Analyses of Pre- and Post-Peak Behavior of Deep …web.itu.edu.tr/~haluk/rc/RCSD_week1_HS.pdf ·...
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Concrete Properties
Reinforced Concrete StructuresMIM 232E
RCSD-1
Dr. Haluk SesigürI.T.U. Faculty of Architecture
Structural and Earthquake Engineering WG
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• Concrete is a composite material (cement+aggregate (sand+ gravels + crushed stones) + water+chemicals)
• Concrete is plastic when it is wet Formability
• ~10 hour setting time; reaches high compressive strength
• High compressive strength & quite low tensile strength
ConcreteProperties
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• Concrete : Cement+ water+aggregate+ chem.additives
1 m3 concrete(vol.)
cement %10
Aggregate(sand+gravel, crushed stone etc.)
%70
water %20
• 1 m3 concrete (~2500kgs)
- %0.5-5 air, additive for a purpose (%0.5-2 of cement)
http://mmf2.ogu.edu.tr/atopcu/index.htm
ConcreteProperties
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• TS EN 197-1/2002
• Function: reaction with water,covering aggregates,
filling the voids between pieces and binding them each other
• Cement may be produced for various purposes (heat, impermeability, etc.)
• It is selected depend on structure dimension and qualification
Concrete componentsCement
Portland cement
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• Usually originates from limestone• Main material of cement is clinker• CEM I (clinker used; 95-100%) ---------Portland cement (most common)
• Mixing limestone and kiln
• heat up with 1300 1500oC and grinding the clinker
• 70% of final strength in 28 days
• Some types; Normal Portland cement (NPÇ 350)High strength Portland Cement (YPÇ 500)High initial strength Portland Cement (İPÇ 600)
Portland Cement
Concrete componentsCement
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Compressive strength and setting time;
• Rapid early strength R• Normal early strength N
http://mmf2.ogu.edu.tr/atopcu/index.htm
Concrete componentsCement
Setting
time
(hour)
Setting
initiation
(min)
strengthStrength
Class
days days days
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• TS EN 1008/2003
• Function: İnitiating and sustaining chemical reactionProviding formable/flowing consistency to concrete
• In concrete;
-Salty, acidic, oily, dirty water is not used
- Sea water is not allowed
Concrete componentsWater
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• Aggregate TS 706 EN 12620/2003
• Sand + Gravel
• Sand + Crushed stone
• Sand + Gravel+ Crushed stone
• Standarts and dimention ranges are available
• Sea water/gravel is not allowed.
Concrete componentsAggregate
Aggregate
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• Chemical admixtures is used for:
• Increase some properties of concrete• Gaining to some properties to concrete
• Such as;
• Mitigation of setting time• Increase the strength (by reducing water)• Preventing freezing• Preventing corrosion etc.
Concrete componentsChemical admixtures
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• Cement content: Cement amount in 1m3 concrete (kgs)
- Common, 300
• Water/cement ratio: the ratio of water to cement in 1m3
concrete- the most important factor on strength
- commonly, 0.40~0.55
• Consistency: formability of wet concrete
SLUMP experiment
Depends on structure type
ConcreteConcepts
pearson
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ConcreteConcepts
pearson
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• Compressive Strength
The maximum stress that can be carried by 28 days 15cmx30cm standard cylinder concrete sample under axial compression
• Tensile Strength:
The stress that causes the cracking of concrete
ConcreteConcepts
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Transporting, casting/pouring, compacting
• Transmixer, concrete pump, wheelborrow• Compacting by vibrator (types...)
• Benefits - Omits the voids, increase the strength- Enhanced the adherence- Concrete become more durable againist env.
Effects.
• Concrete pouring is completed without having a break. If needed, jointings 450 and with rough surface
ConcreteGeneral
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Cure
• Ideal temperature 20-250C• attentive cure for desired strength• Excessively low and high temperature decreases the
strength• Pouring, +5C~+32C
importanceof cure
Without curing, the strength remains smaller
http://mmf2.ogu.edu.tr/atopcu/index.htm
ConcreteGeneral
Cure duration
str
ength
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Keep with curing
Keep without curing
Repeat curing process
After 3 months
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Formwork- Scaffold
• must be able to carry the wet concrete
• Brace/diagonals for horizontal loads
• Resistance to vibrator
• Saturating the formwork to water before casting etc.
