Finite Element Modeling of Seismic Performance of Low Concrete ...
Transcript of Finite Element Modeling of Seismic Performance of Low Concrete ...
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Finite Element Modeling of SeismicPerformance of Low Concrete StrengthExterior Beam-Column Joints
D.Ahmed*, M.K. Rahman*, A.Ilki** and M.H. Baluch*
*King Fahd University of Petroleum & Minerals, Saudi Arabia
** Istanbul Technical University, Turkey
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PRESENTATION OUTLINE
• Introduction•Beam-Column Joint Test at ITU•Finite element modeling using DIANA•Results of Finite Element Analysis•Conclusions•Ongoing work at KFUPM
• Introduction•Beam-Column Joint Test at ITU•Finite element modeling using DIANA•Results of Finite Element Analysis•Conclusions•Ongoing work at KFUPM
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JOINT FAILURE IN BUILDINGS
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BACKGROUND• The Western Region of Saudi Arabia is located in
moderately active seismic zone with recent/historicalseismic events. Many RC buildings in this region werehitherto designed only for gravity loads using lowstrength concrete without any ductile detailing ofbeam-column joints [Alsayed et al]
• An experimental program was conducted at IstanbulTechnical University (ITU) on the behavior of exteriorbeam-column joints subjected to seismic loads. Thesejoints were made with very low strength concrete tosimulate the concrete used in reinforced concretestructures in Turkey prior to 1990’s. [Bedirhanoglu etal, A.Ilki et al]
• The Western Region of Saudi Arabia is located inmoderately active seismic zone with recent/historicalseismic events. Many RC buildings in this region werehitherto designed only for gravity loads using lowstrength concrete without any ductile detailing ofbeam-column joints [Alsayed et al]
• An experimental program was conducted at IstanbulTechnical University (ITU) on the behavior of exteriorbeam-column joints subjected to seismic loads. Thesejoints were made with very low strength concrete tosimulate the concrete used in reinforced concretestructures in Turkey prior to 1990’s. [Bedirhanoglu etal, A.Ilki et al]
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PRE-1990’S DETAILING OF BEAM-COLUMN JOINTS
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BEAM-COLUMN JOINT TEST AT ITU
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GEOMETRY AND REINFORCEMENTDETAILS OF ITU SPECIMEN
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GEOMETRY AND REINFORCEMENTDETAILS OF ITU SPECIMEN
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MATERIAL PROPERTIES
Mechanical properties of reinforcing bars:
Reinforcement
Dia(mm) Fy (Mpa) εy Fs max
(Mpa)
εsmax
Φ16 16 333 0.0017 470 0.2Φ8 8 315 0.0016 433 0.2Φ8 8 315 0.0016 433 0.2
Material properties of concrete:
f’c (Mpa) Ec (Mpa)
8.3 13000
f’c: low strength concrete
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SPECIMEN TESTED AT ITU
• Test specimens selected for F.E modeling areJW1 and JW2 which are with welded hooksand repaired joints with high strength mortar.
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TEST SETUP
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TEST RESULTS FOR JOINT JW2
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ENVELOPE FOR HYSTERESIS
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LOAD VS DISPLACEMENT DIAGRAMFOR JW2
50
60
70
80
90
100LOAD(KN)
0
10
20
30
40
50
0 10 20 30 40 50
LOAD(KN)
DISPLACEMENT(mm)
JW2
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JOINT FAILURE FOR JW2
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FINITE ELEMENT MODELING
• The commercial F.E software DIANA is usedwhich is well known for modeling concretestructures due to its wide range of concretematerial models and advanced numericaltools.
• The non-linear mechanisms that areconsidered in the modeling are cracking andcrushing of concrete and yielding ofreinforcement.
• The finite element model is two dimensionalconsisting of plane stress elements.
• The commercial F.E software DIANA is usedwhich is well known for modeling concretestructures due to its wide range of concretematerial models and advanced numericaltools.
• The non-linear mechanisms that areconsidered in the modeling are cracking andcrushing of concrete and yielding ofreinforcement.
• The finite element model is two dimensionalconsisting of plane stress elements.
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MATERIAL CONSTITUTIVE MODELS
• Concrete Plasticity :
• Concrete is modeled as elastic perfectlyplastic.
• Drucker-Prager yield criterion is used tomodel the stress level at which yieldingof concrete is initiated.
• The yield surface of Drucker-Pragermodel is a circular cone which can berelated to Mohr-Coulomb by expressingα and k in terms of c and φ.
• In Drucker-Prager plasticity model,associated plasticity is established bysetting φ = ψ.
• Concrete Plasticity :
• Concrete is modeled as elastic perfectlyplastic.
• Drucker-Prager yield criterion is used tomodel the stress level at which yieldingof concrete is initiated.
• The yield surface of Drucker-Pragermodel is a circular cone which can berelated to Mohr-Coulomb by expressingα and k in terms of c and φ.
• In Drucker-Prager plasticity model,associated plasticity is established bysetting φ = ψ.
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MATERIAL CONSTITUTIVE MODELS
• The cohesion is related to theconcrete strength through therelation given by
• For the normal strength qualityconcrete, the ratio between thebiaxial compressive strength anduniaxial compressive strength isapproximately 1:1.16 whichresults in a friction angleφ=10deg and cohesion c=0.42f’c
• The cohesion is related to theconcrete strength through therelation given by
• For the normal strength qualityconcrete, the ratio between thebiaxial compressive strength anduniaxial compressive strength isapproximately 1:1.16 whichresults in a friction angleφ=10deg and cohesion c=0.42f’c
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MATERIAL CONSTITUTIVE MODELS• Concrete cracking:
The cracking of theconcrete is specified as acombination of constanttension cut-off, lineartension softening and shearretention.
