Civil Engineering Materials

11
Civil Engineering Materials – CIVE 2110Civil Engineering Materials – CIVE 2110
Concrete MaterialConcrete Material
Stress vs. Strain CurvesStress vs. Strain Curves
Steel ReinforcementSteel Reinforcement

22
Stress-Strain Curve for CompressionStress-Strain Curve for Compression
 Slightly ductile shape of Stress-Strain curve
 A descending branch exists after is reached
 Due to redistribution of load to un-cracked regions with less stress,
'
cf
(MacGregor, 5(MacGregor, 5thth
ed., Fig. 3-26)ed., Fig. 3-26)

33
 Strength of Reinforced Concrete structures controlled by,
 Size of members,
 Shape of members,
 Stress-Strain curves of; - concrete,
- reinforcement.
Five properties of Stress-Strain curves;
(1) - Initial slope, Ec
(2) - Ascending parabola
(3) - Strain at max stress,
(4) - Descending parabola
(5) - Strain at failure
'
cf
(Fig. 3-18, MacGregor, 5(Fig. 3-18, MacGregor, 5thth
ed.)ed.)

44
 (1) - Initial Slope, Ec ;
 ACI 318, Sect. 8.5, 8.6
 sensitive to Eaggregate , Ecement .
 For normal weight concrete;
 For other weight concrete;
 Defined as the slope
of a line drawn from
As water increases, Ec decreases,
because cement paste becomes
'
45.00 cfto == σσ (MacGregor, 5(MacGregor, 5thth
ed., Fig. 3.17)ed., Fig. 3.17)
( ) ( )
( ) '5.1
33
33
16090
ccc
c
fwpsiE
FtLbwFtLb
=
≤≤
( )
( ) '
3
000,57
145
cc
c
fpsiE
FtLbw
=
≈

55
 Lightweight Concrete ;
 ACI 318, Sect. 8.5, 8.6
 sensitive to Eaggregate .
 For all parameters involving
 Each parameter shall be multiplied by a modification factor
for sand-lightweight conc.
for all-lightweight concrete
 If splitting tensile strength, fct , is specified, then
 This accounts for the reduced
capacity of lightweight concrete
due to aggregate failure;
Such as:
 Shear strength
 Splitting resistance
 Concrete-rebar bond
For normal weight concrete the averageFor normal weight concrete the average
splitting tensile strength is;splitting tensile strength is;
( )[ ] 0.17.6/ '
≤= cct ffλ
'
cf
( )'
7.6 cct ff ≈
ed., Fig. 3.26)ed., Fig. 3.26)
( ) ( )
( ) '5.1
33
33
12090
ccc
c
fwpsiE
FtLbwFtLb
=
≤≤
75.0
85.0
=
=
λ
λ
λ

66
 (2) – Ascending Parabola;
 Curve becomes steeper
as increases.'
cf
(Fig. 3.18(Fig. 3.18, MacGregor, 5MacGregor, 5thth
ed.,)ed.,)
 (3) – Strain ( ) at ;
 Strain at max stress increases
as increases.
'
cf
'
cf
 (4) – Slope of descending branch;
 Less steep than ascending branch,
 Slope increases as increases.
'
cf
 (5) – Strain ( ) at failure;
 Decreases with increases in '
cf
0ε
cuε
 (4 and 5) – depend on;
 Specimen size; Load, type, rate
ksifc 6'
≤

77
Stress-Strain Curve forStress-Strain Curve for TensionTension
 Tensile strength of concrete:
 Determined by one of 2 tests:
 (1) Flexure (Modulus of Rupture) test,
 (2) Split Cylinder test, fct

( )
2
3
6
12
2
BH
M
f
BH
HM
f
I
My
f
r
r
Flexurer
=
=
== σ
 (1) Flexure (Modulus of Rupture) test;
 Load until failure due to cracking on tension side,
 ASTM C78 or ASTM C293,
 H = 6”, B = 6” L = 30”
3
PL
H
B
P P
3” 3”
8” 8” 8”
P
-P
V
M
0
0

88
Stress-Strain Curve for TensionStress-Strain Curve for Tension
( )
ld
P
f
ld
P
f
asistingAre
P
f
ldasistingAre
ct
ct
ct
π
π
σ
π
2
2
Re
2
Re
=
=
==
=
 (2) Split Cylinder test, fct ;
 Load in compression along long side,
 ASTM C496,
 a standard 6”x12” cylinder is placed on side,
 Outside surface area,
 Load is resisted by only half of surface area,
dlrlArea ππ == 2
ed., Fig. 3.9)ed., Fig. 3.9)

