of the building.
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mc.upadhyay1 ...
Joined: 26 Jan 2003 Posts: 134
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Posted: Mon Sep 06, 2004 11:18 am Post subject: Strong column and weak beam concept |
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Hello If we consider modulus of elasticity of materials same; before & after earthquake, the moment of resistance (strength) of beams is directly proportional to its moment of inertia (stiffness).
To avoid brittle shear failure; the beams are designed for the shear force due to the formation of plastic hinge at both ends as per IS 13920.
If the bars are not provided as per required development length or the bond strength of concrete is less (due to poor quality of concrete or any other reason), the brittle failure due to insufficient bond strength may occur for normal DL +LL case also; no need of earthquake.
Regards
Mukesh Upadhyay
rudra_nevatia@ya hoo.com To: mc.upadhyay@jil.co.in cc: 09/04/04 05:31 Subject: Strong column and weak beam concept PM Please respond to general
As the name suggests, comparative strength rather than stiffness governs this concept. Beam may be stiffer but should not have more residual strength than the column or the beam-column interface.
A beam-column interface with less residual strength than the beam is equally disastrous. For concrete structures, insufficient bond strength of top *or* bottom bars will lead to brittle failure before a flexural hinge forms in the beam.
Rudra Nevatia
--- mc.upadhyay@jil.co.in wrote:
Quote: | Hello One should have more moment of inertia of columns as compared to beams. So that the probability of forming hinges (during earthquake) will be in beams rather than columns; which will avoid total collapse of the building. |
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Rudra Nevatia ...
Joined: 26 Jan 2003 Posts: 215
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Posted: Tue Sep 07, 2004 5:18 am Post subject: Strong column and weak beam concept |
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Quote: | If we consider modulus of elasticity of materials same; before & after earthquake, the moment of resistance (strength) of beams is directly proportional to its moment of inertia (stiffness).
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Reinforcement determines strength of beams.
Quote: | To avoid brittle shear failure; the beams are designed for the shear force due to the formation of plastic hinge at both ends as per IS 13920.
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Very rightly so.
Quote: | If the bars are not provided as per required development length or the bond strength of concrete is less (due to poor quality of concrete or any other reason), the brittle failure due to insufficient bond strength may occur for normal DL +LL case also; no need of earthquake.
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The emphasis was on bond strength of bottom reinforcement anchored into column which is normally not critical for DL+LL.
Let me assert *again* that residual strength of beam vis a vis residual strengths of column and beam-column interface is crucial for this concept.
Let us take a single-bay, single-storey frame with ultimate strengths of beam and columns as Mub and Muc respectively. (Muc is not a true measure of strength of a column but let us assume it is so for the present).
Let us also assume that for the design basis earthquake, moments in beam and columns are Mb and Mc such that Mb = 0.85Mub and Mc=0.9Muc. In other words, the beam has 15% residual strength and the column has 10% residual strength.
Now, we know that a structure may be subjected to more than the design basis earthquake by a factor R. If actual earthquake exceeds design basis earthquake by 11%, columns would have reached their ultimate capacity whereas beams would still have residual strength of 6%. This is in violation of the strong-column- weak-beam concept.
Regards, Rudra Nevatia
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building-edrc SEFI Member
Joined: 26 Jan 2003 Posts: 14
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Posted: Thu Sep 09, 2004 10:39 am Post subject: Strong column and weak beam concept |
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I hope merely providing a higher stiffness to column than for beam does not suffice "Strong column weak beam" concept. It is also related to the strength.(detailing). For a particular direction of lateral force on the structure, the moment in column and the beam (parallel to direction of force) at the joint are same. If both beam and column designed for the same moment, plastic hinge will form both in column and beam simultaneously (even if column size is more than beam) which is not the requirement for Strong Column weak beam idealisation.
further clarification on this is required.
regards,
P.Hemanth kumar.
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desai_nsu SEFI Member
Joined: 26 Jan 2003 Posts: 5
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Posted: Fri Sep 17, 2004 6:20 am Post subject: Strong column and weak beam concept |
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Dear Shri Padam kumar,
There was a very good article on Strong column weak beam concept in the Indian Concrete Institute Journal (ICI Journal) January March 2002 issue. There were few numerical exmples also. This article makes the concept very clear and I suggest you to please go through the article.
R.K.Desai
padamkr@yahoo.co.in wrote:
Quote: | Hello sefians,
Will anybody clarify ,how to ensure strong column and weak beam concept in a multistoried housing complex
Regards
Padam Kumar
DELHI
padam kumar
Yahoo! India Matrimony: Find your life partneronline.
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