Dr. Salah Altoubat
Text Book
Design of Reinforced Concrete
Jack McCormac and James Nelson
8th Edition, 2009
Dr. Salah Altoubat
Reinforced Concrete
• Concrete is a mixture of
sand and gravel held
together with a paste of
cement and water
– Has high compressive
strength
– Has low tensile strength
• Reinforced Concrete is a
combination of steel and
concrete
– Steel reinforcement
provides the tensile strength
lacking in concrete
story, 723ft high, Atlanta 71
Dr. Salah Altoubat
Advantages & Disadvantages
Advantages
•High compressive strength
•Great resistance to fire
•Long service life
•Economical in most cases
Disadvantages
•Low tensile strength
•Forms are required
•Large members for tall
buildings
•Shrinkage and creep
Dr. Salah Altoubat
Compatibility
• Concrete and steel work together beautifully
• Complement each other
– Concrete is weak in tension, but steel have tensile strengths 100
times greater than that of concrete
– Steel is subject to corrosion but concrete provide a protection
environment
– Enclosure of steel in concrete provides good fire ratings
• Concrete and steel bonds together very well
• Work well together in relation to temperature changes
• Similar coefficient of thermal expansion
Steel 6.5 x 10-6/ oF and concrete 5.5 x 10-6/ oF
Dr. Salah Altoubat
Design Codes
• American Concrete Institute’s Building Code
Requirements for Structural Concrete ACI- 31802
• Design Requirements for various types of
reinforced concrete members are presented along
with “Commentary”
• ACI-318 is revised every 3 years as more
knowledge becomes available
• Other codes: British BS, and AASHTO
Dr. Salah Altoubat
Units
• Most examples in the book are in US
Customary Units (lb, inch, ft…)
• All items pertaining to the SI units such as
equations are presented in Shaded Format
• Example: ACI Equation for Elastic Modulus
of Concrete
Ec  57000 f c
US Customary Units
Ec  4700 f c
SI Units
Dr. Salah Altoubat
Concrete Properties
• Compressive Strength: The compressive
strength of concrete f c is determined by
testing to failure 6-in by 12 in cylinders at
the age of 28 days (units: psi or MPa)
–
–
–
–
3000 - 4000 psi for ordinary applications
5000 - 6000 psi for prestressed applications
Greater than 6000 psi, high strength concrete
9000 psi and greater for high rise buildings up
Dr. Salah Altoubat
Stress-Strain Curves
• The curves are roughly straight
(linear) up to one-third of the
compressive strength
• Behavior is nonlinear after that,
this causes some problems in
the analysis due to this material
nonlinearity
• Regardless of strength all the
concretes reach their ultimate at
strain of 0.002
• No yield strength and rupture
strain of 0.003 to 0.004
Analysis in this course assumes concrete fails at 0.003
Dr. Salah Altoubat
Elastic Modulus
• No clear-cut modulus of elasticity, unlike steel
• Different Definitions
– Initial modulus: slope of the stress-strain curve at the
origin
– Tangent modulus: slope of tangent to the curve at
some point along the curve e.g 50% of ultimate strength
– Secant modulus: slope of line drawn from the origin
to a point on the curve somewhere between 25% and
50% of ultimate strength
• ACI 318-02 suggests Equations for E for both
normal concrete and high strength concrete
Dr. Salah Altoubat
Elastic Modulus: Normal Concrete
ACI-318 Equations
US Customary Units
Ec  w
1.5
c
33 f c
Ec  57000 f c
Ec  psi
3
wc  lb / ft
f c  psi
SI Units
Ec  w
1.5
c
0.043 f c
Ec  4700 f c
Ec  MPa
3
wc  kg / m
f c  MPa
Dr. Salah Altoubat
Elastic Modulus: High Strength Concrete
ACI-318 Equations
US Customary Units