http://mmf2.ogu.edu.tr/atopcu/index.htm
ConcreteGeneral
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http://mmf2.ogu.edu.tr/atopcu/index.htm
ConcreteGeneral
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Removing the formwork
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http://mmf2.ogu.edu.tr/atopcu/index.htm
Factors on concrete strength
• W/C ratio• Cement type, content, strength• Aggregate properties• Water quality• Chemical admixtures• Compacting quality• Environmental effects• Curing quality
ConcreteGeneral
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• C16, C18, C20, C25, C30, C35, C40, C45, C50 Reinforced, normal class strength (TS500)
For Loadbearing members
• Low strength concrete for non-loadbearing members, reinforced or non-reinforced
• C55, C60, C70, C80, C90, C100Reinforced, high class strength (not defined in TS500)
Others:• High performance concrete
(rapid early strength)• Self-compacting concrete• light transmitting concrete
LiTraCon
http://mmf2.ogu.edu.tr/atopcu/index.htm
ConcreteClassification TS500/2000
Sort by weight per unit of volume
W(kgs/m3)
Light weight concrete 800-2000
Normal weigth concrete 2000-2600
Heavyweigth concrete >2600
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http://mmf2.ogu.edu.tr/atopcu/index.htm
ConcreteGeneral
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Self-compacting concrete
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• Characteristic concrete compressive strength (fck):
The strength anticipated in project.İt is tested after casting if it is ok ?
ConcreteMechanical Properties
Concrete compresive strength
Characteristic Concrete compresive strength
Characteristic Concrete tensile strength
Concrete modulus of elasticity
Concrete shear modulus
Poisson ratio
j...(the value at j days)
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ConcreteCharacteristic Strength
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ConcreteCharacteristic Strength
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Concrete also carry some amount of loads after the peak load up to a strain value. Then it reaches the ultimate strain and fails.
http://mmf2.ogu.edu.tr/atopcu/index.htm
Concrete Concrete Stress-Strain (σ-𝞮) Relationship
Str
es
s
Strain
crushing
fc : max. Stress (strength)fcu: crushing stress
(modulus of elasticity of concrete)
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C25
concrete
Characteristic concrete
compressive strength
(fck): 25 N/mm2 (MPa)
(28 days)
• Concrete; good in compression, poor in tension• C20~30 widely used• > C30 generally tall bldg./bridges etc.• Min. C20 in EQ zones
Classfck
(characteristic
concrete
compressive
strength
Equilevent cube
(150mm)
concrete strength
fctk(characteristic
concrete
tensile
strength
Modulus of elasticity
(28 days)
Concrete Concrete class and properties (TS500)
TS500 (Table 3.2)
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• Brittle & ductile behavior
• Strength & ductility in inverse ratio
http://mmf2.ogu.edu.tr/atopcu/index.htm
Concrete Stress-Strain (σ-𝞮) Relationship due to strength
Str
es
s
Strain
brittle
ductile
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• W/C ratio for hydration is 0.25; more water is for workability
• Remained water evaporates and concrete volume decreases. Even without loading, shortening deformation and cracking occur and this phenomenia is called as shrinkage.
• To omit/reduce; cure , (wet)
http://mmf2.ogu.edu.tr/atopcu/index.htm
Concrete shrinkage
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• Creep : Increase of shortening in concrete under constant loading.
• Under compression, water is put out, voids become smaller and deformations occur.
• Shrinkage and creep amount increases in poorly compacted /cured concrete.
Concrete Creep
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• Behavior under triaxial stress
• Due to increase of lateral pressure, deformation capacity, load carrying capaciti and ductility increases.
http://mmf2.ogu.edu.tr/atopcu/index.htm
Concrete Confinement effectS
tre
ss
Strain
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Strength without
transversal stress
Concrete Strength with
transversal stress
Applied transversal
stress
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Column with fret
(spiral) Column with Stirrup
Confinement applies lateral pressure to column; Strength and ductility increase
Most efficient: Spiral reinforcement
Spacings «s» ductility, strength
Increase of the reinforcement area improves the behavior
http://mmf2.ogu.edu.tr/atopcu/index.htm
Concrete Confinement effect in RC Column
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• Confinement -stirrup-fret (spiral) - effect
http://mmf2.ogu.edu.tr/atopcu/index.htm
Concrete Confinement effect in RC ColumnS
tre
ss
Strain
fret
stirrup
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