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Doubt in STAAD modelling of Staircase Midlanding beam

 
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sakumar79
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Joined: 18 Apr 2008
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PostPosted: Sun Nov 07, 2010 11:45 am    Post subject: Doubt in STAAD modelling of Staircase Midlanding beam Reply with quote

Hi,
  I have a small doubt regarding the modelling of staircase midlanding beam in STAAD. If I model the beam at its correct level (midlevel between floors), I am getting Soft Storey warning for the mid landing levels... Design is by IS13920... How to solve the problem?

Thanks in advance
Arun
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sakumar79
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PostPosted: Mon Nov 08, 2010 1:30 pm    Post subject: Reply with quote

1. After going through the help files some more, I found there is a "Floor Height" command, but if I use it, I am getting an error warning during input file loading... But no error message is coming. Does anybody know how to resolve this issue?

2. It appears that IS1893 design module does not accept Floor Weight command... How to distribute the floor load in equivalent fashion - should we use joint weight command or member weight command?

3. I have not modelled the floor slabs (used floor load command in gravity load specifications). Is it necessary to use master-slave command after finding center of mass?

Thanks in advance
Arun
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sakumar79
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PostPosted: Wed Nov 10, 2010 7:33 am    Post subject: Reply with quote

Dear Sirs,
  I havent received any help for this problem so far... Requesting STAAD experts to post their experience...

  For Floor Weight, I replaced with Joint weight by calculating equivalent loads at four corners of each slab and applying the Joint Weight (DL+ part LL)... Checked total seismic mass with total load in individual load case and it is less than 3% error.. So, that issue is solved...

  But how to resolve the warning of soft storey where staircase midlanding beam comes?

Yours sincerely,
Arun
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va
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PostPosted: Wed Nov 10, 2010 7:49 am    Post subject: Doubt in STAAD modelling of Staircase Midlanding beam Reply with quote

Dear Arun,
Soft storey is a warning message only. Since you have provided all mid landing beams the column height is half and it becomes stiffer compared to other frames. For stiffness variation of 70% you will get this warning as per code definition of soft storey.
Generally stair cases slab and beams need not be considered in analysis model.

Hemant Vadlkar
STADD Engineers Mumbai.


From: sakumar79 [mailto:forum@sefindia.org]
Sent: Wednesday, November 10, 2010 1:03 PM
To: general@sefindia.org
Subject: [SEFI] Re: Doubt in STAAD modelling of Staircase Midlanding beam



Dear Sirs,
I havent received any help for this problem so far... Requesting STAAD experts to post their experience...

For Floor Weight, I replaced with Joint weight by calculating equivalent loads at four corners of each slab and applying the Joint Weight (DL+ part LL)... Checked total seismic mass with total load in individual load case and it is less than 3% error.. So, that issue is solved...

But how to resolve the warning of soft storey where staircase midlanding beam comes?

Yours sincerely,
Arun

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sukanta.adhikari
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Joined: 26 Jan 2003
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PostPosted: Wed Nov 10, 2010 9:35 am    Post subject: Reply with quote

Dear Er. Arun,

Please note STAAD accepts floor load command for generating seismic load by IS 1893:2002.

Whil defining the load follow the sequence..

Selfweight
Joint Weight
Member weight
Floor load.
etc

If u give Floor load first then it will not accept.

If u want I can upload a file or else upload ur file.I will try to sort it.

Regards,
S.Adhikari






sakumar79 wrote:
1. After going through the help files some more, I found there is a "Floor Height" command, but if I use it, I am getting an error warning during input file loading... But no error message is coming. Does anybody know how to resolve this issue?

2. It appears that IS1893 design module does not accept Floor Weight command... How to distribute the floor load in equivalent fashion - should we use joint weight command or member weight command?

3. I have not modelled the floor slabs (used floor load command in gravity load specifications). Is it necessary to use master-slave command after finding center of mass?

Thanks in advance
Arun
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sukanta.adhikari
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Joined: 26 Jan 2003
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PostPosted: Wed Nov 10, 2010 9:39 am    Post subject: Reply with quote

Attached is a STAAD file.May be helpful to u.

Regards,
S.Adhikari



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Staad file.zip
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sakumar79
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PostPosted: Wed Nov 10, 2010 11:58 am    Post subject: Reply with quote

Dear Sir

Which version of Staad is this based on? And are you using IS1893 old code or 2002 code? I am using Staad Pro v8i and IS1893:2002 code... First I tried to create the loads by adding as weights in the Commands->Loading->Define Seismic Loading, but some problem happened and even though I had added weights, it would not accept "Ok" button, warning that weights are not yet entered... So, I tried entering it through input file... First it seemed to accept, then suddenly it gave error warning without any error message... Then when I opened the file, the commands were gone... So, I assumed it does not take floor weights... Will check again...

And what about the other queries - 1. Soft storey warning for levels with only midlanding beam of staircase, 2. Is master-slave command necessary if slabs are not modelled?

Thanks again
Arun
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sakumar79
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PostPosted: Fri Nov 12, 2010 1:18 pm    Post subject: Reply with quote

Dear Sirs,

1. I checked again - floor weight command is working...

2. Mr. Hemant Vandlkar mentioned that it is not necessary to model the staircase midlanding beam - So, should we design the beam separately and apply its reaction to the upper floor and lower floor proportionately as nodal loads? Is it okay to just ignore the warning and use the model as it is?

3. Is master-slave command necessary if slabs are not modelled? How to use it?

Thanks again
Arun
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sukanta.adhikari
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PostPosted: Fri Nov 12, 2010 3:57 pm    Post subject: Reply with quote

Dear Er. Arun,

I will also agree with u that we should not ignore modelling staircase beam in STAAD model.Especially in industrial building where I sometimes have to design a 6 m span staircase and the load coming on the beam is not negligible.

If we provide a tie beam also..STAAD treats it as a storey....

It is not mandatory to use master slave command...Generally we treat the slab as flexible diaghpragm in STAAD and simply apply the floor laod..However if u want to consider Rigid action of slab..u can model it by master slave.

For modelling by master slave..u may refer STAAD help menu..It is self explanatory.

Regards,
S.Adhikari


sakumar79 wrote:
Dear Sirs,

1. I checked again - floor weight command is working...

2. Mr. Hemant Vandlkar mentioned that it is not necessary to model the staircase midlanding beam - So, should we design the beam separately and apply its reaction to the upper floor and lower floor proportionately as nodal loads? Is it okay to just ignore the warning and use the model as it is?

3. Is master-slave command necessary if slabs are not modelled? How to use it?

Thanks again
Arun
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