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[Econf_Moderator]

Dear All,


Thank you very much for the interesting discussions on the Day 1 of the E-conference on "IS 16700- Criteria for Structural Safety of Tall Concrete Buildings".


We would like to clarify some of the points raised during the discussion and would try to cover as many items are possible in our subsequent posts.


Comment: Deformation limit (Section 5.4): The section recommends the use of 50 year return period for the service wind drift limit. I feel this bit conservative. International codes generally considers 10 years return period for the service drift limitation.

Response: Noted and comment will be put up to Drafting group for discussion
  
Comment: “what is the Way forward,for the existing and under construction buildings” what about the thousands of Moment Frame Buildings, now not allowed in Zones IV and V at all?

Comment: As per Table 1 and Table 2, Moment Frame System is not applicable for buildings in seismic Zone IV and V. Basis for eliminating framing system altogether in high seismic zones is not made clear. This may require a review. As per fib bulletin-73, framing system is permitted in tall buildings upto a height of about 75m. This clause therefore should be reviewed.


Response: The code need not be applied for projects under construction or for which the authority approvals are already obtained.  Tall buildings of 50m and above are normally with lift core which can be used structurally to enhance the lateral stiffness of the building.  The structural system then becomes Structural Wall + Moment Frame.  It would be seldom possible to have tall buildings with only moment frames and would not be advisable to ignore the lift cores in the analysis.

Comment: 1.3 Is this a group pf buildings or a single building? Why is this applicable?
  
Response:  Buildings with very high density need special features and enhanced building behaviour. This is a requirement in the aftermath of the collapse of World Trade Towers where it was understood that buildings with high density, regardless of how well they have been designed or constructed. have special requirements and need to be approached differently

Comment: Under floor system 5.6 sub clause 5.6.2.3 it is mentioned that "At any storey , the minimum width of floor slab along any section after deduction of openings shall not be less than 5 m and the minimum width of the slab beyond an opening to edge shall not be less than 2m".
Can anyone clarify the above clause  also is it 5 sq m instead of 5 m.


Comment: 5.6.2.1  What is the criteria- unsupported length of the opening / slenderness limit/ axial force ?  As we are using rigid diaphragm in most cases, this does not effect the analysis     


Response: Diaphragm  requirements are in line with those in international codes. Also refer to “Some Concepts in Earthquake Behaviour of Buildings”, Gujarat State Disaster Management Authority  2013 http://www.iitk.ac.in/nicee/IITK-GSDMA/EBB_001_30May2013.pdf for a better understanding of effect of cutouts on diaphragm action.


Best Regards,


E-Conference Moderators

[hemalmistry]

Waiting for response on query regarding maximum permissible concrete grade of M70

[abhio]

Dear Sir/ Madam,

Please also note the following:


CL 5.6.3. IN THIS IT IS STATED THAT " NATURAL VERTICAL  
VIBRATION FREQUENCY OF ANY FLOOR SYSTEM SHALL NOT EXCEED 3 HZ
I believe this is an error in the Code. The 3 Hz limitation ought to be a lower bound, and not upper bound on the natural frequency of the floor.

Regards,

A S Oundhakar

[alpa_sheth]

I agree, this is a mistake and will be corrected in the eraata to be issued. 


Alpa 

On Wed, Mar 14, 2018 at 10:28 AM, abhio <forum@sefindia.org (forum@sefindia.org)> wrote: