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Dr. N. Subramanian General Sponsor
Joined: 21 Feb 2008 Posts: 5538 Location: Gaithersburg, MD, U.S.A.
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Posted: Fri Feb 04, 2022 6:42 pm Post subject: Considering loads for Vertical+ Horizontal Earthquake |
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An Engineer raised this question: As per IS 1893:2016, for a zone-4 building vertical earthquake effects are considered by a consultant as per 6.3.3.1
But they haven't considered vertical load combinations given in 6.3.4.1
They're citing clause 6.3.4.4 for not considering the vertical combinations.
Is this Correct Sir?
My reply: Clause 6.3.3.3 states that when both vertical earthquake and horizontal earthquake are considered, loading as per Clause 6.3.4.1. shall be considered! But Clause 6.3.4.4 is a bit confusing!
I want others also to comment on this! |
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vikram.jeet General Sponsor
Joined: 26 Jan 2003 Posts: 3839
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Posted: Sat Feb 05, 2022 10:32 am Post subject: |
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Vertical seismic component
Not a researcher of the subject on EQ engineering , just from practice point of view
Considering structure to be orthagonal , 100 % Horizontal component of EQ is considered in one direction at a time as age old practice ( as also given in cl 6.3.2.1) . But Vertical seismic always co-exist to its 100% value and was always considered to its full value . Earlier practice on Bridge as well as building designs was done on this logic.
Therefore considering only 30% of co- existing vertical EQ as per combinations given seems out of logic but researcher on EQ wave motions can comment the reasoning behind this.
As a personal opinion , full vertical component to be taken .
However as per Code , if Structure is not orthogonal the 100% Plus 30% in other dir but still 100% vertical EQ logically. |
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vikram.jeet General Sponsor
Joined: 26 Jan 2003 Posts: 3839
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Posted: Sat Feb 05, 2022 11:32 am Post subject: |
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As per IRC 6 , 2000 version
Clause 222.1 clearly say that Vertical seismic coefficient shall be considered on all bridges in Zone V and IV. Horizontal and vertical seismic coefficient shall be considered acting simultaneously.
Not able to download IRC 6 2017 version . |
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vikram.jeet General Sponsor
Joined: 26 Jan 2003 Posts: 3839
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Posted: Sat Feb 05, 2022 11:48 am Post subject: |
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Yes , checked IRC 6 , 2017 version
The load combinations given are in line with IS 1893 . It considers 30% vertical EQ.
Outcome of latest research could be the reason . |
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sspawar ...
Joined: 05 Jun 2009 Posts: 1205
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Posted: Sun Feb 06, 2022 9:26 am Post subject: Re: Considering loads for Vertical+ Horizontal Earthquake |
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Dr. N. Subramanian wrote: | An Engineer raised this question: As per IS 1893:2016, for a zone-4 building vertical earthquake effects are considered by a consultant as per 6.3.3.1
But they haven't considered vertical load combinations given in 6.3.4.1
They're citing clause 6.3.4.4 for not considering the vertical combinations.
Is this Correct Sir?
My reply: Clause 6.3.3.3 states that when both vertical earthquake and horizontal earthquake are considered, loading as per Clause 6.3.4.1. shall be considered! But Clause 6.3.4.4 is a bit confusing!
I want others also to comment on this! |
I am not design expert-- but what Clause 6.3.4.4 states is about the equations - can be modified as per the particular case. x, y or z any one can be eliminated if it is not in consideration in a particular case.
It is telling about flexibility of equations, though the section is concerned about the vertical motion, so only two horizontal plans at a time should not be the matter of concern. But the equations are so effective that it works in 2 H- plans also.
Regards |
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sakumar79 ...
Joined: 18 Apr 2008 Posts: 713
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Posted: Sun Feb 06, 2022 11:44 am Post subject: |
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Dear Sirs,
As I understand, the omission of vertical component in load combinations is incorrect.
The purpose of clause 6.3.4.4 is for cases where the frames are orthogonal (due to which 30% EL of opposite direction is not needed), or when vertical component is not required.
If vertical component is needed in design as per 6.3.3, load combinations as per 6.3.4.1 (or) as per 6.3.4.2 should be considered for design.
At most, if the frames are orthogonal, we can consider ELx+/-0.3ELz and ELy+/-0.3ELz as the EQ component instead of ELx+/-0.3ELy+/-0.3ELz and ELy+/-0.3ELx+/-0.3ELz
Yours sincerely
S Arunkumar |
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hemalmistry ...
Joined: 01 Jul 2009 Posts: 70
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Posted: Mon Feb 07, 2022 7:51 am Post subject: |
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Dear S Arunkumar,
I agree with your clarification that Vertical EQ actions shall be combined with only one horizontal EQ actions at a time for orthogonal LLRS and with both
horizontal EQ actions for Non-orthogonal LLRS (horizontal irregularity of non parallel lateral force system),
However, i would like to modify last two lines of your explanation as below:
At most, if the frames are orthogonal but requires to include vertical seismic effect as per 6.3.3.1, we can consider
+/-ELx+/-0.3ELz,
+/-ELy+/-0.3ELz,
+/-ELz+/-0.3ELx,
+/-ELz+/-0.3ELy,
as the EQ component instead of
+/-ELx+/-0.3ELy+/-0.3ELz,
+/-ELy+/-0.3ELx+/-0.3ELz,
+/-ELz+/-0.3ELx+/-0.3ELy.
Recent version of ASCE 7, also requires load combinations of non-orthogonal LLRS to be considered for buildings in high seismic zones (SDC D,E,F) with orthogonal LLRS but with torsional irregularity. If Such buildings qualifies for vertical EQ effects, all three EQ components needs to be combined with 100/30 rule.
Regards,
Hemal Mistry |
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sakumar79 ...
Joined: 18 Apr 2008 Posts: 713
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Posted: Sat Feb 19, 2022 8:59 am Post subject: |
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Dear Er Hemal Mistry,
Your corrections are in order. Hope other senior engineers concur and if not, may put forth their point of view.
Yours sincerely
S Arunkumar |
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