1 class #25.1 civil engineering materials – cive 2110 definitions material properties concrete...

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Class #25.1Class #25.1

Civil Engineering Materials – CIVE 2110Civil Engineering Materials – CIVE 2110

DefinitionsDefinitions

Material Properties Material Properties

Concrete Compressive Strength, f’Concrete Compressive Strength, f’cc

Fall 2010Fall 2010

Dr. GuptaDr. Gupta

Dr. PickettDr. Pickett

22

Advantage Disadvantage Advantage Disadvantage

Shapes Any shape Must make forms Manufactured shapes

Limited shapes

Fire resistance

1-3 Hr. resistance with NO coating

Must add

fire-proof coating

Maintenance

Less,

No need to paint

More,

Must paint for corrosion resistance

Time dependent

Creep due to long term load.

Shrinkage due to curing.

More thermal expansion and

contraction

Strength

Low tensile strength.

Low

strength/volume ratio.

High tensile strength.

High

strength/volume ratio.

Weight

Higher,

More seismic load

Lower,

Less seismic load

Stiffness

Rigid,

Less; drift, deflection, vibrations.

Flexible ,

More; drift, deflection, vibrations.

Reinforced Concrete Structural Steel

33

What is Reinforced Concrete?What is Reinforced Concrete? DefinitionDefinition: :

A construction material composed of:A construction material composed of: Course Aggregate – particles > 0.25“ diameter, retained on #4 sieve.Course Aggregate – particles > 0.25“ diameter, retained on #4 sieve. Fine Aggregate – Sand particles < 0.25” diameter, pass #4 sieve.Fine Aggregate – Sand particles < 0.25” diameter, pass #4 sieve. Water Water Cement powder Cement powder cement paste, cement paste,

Forms a gluing paste, when mixed with proper amount of waterForms a gluing paste, when mixed with proper amount of water Reinforcement bars – steel (if no reinforcement, use ACI 318, Ch.22)Reinforcement bars – steel (if no reinforcement, use ACI 318, Ch.22)

Two Methods of Reinforced Concrete Construction: Two Methods of Reinforced Concrete Construction: Cast-in-Place: : members are constructed at their final location;members are constructed at their final location;

A form (wood) or mold (steel) is built in the shape of the member,A form (wood) or mold (steel) is built in the shape of the member, Reinforcement bars are placed inside form (mold);Reinforcement bars are placed inside form (mold); Concrete is poured into form (mold).Concrete is poured into form (mold).

Pre-Cast: : members are constructed off-site;members are constructed off-site; Members are transported to their final location,Members are transported to their final location, Members are erected and joined to form a structure.Members are erected and joined to form a structure.

44

Cast-In-Place ConcreteCast-In-Place Concrete

I-75, Suder Ave. ramp

McCormac, 8th ed., p.73

55

Pre-Cast ConcretePre-Cast Concrete

Veterans Glass City Skyway bridge

66

Reinforced Concrete StructuresReinforced Concrete StructuresLoad bearing

masonry walls.

Gravity loads supported

by columns.

Fig. 4-1,MacGregor, 5th edition, 2009, Pearson/Prentice Hall

One-way slab

One-way slab

Two-way slab

One-way slab

MacGregor, 5th ed., Fig. 4-1

77

Reinforced Concrete StructuresReinforced Concrete Structures Floor slabs: One-way or Two-way;

One-way slab: Takes load in only One direction, Slab forms top flange of T-beam joist,

T-beam takes load in only One direction, Load transferred to T-beam joist, T-beam transfers load to girder, Girder transfers load to column (or wall), Column (or wall) transfers load to;

Piles, Spread footings.