• Reinforcement:
For reinforcement Von-Mises-Plasticity with workhardening is used.
• Concrete cracking:
The cracking of theconcrete is specified as acombination of constanttension cut-off, lineartension softening and shearretention.
• Reinforcement:
For reinforcement Von-Mises-Plasticity with workhardening is used.
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2-D MODEL WITH REINFORCEMENT
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BOUNDARY CONDITIONS ANDLOADING DETAILS
• Top end of the columnsurface is constrained in Xand Y direction
• Bottom end of the columnis constrained in X axis andfree in Y direction due toupward axial pressure(0.125*f’c).
• Near the tip of beam pointis constrained in y directionbecause loading method isdisplacement controlwhich is 50mm
• Top end of the columnsurface is constrained in Xand Y direction
• Bottom end of the columnis constrained in X axis andfree in Y direction due toupward axial pressure(0.125*f’c).
• Near the tip of beam pointis constrained in y directionbecause loading method isdisplacement controlwhich is 50mm
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BOUNDARY CONDITIONS ANDLOADING DETAILS
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FINITE ELEMENT MESH
• The concrete is modeled byeight-noded quadrilateralisoparametric plane stresselement CQ16M.
• The mesh size of concreteelement is 50x50 (mm).
• Reinforcements are modeledas embedded reinforcement.
• The concrete is modeled byeight-noded quadrilateralisoparametric plane stresselement CQ16M.
• The mesh size of concreteelement is 50x50 (mm).
• Reinforcements are modeledas embedded reinforcement.
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MESH WITH REINFORCEMENT
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DIANA ANALYSIS
• DIANA needs two files to start the analysis
1. (.dat) file which contains material properties for concreteft=0.73Mpa at 28 days, c=2.15Mpa (calibrated to matchexperimental data), φ = ψ=10deg, beta=0.9 (smaller valueslead to premature curtailment of P-∆ curve), E=12000Mpaand steel (hardening diagram and modulus of elasticity) ,Nodal coordinates , Reinforcement coordinates, Boundaryconditions and Load cases.
2. (.com) file where we define the iteration method, step size(load step 0.050mm) and convergence criteria for analysis.
• DIANA needs two files to start the analysis
1. (.dat) file which contains material properties for concreteft=0.73Mpa at 28 days, c=2.15Mpa (calibrated to matchexperimental data), φ = ψ=10deg, beta=0.9 (smaller valueslead to premature curtailment of P-∆ curve), E=12000Mpaand steel (hardening diagram and modulus of elasticity) ,Nodal coordinates , Reinforcement coordinates, Boundaryconditions and Load cases.
2. (.com) file where we define the iteration method, step size(load step 0.050mm) and convergence criteria for analysis.
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FINITE ELEMENT ANALYSISRESULTS
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LOAD VS DISPLACEMENT DIAGRAMFOR JW2 AND DIANA MODEL
50
60
70
80
90
100
LOAD(KN)
0
10
20
30
40
50
0 20 40 60
LOAD(KN)
DISPLACEMENT(mm)
experiment
DIANA model
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STRESS IN STEEL SXX (BEAM)
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STRESSES IN CONCRETE SYY (COLUMN)
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STRESSES IN CONCRETE SXY
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CRACK PATTERNS
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CONCLUSIONS• The finite element simulation of the represented by the load-
deflection shows good agreement with the test data whichindicates that DIANA software with its 2-D plane stress model isable to capture the behavior of beam-column joint well.
• The crack patterns at various loads from the FE model correspondwell with the experimentally observed failure modes, stresses inthe beam, column and joints are in agreement.
• The finite element simulation of the represented by the load-deflection shows good agreement with the test data whichindicates that DIANA software with its 2-D plane stress model isable to capture the behavior of beam-column joint well.
• The crack patterns at various loads from the FE model correspondwell with the experimentally observed failure modes, stresses inthe beam, column and joints are in agreement.
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WORK IN PROGRESS AT KFUPM
• In a collaborative program presently underwaybetween Istanbul Technical university (ITU) andKing Fahd University of Petroleum and Minerals(KFUPM) an experimental program is beingconducted at KFUPM on the beam-column jointsused in old reinforced concrete buildings in SaudiArabia.
• Finite element simulation has been done for thestatic load test to capture the nonlinear behaviorof the joint.
• In a collaborative program presently underwaybetween Istanbul Technical university (ITU) andKing Fahd University of Petroleum and Minerals(KFUPM) an experimental program is beingconducted at KFUPM on the beam-column jointsused in old reinforced concrete buildings in SaudiArabia.
• Finite element simulation has been done for thestatic load test to capture the nonlinear behaviorof the joint.
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ACKNOWLEDGEMENT KFUPM
• The study is being funded by King FahdUniversity of Petroleum & Minerals underproject number RG1111-1 & RG1111-2 which isgratefully acknowledged.
• The authors acknowledge the mentoringprovided by ITU to the KFUPM graduatestudents involved in this project.
• The study is being funded by King FahdUniversity of Petroleum & Minerals underproject number RG1111-1 & RG1111-2 which isgratefully acknowledged.
• The authors acknowledge the mentoringprovided by ITU to the KFUPM graduatestudents involved in this project.