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Strong column and weak beam concept

 
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padamkr1
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Joined: 26 Jan 2003
Posts: 18

PostPosted: Fri Sep 03, 2004 4:08 pm    Post subject: Strong column and weak beam concept Reply with quote

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
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Joined: 26 Jan 2003
Posts: 473

PostPosted: Sat Sep 04, 2004 5:13 am    Post subject: Strong column and weak beam concept Reply with quote

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
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Joined: 26 Jan 2003
Posts: 134

PostPosted: Sat Sep 04, 2004 6:27 am    Post subject: Strong column and weak beam concept Reply with 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.


Regards

Mukesh Ch. Upadhyay

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Rudra Nevatia
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Joined: 26 Jan 2003
Posts: 207
Location: Mumbai

PostPosted: Sat Sep 04, 2004 12:07 pm    Post subject: Strong column and weak beam concept Reply with quote

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
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Joined: 26 Jan 2003
Posts: 134

PostPosted: Mon Sep 06, 2004 11:18 am    Post subject: Strong column and weak beam concept Reply with quote

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: 207
Location: Mumbai

PostPosted: Tue Sep 07, 2004 5:18 am    Post subject: Strong column and weak beam concept Reply with quote

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).

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.

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.

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
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Joined: 26 Jan 2003
Posts: 14

PostPosted: Thu Sep 09, 2004 10:39 am    Post subject: Strong column and weak beam concept Reply with quote

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
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Joined: 26 Jan 2003
Posts: 5

PostPosted: Fri Sep 17, 2004 6:20 am    Post subject: Strong column and weak beam concept Reply with quote

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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