1.5
wc 

Ec  40000 f c  10 

 145 
3
Ec  psi wc  lb / ft
6
f c 
psi
SI Units


1.5
wc 

Ec  3.32 f c  6895 

 2320 
3
f c  MPa Ec  MPa wc  kg / m
Dr. Salah Altoubat
Poisson’s ratio
• Lateral deformation due to axial
deformation is related to Poisson's ratio
• Typically 0.11 for high strength concrete
• Typically 0.2 for low grade normal concrete
strength
• Average typical value is 0.16 for concrete
Required only in special analysis
Dr. Salah Altoubat
Tensile Strength
• Tensile strength of concrete varies between
8 and 15 % of its compressive strength
• Presence of micro cracks in concrete cause
the low tensile strength
• Neglected in design but it affects size of
cracks and deflection of members
• Tensile strength is important in flexure
when considering cracks and deflection
Tensile strength obtained from the modulus of rupture test
Dr. Salah Altoubat
Modulus of Rupture
• Defined as the flexural tensile strength of
concrete
• Obtained form plain concrete beam tests in
one-third loading configuration (ASTM
C496-96)
• Standard Beam Size 6in x 6in x 30in
MC
M ( h / 2) 6 M
fr 


3
I
bh / 12
bh 2
Dr. Salah Altoubat
Modulus of Rupture: Normal Concrete
ACI-318 Equations
US Customary Units
SI Units
f r  7.5 f c
f r  0.7 f c
f r  psi
f r  MPa
f c 
f c  MPa
psi
Dr. Salah Altoubat
Tensile Split Test
• In some cases, the
split-cylinder strength
can be used to
represent the tensile
strength of concrete
2P
ft 
LD
Dr. Salah Altoubat
Reinforcing Steel
• Reinforcing bars are referred as plain and
deformed bars
• Deformed bars have ribbed projections
rolled onto their surfaces to provide better
bonding between the steel and concrete
• Plain bars are not used very often except for
wrapping around primary reinforcement
(stirrups in beams and columns)
Dr. Salah Altoubat
Reinforcing Steel
• Deformed bars are
round and vary in
sizes from #3 to #11,
with two large sizes
#14 and #18
• Plain bars are
indicated by their
diameters in fraction
3”/8 ø, 5”/8 ø…
Dr. Salah Altoubat
Grades of Reinforcing Steel
• Several types of
reinforcing bars
designated by ASTM
exist
– ASTM A615: marked
with the letter S are the
most widely used
– ASTM A706: low alloy,
marked with the letter W,
used where controlled
tensile strength /chemical
composition for welding
– ASTM A996: Deformed
rail steel, marked with the
letter R
Dr. Salah Altoubat
Grades of Reinforcing Steel
• Several grades of
reinforcing bars exist
– Grade 40: Yield strength
is 40,000 psi
– Grade 50: Yield strength
is 50,000 psi
– Grade 60: Yield strength
is 60,000 psi (most
commonly used)
– Grade 75: Yield strength
is 75000 psi, (in high rise
building with high
strength concrete)
Es  29 x10 psi
6
Dr. Salah Altoubat
Grades of Reinforcing Steel in SI
• Several grades of
reinforcing bars exist
– Grade 300: Yield strength
is 300 MPa
– Grade 350: Yield strength
is 350 MPa
– Grade 420: Yield strength
is 420 MPa (most
commonly used)
– Grade 520: Yield strength
is 520 MPa
Es  200 x10 MPa
3
Dr. Salah Altoubat
Loads
• Accurate estimation of the loads that may
be applied to a structure is important,
thus difficult task faced by structural
designer
• No Loads that may reasonably be
expected to occur may be overlooked
• Next step is to determine the worst possible
combination of these loads
Dr. Salah Altoubat
Classes of Loads
• Dead Load
• Live Load
• Environmental
– Snow
– Wind
– Seismic Loads (earthquake)
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Dead Loads
• Loads of constant magnitude that remain
in one position (own weight plus
permanent fixtures)
Dr. Salah Altoubat
Live Loads
• Loads that change in magnitude and position
–
–
–
–
–
–
Occupancy loads
Warehouse materials
Construction loads
Equipment
Traffic loads
Impact loads
• Generally act downward and are distributed
uniformly over the entire floor as in Table 1.3
Dr. Salah Altoubat
Typical Live Load (ASCE 7-02)