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.

Flat Slab
Goto page Previous  1, 2
 
Post new topicReply to topic Thank Post    www.sefindia.org Forum Index -> SEFI General Discussion
View previous topic :: View next topic  
Author Message
vikram.jeet
General Sponsor
General Sponsor


Joined: 26 Jan 2003
Posts: 2212

PostPosted: Fri Jul 09, 2010 5:04 am    Post subject: Flat Slab Reply with quote

Dear Er Rakesh Kumar,

In a building system comprising of frames with columns and Flat slabs ,
in absence of shear walls, may have to depend largely upon the
Edge columns with marginal beams in either directions for carrying
the lateral loading. Edge columns needs to be heavy and so be the
marginal beams incorporating ductility provisions.

The inner columns and ( Flat slab-columns strips) could be
designed for 25% EQ.

It may be also noted that carrying 100% EQ through column strips  
would be very difficult, if not impossible, but ductility requirements
which are very essential for structural safety during EQ
are difficult to meet within column- strips in a flat slab
system.The frames have to be OMRF due to difficulty in provision
of ductiility in ( Flat slab-column strips) and thus requiring higher seismic
coefficient.

May also see following posting by Er Madam Sangeeta for  
other possible solutions and advice.

best regards

vikramjeet




Now perhaps, it may be clearer why many members categorically mentioned, during the earlier discussions, unsuitability of Flat Slab system in high seismic zones as in many Architectural Projects, it is difficult to find suitable symmetric locations for Shear Walls, and for obvious reasons, column strips are not as good as old fashioned beams. In buildings with false ceiling, providding beams is a better option (in fact, many Architectural Projects have inverted beams and the slab top is filled up with light wt materials,before providing flooring)

regards
Sangeeta



Dear Vikram Sir,

Sir, then what would be the better idea, to provide shear wall or doing frame(seismic) analysis without shear wall. And sir, can we design shear wall as column, taking max load and max moments.

And do flat slab transfer successfully lateral loads to the column, as beam does?

Can we successfully analyse the structure with flat slab and shear wall using STAAD. if we need to reduce the earthquake loads on frames, say 25% and 75% on shear walls. In this case, can we generate the loads using staad, or we need to calculate the earthquale loads manually. Please anyone can explain.

thanking you sir

with regards
RAKESH KUMAR

--

Posted via Email
Back to top
View user's profile Send private message
prof.arc
...
...


Joined: 26 Jan 2003
Posts: 701

PostPosted: Sun Jul 11, 2010 3:07 pm    Post subject: Flat Slab Reply with quote

If the centre of mass and centre of rigidity are far apart, there will be torsional forces exerted on the system. A 3D modelling will automatically reflect this effect.the designer can then decide whether additional shear /infill walls be located to reduce this eccentricity between centre of mass & rigidity or change the design of lift wall so as to contribute negligible effect on stiffness [say a masonry infill not fully tied]
It is a good idea to have minimal torsion.


ARC

On Thu, Jul 8, 2010 at 5:53 AM, truenotesrakesh <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Sir,
Thanking you for the valuable advice. But if shear wall do not tend to the
integrity of the structure, in that case providing shear wall is of waste.
In my project the lift component, where we usually provide shear wall is at
the right edge(30 south east part) of the building, if it is a 30x40 plot.
30 south 40 east. Could the provision of shear wall will be sufficient in
this case. While as i have observed, positioning of sheae walls is not at
all considered as the mere importance, if structural intergrity is not with
shear wall, its provisions is utter waste. Shear walls has to be
symmetrical, centered, connected with the structure. Am i right sir?.
Am attaching my staad model, please guide me, do the shear wall at the lift
portion is sufficient. Am i doing the right kind of analysis?.
thanking you
with regards
RAKESH KUMARRAKESH KUMAR
TRUE NOTES
BUILDING DESIGN ENGINEER





Posted via Email
Back to top
View user's profile Send private message
Dr. N. Subramanian
General Sponsor
General Sponsor


Joined: 21 Feb 2008
Posts: 5172
Location: Gaithersburg, MD, U.S.A.

