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[pvspk132]

This is regarding few clarifications and suggestions on code clarifications.

1. IS16700:2023 (Sep 2023 Issued) have relaxed to use time period as per mode shapes having max. Time period as per 6.3.4 for evaluating Seismic forces. Does this clause overrides/supercedes Fundamental time period calculation defined in IS 1893:2016???I am raising this query as during working, when we evaluated for a building of 60m we are obtaining 60-70% reduction from this new formulae.

2. IS 1893:2016 talks about Structural wall system where Frames are not participating or not fulfilling dual system requirements. For a case where we have Frame only in one direction and other direction only peripheral beam, making complete one-way slab system, We can use R=4 for ductile wall system ??  Or as there is no frame, we shall use Flat slab /Plate approach for one direction ???

3. height of building convention as per IS16700 shall be considered till last connected height. But this includes mumpty or Raised portion of 15-25% of plan area of building . I.e only 25% of plan area is being raised for 7-10m, Does this needs to be considered in evaluating height of building in evaluating timeperiods ???

Please guide me over the above understanding which will be very much helpful.

[alpa_sheth]

Hi,


1. Please refer to Clause 1.6 of IS 16700-2023 and Clause 6.3.4 first sentence. Together they will answer your query 1. I am assuming your structure is >50 m height else you cannot use the equations of 6.3.4


2. You are at liberty to use a different R in the two different orthogonal directions, based on your Lateral load resisting system  in each of the directions. I am sure you are aware that you cannot use a Flat slab/ flat plate as a Lateral Load resisting system. You may want to ensure that you have sufficient structural walls in both the directions as a building > 50 m height will not work without structural walls and just a perimeter frame or a moment frame alone in any direction may not work.  Do take a look at Table 1 of IS 16700-2023 and check for conformance


Best regards,


Alpa Sheth


1. IS16700:2023 (Sep 2023 Issued) have relaxed to use time period as per mode shapes having max. Time period as per 6.3.4 for evaluating Seismic forces. Does this clause overrides/supercedes Fundamental time period calculation defined in IS 1893:2016???I am raising this query as during working, when we evaluated for a building of 60m we are obtaining 60-70% reduction from this new formulae.

2. IS 1893:2016 talks about Structural wall system where Frames are not participating or not fulfilling dual system requirements. For a case where we have Frame only in one direction and other direction only peripheral beam, making complete one-way slab system, We can use R=4 for ductile wall system ??  Or as there is no frame, we shall use Flat slab /Plate approach for one direction ???

3. height of building convention as per IS16700 shall be considered till last connected height. But this includes mumpty or Raised portion of 15-25% of plan area of building . I.e only 25% of plan area is being raised for 7-10m, Does this needs to be considered in evaluating height of building in evaluating timeperiods ???

Please guide me over the above understanding which will be very much helpful.[/quote]

[pvspk132]

Thanks madam for response,

For Point No.1 I Understand that IS16700 supersedes IS1893 Time period in cases of ambiguity (As per Clause 1.6 of IS16700). Hence, The reduction in base shear is acceptable for all type of buildings (>50m).
Also, I Understand there is no restriction on Storey heights/Mass based on historic data we have in increased time periods for high rise buildings.

For point No.2 , My query is System with one direction beams will be falling under SI No. iii or v as per Table 9 of IS1893:2016 in deciding R factor of the system.
Note: System under discussion is not Flat slab, Its one direction beams connecting all Gravity Columns, Other direction columns are only connected by One way slab spanning between beams. While LRFS is Ductile Shear walls.