Experimental and Analytical Studies on Post Punching Behavior of RC Flat Slabs:Experimental and Analytical Studies on Post‐Punching Behavior of RC Flat Slabs:Experimental and Analytical Studies on Post Punching Behavior of RC Flat Slabs: p y gL l F il d P i C ll A l i f SLocal Failure and Progressive Collapse Analysis of StructuresLocal Failure and Progressive Collapse Analysis of StructuresLocal Failure and Progressive Collapse Analysis of Structures

Yaser Mirzaei and Mehrdad Sasani (y mirzaei@neu edu and sasani@neu edu)Yaser Mirzaei and Mehrdad Sasani (y mirzaei@neu edu and sasani@neu edu)Yaser Mirzaei and Mehrdad Sasani (y.mirzaei@neu.edu and sasani@neu.edu)(y )f l d l hDepartment of Civil and Environmental Engineering Northeastern University Boston MADepartment of Civil and Environmental Engineering, Northeastern University, Boston, MA p g g y

b h l d lAbstract Mechanical Model•Tensile reinforcement contribution is not significant because ofAbstract Mechanical Model•Tensile reinforcement contribution is not significant because of concrete spalling and possible anchorage problemsColumn failure due to an explosion, impact, or other accidental • A generic procedure was developed capable of predicting theconcrete spalling and possible anchorage problemsColumn failure due to an explosion, impact, or other accidental 

t t i th t t th h hi hA generic procedure was developed capable of predicting the 

b h i f ll ibl h i• Integrity reinforcement and bent‐up bars providesevents can propagate in the structure through punching shear  behavior of all possible mechanismsIntegrity reinforcement and bent up bars provides id bl t hi i t

p p g g p gfailure at the location of the neighboring columns leading to

p• Concept of concrete breakout strength maximum concreteconsiderable post‐punching resistancefailure at the location of the neighboring columns, leading to  • Concept of concrete breakout strength, maximum concrete p p g

• Hot rolled steel is strongly recommended for integrityprogressive collapse Using a mechanical model previously breakout strength spalling strength of concrete cover and• Hot‐rolled steel is strongly recommended for integrity progressive collapse. Using a mechanical model previously  breakout strength, spalling strength of concrete cover, and reinforcement to provide large deformation capacity

) l d bdeveloped by Mirzaei, an analytical model is developed to be strain‐based failure criterion in post‐punching were introducedreinforcement  to provide large deformation capacity 

a) Various critical zones due to interaction between concrete developed by Mirzaei, an analytical model is developed to be 

d i fi it l t d l f fl t l t / l b t t tstrain based failure criterion in post punching were introducedV i h d t id b th th )

d i f i b d b) iti l f t b k tused in finite element models of flat plate/slab structures to  • Various approaches were proposed to consider both the 

and reinforcing bars and b) critical zone of concrete breakout p

estimate the initiation of punching shear failure as well as postpp p p

elastic and the plastic behavior of reinforcing bars crossing theover integrity reinforcement

estimate the initiation of punching shear failure as well as post‐ elastic and the plastic behavior of reinforcing bars crossing the over integrity reinforcementpunching shear response using ABAQUS The mechanical model punching conepunching shear response using ABAQUS. The mechanical model 

d d h h l f h l lpunching cone

is used to determine the mechanical properties of the analytical p p yd l f th ti hi h i b t i id fmodel of the connection zone, which is between a rigid zone of 

slab directly above the column and the rest of the slab Theslab directly above the column and the rest of the slab. The model of the connection zone simulates the contribution of themodel of the connection zone simulates the contribution of the i f i b h h f f hi hreinforcing bars to the shear transfer after a punching shear g p g

failure The analytical model and the results of system levelfailure. The analytical model and the results of system level study can be of interest in assessing progressive collapsestudy can be of interest in assessing progressive collapse resistance of existing structures and in design of new structures. I t it i f t T il i f tresistance of existing structures and in design of new structures.

Load deflection response of all test specimensIntegrity reinforcement Tensile reinforcement

Load‐deflection response of all test specimensg y

C i f th ti l d i t l ltB k d

232Øi (1 )INV N f

Comparison of theoretical and experimental resultBackground 2

, 2sin (1 )cos3

IM i I M sy MV N f

L N

p p

b) S L l RBackground 3 y

yL N

b) System‐Level Responseg

O J 25 1971 t thi d f 16 t t t b) S t L l R23Ø N b) System‐Level ResponseOn January 25, 1971, two thirds of a 16‐story apartment  b) System‐Level Response 22

Øsin (1 )cosID i I D sy D

NV N f ) y py y pbuilding collapsed at 2000 Commonwealth Avenue Boston

b) System‐Level Response , 2s ( ) cos3D i I D sy D

y

V N fL N

building collapsed at 2000 Commonwealth Avenue, Boston, 

) y py

m n

Massachusetts Four workers died after a failure on the roofm n

V V V V V Massachusetts. Four workers died after a failure on the roof  , ,pp M D M i D ii i

V V V V V instigated a progressive collapse all the way to the basement,  i iinstigated a progressive collapse all the way to the basement,h th f dwhere the men were found.

