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CHECKING OF THE STRUCTURE AGAINST OVERTURNING
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suresh_sharma
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Joined: 23 Mar 2011
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PostPosted: Mon Oct 29, 2012 9:04 am    Post subject: Reply with quote

Dear Vikram,

After going thrugh the writing of Prof ARC it appears to me that it is not possible to check the structure against oveturning for the earthquake load because of its dynamic and reversible nature. The static analysis that we do for the EQ is a simplification of the real problem and it can be applied for checking against overturning for buildings of smaller height and not for the stack like structures.

Any other view.
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vikram.jeet
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PostPosted: Tue Oct 30, 2012 6:20 am    Post subject: CHECKING OF THE STRUCTURE AGAINST OVERTURNING Reply with quote

Still as a layman's view - - -

I think Tall structures vibrating in Ist Mode (like a pendulum) have chances of toppling
and have to be seen for OT check under MCE.
In other modes of dynamic motion, structure along its height may have some part on
this side and other on other side like a dancer ,and toppling is not anticipated ,but  
vibration like pendulum is cause of concern for OT.


best regds

vikramjeet




Dear Vikram, After going thrugh the writing of Prof ARC it appears to me that it is not possible to check the structure against oveturning for the earthquake load because of its dynamic and reversible nature. The static analysis that we do for the EQ is a simplification of the real problem and it can be applied for checking against overturning for buildings of smaller height and not for the stack like structures. Any other view.
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suresh_sharma
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PostPosted: Tue Oct 30, 2012 8:56 am    Post subject: Reply with quote

Yes, Vikram, I agree with you that bulding can overturn due to eartquake in the first or at best during the second mode of vibration. This explanation I could  ultimately get from the book of Dr. Anil Chopra. Before that I discussed the matter with so many designers. None could give a convincing reply. Of course overturning due to Wind load could be a matter of concern.

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vikram.jeet
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PostPosted: Tue Oct 30, 2012 10:02 am    Post subject: CHECKING OF THE STRUCTURE AGAINST OVERTURNING Reply with quote

Dear Er Suresh ji

I appreciate your attitude for raising very pertinent queries on sefi for all of us to
think deeply as result of your in- depth thinking about structural aspects. I further  
thank you for citing Dr Chopra's book.

EQ design philosophy - - - - -Material design is based on DBE plus Ductile Detailing
But Stability aspect like OT and Sliding must cater for MCE (as discussed in current discussions)

As regards Wind condition
Wind Case - - - The quantum of wind force is almost known and structure is designed for maximum
force. Gust, hurricanes, tornado storms are exceptional but since wind is surface/geometry phenomenon
(compared to EQ which is influenced by mass of structure ) , the Stability against OT during wind  
cannot exceed the FOS considering exceptional winds. Also Wind tunnel tests can predict the  
quantum of wind forces and their distribution for a particular structure/situation.  

best regds

vikramjeet





Yes, Vikram, I agree with you that bulding can overturn due to eartquake in the first or at best during the second mode of vibration. This explanation I could ultimately get from the book of Dr. Anil Chopra. Before that I discussed the matter with so many designers. None could give a convincing reply. Of course overturning due to Wind load could be a matter of concern. Thanks
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Manoharbs_eq
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PostPosted: Tue Oct 30, 2012 12:28 pm    Post subject: Reply with quote

Dear all,

Over turning of structure due to wind load is easily predictable and can be easily tabulated. generally too slender buildings are vulnerable to wind. especially steel structures are of concern.

However overturning by equivalent static method is not a complete procedure. overturning of structure due to earthquake is tricky since it is inertial force acts at the base of the structure hence number of coefficients have to be considered,


Isnt it tricky if structure is tall slender and light weight then wind overturns the structure, If the structure is heavy seismic case govern as lumped at higher level causes more force.
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