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Calculation of Kz, Ky, Ly and Lz
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sandeepb
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PostPosted: Mon Mar 07, 2011 5:29 am    Post subject: Calculation of Kz, Ky, Ly and Lz Reply with quote

Can any one share 3D model with description for calculation of Kz, Ky, Ly and Lz based on Alignment chart?

I always have problem with it.

For reference I have attached one shelter model in *.txt format

Regards,
Sandeep.



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suresh_sharma
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PostPosted: Sun Apr 10, 2011 1:52 pm    Post subject: Reply with quote

To my knowledge, no body is assigning Ky, Kz, Ly and Lz to the model in Staad Pro with clear conception. If you have some idea even if cryptic let me know to expand the same further. To my vague knowledge the mdel requires to be analysed for determining Ky and Kz. Ly and Lz needs to be assigned to each member as known to the designer. The above command pertains to the column member only.
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debayan
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PostPosted: Mon Apr 11, 2011 3:27 am    Post subject: Reply with quote

@Suresh Sharma :- Only Ky and Kz are column parameters, Ly and Lz are parameters which are to be given for each and every member which have these values other than their default length.

@sbarwal1:- I do agree it is confusing, but this is one of the most fundamental propeties that have to be assigned to STAAD and we better get comfortable with it whether we like it or not! I am sure after doing a few structures in STAAD you will more comfortable with it.

All parameters like Ly, Lz and Ky, Kz are to be assigned based on local axis of the member. Not the STAAD global axis. If you want to see your member local axis, please press Shift+o (letter o, not digit zero).

Please refer attached sketches for Ly and Lz

In your case, lets take column on support node no 2. For I sections minor axis is always Ly and major axis is always Lz.

Lz:- Member no 719 and 720 is breaking the major axis of the column at 1.09 and 5.76 m respectively.

Ly :- Member no 27 and 66 are breaking the mainor axis of the column at 2.09 and 4.76 m respectively.

Pls note member no 604 cannot be considered as a restraint.

Therefore

Member no 320 :- Ly = 2.09 m and Lz = 1.09 m
Member no 22   :- Ly = 2.09 m and Lz = 5.76 m
Member no 738 :- Ly = 4.76 m and Lz = 5.76 m
Member no 750 :- Ly = 4.76 m and Lz = 5.76 m

For Ky, Kz

Ky and Kz are effective length parameters which depend from code to code. Generally for indian codes it depends on the type of restraint you have.  So you can refer that and the application procedure is same as for Ly and Lz.

Hope it is clear. Refer the sketches when you are reading this. I am sure it will be clear.

Please let me know if it is not clear to you still

Regards,
Debayan



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suresh_sharma
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PostPosted: Mon Apr 11, 2011 5:24 pm    Post subject: Reply with quote

I could now understand what you mean to convey about Lx and Ly but how can the Kx and Ky factor be determined. Please clarify.
I also suppose that Lx and Ly are not required to be assigned when they are same both in Local x and local y direction. Is it ok. Because the software will consider the default value which is as good as actual value.
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suresh_sharma
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PostPosted: Mon Apr 11, 2011 5:40 pm    Post subject: Reply with quote

Lx and Kx should be considered as Lz and Kz in my above reply.
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Ramakrishna
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PostPosted: Tue Apr 12, 2011 4:28 am    Post subject: Calculation of Kz, Ky, Ly and Lz Reply with quote

THis clarifies me. I have a doubt. As per IS code we have to define Ley and Lez. Ley=Ly*Ky and Lez=Lz*Kz. Is it correct?

Regards
Ram

--- On Mon, 4/11/11, debayan <forum@sefindia.org> wrote:
Quote:

From: debayan <forum@sefindia.org>
Subject: [SEFI] Re: Calculation of Kz, Ky, Ly and Lz
To: general@sefindia.org
Date: Monday, April 11, 2011, 8:57 AM

@Suresh Sharma :- Only Ky and Kz are column parameters, Ly and Lz are parameters which are to be given for each and every member which have these values other than their default length.

@sbarwal1:- I do agree it is confusing, but this is one of the most fundamental propeties that have to be assigned to STAAD and we better get comfortable with it whether we like it or not! I am sure after doing a few structures in STAAD you will more comfortable with it.

