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.

Pointed discussions on tall buildings - Use of Flat Slab -co
Goto page Previous  1, 2, 3
 
This forum is locked: you cannot post, reply to, or edit topics.This topic is locked: you cannot edit posts or make replies. Thank Post    www.sefindia.org Forum Index -> E-Conference on Tall Buildings
View previous topic :: View next topic  
Author Message
gautam chattopadhyay
...
...


Joined: 17 Feb 2009
Posts: 128

PostPosted: Sun Nov 25, 2012 5:26 am    Post subject: Pointed discussions on tall buildings - Use of Flat Slab -co Reply with quote

RCC shear walls can be assumed analogous to braced towers in industrial buildings in structural steel. Those who are conversant with design of industrial buildings in steel can remember the usual practice of assuming that braced towers resist the entire horizontal thrust due to wind and crane sugre. However in case of industrial buildings we provide wind girders to stiffen the cladding stanchions subjected to transverse wind.

I feel in a shear model, if we consider stiffness of shear walls along with those of the columns occuring in respective floors, center of stiffness may be a more eccentric from center of mass causing more torsion at floor but the analysis will be realistic enough. The assumption that shear wall does not carry vertical load is not correct since it is not compatible with practice. Shear walls are active to both vertical and horizontal forces but because of high stiffness as compared to the columns occuring along with it absorbs more horizontal thrust than the columns. Shear wall is nothing but a very wide column.


On Thu, Nov 22, 2012 at 1:06 PM, SANGEETA WIJ <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Alpa
I had raised a query a few weeks ago to ask the following:
whether there is a rule as to what % of tower columns must go to the basement raft level(hypothetically, the architect wants all tower columns to be supported only on transfer girders, letís take a typical tower of G+20 and three basements which are full plot size). How does the overall tower stability get affected in such a case, especially in zone-IV EQ?
What are the guidelines for Seismic separation/Expansion joints in such large basements(say itís a 100 acre plot with 20 scattered towers).Do we or do we not give joints in the non-tower basement structure? If yes, then at what spacing? (chances are, that each part of basement may carry more than one tower, making it a very complex modelling challenge)
When does the wind tunnel test become mandatory, between two adjacent high rise blocks?

Regards
Sangeeta Wij

From: shekhar at shekharpana... [mailto:forum@sefindia.org (forum@sefindia.org)]
Sent: 21 November 2012 10:36
To: econf34289@sefindia.org (econf34289@sefindia.org)
Subject: [E-CONF] Re: Pointed discussions on tall buildings - Use of Flat Slab -co




Lets get going....

The three basic framing systems to resist lateral loads in high-rise buildings are: (1) Frames, (2)shear walls coupled or acting individually and (3) frames interacting with shear walls.
As an economical form of construction a shear wall structure incorporating a flat plate system is almost ideal.The flat plate system is very efficient in resisting gravity loading while the shear wall provides the resistance to lateral loads.

- Shekhar Panandiker

Please reply on our new id:
shekhar@shekharpanandiker.com (shekhar@shekharpanandiker.com) (shekhar@shekharpanandiker.com (shekhar@shekharpanandiker.com)) (shekhar@shekharpanandiker.com (shekhar@shekharpanandiker.com) (shekhar@shekharpanandiker.com (shekhar@shekharpanandiker.com))) OR
info@shekharpanandiker.com (info@shekharpanandiker.com) (info@shekharpanandiker.com (info@shekharpanandiker.com)) (info@shekharpanandiker.com (info@shekharpanandiker.com) (info@shekharpanandiker.com (info@shekharpanandiker.com)))

SHEKHAR PANANDIKER & ASSOCIATES,
Consulting Structural Engineers & Architects,
Wing A, second Floor, Hiraniketan,
Margao - Goa 403601

Tel: +91-832-2738399, 2705947
Fax: +91-832-2705947

Visit us at: www.shekharpanandiker.com
--auto removed--
     



     
Download Attachments:

~WRD395.jpg





Posted via Email
Back to top
View user's profile Send private message
rejizac
SEFI Member
SEFI Member


