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IS:1893-2016
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VIJAY N RATHOD
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PostPosted: Tue Jul 11, 2017 3:10 pm    Post subject: IS:1893-2016 Reply with quote

Dear Sefians,

Please help me out,

My building has Flat slab system (5-Basement + G +25 floor)


1) How to give 100% Base shear to the shear wall of the building.

2) How to give 25% Base shear to perimeter frame. (COLUMN+BEAM)

as per new code 1893-2016, Table-9,point-5. we have to follow this clause, but how to in corporate such thinking in to the model.

* 25% base shear should take the perimeter frame up to that this is fine, but now 100% base shear should be taken by shear wall, how to tackle this problem???



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arunangshu
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PostPosted: Wed Jul 12, 2017 6:08 am    Post subject: Reply with quote

Hi Vijay,<o></o>
<o> </o>
My current project is also using flat slabs and I haveadopted the following methodology. It is still subjected toverification/authorisation but I think the logic flow is acceptable.<o></o>
<o> </o>

  1. How   to give 100% Base shear to the shear wall of the building?<o></o>

To address this, I suggestyou to release all the columns/moment frames of your structure. This willensure that the total diaphragm force (100%) is channelized through your shearwalls only.<o></o>

  1. How   to give 25% Base shear to perimeter frame?<o></o>

From the above model, youhave a base shear say V. Now prepare a new model where you minimise the bendingstiffness (in-plane and out-plane both) of your walls to 0.001 or similar. Donot alter the shear properties and make sure you are not altering the axialload carrying capacity of the walls; e.g. if you are using ETABS, then keep f22 = 1 but changeothers. This will ensure that your gravity load path is not altered majorly. Now,remove all the releases of your perimeter frames and any other frames that youintend to resist your lateral loads. Scale down the base shear to 0.25V.<o></o>
Analyse and design theframes using this model. <o></o>
I found a reference document“FEMA 451, NEHRP Recommended Provisions:Design Examples”, where it recommends the following:<o></o>
“The 25 percent analysiswas carried out using the ETABS program with the mathematical model of the buildingbeing identical to the previous version except that the panels of thestructural wall were removed. The boundary elements of the walls were retainedin the model so that behaviour of the interior frames would be analysed in arational way.”<o></o>
Please note that, the abovedocument highlights the dual system design procedure described in Americancodes which is similar to our situation. This is a big document, I haven’t beenthrough fully. If you want to have a look, then please download it from thelink below, it is free.<o></o>
<o> </o>
Hope this helps. Let me know your opinion on this and howyou moved finally.<o></o>
<o> </o>
Best Regards<o></o>

Arun<o></o>



https://www.fema.gov/media-library/assets/documents/9228
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deviationz
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PostPosted: Wed Jul 12, 2017 4:29 pm    Post subject: Reply with quote

Unless you have a lot of shear wall in the building, you won't be able to meet the H/1000 drift limit for seismic. See Note 4. So before you go down too far into the process, check drift to make sure you satisfy the requirement of Note 4.
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Abishek_Siingh
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PostPosted: Thu Jul 13, 2017 6:38 am    Post subject: Reply with quote

Additionally, flat slab systems are no more allowed in Zones 3 4 and 5.

The BIS is bullying us now.
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arunangshu
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PostPosted: Thu Jul 13, 2017 7:20 am    Post subject: Reply with quote

Kumar_Abhishek_Singh wrote:
Additionally, flat slab systems are no more allowed in Zones 3 4 and 5.

The BIS is bullying us now.


Abhishek,

Presumably you are referring to Note 1 of Table 9 which is not appropriate for flat slab system; only Note 4 is relevant to flat slabs.

Best regards
Arun
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arunangshu
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PostPosted: Thu Jul 13, 2017 9:22 am    Post subject: Reply with quote

deviationz wrote:
Unless you have a lot of shear wall in the building, you won't be able to meet the H/1000 drift limit for seismic. See Note 4. So before you go down too far into the process, check drift to make sure you satisfy the requirement of Note 4.