- one-way slab; L- one-way slab; L2/L/L11 > 2 > 2

- two-way slab; L- two-way slab; L2/L/L1 < 2 < 2

L2

L1

One-way slab



88

Reinforced Concrete StructuresReinforced Concrete Structures Floor slabs: One-way or Two-way;

Two-way slab: ACI 318, Chapter 13, Transfers load in Two directions

to girder or column,

Two-way slab



99

The design Engineer must:specify the exterior dimensions of members so that

the members have;Adequate strength to resist loads,

ACI 318, Ch. 9-21.Adequate stiffness to prevent excessive deflections,

ACI 318, Sect. 9.5.

specify the reinforcement, - size, quantity, location.

ensure constructability of members;Rebars must not interfere with each other,Need space for concrete to flow around rebars,Adequate strength during – erection, curing.

Dimensions and TolerancesDimensions and Tolerances

1010


The design Engineer should specify:Calculations;

3 significant digits,Exterior dimensions of beams, columns;

In whole inch increments, Slab thickness;

In half-inch increments, Rebar size, length;

Bar sizes are manufactured in 1/8 in. increments,Length in two-inch increments, ACI 318, Sect. 7.5.

Concrete cover;In half-inch increments,

Rebar diameter = 9/8”

1111


The design Engineer should ensure

construction tolerances of:Exterior dimensions of beams and columns;

0.5 inch,

Slab thickness; 0.25 inch,

Concrete cover; ACI 318, Sect. 7.5.2.1; 0.375 inch, effective depth, d 8 inch, 0.5 inch, effective depth, d > 8 inch,

1212

Material PropertiesMaterial Properties

In any beam (concrete, steel, masonry, wood): Applied loads produce

Internal resisting Couple,Tension and Compression

forces form couple.

Positive bending moment, Axial Compression forces

in the top regions,Axial Tension forces

in the bottom regions,


1313


In a concrete beam:In a concrete beam:

- - Cracks occur in areas of occur in areas of Tension,,

- - Beam will have sudden Beam will have sudden Brittle failure failure unless Steel reinforcement is reinforcement is

present to take present to take Tension.


1414


Concrete is: Strong in Compression, Weak in Tension,

Cracks occur in Concrete when:Cracks occur in Concrete when:

Tensile Stress can be due to:Tensile Stress can be due to:LoadsLoadsRestrained shrinkage during curing Restrained shrinkage during curing Temperature changes Temperature changes

ConcreteofStrengthTensileConcreteinStressTensile

'10.005.0 ct ff

1515


= Specified Compressive Strength of Concrete Nominal strength ( n ) is based upon

Design Strength ≥ Required StrengthReduced Nominal Strength ≥ Factored Up Load

n ≥ U

ACI 318, Sect. 5.3;ACI 318, Sect. 5.3; In order to validate a specifiedIn order to validate a specified , concrete plant must have;, concrete plant must have;

Strength test records Strength test records 12 months old, 12 months old, A sample standard deviation, A sample standard deviation,

established from 30 consecutive compressive strength testsestablished from 30 consecutive compressive strength tests 2 cylinders tested per test 2 cylinders tested per test

'cf

'cf

'cf

ss

1616


ACI 318, Sect. 5.3;ACI 318, Sect. 5.3; In order to validate a specifiedIn order to validate a specified ;;

A Required Average Compressive Strength, , must be obtained;A Required Average Compressive Strength, , must be obtained;

ForFor

Use the Use the larger value computed from Eq. (5-1) and Eq. (5-2); computed from Eq. (5-1) and Eq. (5-2); Eq. (5-1)Eq. (5-1)

Eq. (5-2)Eq. (5-2)

Eq. (5-1) is based on a probability of 1-in-100 that the average of Eq. (5-1) is based on a probability of 1-in-100 that the average of 3 consecutive tests may < specified.3 consecutive tests may < specified.