Joined: 20 May 2011
Posts: 4

PostPosted: Sun Nov 25, 2012 1:44 pm    Post subject: Pointed discussions on tall buildings - Use of Flat Slab -co Reply with quote

SirThe structural system should be able to withstand the forces acting on that. As the height goes up the strength of the members also should increase. If this system works for 15m, it can work for 50, or 500m. Hence we don't have to restrict the use of flat slab and core for this upto any height or for any zones. There may be better models but if somebody wants the advantage of this system let them have it.Reji Zachariah- from Vodafone
From: "prof.arc" <forum@sefindia.org>
Date: Thu, 22 Nov 2012 12:32:17 +0530
To: <econf34289@sefindia.org>
ReplyTo: econf34289@sefindia.org
Subject: [E-CONF] Re: Pointed discussions on tall buildings - Use of Flat Slab -co

     I had seen some MS-Buildings having flat slabs only and apparently no core shear walls except for lift well I could not get an answer regarding modelling such systems except a vague statement that commercial software was used I wonder whether modelling columns as 3D beam elements and the flat slab as some sort of FEM elements or even equivalent beam is appropriate I hope some engineers of this forum who might have modelled such flat slab system - without beams - would come forward to share their thoughts  ARC  On 11/20/12, Econf_Moderator  wrote:        --auto removed--

Posted via Email
Back to top
View user's profile Send private message
swamikrishnan
E-Conference Moderator


Joined: 28 Jul 2011
Posts: 18

PostPosted: Tue Nov 27, 2012 1:32 am    Post subject: Re: Pointed discussions on tall buildings - Use of Flat Slab Reply with quote

I would like to follow up on Er. Sangeeta's 2 questions and
Er. Ranjith's response to her second question.  I am actually not sure
that this topic belongs to this thread [two notes to all participants:
(i) please start a new thread if the content of your post does not
fall under topics being discussed in existing threads; (ii) likewise,
before starting a new thread, please ensure that there is no thread
already existing on the topic of your intended posting], nevertheless,
I am going to continue the discussion here so as to maintain
continuity.

(a) Er. Sangeeta's question on the percentage of columns that can be
transferred without being carried down to the foundation and its
effects on the stability during an earthquake event:

I don't believe there is a golden rule on this.  In general, the more
the number of column transfers, the less robust will the structure's
ability to resist ground motion be.  One can design the transfer
girders to remain elastic under design level earthquake ground motion.
However, when and if design ground shaking is exceeded (and this
happens more often than one might imagine), there is great risk of
gravity-driven progressive collapse of the tower; especially because
the transfers you are referring to occur at the very bottom, with the
columns carrying gravity loads of several tens of stories.  I would
say that if you are transferring more than any every alternate tower
column, you are a bold engineer indeed Smile Of course, this depends on
several other factors such as the spacing of the tower columns, the
loads that they are carrying, whether the columns being transferred
are part of the lateral force-resisting system or are they gravity
columns, is there a shear wall core that is being carried all the way
down to the foundation, etc.  A clear, continuous, and "natural" load
path (for both gravity and lateral forces) is a critical
distinguishing factor between good and poor seismic performance.  It
is important to work with the Architect at the very outset (in the
schematic design phase) to establish the gravity/lateral load path,
i.e., column/wall locations, etc. over the height of the tower and
into the basements, in order to realize aesthetic/functional
architecture and robust engineering harmoniously.  This is especially
true in the case of tall buildings, where the structure is such a big
part of the architecture.

(b) Er. Sangeeta's question on the provision of seismic joints in
large basements that carry several towers within their footprint and
the complications associated with modeling the towers-basement system
if joints are not provided: I will address Er. Sangeeta's question and
Er. Ranjith's response separately, as I am not sure that they are
referring to the same issue.