99
1max σσ =Tension
ApCσσ =2
2
max
ApCσ
τ =
σ
τ
2x90˚
Compression
Tension
Concrete always cracks
on plane of MaxTensionσ
Split Cylinder Test
Bi-Axial Stress

1010
 Determined by one of 2 tests:
 (1) Flexure (Modulus of Rupture) test,
 (2) Split Cylinder test,
rf
 Tensile strength from
Split Cylinder test
is less than that from
Flexure (modulus of Rupture) test
because;
 In Flexure test, only bottom of beam reaches
 In Split Cylinder test, majority of cylinder reaches
ctf
MaxTensionσ
MaxTensionσ
ctr ff 5.1≈
H
B
P P

1111
 Results from various Split Cylinder
tests vs. are plotted in Fig. 3.10
 The mean Split Cylinder strength is:
 ACI 318, Sect. R8.6.1 states;
 The mean Modulus of Rupture
strength is:
 ACI 318, Sects. 8.6.1 & 9.5.2.3 state,
for deflection calculations:
'
3.8 cr ff =
'
4.6 cct ff =
ed., Fig. 3.10)ed., Fig. 3.10)
'
cf
'
7.6 cct ff ≈
0.1
7.6
5.7
'
'
≤=
=
c
ct
cr
f
f
ff
λ
λ
concretetlightweighallfor
concretetlightweighsandfor
concreteweightnormalfor
−=
−=
=
75.0
85.0
0.1
λ
λ
λ

1212
( ) ''
15.008.0 ct ff →=
 Concrete tensile failure is BRITTLE.
 Same factors affect as ;
 Water/Cement ratio,
 Type of Cement,
 Type of Aggregate,
 Curing Moisture conditions,
 Curing Temperature,
 Age,
 Maturity,
 Loading rate.
(MacGregor,(MacGregor,
55thth
ed., Fig. 3-21)ed., Fig. 3-21)
'
tf '
cf
''
'
'
4.6
8.1
cctt
c
t
t
fff
where
E
f
==
=ε
E
tinitial=linear
flexurefor
tensionpurefor
MAX
MAX
t
t
0002.000014.0
0001.0
'
'
→=
=
ε
ε
'
5.0 tfFrom: 0 →
c
t
t E
f '
'
=ε
''
5.0 tt ff →From:
''
5.0 tt ff →
'
5.0 tf

1313
Steel Reinforcement in ConcreteSteel Reinforcement in Concrete
 In any beam (concrete, steel, masonry, wood):
 Applied loads produce
Internal resisting Couple,
Tension and Compression
forces form couple.
MacGregor, 5th
ed.
Fig. 1-4
In a concrete beam:In a concrete beam:
-- Cracks occur in areas ofoccur in areas of Tension,,
-- Beam will have suddenBeam will have sudden Brittle failurefailure
unless Steel reinforcementreinforcement
is present to takeis present to take Tension.

1414
Mohr’s Circle Method – Failure ModesMohr’s Circle Method – Failure Modes
ionslightTens=maxσ
Brittle concrete fails on plane of max normal (tension) Stress.
Failure stress located at: 2x90˚=180˚on Mohr Circle
ApCσσ =min
2
max
ApCσ
τ =
σ
τ
2x45˚
2x90˚
tensionσ
Shear Stress Normal Stress Principal
Stress
Neutral Axis
90˚
tensionσ
Plane of
max
Tension
Concrete
Brittle

1515
 Steel Reinforcement:
Hot-Rolled deformed bars (rebars)
Welded wire fabric
Reinforcement Bars (Rebars):
ASTM specs specify;ASTM specs specify;
- diameter, cross-sectional area- diameter, cross-sectional area
- sizes in terms of 1/8 inch- sizes in terms of 1/8 inch
- #4 rebar, diameter = 4/8 in.- #4 rebar, diameter = 4/8 in.
- metallurgical properties- metallurgical properties
- mechanical properties- mechanical properties
- Grade- Grade →→ min. Tensile Yield Strengthmin. Tensile Yield Strength
- Grade 60, Yield Strength = f- Grade 60, Yield Strength = fyy = 60 ksi= 60 ksi
ASTM A 615:ASTM A 615:
- made from steel billets- made from steel billets
- most commonly used- most commonly used
ASTM A 706:ASTM A 706:
- made from steel billets- made from steel billets
- for seismic applications- for seismic applications
- better - ductility- better - ductility
- bendability- bendability
- weldability- weldability