Hi,

The background/reference of Note 4 can be found in Section 7.2 | ACI 352.1R-11 “Guide for Design of Slab-Column Connections in Monolithic Concrete Structures”.
For non-PT flat slab (without shear reinforcement), the story drift is limited to 0.5%. Else, design and provide shear reinforcement.
The whole idea is to limit the gravity shear ratio (without any unbalance moment) and maintain a buffer for unbalance moment transfer at the junction in the event of any seismicity.
In my knowledge, our Note 4 is influenced by the same clause however we have enforced a further Factor of Safety = 5.

During a recently concluded workshop, I have discussed this issue with Dr. Yogendra Singh (IIT Roorkee). He suggested that, we can follow the ACI guidelines in practice and can approach the reviewer/client with the same reference.

Once can read the following paper (along with ACI 352.1R-11) which presents an interesting research study on this topic.

Hope this helps.

Best Regards
Arun


http://www.iitk.ac.in/nicee/wcee/article/13_2832.pdf
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Abishek_Siingh
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PostPosted: Fri Jul 14, 2017 9:25 am    Post subject: Reply with quote

Agreed....my bad!!

But BIS is still bullying us!

Abhishek



arunangshu wrote:
Kumar_Abhishek_Singh wrote:
Additionally, flat slab systems are no more allowed in Zones 3 4 and 5.

The BIS is bullying us now.


Abhishek,

Presumably you are referring to Note 1 of Table 9 which is not appropriate for flat slab system; only Note 4 is relevant to flat slabs.

Best regards
Arun
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sakumar79
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PostPosted: Sat Jul 15, 2017 6:53 am    Post subject: Reply with quote

Dear Sirs,
   IMHO, the easiest way to handle the codal requirement is to prepare separate load combinations for shear wall, perimeter frames and the internal columns.

   For example, let us consider an imaginary situation for EQX in a building where
a. the total reaction is 100 kN
b. reaction to supports of shear walls along X direction is 80 kN.
c. Reactions to perimeter columns along X direction is 10 kN.
d. Reactions to other columns is 10 kN.

   I would suggest the following methodology for design

a. Shear walls need to take 100% of load ie, 100 kN instead of 80 kN. Hence, the load combination factors for EQX need to be boosted by 25%.
1.5 DL + 1.5 ELX becomes 1.5 DL + 1.875 ELX,
1.2 (DL + LL + ELX) becomes 1.2 (DL + LL) + 1.5 ELX, and
0.9 DL + 1.5 ELX becomes 0.9 DL + 1.875 ELX.
    The shear walls along X direction shall be designed for these modified combinations along with the other standard load combinations for D+L and D+L+W.
     Adopt similar design load combinations for ELZ.

b. Similarly, for the perimeter columns along X direction, the 10 kN reaction needs to be boosted to 25 kN (ie, 2.5 times). Similar set of load combinations shall be prepared for the perimeter columns in Z direction

c. The internal columns can be designed for Dead, Live and Wind load combinations only.

     By this method, we will not only get results consistent with the codal requirements but it will also be easy to submit documentation to prove that we are complying with the codal requirement.

Yours sincerely
Arunkumar
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sakumar79
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PostPosted: Sat Jul 15, 2017 7:18 am    Post subject: Reply with quote

Dear sir,
    One more point I would like to add... During the ongoing SEWC India colloquium at Bengaluru, Dr S C Mehrothra, one of the invited speakers, who is also in the panel for IS 1893 code preparation etc informed that a review meeting is planned on 19th July if I remember correctly. He suggested practising consultants to send their comments regarding practical difficulties of the IS 1893 and IS 13920 to Shri S Arunkumar, Member Secretary at his email ID sak@bis.gov.in so that the same may be discussed at the meeting.

Yours sincerely
Arunkumar
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VIJAY N RATHOD
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PostPosted: Sun Jul 16, 2017 2:40 pm    Post subject: Reply with quote

Dear Arun,


Thanks for sharing information.

We have already adopted this methodology of giving shear release to all Columns, but in such analysis again as per new codal provision vertical acceleration we have to incorporate in the model so in such case Z-direction mass participation become zero. As we know it will not govern but in some vulnerable case it may also govern.

If we not considered vertical acceleration then this methodology can be adopted as per my understanding.

if you have face any other doubt then please highlight it.


thanks

vijay
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