Eq. (5.2) is based on a probability of 1-in-100 that an individual test Eq. (5.2) is based on a probability of 1-in-100 that an individual test may be more than 500 psi below specified.may be more than 500 psi below specified.

sccr sff 34.1''

'cf '

crfpsifc 5000'

50033.2'' sccr sff

'cf

'cf

1717


ACI 318, Sect. 5.3;ACI 318, Sect. 5.3; In order to validate a specifiedIn order to validate a specified ;;

A Required Average Compressive Strength, , must be obtained;A Required Average Compressive Strength, , must be obtained;

ForFor

Use the Use the larger value computed from Eq. (5-1) and Eq. (5-3); computed from Eq. (5-1) and Eq. (5-3); Eq. (5-1)Eq. (5-1)

Eq. (5-3)Eq. (5-3)

Eq. (5-1) is based on a probability of 1-in-100 that the average of Eq. (5-1) is based on a probability of 1-in-100 that the average of 3 consecutive tests may < specified.3 consecutive tests may < specified.

Eq. (5.3) is based on a probability of 1-in-100 that an individual test Eq. (5.3) is based on a probability of 1-in-100 that an individual test may be < specified.may be < specified.

sccr sff 34.1''

'cf

'crf

psifc 5000'

sccr sff 33.290.0 ''

'cf

'90.0 cf

1818


ACI 318, Compressive Strength Test;ACI 318, Compressive Strength Test; Standard Cylinders;Standard Cylinders; Concrete samples taken per ASTM C172, Concrete samples taken per ASTM C172, Concrete samples molded, cured per ASTM C31,Concrete samples molded, cured per ASTM C31, Concrete strength tested per ASTM C39;Concrete strength tested per ASTM C39;

6”x12” cylinders, 6”x12” cylinders, Fill cylinder with concrete,Fill cylinder with concrete, Allow concrete to harden in cylinder,Allow concrete to harden in cylinder,

24 hours, 6024 hours, 60˚̊ 80˚F, no moisture loss, 80˚F, no moisture loss, Strip the cylinder mold,Strip the cylinder mold,

Place cylinder in a curing room (100% humidity) Place cylinder in a curing room (100% humidity) or water tank at or water tank at 72˚F,72˚F,

After 28 days, After 28 days, Load 2 cylinders in compression at rate of 35 psi/sec.Load 2 cylinders in compression at rate of 35 psi/sec. Record failure load, calculate failure stress.Record failure load, calculate failure stress.

ComprApC max

ComprApC max

6”

12”

1919

Cracking & Failure Mechanisms Cracking & Failure Mechanisms

Concrete (and all Concrete (and all Brittle materials) materials)

fail on the plane of on the plane of

Max Normal Tension Stress Stress

Will have Tension cracksWill have Tension cracks

parallel to applied load, parallel to applied load,

on plane of on plane of ApC

ApC

P

P

Apply a Normal Stress in Compression – concrete Compression Cylinder Test:

ApC

Tensionmax

ComprApC max

ComprApC max

Tensionmax Tmax

Plane of max Tension

2020

Mohr’s Circle Method – Failure ModesMohr’s Circle Method – Failure ModesApply a Normal Stress in Compression – Split Cylinder Test:

max

ApC

Ductile Material fails by Buckling.

Brittle Material fails on plane of max

NORMAL (Tension) Stress,

Failure stress is 2x90˚=180˚

on Mohr Circle from applied stress

90˚ApC min

2maxApC

2x90˚

Steel Ductile

Concrete

Brittle

tension

90˚Plane of max Tension

Tensionmax

ApCTensionmax

CompressionTension

ApC

2121

Mohr’s Circle Method – Failure ModesMohr’s Circle Method – Failure ModesApply a Normal Stress in Tension:

ApT max

ApT

Ductile Material fails on plane of

From to failure stress = 2x45˚=90˚

on Mohr Circle

Brittle Material fails on plane of

acts on plane perpendicular

to applied Tension load.