Research to RealityResearch to RealityResearch to RealityFollowing the Alfered P Murrah Federal Building attack in 1995Following the Alfered P. Murrah Federal Building attack in 1995 and the establishment of the Interagency Security Committeeand the establishment of the Interagency Security Committee (ISC) f d l f i d d f f d l(ISC) for development of construction standards for federal ( ) pbuildings subject to terrorist attack the General Servicesbuildings subject to terrorist attack, the General Services Administration (GSA) published guidelines for progressiveAdministration (GSA) published guidelines for progressive collapse analysis and design of structures. The outcomes of thiscollapse analysis and design of structures. The outcomes of this 

h li d ith t d t h hresearch are aligned with an urgent need to enhance such g gguidelines for punching shear in flat slab structures which can Response of an actual two‐story parking garage with flat slab Analytical model of the system level study of progressive collapseguidelines for punching shear in flat slab structures, which can  Response of an actual two‐story parking garage with flat slab  Analytical model of the system level study of progressive collapse be used to mitigate the likelihood of progressive collapse following column explosion is experimentally evaluated due to punching shear failurebe used to mitigate the likelihood of progressive collapse.  following column explosion is experimentally evaluated 

( d d d f ti h b l )due to punching shear failure 

E periments (recorded deformation shown below)Experiments ( )ExperimentsComparison of theoretical and experimental results

) l b h iComparison of theoretical and experimental results

a) Local behavior A l ti l Si l tia) Local behavior Analytical Simulation)l f l b h f

Analytical Simulation• A total of 24 slab specimens with various reinforcement 

) l b h ip

l t t t d t th EPFL S it l d a) Local behaviorlayouts were tested at the EPFL, Switzerland.  a) Local behavior• Effects of tensile reinforcement integrity reinforcement

)• Effects of tensile reinforcement, integrity reinforcement passing through the column bent‐up‐bars and anchorage Slab deflection right before (0 00228 m) and right after punchingpassing through the column, bent up bars, and anchorage d il i i d

Slab deflection right before (0.00228 m) and right after punching details were investigated.  shear failure of column B (0 00408 m)g shear failure of column B (0.00408 m)

ReferencesReferencesReferences[1] Sasani, M.; Bazan, M.; and Sagirogu, S., “Experimental and Analytical Progressive [ ] , ; , ; g g , , p y gCollapse Evaluation of an Actual Reinforced Concrete Structure,” ACI Structural Journal, V.Collapse Evaluation of an Actual Reinforced Concrete Structure,  ACI Structural Journal, V. 104 No 6 pp 731‐739 Nov ‐Dec 2007

a) Parking garage 1st Floor b) Parking garage 1st Floor104, No. 6, pp. 731‐739, Nov.‐Dec. 2007.[2] Mirzaei Y “Post punching behavior of reinforced concrete slabs” EPFL Thesis Noa) Parking garage 1st Floor 

l b f lb) Parking garage 1st Floor l f l

[2] Mirzaei Y.,  Post‐punching behavior of reinforced concrete slabs , EPFL Thesis No. 4613 230 L S it l d 2010column before explosion column after explosion 4613, pp. 230, Lausanne, Switzerland, 2010.p p[3] Muttoni A., “Punching shear strength of reinforced concrete slabs without transverse reinforcement”, ACI Structural Journal, V. 105, N° 4, pp. 440‐450, USA, July‐August, 2008.pp y g[4] Mirzaei Y., and Sasani, M, “Finite Element Modeling of Post‐Punching Behavior of

c) Vertical displacement of[4] Mirzaei Y., and Sasani, M,  Finite Element Modeling of Post Punching Behavior of Reinforced Concrete Flat Slab Structures ” IMPLAST 2010 Plasticity Impact andc) Vertical displacement of  Reinforced Concrete Flat Slab Structures,  IMPLAST 2010, Plasticity, Impact, andBlast Symposium Society for Experimental Mechanics Providence RI October 2010

flat slab following explosionBlast Symposium, Society for Experimental Mechanics, Providence, RI, October, 2010.

This material is based upon work supported by the U S Department of Homeland Security underflat slab following explosion 

This material is based upon work supported by the U.S. Department of Homeland Security under A d N b 2008 ST 061 ED0001 Th i d l i t i d i thi d tversus time Award Number 2008‐ST‐061‐ED0001. The views and conclusions contained in this document are versus time 

Geometry and mesh generation of the finite element model those of the authors and should not be interpreted as necessarily representing the official policies, Geometry and mesh generation of the finite element model ( ) either expressed or implied of the U.S. Department of Homeland Security.(simulation of the local post‐punching behavior)Test setup and typical slab plan section p p p y(simulation of the local post punching behavior)Test setup and typical slab plan section