Response to Er. Sangeeta: I would engage as much of the structure as
possible wherever and whenever I can get it, i.e., go with no seismic
joints, engage the entire basement (with its long retaining walls),
provide a sturdy diaphragm slab with collector elements (where
needed).  You will need to specify pour strips around each tower to
allow for the tower short-term deflections under gravity. You should
also compute long-term tower column/wall shortening due to creep and
design the slabs for the moments induced by the differential
settlement between the tower and the basement.  As far as modeling is
concerned, you would not be way off the mark if you have separate
fixed base models for the towers, and one combined basement model to
design the diaphragm, collectors, and the retaining walls (for lateral
loading).

Er. Ranjith's response about towers with podiums: I have an alternate
view.  As I noted previously, I would want to engage as much of the
structure (in plan) as possible so as to cut the free height of the
tower (and lower its slenderness, from both wind and earthquake
loading perspectives).  I would generally not provide a seismic
joint between the tower and the podium; instead work with the
Architect to provide allowance for additional lateral force-resisting
elements in the podium outside the footprint of the tower; and use
pour strips to minimize the differential settlement by allowing for
the free short-term settlement of the tower under gravity loading;
would still have to design for the effects of long-term axial
shortening of columns due to creep.

Swaminathan Krishnan
California Institute of Technology
http://krishnan.caltech.edu


[quote="Ranjith.Chandunni"]Dear SEFIans,

To answer the query regarding movement joints raised by Sangeeta, I would like to add the following:

Ideally itís the best practice to separate the structures of tower from podium with movement joints simplifying the complexities of interaction between the two structures and simplifying differential settlement issues. However this is easily said than done in the real practice owing to having inadequate stability system for podium and having to deal with too many joints which often becomes an expensive affair. A practical option would be to have at least one movement between two towers on same podium with part of podium attached to each towers. How big that part of podium should be is left to the judgement of the engineer giving due consideration to size of podium part, plan geometry, number floors and temperature effects.

Continuing the joints through the foundation is not required for obvious reason that there is hardly any relative horizontal movement at foundation level however due care should be given to shrinkage and temperature effect by design and by carefully planning concrete pouring sequence. One has to also consider differential settlement issues on raft between tower and podium.

Whether to start the movement joint at first basement level or above ground level is a question which needs some careful consideration. From practical perspective its good not to have joints in basement or even ground level slab which to a large extent can be engineered by providing post pour strips. However, what about the interaction of one tower on the other under dynamic lateral loads and whatís its effect on a continuous floor of basement/podium if no joints are present? A complex issue to analyse and trying to model this effects with FEM could be highly challenging. Itís important to understand the real effect of interaction between the two towers, the magnitude and nature of the influence and itís quite possible that real nature of influence can get lost in a complex modelling.

A simplified approach would be to adopt stick modelling techniques appropriately representing mass and stiffness properties of towers and podium in stick models. In order to understand the behaviour under seismic loading, a time history analysis is required to be carried out. To understand behaviour under wind loading, information about along wind and across wind dynamic components of wind loads is required which can only be obtained from wind tunnel studies. Many of these dynamic effects act out of phase on the structure at times. Are these data available in the first place?

One has to decide to what extent one is willing to go analysing these effects in order to minimise or eliminate movement joints. Is such an approach necessary for the project. Donít be surprised to find some really high in plane forces being developed in the floors if towers get connected at basement or podium levels. The behaviour can get complicated if openings are present which is common due to ramps, stairs, atriums etc.

Other than the raft, one can possibly eliminate the movement joints in basement walls provided shrinkage and temperature effects are taken care of besides the interaction effects from the tower/podium structures. The interaction effects are substantially minimal on basement walls even if movement joints are present in the floors and if the basement walls are not very close to the main cores of the tower.