45˚

45˚

45˚

45˚

90˚0min

2maxApT

2x45˚

Steel Ductile

Cast Iron Plexiglass

Brittle


maxTensionmax

TensionmaxTensionmax

max

max

TensionCompression

2222

Mohr’s Circle Method – Failure ModesMohr’s Circle Method – Failure Modes

ionslightTensmax

Brittle concrete fails on plane of max normal (tension) Stress.

Failure stress located at: 2x90˚=180˚on Mohr Circle

ApC min

2maxApC

2x45˚

2x90˚

tension

Shear Stress Normal Stress Principal Stress

Neutral Axis

90˚

tension


Concrete Brittle

2323


Concrete cracking process;Concrete cracking process; - - 4 stages: : (MacGregor, 5(MacGregor, 5thth ed., pp. 41-43) ed., pp. 41-43)

(0) Overall Cracking Process ; ;- individually, cement paste & aggregateindividually, cement paste & aggregate

each have brittle, linear stress-strain curves,each have brittle, linear stress-strain curves,- during a cylinder compression test,during a cylinder compression test,

- friction between test machine head-plates and cylinder ends,friction between test machine head-plates and cylinder ends,- prevents lateral expansion at cylinder ends,prevents lateral expansion at cylinder ends,- this restrains vertical cracking near cylinder endsthis restrains vertical cracking near cylinder ends,,

- this strengthens conical regions near cylinder ends,this strengthens conical regions near cylinder ends,- vertical cracks at mid-height of cylinder do not enter conical regions.vertical cracks at mid-height of cylinder do not enter conical regions.

ApC

ApC

But, in the concrete mixture, But, in the concrete mixture, the cement paste & aggregate together the cement paste & aggregate together produce a non-linear stress-strain curve, produce a non-linear stress-strain curve, that appears slightlythat appears slightly ductile,ductile,

due to the gradual micro-cracking due to the gradual micro-cracking within the mixture and within the mixture and redistribution of stress throughoutredistribution of stress throughout the concrete mixture.the concrete mixture.

(MacGregor, 5th ed., Fig. 3.13)

2424



(1) No-Load Bond Cracking during curing; during curing;

- cement paste shrinks,- cement paste shrinks,

- shrinkage restrained by non-shrinking - shrinkage restrained by non-shrinking aggregate,aggregate,

- shrinkage causes tension in the concrete,- shrinkage causes tension in the concrete,

- - No-Load Bond Cracks occur along interface occur along interface

between cement paste and aggregate,between cement paste and aggregate,

- cracks have little effect on concrete at low loads,- cracks have little effect on concrete at low loads,

- stress-strain curve remains nearly linear up to - stress-strain curve remains nearly linear up to

'3.00 cApC f

'3.0 cApC f

ApC

2525


(MacGregor, 5(MacGregor, 5thth ed., Fig. 3.1) ed., Fig. 3.1)

'3.0 cf

'5.0 cf

'75.0 cf

'cf

2626



(2) Stable Crack Initiation ; ;

- - Bond Cracks occur from one aggregate to occur from one aggregate to

another piece of aggregate,another piece of aggregate,

- cracks are stable, - cracks are stable,

- cracks will propagate only if load is increased,- cracks will propagate only if load is increased,

- additional load is redistributed to un-cracked - additional load is redistributed to un-cracked portions,portions,

- causes gradual curving of stress-strain curve. - causes gradual curving of stress-strain curve.

ApC

'5.03.0 cApC f

2727



(3) Stable Crack Propagation ; ;- - Mortar Cracks occur between Bond Cracks, occur between Bond Cracks,

- cracks develop parallel to the compressive load, - cracks develop parallel to the compressive load, due todue to

local stress reaching (Mohr Circle),local stress reaching (Mohr Circle),- crack do not grow during constant load,- crack do not grow during constant load,- cracks propagate only with increasing load,- cracks propagate only with increasing load,

- stress-strain curve continues to curve. - stress-strain curve continues to curve. - the onset of this stage is called the - the onset of this stage is called the Discontinuity

Limit..

