www.sefindia.org

STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

 Forum SubscriptionsSubscriptions DigestDigest Preferences   FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups  RegisterRegister FAQSecurity Tips FAQDonate
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log in to websiteLog in to websiteLog in to websiteLog in to forum 
Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.

Seismic Design
Goto page Previous  1, 2, 3, 4 ... 42, 43, 44  Next
 
Post new topicReply to topic Thank Post    www.sefindia.org Forum Index -> SEFI General Discussion
View previous topic :: View next topic  
Author Message
prof.arc
...
...


Joined: 26 Jan 2003
Posts: 703

PostPosted: Tue Apr 05, 2011 12:06 am    Post subject: No Title Reply with quote

Vertical Component of earthquake EXISTS along with horizontal component.

Theoretically it must be CONSIDERED always.
[for that matter, it is speculated that torsional and rotational components also exist - in other words, six components of motion -
read Prof. Trifunac's papers]
we also consider only one horizontal component at a time in most designs
DESIGN is a FICTION and assumptions can and are made as long as protection is given in the form of a Code of Practice


Even in some actual designs, some like me have considered simultaneous three component of motion


In summary, if a code says IGNORE - you are protected legally


ARC

On Sun, Apr 3, 2011 at 6:07 AM, bipinsh <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
     
[edited]
            thirumalaichettiar wrote:                Need Seniors and experienced engineers share their ideas for the following doubts?



7.When need to consider the Vertical force of EQ ?

8. Is Equivalent Static method consider the Vertical force of Earthquake?

9. Why moment redistribution is not considered in EQ analysis?

10.If a structure has long span or if the cantilever is more than 5m is worth to neglect the vertical force of EQ?

More to come.

 



Posted via Email
Back to top
View user's profile Send private message
thirumalaichettiar
Silver Sponsor
Silver Sponsor


Joined: 26 Jan 2003
Posts: 3459

PostPosted: Tue Apr 05, 2011 1:02 pm    Post subject: Reply with quote

Respected Prof.ARC Sir,

Thanks for your valuable posting but I expect more answers for other questions to learn more.

Even the code say IGNORE, a good engineer having GOD fearing can not IGNORE to save lives from EQ.


7.When need to consider the Vertical force of EQ ?

VERTICALFORCES :

Eurocode8 requires vertical seismic loading to be considered in areas of high seismicityin the design of the following types of structural element
(a)beams exceeding 20m span
(b)cantilevers beams exceeding 5m
(c)prestressed concrete beams
(d) beams supporting columns
(e)base-isolated structures.
Rulesare given for the vertical response spectrum, which is independent of the soiltype. Vertical and horizontal seismic effects can be combined either using an SRSSrule or a 100%ž30%ž30%rule, similar to that discussed above for the horizontaldirections.


IBCrequires that a vertical seismic load should be considered in all structures.
This is calculated simply as a proportion of the dead load, the proportion increasingwith the seismicity of the site.

A few words from a good EQ book is:

The need to learn from earthquake damage studies and to apply good engineering sense and judgement based on this learning cannot be emphasised too strongly. It is far more important than any amount of computation and analysis.

The common sense lessons from damage studies are as follows.

(a) All frame elements must be detailed so that they can respond to strong earthquakes in a ductile fashion. Elements that are incapable of ductile behaviour
must be designed to remain elastic at ultimate load conditions.

(b) Non-ductile modes such as shear and bond failures must be avoided. This
implies that the anchorage and splicing of bars should not be done in
areas of high concrete stress, and a high resistance to shear should be
provided.

(c) Rigid elements should be attached to the structure with ductile or flexible
fixings.

(d ) A high degree of structural redundancy should be provided so that as many
zones of energy-absorbing ductility as possible are developed before a failure
mechanism is created.

(e) Joints should be provided at discontinuities, with adequate provision for
movement so that pounding of the two faces against each other is avoided.

T.RangaRajan.


