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Pointed discussions on tall buildings - Use of Flat Slab -co

 
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pradeep joshiaaa
SEFI Member
SEFI Member


Joined: 13 Jul 2010
Posts: 13

PostPosted: Tue Dec 04, 2012 4:49 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 √fc.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.

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