Regards,

Ranjith Chandunni
Buro Happold



From: SANGEETA WIJ [mailto:forum@sefindia.org]
Sent: 22 November 2012 13:07
To: econf34289@sefindia.org
Subject: [E-CONF] Re: Pointed discussions on tall buildings - Use of Flat Slab -co



Dear Alpa
I had raised a query a few weeks ago to ask the following:
∑ whether there is a rule as to what % of tower columns must go to the basement raft level(hypothetically, the architect wants all tower columns to be supported only on transfer girders, letís take a typical tower of G+20 and three basements which are full plot size). How does the overall tower stability get affected in such a case, especially in zone-IV EQ?
∑ What are the guidelines for Seismic separation/Expansion joints in such large basements(say itís a 100 acre plot with 20 scattered towers).Do we or do we not give joints in the non-tower basement structure? If yes, then at what spacing? (chances are, that each part of basement may carry more than one tower, making it a very complex modelling challenge)
∑ When does the wind tunnel test become mandatory, between two adjacent high rise blocks?

Regards
Sangeeta Wij


Back to top
View user's profile Send private message Visit poster's website
bijay sarkar
...
...


Joined: 14 Dec 2009
Posts: 314

PostPosted: Tue Nov 27, 2012 5:16 am    Post subject: Reply with quote

Dear Sir,

Your vivid reply cleared many doubts about "podium slab with towers".

Please talk more about the torsional effects due to multi towers on the podium slab & below structures.


with regards,

bijay sarkar
Back to top
View user's profile Send private message
dipakdgaikwad
...
...


Joined: 01 Apr 2008
Posts: 77
Location: Mumbai

PostPosted: Wed Nov 28, 2012 3:20 pm    Post subject: Re: Pointed discussions on tall buildings - Use of Flat Slab Reply with quote

Dear Sir,<xml><o></o>
In your reply you said,<o></o>
Er. Ranjith's response about towers with podiums: I have an alternate


view.  As I noted previously, I would want to engage as much of the
structure (in plan) as possible so as to cut the free height of the
tower (and lower its slenderness, from both wind and earthquake
loading perspectives).  I would generally not provide a seismic
joint between the tower and the podium; instead work with the
Architect to provide allowance for additional lateral force-resisting
elements in the podium outside the footprint of the tower; and use
pour strips to minimize the differential settlement by allowing for
the free short-term settlement of the tower under gravity loading;
would still have to design for the effects of long-term axial
shortening of columns due to creep.
<o></o>
<o> </o>
            But if we donít provide seismic separation joint between podium(with additional lateral force-resisting elements) and Tower, difference between the stiffness of combined structure (Tower + Podium) and Tower alone above podium level will be very high. This sudden change in stiffness will make the tower story just above podium a SOFT STORY.
<o></o>
<o> </o>
            Correct me if I am wrong!<o></o>
<o> </o>
Thanks and Regards<o></o>
Dipak D Gaikwad
<o></o>



[quote="swamikrishnan"]I would like to follow up on Er. Sangeeta's 2 questions and
Er. Ranjith's response to her second question.  I am actually not sure
that this topic belongs to this thread [two notes to all participants:
(i) please start a new thread if the content of your post does not
fall under topics being discussed in existing threads; (ii) likewise,
before starting a new thread, please ensure that there is no thread
already existing on the topic of your intended posting], nevertheless,
I am going to continue the discussion here so as to maintain
continuity.

(a) Er. Sangeeta's question on the percentage of columns that can be
transferred without being carried down to the foundation and its
effects on the stability during an earthquake event:

I don't believe there is a golden rule on this.  In general, the more
the number of column transfers, the less robust will the structure's
ability to resist ground motion be.  One can design the transfer
girders to remain elastic under design level earthquake ground motion.
However, when and if design ground shaking is exceeded (and this
happens more often than one might imagine), there is great risk of
gravity-driven progressive collapse of the tower; especially because
the transfers you are referring to occur at the very bottom, with the
columns carrying gravity loads of several tens of stories.  I would
say that if you are transferring more than any every alternate tower
column, you are a bold engineer indeed Smile Of course, this depends on
several other factors such as the spacing of the tower columns, the
loads that they are carrying, whether the columns being transferred
are part of the lateral force-resisting system or are they gravity
columns, is there a shear wall core that is being carried all the way
down to the foundation, etc.  A clear, continuous, and "natural" load
path (for both gravity and lateral forces) is a critical
distinguishing factor between good and poor seismic performance.  It
is important to work with the Architect at the very outset (in the
schematic design phase) to establish the gravity/lateral load path,
i.e., column/wall locations, etc. over the height of the tower and
into the basements, in order to realize aesthetic/functional
architecture and robust engineering harmoniously.  This is especially
true in the case of tall buildings, where the structure is such a big
part of the architecture.