Last edited by thirumalaichettiar on Tue Apr 05, 2011 6:17 pm; edited 4 times in total
Back to top
View user's profile Send private message
thirumalaichettiar
Silver Sponsor
Silver Sponsor


Joined: 26 Jan 2003
Posts: 3459

PostPosted: Tue Apr 05, 2011 2:00 pm    Post subject: Reply with quote

A PDF file explaining some guide line for the PRELIMINARY SIZING OF STEEL STRUCTURE is attached taking the reference from a good book on EARTHQUAKE DESIGN PRACTICE FOR BUILDINGS By Edmund Booth.
It is based on Eurocode but the guidance is good enough to follow even the IS 800-2007 as the new code is in par with Eurocode.

Very useful ideas are given.

T.RangaRajan.



Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.
Preliminary sizing.pdf
 Description:

Download
 Filename:  Preliminary sizing.pdf
 Filesize:  106.24 KB
 Downloaded:  1429 Time(s)

Back to top
View user's profile Send private message
thirumalaichettiar
Silver Sponsor
Silver Sponsor


Joined: 26 Jan 2003
Posts: 3459

PostPosted: Tue Apr 05, 2011 3:03 pm    Post subject: Reply with quote

Further to continue to answer :


3.When P-Delta effect will have to be considered? Its effect on concrete and steel structures?

Lateral deflections give rise to gravity-induced moments . Usually the
moments are small, but where the product of gravity load (P) and the lateral deflection (delta)  is a significant fraction of the seismic overturning moment, the resulting‘P–delta’ effect should be allowed for. It can be easily incorporated into a nonlinear analysis


P-Delta effect is more pronounced in a frame more than 10 storeys.  in the Atkin manual it is stated the the P-Delta effect can be considered for floor above 12 storeys.

Codes such as Eurocode 8 and IBC state that P–delta effects can be neglected if
specified deflection limits are not exceeded.


Normally the deflections (Drift) will be restricted in EQ structures and hence P-Delta can be of more effective in structures more than say 10 storey.


4.Can we make use of Concrete of grade greater than M50 as it becomes more brittle on higher grade?
In the text book R.C.DESIGN  by Uniikrishnan and Pillai on page 576, it is stated "HIGH GRADE STRENGTH CONCRETE IS ALSO UNDESIRABLE DUE TO ITS LOWER ULTIMATE COMPRESSIVE STRAIN WHICH REDUCES DUCTILITY....BASED ON THIS FACTOR THE AMERICAN AND CANADIAN CODES LIMITS THE MAXIMUM CYLINDER STRENGTH OF LOW DENSITY CONCRETE TO A VALUE OF M30 FOR USE IN EQ RESISTANT DESIGN". But some author say since we are adding steel reinforcement it is of less concern.

But Eurocode specify M50. Vide the attached pdf file.



5. Can we use Fy=550 steel bars if the elongation is less than 14.5%?
The answer is NO since Ductility is very important for EQ structure.

T.RangaRajan.



Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.
Page 153.pdf
 Description:

Download
 Filename:  Page 153.pdf
 Filesize:  117.85 KB
 Downloaded:  687 Time(s)



Last edited by thirumalaichettiar on Wed Apr 06, 2011 12:26 am; edited 1 time in total
Back to top
View user's profile Send private message
bipinsh
...
...


Joined: 16 Oct 2008
Posts: 65

PostPosted: Tue Apr 05, 2011 5:01 pm    Post subject: Reply with quote

thirumalaichettiar wrote:


Even the code say IGNORE, a good engineer having GOD fearing can not IGNORE to save lives from EQ.


7.When need to consider the Vertical force of EQ ?

T.RangaRajan.


Respected Rangarajan Sir,
Fully agree with your statement.
Although some provision on  need of consideration of Vertical EQ force on seismic resistant design of structure are there its has hardly been followed.
Sir I will also want to have your opinion of scaling of horizontal spectrum to represent vertical motion. since vertical ground motion unlike horizontal are rich in high frequency content, shouldn't we be using separate spectrum for Vertical and horizontal motion?
And also i m bit critical about the 1/2 to 2/3 rule often used to represent the vertical motion. We have in past seen that vertical ground motion could exceed horizontal motion in many occasions so will it be rational to stick with the same ratio?
Since many recent researches has shown that the short period ratio of Vertical to horizontal spectrum could exceed 1(especially at near distance to the fault) don't
we need to upgrade our code to be capable to cater such situation?
Finally is the code, presently we are using conservative enough to Warranty against failure due to above mentioned matters?
Want to have expert opinion of SEFI seniors on these matters.

