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[Econf_Moderator]

Dear All:

Here are responses to some of your queries. These are by no means exhaustive and some queries will need more time form our end. So do bear with us.


Comment

In IS codes 1893/2016, 13920/2016 and IS 875 part 3 /2015 and the new code 16700/2017, most of the provisions are inter connected. Some of the clauses in 16700 is confusing with the provisions of the other codes mentioned above.


Generally speaking ,therefore, in my opinion, an explanatory addition to 16700/2017 , in the form of a Special publication, is necessary , interpreting the various clause to understand this new code fully ,and adapt for practical application.


Response

Your comment is noted and many SEFIans have shared the same thought.
We too hope that the Bureau of Indian Standards ​will consider coming out with a commentary on this code.


Comment

Another important requirement in Tall Buildings is DAMPERS.
This aspect has not been mentioned or highlighted in this code. In almost all tall builngs, already constructed ,different types of dampers have been used to reduce drift ,lateral deflection and vibrations due to dynamic wind loads. There are positive Visco Elastic dampers, Tuned Mass dampers, Sloshing Warer Dampers, Tuned Liquid Dampers and Simple Pedulum dampers. Most of the Tall & super tall bldgs. already constructed have used one or other types of dampers. This aspect needs inclusion in the new code.


Response

The present code covers only buildings that can be covered in a prescriptive code. As mentioned in the foreword, structures with dampers fall within "code-exceeding buildings". This is also in line with the fact that the current IS 1893 part 1 does not cover dampers nor does the wind code. There is a code in preparation for use of such special systems. Once that is released, other codes can refer to it.


Comment:

Annexure A talks about code exceeding buildings and procedure for its approval. Question is who is going to implement it and there is no administrative mechanism to follow the guide lines ? It is not clear whether state Govt will provide the directions to form the expert review panel or local corporations do it on their own? Every one knows how Govt. departments function. We have very good laws but we lack in implementation. I feel Chairman of BIS should write to all State Governments / Urban Development Departments to form ERP for the respective states / corporation levels to implement the code guidelines. Otherwise it will remain on paper only.

Response

The need for the setting up of the ERP committee cannot be stressed enough. The issue is about mandate and jurisdiction. BIS has no authority to direct states or municipal authorities to do anything but perhaps it can engage the UDD at the centre who can then action it via directives to the States who will then direct the municipal bodies. It's a process but it should be started ASAP.


Comment

Questions are asked by many whether codes are only for guidance or they are legally binding? My personal view is that code are for guidance only but when the code reference is mentioned in the contract document / tender document it becomes legally binding for that contract.

Response

As per our understanding, a code on its own has not legal status. It needs to be mandated by the municipal body vide its development control regulations for it to be binding. Almost all municipal bodies require NBC to be followed which in turn means all BIS codes need to be followed.


best regards,


Ranjith Chandunni and Alpa Sheth
Econference Moderators.

Posted via Email

[keyulmehta]

Respected sir/madam          In design of tall building governing load combination is most probably include dynamic wind load.
In order to analyze any passive dampers in software we have to input spectra of force which contains ( Force vs. Time ) 
IS 875- part 3 does not explain or mention this spectra, it gives the procedure to use gust factor for the calculation so ultimately it convert dynamic wind load into equivalent static force.
In any software one can not analyze working of passive dampers for dynamic wind loading.


On 17-Mar-2018 9:55 PM, "Econf_Moderator" <forum@sefindia.org (forum@sefindia.org)> wrote:

[Econf_Moderator]

Here are the response for some of the queries received recently. The queries related to the section on foundation have been referred to the Geotechnical expert and would be responded shortly.

Comment: Clause 7.3.11 does not allow contribution of flat slab (slab-column frame) and clause 8.6.1 column strip of flat slab in resisting lateral load. I think rather than using two different terms (though having same meaning) a single term shall be used.
Anyway, my query is that, if i am neglecting stiffness of flat slab (Ieff=0) to exclude it from lateral load resisting system, how sensitivity analysis for backstay can be carried out as per cl. 8? if i have flat slab (with shear wall and perimeter frame) building (or buildings) with large podium. Do i need to modify only area of backstay diaphragm (flat slab) with upper and lower bound?


Response: The comment regarding flat slab stiffness is noted however, the two clauses are in different context.
Only the out of plane stiffness of flat slab which contributes to the lateral stiffness of the building should be neglected and not the in plane stiffness which should be considered at lower and upper bound for sensitivity analysis.

Comment: More clarification on Cl7.3.10 on how to calculate inter storey drift stability coefficient is required which is not clear. If someone explains with some numbers it will be helpful.

Comment: Cl. 7.3.10 The flexibility of the building shall be such that the flexibility of inter storey drift stability coefficient -[theta (Pu Delta/H)] exceeds 0.2 ,where Theta is not defined. This may be clarified or defined. whether Pu refers to the particular floor for which inter storey drift is calculated or not. Pu is defined in cl.4 symbols.

Response: The comments are noted; there is typo error in the stability index formula which will be clarified in the errata to be issued.
We too hope that the Bureau of Indian Standards will consider coming out with a commentary on this code.

Comment: Cl. 7.3.14 multiple towers connected by a single podium shall be modelled separately and integrally. DOES THIS MEAN THAT EACH TOWERS SHALL BE MODELLED SEPARATELY WITH THE PODIUM OR WITHOUT THE PODIUM AND ANOTHER MODEL WITH TWO TOWERS TOGETHER WITH THE PODIUM. IS THIS THE SAME CASE WHEN THERE IS EXPANSION JOINT WITH PODIUM AND TWO TOWERS.

Response: While modelling multiple towers, each tower to be modelled separately as well as integrally. When separate towers are modelled, if the part of podium attached to the tower is with more than two spans, and the lateral resistance system outside the footprint of the tower is sufficiently stiff to cater for the lateral resistance of the podium outside the footprint of the tower, at least two spans to be modelled with the tower if not the entire podium is modelled. Further guidance is available under section 8.1.3. Multiple tall building connected a common podium.


Best regards,
EConference Moderators

Posted via Email

[hemalmistry]

In response to query regarding "integral and separate tower" modeling for backstay effect, moderator have mentioned about modeling of 2 podium panels adjoining to tower for "separate tower" modeling. This requirement is there in Clause 5.1.14 of JGJ-3_2010 and in clause 7.3.15 in draft IS:16700-2017 but removed in final IS:16700_2017. Is it removed intentionally?