ApC

'75.05.0 cApC f

Tensionmax

2828



(4) Un-Stable Crack Propagation ; ;- - Mortar Cracks lengthen with constant load, lengthen with constant load,- additional cracks form,- additional cracks form,- few undamaged portions remain- few undamaged portions remain to carry additional load,to carry additional load,- cracks propagate without increasing load,- cracks propagate without increasing load,- this is an - this is an unstable condition, condition,

- stress-strain curve becomes very non-linear,- stress-strain curve becomes very non-linear,- eventually, stress-strain curve begins to flatten,- eventually, stress-strain curve begins to flatten,- failure will occur.- failure will occur.

- The onset of this stage is called - The onset of this stage is called Critical Stress at at

ApC

'75.0 cApC f

'75.0 cApC f

2929


Concrete cracking process;Concrete cracking process; - - 4 stages: : (MacGregor, 5(MacGregor, 5thth ed., pp. 41-43)) ed., pp. 41-43))

(4) Un-Stable Crack Propagation ; ;- - Critical Stress; - significant lateral strains caused by lateral strains caused by

large amount of micro cracks,large amount of micro cracks, - volumetric strain increases, significantly,- volumetric strain increases, significantly, - causes outward force on lateral confining reinforcement,- causes outward force on lateral confining reinforcement,

- spirals, - spirals, - lateral ties,- lateral ties,

- confining reinforcement becomes in Tension, - confining reinforcement becomes in Tension, - confining Steel restrains concrete expansion and disintegration,- confining Steel restrains concrete expansion and disintegration, - puts column in a state of Triaxial Compressive Stress. - puts column in a state of Triaxial Compressive Stress.

ApC

'75.0 cApC f

'75.0 cApC f

3030

Uni-Axial vs. Bi-Axial Loadings Uni-Axial vs. Bi-Axial Loadings So far, discussion has So far, discussion has

involvedinvolved Uni-Axial loading;


Uni-Axial tension, points B or B’

Uni-Axial compression, points A or A’

Concrete always cracks on plane of MaxTension

3131

Uni-Axial vs. Bi-Axial Loadings Uni-Axial vs. Bi-Axial Loadings


Bi-Axial Compression; from points A-C-A’

- Delays the formation of - Bond Cracks- Bond Cracks

- Mortar Cracks- Mortar Cracks

- Stable crack propagation - longer time - Stable crack propagation - longer time

- higher load- higher load

Due to Bi-Axial Compression; failure at point C ≈ '07.1 cf

3232

Tri-Axial Loadings Tri-Axial Loadings


(MacGregor, 5(MacGregor, 5thth ed., Fig. 3.16) ed., Fig. 3.16)33.4 Failure

Tri-axial Compression ;

- Compared to uni-axial compression;

- higher compressive

strength,

- more ductile,

In columns: In columns: - Uni-axial compression causes Uni-axial compression causes

outward force on outward force on lateral confining reinforcement, lateral confining reinforcement, - spirals - spirals - ties- ties- confining Steel restrains concrete - confining Steel restrains concrete

expansion and disintegration,expansion and disintegration,- reinforcement becomes in Tension, - reinforcement becomes in Tension,

as it restrains concrete expansion as it restrains concrete expansion - puts column into - puts column into Triaxial Compression

3333

Cracking & Failure Mechanisms Cracking & Failure Mechanisms Confining reinforcement ;Confining reinforcement ; - - saved Olive View Hospital

from complete collapse;

- - saved building in Philippines

from complete collapse;

3434


ConfiningConfining

reinforcement ;reinforcement ; - double spiral

reinforcement

used in

bridge piers

by CALTRANS,

- puts column - puts column

into a state of into a state of

Triaxial Triaxial

CompressiveCompressive

Stress. Stress.

1 class #25.1 civil engineering materials – cive 2110 definitions material properties concrete...

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