(b) Er. Sangeeta's question on the provision of seismic joints in
large basements that carry several towers within their footprint and
the complications associated with modeling the towers-basement system
if joints are not provided: I will address Er. Sangeeta's question and
Er. Ranjith's response separately, as I am not sure that they are
referring to the same issue.

Response to Er. Sangeeta: I would engage as much of the structure as
possible wherever and whenever I can get it, i.e., go with no seismic
joints, engage the entire basement (with its long retaining walls),
provide a sturdy diaphragm slab with collector elements (where
needed).  You will need to specify pour strips around each tower to
allow for the tower short-term deflections under gravity. You should
also compute long-term tower column/wall shortening due to creep and
design the slabs for the moments induced by the differential
settlement between the tower and the basement.  As far as modeling is
concerned, you would not be way off the mark if you have separate
fixed base models for the towers, and one combined basement model to
design the diaphragm, collectors, and the retaining walls (for lateral
loading).

Er. Ranjith's response about towers with podiums: I have an alternate
view.  As I noted previously, I would want to engage as much of the
structure (in plan) as possible so as to cut the free height of the
tower (and lower its slenderness, from both wind and earthquake
loading perspectives).  I would generally not provide a seismic
joint between the tower and the podium; instead work with the
Architect to provide allowance for additional lateral force-resisting
elements in the podium outside the footprint of the tower; and use
pour strips to minimize the differential settlement by allowing for
the free short-term settlement of the tower under gravity loading;
would still have to design for the effects of long-term axial
shortening of columns due to creep.

Swaminathan Krishnan
California Institute of Technology
http://krishnan.caltech.edu


Ranjith.Chandunni wrote:
Dear SEFIans,

To answer the query regarding movement joints raised by Sangeeta, I would like to add the following:

Ideally itís the best practice to separate the structures of tower from podium with movement joints simplifying the complexities of interaction between the two structures and simplifying differential settlement issues. However this is easily said than done in the real practice owing to having inadequate stability system for podium and having to deal with too many joints which often becomes an expensive affair. A practical option would be to have at least one movement between two towers on same podium with part of podium attached to each towers. How big that part of podium should be is left to the judgement of the engineer giving due consideration to size of podium part, plan geometry, number floors and temperature effects.

Continuing the joints through the foundation is not required for obvious reason that there is hardly any relative horizontal movement at foundation level however due care should be given to shrinkage and temperature effect by design and by carefully planning concrete pouring sequence. One has to also consider differential settlement issues on raft between tower and podium.

Whether to start the movement joint at first basement level or above ground level is a question which needs some careful consideration. From practical perspective its good not to have joints in basement or even ground level slab which to a large extent can be engineered by providing post pour strips. However, what about the interaction of one tower on the other under dynamic lateral loads and whatís its effect on a continuous floor of basement/podium if no joints are present? A complex issue to analyse and trying to model this effects with FEM could be highly challenging. Itís important to understand the real effect of interaction between the two towers, the magnitude and nature of the influence and itís quite possible that real nature of influence can get lost in a complex modelling.

A simplified approach would be to adopt stick modelling techniques appropriately representing mass and stiffness properties of towers and podium in stick models. In order to understand the behaviour under seismic loading, a time history analysis is required to be carried out. To understand behaviour under wind loading, information about along wind and across wind dynamic components of wind loads is required which can only be obtained from wind tunnel studies. Many of these dynamic effects act out of phase on the structure at times. Are these data available in the first place?

One has to decide to what extent one is willing to go analysing these effects in order to minimise or eliminate movement joints. Is such an approach necessary for the project. Donít be surprised to find some really high in plane forces being developed in the floors if towers get connected at basement or podium levels. The behaviour can get complicated if openings are present which is common due to ramps, stairs, atriums etc.