PostPosted: Mon Jul 12, 2010 2:49 pm    Post subject: Re: Flat Slab Reply with quote

Dear All,

I fully agree with Er Sangeeta's comments.

Some of you may be interested to read the report on SEISMIC VULNERABILITY OF FLAT-SLAB STRUCTURES at the link: http://mae.cee.uiuc.edu/documents/cd_rom_series/03-06/Report%2003-06.pdf

Best wishes
NS
sdec.in wrote:
Dear Er Rakesh

Now perhaps, it may be clearer why many members categorically mentioned, during the earlier discussions, unsuitability of Flat Slab system in high seismic zones as in many Architectural Projects, it is difficult to find suitable symmetric locations for Shear Walls, and for obvious reasons, column strips are not as good as old fashioned beams. In buildings with false ceiling, providding beams is a better option (in fact, many Architectural Projects have inverted beams and the slab top is filled up with light wt materials,before providing flooring)

regards
Sangeeta
Quote:
----- Original Message -----
From: vikram.jeet (forum@sefindia.org)
To: general@sefindia.org (general@sefindia.org)
Sent: Thursday, July 08, 2010 5:08 PM
Subject: [SEFI] Re: Flat Slab


Dear Er Rakesh Kumar ,

Yes , you are right. If shear walls are not favorably(symmetrically) located, the major
advantage of providing S/walls is lost as the lateral eccentricity i.e.distance between
centre of mass and centre of rigidity of structural system (with shear walls located at
one corner) would be quite high and structural system would be acted upon by the
torsions (in plan) (during EQ) ,thus offseting the the advantage.

best regards

vikramjeet
--







Posted via Email
Back to top
View user's profile Send private message
Dr. N. Subramanian
General Sponsor
General Sponsor


Joined: 21 Feb 2008
Posts: 5172
Location: Gaithersburg, MD, U.S.A.

PostPosted: Thu Jul 15, 2010 3:59 am    Post subject: Re: Flat Slab Reply with quote

Hi All,

I wish to inform you that an interesting article "Design of Flat-Plate Floors for Progressive Collapse Using Yield-Line Analysis" has appeared in the July 2010 issue of Concrete International, ACI. The abstract is given below:

A practical method of progressive collapse analysis of reinforced concrete flat-plate buildings using yield-line method is suggested. Methods for calculation of punching shear and evaluation of inelastic deformations are proposed and illustrated using a building example. The outlined procedure allows the designer to evaluate the resistance of flat-plate structures to progressive collapse, using tools already available in most design offices. The proposed method also allows the designer to clearly identify places where additional reinforcing will effectively increase building robustness, thereby reducing the total use of material and labor in field.

Interested engineers may refer CI for the full paper.

Best wishes
NS
Back to top
View user's profile Send private message
Rajesh.M
SEFI Regulars
SEFI Regulars


Joined: 21 Aug 2010
Posts: 25
Location: Pune, Mumbai, Chennai

PostPosted: Sat Aug 21, 2010 11:44 am    Post subject: Reply with quote

Unfortunately 'Flat Slabs Under Lateral Loads' is a Topic missing in any Indian Codes though Flat Slabs are adapted in numerous Commercial Buildings.

Flat Slabs are to be Designed as Rigid Diaphragms transferring the Lateral Thrust to the Corewalls and other lateral load resisting members. This would not be a problem considering the Infinite Stiffness of the Slab in the Lateral Direction.
Detailing wise, the Cutouts in the Slabs should be located such that they dont affect the Diaphragm action of the Slab. Cutouts shall be preferably enclosed by Beams stiffening them laterally.
Also the junction of Slabs and Shear should be detailed such that the Slab does not Pull out due to the Difference in Stiffness in the members. (Along the Axis of the Shearwall.)

Please Comment!
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
Page 2 of 2

 

 
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