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[hemalmistry]

Clause 6.2.2.4 requires damping ratio of 2% for concrete. Design acceleration spectrum as per IS 1893-1_2016 is for 5% damping. Which spectrum shall be used for 2% damping as per IS 16700?

IS 1893-1_2002 was having multiplying factor for dampling other than 5%.


Regards
Hemal mistry
Surat

[bsec]

Dear Hemal,

I think 2% damping is for wind analysis and not for seismic analysis. For seismic analysis the spectrum is with 5% damping. Difference is possibly due to the philosophical difference in treatment of wind and seismic loads for design. Building is supposed to remain elastic with characteristic Wind load, while the building is allowed to go into in-elastic range under seismic loads.


Best Wishes


Alok Bhowmick 


On Wed, Mar 14, 2018 at 12:12 AM, hemalmistry <forum@sefindia.org (forum@sefindia.org)> wrote:

[indrajit-chowdhury]

I would multiply the response spectrum value Sa/g furnished in code by a factor sqrt ( 10/7) to arrive at value for 2 % damping.

On 14 Mar 2018 10:14 am, "hemalmistry" <forum@sefindia.org (forum@sefindia.org)> wrote:

[alpa_sheth]

You are right, Alok. 2% damping is only for wind loads. Seismic stays at 5%, you have articulated the philosophy. 


regards,
Alpa 










On Wed, Mar 14, 2018 at 10:32 AM, bsec <forum@sefindia.org (forum@sefindia.org)> wrote:
[quote]            Dear Hemal,

I think 2% damping is for wind analysis and not for seismic analysis. For seismic analysis the spectrum is with 5% damping. Difference is possibly due to the philosophical difference in treatment of wind and seismic loads for design. Building is supposed to remain elastic with characteristic Wind load, while the building is allowed to go into in-elastic range under seismic loads.


Best Wishes


Alok Bhowmick 


On Wed, Mar 14, 2018 at 12:12 AM, hemalmistry forum@sefindia.org (forum@sefindia.org))> wrote:
      --auto removed--

Posted via Email

[alpa_sheth]

I think we should not mix apples and oranges. As Senior Designer Alok Bhowmick has already explained, you are working in elastic range in Wind loads and in the in elastic range in Earthquake loads. 
5% damping for earthquake loads and use IS 1893 spectrum. No scaling etc is required. 





best regards,Alpa Sheth 




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On Wed, Mar 14, 2018 at 10:47 AM, indrajit-chowdhury <forum@sefindia.org (forum@sefindia.org)> wrote:
[quote]            I would multiply the response spectrum value Sa/g furnished in code by a factor sqrt ( 10/7) to arrive at value for 2 % damping.

On 14 Mar 2018 10:14 am, "hemalmistry" forum@sefindia.org (forum@sefindia.org))> wrote:       --auto removed--

Posted via Email

[hemalmistry]

Alpa mam, alok sir,

Thanx for the clarification. I think it should be mentioned in amendment of IS:16700 that 2% damping is for wind load.

Regards
hemal

[Gangisetty Krishna]

Alok Sir,

I have gone through the literature regarding the tall structure damping ratio. In the document PEER/ATC72-1 in section 2.1.3 that the damping is substantially different from values typically assumed in low rise building. Is there any chance of changing the damping ratio of the concrete building to 2% for tall building in future amendments.

[SACHINbidar]

MamWhy IS 16700 doesn't cover structures with steel 


On 14-Mar-2018 11:17 AM, "alpa_sheth" <forum@sefindia.org (forum@sefindia.org)> wrote:

[imteyaz_ahmad]

Clause 7.3.11 is in contradiction with Table 1 in Section 5, which prohibits use of flat slab in Zone IV & V. But 7.3.11 says to ignore ignore stiffness of flat slab. Code should be consistent with its provisions, one can be confused to use whether use flat slab system or not in those zones.


On 14 March 2018 at 00:12, hemalmistry <forum@sefindia.org (forum@sefindia.org)> wrote:

[sangeeta_wij]

Yes Hemal, but you are right that we will then need to carry out two separate sets of analysis, one with Wind and 2% damping and the second with Seismic and 5% damping and then select the governing one for each member.For large and complicated structures, it really will be a challenge unless ETABS comes up with a better way forward!




Best Regards
Sangeeta Wij
President,WISE India
Managing Partner
SD Engineering Consultants LLP
Vice President(North),Indian Association of Structural Engineers,
Fellow and Chartered Engineer, Institution of Engineers
H333 New Rajinder Nagar(Lower Ground Floor),
New Delhi-110060
Ph:9811776210;01145128530


From: hemalmistry [mailto:forum@sefindia.org]
Sent: 14 March 2018 11:27
To: econf@sefindia.org
Subject: [E-CONF] Re: clause 6.2.2.4_damping ratio



Alpa mam, alok sir,

Thanx for the clarification. I think it should be mentioned in amendment of IS:16700 that 2% damping is for wind load.

Regards
hemal

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