Regards
Bipin Shrestha
Back to top
View user's profile Send private message
thirumalaichettiar
Silver Sponsor
Silver Sponsor


Joined: 26 Jan 2003
Posts: 3459

PostPosted: Tue Apr 05, 2011 6:19 pm    Post subject: Reply with quote

10.If a structure has long span or if the cantilever is more than 5m is worth to neglect the vertical force of EQ?

Please refer to my posting in this same page against Prof.ARC where the answer for Q7 will hold good for this also.

T.RangaRajan.


Back to top
View user's profile Send private message
thirumalaichettiar
Silver Sponsor
Silver Sponsor


Joined: 26 Jan 2003
Posts: 3459

PostPosted: Tue Apr 05, 2011 7:17 pm    Post subject: Reply with quote

6. Why the codes specify the limits on b/D or the dimensional restrictions for EQ design?

The restrictions on beam-to-column width ratios are to ensure a flow of moment between beams and columns without undue stress concentrations and to harness benefit from the improvement that column compression has on the bond of beam reinforcement passing through the joint region; the restrictions effectively prohibit
the use of flat slab systems as ductile frames, since they perform poorly under earthquake loading.

Depth-to-width ratios within individual elements are restricted to prevent buckling instability. Low beam span-to-depth ratios are likely to result in members governed by shear rather than flexure. This will restrict their ductility unless special measures are taken, such as provision of diagonal steel.

Any other explanations from seniors are welcome to learn more and need more comments on this topic.

T.RangaRajan.
Back to top
View user's profile Send private message
thirumalaichettiar
Silver Sponsor
Silver Sponsor


Joined: 26 Jan 2003
Posts: 3459

PostPosted: Tue Apr 05, 2011 8:51 pm    Post subject: Reply with quote

PRELIMINARY SIZING OF MEMBERS -R.C.C. STRUCTURES FOR EQ:

I attach some guide line as furnished for EC and ACI which are in line with our code but reference can be made io IS 13920 and IS 1893-2002 for further clarifications.

T.RangaRajan.



Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.
Preliminary sizing for Reinforced concrete structures1.pdf
 Description:

Download
 Filename:  Preliminary sizing for Reinforced concrete structures1.pdf
 Filesize:  994.64 KB
 Downloaded:  1375 Time(s)

Back to top
View user's profile Send private message
bipinsh
...
...


Joined: 16 Oct 2008
Posts: 65

PostPosted: Wed Apr 06, 2011 8:35 am    Post subject: Reply with quote

3.When P-Delta effect will have to be considered? Its effect on concrete and steel structures?

A well designed building should not have significant P-Delta effects. Analysis
with and without the P-Delta effects will yield the magnitude of the P-Delta
effects separately. If those lateral displacements differ by more than 5% for the same lateral load, the basic design may be too flexible and a redesign should be considered.
Refreed form "Three-Dimensional Static and dynamic Analysis of Structures" by Prof. Emeritus Edward L. Wilson

Regards
Bipin Shrestha
Back to top
View user's profile Send private message
thirumalaichettiar
Silver Sponsor
Silver Sponsor


Joined: 26 Jan 2003
Posts: 3459

PostPosted: Wed Apr 06, 2011 10:44 am    Post subject: Reply with quote

Seismic design- column joint was posted in the link below.


http://www.sefindia.org/forum/viewtopic.php?t=8852

T.RangaRajan.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topicReply to topic Thank Post    www.sefindia.org Forum Index -> SEFI General Discussion All times are GMT
Goto page Previous  1, 2, 3, 4 ... 42, 43, 44  Next
Page 3 of 44

 

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


© 2003, 2008 SEFINDIA, Indian Domain Registration
Publishing or acceptance of an advertisement is neither a guarantee nor endorsement of the advertiser's product or service. advertisement policy