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[arch.alex]

IS 16700 says:
5.3 Storey Stiffness and Strength
a) Lateral translational stiffness of any storey shall not be less than 70 percent of that of the storey above.


Wheras IS 1893 says:
7.1 Regular and Irregular Configurations
...All efforts shall be made to eliminate irregularities by modifying architectural planning and structural configurations...

Table 6 (i): [Vertical] Stiffness irregularity (Soft Storey) � It is one in which the lateral stiffness is less than that in the storey above. (Definition same as 4.20.1)


My question:
Is it ok that some structures (of height > 50m), just in case, need to satisfy only IS 16700, and not IS 1893?

[ronak_shah]

Hello this is another question on similar lines about the soft storey effect

The code suggests to check for soft storey but has not further guidelines about the design about the soft storey when it occurs in particularly fire check floors

As in most of the high rise we have a fire check floor which is normally of very less height as compared to the normal floors so it is bound to become a soft storey in the structure

Regards
Ronak

[alpa_sheth]

Yes, that is so. It is okay to satisfy IS 16700. This is a relaxation given in IS 16700. Pl read the foreword about which code clauses shall govern in case of discrepancy.�

best regards,Alpa Sheth�




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On Tue, Mar 13, 2018 at 1:10 PM, arch.alex forum@www.buonovino.com)> wrote:

[pushpinder84]

Clause 7.10.3 gives an extension to the weak storey clause by having the limits as
1. Lateral stiffness minimum 80% of the storey above.
2. Lateral strength minimum 90% of the storey above.

However Stiffness corresponds to "soft storey" and strength corresponds to "Weak storey"

Thus we have IS-1893 giving a limit of 80% for storey to storey stiffness against 70% in IS-16700 and a limit of 90% for storey to storey strength against 100% in IS-16700.

[B.V.Harsoda]

Review of Various National & International Codes about soft Story:-

1. IS 15988:2013:-The stiffness of vertical lateral load resisting system in any story shall not be less than 60 % of the stiffness in adjacent story or less than 70 % of the average stiffness of the three stories above.

2. FEMA 310 :-The stiffness of vertical lateral load resisting system in any story shall not be less than 70 % of the stiffness in adjacent story

3. Eurocode 8:-At any story the maximum displacement in the direction of the seismic force should not exceed the average story displacement by more than 20%

4. IS 1893 (Part I):Table 5 ( Clause 7.1)
(A) Soft story:A soft story is one in which the lateral stiffness is less than 70 % of that in story above or 80 % of the average lateral stiffness of the three stories above.
(B) Extreme Soft story:A extreme soft story is one in which the lateral stiffness is less than 60% of that in story above or less than 70 % of the average stiffness if the three stores above. i.e. Buildings on STILTS will fall under this category.

5. IS 1893 (Part I)2016: Table 6(Clause 7.1)
A soft story is story whose lateral stiffness is less than that of story above. As per cl. 7.9 when SPD of masonry infill exceeds 20 %, the effect of UMR shall be considered in structural analyses. the design forces for RC members shall be larger of bare frame & Frame with URM Shall be considered. The inter-story drift shall be limited to 0.2 %.

6. BIS Draft of IS 16700 :-

Clause 5.3 Story Stiffness:-Lateral translation stiffness of any story shall not be less than that of story above.

7. IS 16700:2016:

Clause 5.3:Lateral translation stiffness of any story shall not be less than 70 % of the of story above.


Conclusion:-As per my opinion provision of BIS Draft for IS 16700 & provision of IS 1893 (Part I): 2016 is better for safe tall structures.




Regards,
Er. B. V. Harsoda

[B.V.Harsoda]

Review of Various National & International Codes about soft Story:-
1.IS 15988:2013:- The stiffness of vertical lateral load resisting system in any story shall not be less than 60 % of the stiffness in adjacent story or less than 70 % of the average stiffness of the three stories above.


2.FEMA 310:- The stiffness of vertical lateral load resisting system in any story shall not be less than 70 % of the stiffness in adjacent story


3.Eurocode 8:- At any story the maximum displacement in the direction of the seismic force should not exceed the average story displacement by more than 20%


4.IS 1893 (Part I):Table 5 ( Clause 7.1)
(A) Soft story: A soft story is one in which the lateral stiffness is less than 70 % of that in story above or 80 % of the average lateral stiffness of the three stories above.
(B) Extreme Soft story: A extreme soft story is one in which the lateral stiffness is less than 60% of that in story above or less than 70 % of the average stiffness if the three stores above. i.e. Buildings on STILTS will fall under this category.


5.IS 1893(Part I)2016: Table 6(Clause 7.1)
A soft story is story whose lateral stiffness is less than that of story above. As per cl. 7.9 when SPD of masonry infill exceeds 20 %, the effect of UMR shall be considered in structural analyses. the design forces for RC members shall be larger of bare frame & Frame with URM Shall be considered. The inter-story drift shall be limited to 0.2 %.


6.BIS Draft of IS 16700:-

Clause 5.3 Story Stiffness:- Lateral translation stiffness of any story shall not be less than that of story above.


7.IS 16700:2016:

Clause 5.3: Lateral translation stiffness of any story shall not be less than 70 % of the of story above.



Conclusion:- As per my opinion provision of BIS Draft for IS 16700 & provision of IS 1893 (Part I): 2016 is better for safe tall structures.




Regards,
Er. B. V. Harsoda

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