All parameters like Ly, Lz and Ky, Kz are to be assigned based on local axis of the member. Not the STAAD global axis. If you want to see your member local axis, please press Shift+o (letter o, not digit zero).

Please refer attached sketches for Ly and Lz

In your case, lets take column on support node no 2. For I sections minor axis is always Ly and major axis is always Lz.

Lz:- Member no 719 and 720 is breaking the major axis of the column at 1.09 and 5.76 m respectively.

Ly :- Member no 27 and 66 are breaking the mainor axis of the column at 2.09 and 4.76 m respectively.

Pls note member no 604 cannot be considered as a restraint.

Therefore

Member no 320 :- Ly = 2.09 m and Lz = 1.09 m
Member no 22 :- Ly = 2.09 m and Lz = 5.76 m
Member no 738 :- Ly = 4.76 m and Lz = 5.76 m
Member no 750 :- Ly = 4.76 m and Lz = 5.76 m

For Ky, Kz

Ky and Kz are effective length parameters which depend from code to code. Generally for indian codes it depends on the type of restraint you have. So you can refer that and the application procedure is same as for Ly and Lz.

Hope it is clear. Refer the sketches when you are reading this. I am sure it will be clear.

Please let me know if it is not clear to you still

Regards,
Debayan







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suresh_sharma
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PostPosted: Tue Apr 12, 2011 8:38 am    Post subject: Reply with quote

I believe your conception about Lez = Kz X Lz is correct but please but let me know how shall I work out Kz? my vague conception is that I will have to take the help of beta1 and beta2 mentioned in IS 456 and IS 800. Please clarify.  Is it possible to work out K factor with Staad?
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bijay sarkar
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PostPosted: Tue Apr 12, 2011 10:16 am    Post subject: Reply with quote

Dear Er Suresh Sharma & Others,

In Staad, effective length parameters for each and every member are to be given as input along with other design parameters. Say, a beam member is pin connected at both ends with columns.

As per prevailing method, we consider centre to centre of the beam as its effective length in the major axis, if there is no vertical bracing supporting the beam from underneath.  Therefore Leff-Zaxis = Column Centre to Column Centre = 6M say. i.e. Lz = 6

Now say one secondary floor beam is connected to this main beam at centre. Therefore, Leff-Yaxis = 0.5 * 6 = 3M. i.e. Ly = 3

Now as the beam is shear connected at ends, we consider, there is no torsional resistance at ends. i.e. UNL = 6

These three parameters so far the effective lengths of the members are concerned (i.e. Lz, Ly and UNL as per Staad 2006) are required in Staad as input.

You can directly put these length parameters as Lz, Ly, UNL and also u can put these parameters indirectly through Kz, Ky, UNF.

Now, how to calculate these Kz, Ky, UNF. Here staad model comes into play. As during creation of the secondary beam, a node has been created at mid length, you should be cautious about that node in defining Kz, Ky, UNF.

If someone do not provide these parameters, staad takes node to node distance as the Lz, Ly, UNL. It means that default values of these parameters are Lz = 3M, Ly = 3M, UNL = 3M. If we intend these parameters changed as required for actual case, we are to provide multiplication factors which are Kz, Ky, UNF. Therefore, Kz = 2, Ky = 1, UNF = 2. Many of the design engineers are not considering this kind of node creation. This is a software oriented problem which must be taken care of.

Input Parametrs : Lz = 6, Ly = 3, UNL = 6
Or,                        Kz = 2, Ky = 1, UNF = 2
Or, Combination of these.

regards,

bijay sarkar
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sandeepb
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PostPosted: Tue Apr 12, 2011 10:27 am    Post subject: Reply with quote

I have a basic question. Kz is about or along local z axis of column?

As in staad manual:

    Kz :  K value in local Z axis- Usually major axis



And



LZ: Length to calculate slenderness ratio for buckling about  local Z axis.





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bijay sarkar
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PostPosted: Tue Apr 12, 2011 10:32 am    Post subject: Reply with quote

Kz is a factor of Lz. The other factor of Lz is the default value of staad i.e. Node to Node distance.

Kz is about local Z - axis.


regards,

bijay sarkar
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