Other than the raft, one can possibly eliminate the movement joints in basement walls provided shrinkage and temperature effects are taken care of besides the interaction effects from the tower/podium structures. The interaction effects are substantially minimal on basement walls even if movement joints are present in the floors and if the basement walls are not very close to the main cores of the tower.

Regards,

Ranjith Chandunni
Buro Happold



From: SANGEETA WIJ [mailto:forum@sefindia.org]
Sent: 22 November 2012 13:07
To: econf34289@sefindia.org
Subject: [E-CONF] Re: Pointed discussions on tall buildings - Use of Flat Slab -co



Dear Alpa
I had raised a query a few weeks ago to ask the following:
∑ whether there is a rule as to what % of tower columns must go to the basement raft level(hypothetically, the architect wants all tower columns to be supported only on transfer girders, letís take a typical tower of G+20 and three basements which are full plot size). How does the overall tower stability get affected in such a case, especially in zone-IV EQ?
∑ What are the guidelines for Seismic separation/Expansion joints in such large basements(say itís a 100 acre plot with 20 scattered towers).Do we or do we not give joints in the non-tower basement structure? If yes, then at what spacing? (chances are, that each part of basement may carry more than one tower, making it a very complex modelling challenge)
∑ When does the wind tunnel test become mandatory, between two adjacent high rise blocks?

Regards
Sangeeta Wij


Back to top
View user's profile Send private message
swamikrishnan
E-Conference Moderator


Joined: 28 Jul 2011
Posts: 18

PostPosted: Wed Nov 28, 2012 7:34 pm    Post subject: Re: Pointed discussions on tall buildings - Use of Flat Slab Reply with quote

Dear Er. Dipak,

Soft story is defined as "one in which the lateral stiffness is less than 70% of that in the story ABOVE or less than 80% of the average stiffness of the three stories ABOVE".  Ref: UBC.  It has been defined this way, because having a soft story such as this will tend to localize much of the deformation demand in this story, resulting in heavy localized damage in this story.  You want to distribute the damage (if any) over as many stories as possible, not localize it in a single story, in order to minimize the risk of gravity-driven (P-Delta) collapse.

Stories below can be much stiffer, so the podium below being much stiffer is not an issue.

Swaminathan Krishnan
California Institute of Technology

[quote="dipakdgaikwad"]Dear Sir,<xml><o></o>
In your reply you said,<o></o>
Er. Ranjith's response about towers with podiums: I have an alternate


view.  As I noted previously, I would want to engage as much of the
structure (in plan) as possible so as to cut the free height of the
tower (and lower its slenderness, from both wind and earthquake
loading perspectives).  I would generally not provide a seismic
joint between the tower and the podium; instead work with the
Architect to provide allowance for additional lateral force-resisting
elements in the podium outside the footprint of the tower; and use
pour strips to minimize the differential settlement by allowing for
the free short-term settlement of the tower under gravity loading;
would still have to design for the effects of long-term axial
shortening of columns due to creep.
<o></o>
<o> </o>
            But if we donít provide seismic separation joint between podium(with additional lateral force-resisting elements) and Tower, difference between the stiffness of combined structure (Tower + Podium) and Tower alone above podium level will be very high. This sudden change in stiffness will make the tower story just above podium a SOFT STORY.
<o></o>
<o> </o>
            Correct me if I am wrong!<o></o>
<o> </o>
Thanks and Regards<o></o>
Dipak D Gaikwad
<o></o>
Back to top
View user's profile Send private message Visit poster's website
kapildingare
...
...


