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Design for Vertical Earthquake Effects as per IS 1893 Part1: 2016

 
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aditya
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Joined: 05 Apr 2008
Posts: 168

PostPosted: Mon May 21, 2018 4:33 pm    Post subject: Design for Vertical Earthquake Effects as per IS 1893 Part1: 2016 Reply with quote

Dear Sefians,
I need to carrry out seismic analysis and design of a multi-storeyed building in Zone V. As per clause 6.3.3.1 of IS 1893: Part 1-2016, we need to consider vertical earthquake effects. I need clarifications on the following points regarding the application of clause:
1.  Design vertical seismic coefficient=(2/3)x design horizontal seismic coefficient. Now shall we calculate base shear=design vertical seismic coefficient x seismic weight?
2. base shear calculated in point 1 above shall be applied in +/- vertical direction (i.e. down and up?)?
3. How shall we carry out storey-wise distribution of this "vertical?"base shear?
4. What will be the point of application of storey-wise vertical seismic forces? Centre of mass of each storey?
5. Shall we consider separate load cases EQz+ and EQz-?
6. Load combinations shall be as per clause 6.3.4.1?
Can somebody help in this regard with example?
with best regards,
Aditya
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u.mukesh
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Joined: 26 Jan 2003
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PostPosted: Thu May 24, 2018 7:30 am    Post subject: Design for Vertical Earthquake Effects as per IS 1893 Part1: 2016 Reply with quote

Hello dear

Vertical earthquake will increase (when downward) the moments in beams;
and all these reactions from beams (at diff floors) will increase the axial force in columns.


You should make proper combinations and you will get the forces.
There is no logic of vertical base shear..........


as vertical loads will create additional axial forces in columns and foundations.


Regards


Mukesh Upadhyay


On Mon, May 21, 2018 at 10:03 PM, aditya <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Sefians,
I need to carrry out seismic analysis and design of a multi-storeyed building in Zone V. As per clause 6.3.3.1 of IS 1893: Part 1-2016, we need to consider vertical earthquake effects. I need clarifications on the following points regarding the application of clause:
1. Design vertical seismic coefficient=(2/3)x design horizontal seismic coefficient. Now shall we calculate base shear=design vertical seismic coefficient x seismic weight?
2. base shear calculated in point 1 above shall be applied in +/- vertical direction (i.e. down and up?)?
3. How shall we carry out storey-wise distribution of this "vertical?"base shear?
4. What will be the point of application of storey-wise vertical seismic forces? Centre of mass of each storey?
5. Shall we consider separate load cases EQz+ and EQz-?
6. Load combinations shall be as per clause 6.3.4.1?
Can somebody help in this regard with example?
with best regards,
Aditya
     



     


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aditya
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Joined: 05 Apr 2008
Posts: 168

PostPosted: Fri May 25, 2018 2:10 am    Post subject: Reply with quote

Dear Er. Mukesh Upadhyay Sir,
Thanks a lot for your suggestions. I am looking after how to calculate the earthquake forces to simulate the effect of vertical seismic forces in a building and how to apply it as per codal provisions. It would be great if somebody would suggest on how to model it in seismic coefficient method through Staad.pro/SAP2000/ETABS software or even through manual calculation.
with best regards and thanks,
Aditya
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aditya
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PostPosted: Fri Feb 14, 2020 1:33 pm    Post subject: Reply with quote

Dear Sefians,
Can somebody guide me on how to apply vertical seismic forces in different storeys as per IS 1893 Part 1: 2016? Will its distribution similar to horizontal seismic forces in different storeys? Code seems silent on this topic.
with regards,
Aditya
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mallan
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Joined: 17 Mar 2016
Posts: 21

PostPosted: Sun Feb 16, 2020 8:43 am    Post subject: Reply with quote

I agree with Er. Mukesh's comment above.

At any point of time, each and every mass on the building is continuously excited at acceleration = g. However, during an earthquake event, the building gets excited similar to a person standing in an elevator. So, if i call the acceleration produced by vertical earthquake as z, the weight of each and every mass on the structure becomes m*(g+z) or m*(g-z). So, just adding or subtracting a load equal to a fraction of the seismic weight should be sufficient (value of fraction depends on the Av).

For example, lets say Av as per IS1893 = 5%, i.e. EQZ = 0.05(DL+0.5LL)
I would apply it by increasing/decreasing gravity loads as -
1.5DL+1.5EQX+(1.5*0.3)EQZ = 1.5225DL+0.01125LL+1.5EQX
0.9DL+1.5EQX -(1.5*0.3)EQZ = 0.8775DL -0.01125LL+1.5EQX

Let me know what you think of this.

-Akshay Mallan
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aditya
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Joined: 05 Apr 2008
Posts: 168

PostPosted: Sun Feb 16, 2020 1:32 pm    Post subject: Reply with quote

Dear Akshaya Mallan Sir,
Thanks a lot for responding to my query. The solution suggested by you will work for design in the case of Equivalent Static Method. The problem I am facing is how to distribute the total base shear at each storey so that I can apply the load in the analytical model and use the results later in response spectrum method for scaling of the base shear as per codal provision. Is there any work around?
with best regards,
Aditya
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