1616
Upper Limit on
( )dStrengthactualYielygthnsileStrenUltimateTe f σσ =≤ 25.1
ed., Table 3-4)ed., Table 3-4)

1717
Rebars in US customary units:
- Grade 60, →
- # 11 →
Rebars in metric units:Rebars in metric units:
- just numerical conversions- just numerical conversions
of US customary sizes.of US customary sizes.
- #36- #36 →
- Grade 420,- Grade 420, → MPafy 420=
ksify 60=
ed., Fig. 3-30)ed., Fig. 3-30)
"41.1"375.1
8
"11
≈==d "409.1
"14.25
8.35
==
mm
mm
d

1818
Reinforcement Bars (Rebars): (MacGregor, 5(MacGregor, 5thth
ed., Table A-1)ed., Table A-1)

1919
Reinforcement Bars (Rebars): (MacGregor, 5(MacGregor, 5thth
ed., Table A-1M)ed., Table A-1M)

2020
- modulus of Elasticity,
ES = 29,000,000 psi
ACI 318, Sect. 8.5.2
- for rebars with
fy > 60,000 psi
must use
fy = ES x ( )
ACI 318, Sect. 3.5.3.2
0035.0=Sε
ed., Fig. 3-31)ed., Fig. 3-31)

2121
- at temperatures > 850at temperatures > 850˚F˚F
ffyy and fand fultimateultimate
drop significantlydrop significantly
- concrete cover- concrete cover
over the rebarsover the rebars
helps to delay losshelps to delay loss
loss during firesloss during fires
ed., Fig. 3-34)ed., Fig. 3-34)

2222
Fatigue Strength of rebars:
- Bridge decks subjected to large number of load cycles
- Stress Range, Sr =
ed., Fig. 3-33)ed., Fig. 3-33)
- Fatigue failure may
occur if at least one
stress is tensile
and Sr > 20 ksi
- Fatigue failure will not
occur if;
cyclesany
cyclesiniteksi
Max
Max
000,20
inf20
=
<
σ
σ
- Fatigue strength
reduced at: Bends, Welds
( ) ( ) cyclesameinMinStresscycleainStressMaxTensile σσ −

2323
Example: Fatigue Failure not possible;
Fatigue Strength of rebars:
- Stress Range, Sr = ( ) ( ) cyclesameinMinStresscycleainStressMaxTensile σσ −
( ) ( )
ksiS
ksiksiS
r
cyclesameincycleainr
21
165
=
−−=
( ) ( )
ksiS
ksiksiS
r
cyclesameincycleainr
21
265
=
−−−=
Example: Fatigue Failure possible;

2424
Welded-Wire Reinforcement:
- used in: Walls, Slabs, Pavements.
- due to cold-working process used in drawing the wire
strain-hardening occurs, so wire is BRITTLE.
- Plain wire; ASTM A82; A185;
ACI 318, Sect. R3.5.3.6 → fy = 60,000 psi
- mechanical anchorage in concrete provided by
- cross-wires
- Deformed wire; ASTM A496; A497;
ACI 318, Sect. R3.5.3.7
→ fy = 60,000 psi
- mechanical anchorage
in concrete provided by
- cross-wires

2525
- Wire diameter = 0.125” → 0.625”
- Wire area → increments of 0.01 in2
.
- Plain wire; W
- Deformed wire: D
- ACI 318, Sect. 3.5.3.5
D-4 ≤ wire size ≤ D-31
area = 0.04 in2
area = 0.031 in2
.
-
ed., Table A-2a)ed., Table A-2a)

2626
- Wire area → increments of 0.01 in2
.
- Wire center-center spacing → a x b , inches
- Plain wire; W
-
ed., Table A-2b)ed., Table A-2b)

Civil Engineering Materials

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (20)

Similar to Civil Engineering Materials

Similar to Civil Engineering Materials (20)

More from Latif Hyder Wadho

More from Latif Hyder Wadho (20)

Recently uploaded

Recently uploaded (20)

Civil Engineering Materials