Joined: 15 May 2009
Posts: 104

PostPosted: Thu Nov 29, 2012 8:16 am    Post subject: Reply with quote

Resp Swaminathanji,

                            Many many thanks ,for explanation with respect to joint between podium slab and tower frame and specially for soft storey (ABOVE)

                            Kapil Dingare
Back to top
View user's profile Send private message
pradeep joshiaaa
SEFI Member
SEFI Member


Joined: 13 Jul 2010
Posts: 13

PostPosted: Tue Dec 04, 2012 4:38 am    Post subject: Pointed discussions on tall buildings - Use of Flat Slab -co Reply with quote

My suggestion in use of flat plate/ flat slab with drop with primary load resisting vertical members in high seismic zone ( zone 4/5) is vulnerable till our knowledge of anticipation of dynamic behavior of 

structure with very due regard to soil also is not amplified to extent of no damage .   


outline of behavioral pattern needed to be understand and incorporated in design for perfect working in ductile manner of FLAT SLAB/ FLAT PLATE.


1. PUNCHING RATIO


2. R/F METHODOLGY


3. USE OF INTERGRITY R/F DETAILING PRACTICE


4. DRIFT CONTROL


5. FLAT SLAB/ PLATE AND SHEAR WALL/ COLUMN JUNCTION INTERACTIONS.


6. STRUCTURAL ANALYSIS METHODOLOGY ADOPTED FOR PREDICTING ACCURATE BEHAVIOUR OF FLAT SLAB/PLATE WITH REST OF STRUCTURE.


7. DEFLECTION ( LONG TERM / SHORT TERM) AND CRACK PATTERN.


8. USE OF STUD R/F


9. INTERIOR/ EXTERIOR CONNECTION 


10. SOIL STRUCTURE INTERACTION WITH SHEAR WALL/ COLUMN AND IMPACT ON FLAT SLAB/ PLATE DESIGN.


11. DUCTILITY AND ENERGY ABORPTION


12. ROTATION BEHAVIOUR AT FLAT SLAB /PLATE AT JUNCTIONS




(A) Acc to ACI - ASCE committe 352 recommendation - Type 2 slab column connection must posses sustained strength under moderate deformations into elastic range, including connections subjected


 to load reversals. All type 2 connections which have no shear reinforcement the max shear stress caused by Vu acting on the connection in conjuction with inelastic moment transfer should not exceed


¬†0.4. of the value Vn = Vc=0.33¬†‚ąöfc.In order to achieve adequate ductility and lateral drift capacity.


(B) Structural force resisting element should be combined with flat plates/slab in order to limit the inelastic storey drift ratio to 1.5%, consequently it is required that slab column connections will


 withstand at least a 1.5% inter storey drift ratio without punching shear failure. 


(C) Modelling methodology - :  Develop a flat slab member model which include the torsional shear transfer of the unbalanced moment in contrast with the proposed effective slab width model which only 


accounts for flexural transfer , possibility of punching shear failure can be satisfactorially predicted from unbalanced moment output from an inelastic static pushover analysis.




Past , Present & Future.


We have many failure buildings from past record  stating that particular system ( especially flat slab/plate is biggest culprit known so far ) is vulnerable in dynamic load , but my assement in this situation


is that do not comment on failure of a particular framing system till you incorporate all required details for it's smooth functioning, Detailing , lack of structural understanding behavior of flat plate/slab in


 seismic zones and last not the least execution ( i feel a good design is weak till it is properly executed with perfection , if you see all past monuments around DELHI/ NCR region they should have fallen 


till now because they lack P-delta concept and attract a lot of torsion but they have withstand centuries just because they were executed with 100% satisfaction). many building with flat plate/slab even


 with shear walls failed why again loaction of shear walls were ampilfying torsion which flat slab could not digest.


At present many highrise tower residential as well as commercial are standing tall in U.S.A. , JAPAN , CHINA, 


Future expect better performance of structural systems developed by structural engineers only.




Regard's


PRADEEP JOSHI


pradeepjoshiaaa@gmail.com (pradeepjoshiaaa@gmail.com)


PH- 09968369045.






 




 
     

Posted via Email
Back to top
View user's profile Send private message
Display posts from previous:   
This forum is locked: you cannot post, reply to, or edit topics.This topic is locked: you cannot edit posts or make replies. Thank Post    www.sefindia.org Forum Index -> E-Conference on Tall Buildings All times are GMT
Goto page Previous  1, 2, 3
Page 3 of 3

 

 
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