Erbil Technical Engineering Collage

Department of Highway Engineering

• RCD 502
• Reinforced Concrete Design
• September, 2024

General Introduction

• Bakhtyar Nassih Najar MSCE, PE

• EPU Chat
• Email: bakhtyar.najar@epu.edu.iq

Text Book and References: RCD 502 Reinforced Concrete Design

1. Reinforced Concrete Design, Ninth Edition, CHU-KIA WANG CHARLES G. SALMON

2. Structural Concrete Theory and Design, 7th Edition, Nadim Hassoun, Aktham Al-Manaseer
3. Reinforced Concrete a Fundamental Approach, Edward Nawy.
4. Design of Concrete Structures, 14th Edition, Arthur Nelson.
5. Reinforced Concrete Mechanics and Design, Sixth Edition, James MacGregor.

2
 ACI Building Code.
Whenever two different materials used, such as steel and concrete, acting together, it is understandable that
the analysis for strength of a reinforced concrete member has to be partial empirical although rational. These
semi-rational principles and methods are being constant revised and improved as a result of theoretical and
experimental research accumulate. The American Concrete Institute (ACI), serves as clearing house for these
changes, issues building code requirements.

Reinforced concrete: It is a mixture of concrete and steel. Such a mixture combines the best properties of both
materials to overcome their deficiencies.

Main properties of concrete:

RCD 502 Reinforced Concrete Design

1. Good in compression
2. Low tensile strength
3. Good in fire resistance

Reinforcing steel:
1. High tensile strength
2. Low fire resistance 3

Concrete Properties
The standard strength test generally uses a cylindrical sample. It is tested after 28 days to test for strength,
𝑓 . The concrete will continue to harden with time and for a normal Portland cement will increase with
time as follows:

The modulus of elasticity, Ec, can be defined as the change of stress concerning strain in the elastic range.
The modulus of elasticity is a measure of stiffness, or the resistance of the material to deformation. In concrete,
as in any elastoplastic material, the stress is not proportional to the strain, and the stress-strain relationship is a
curved line. The actual stress-strain curve of concrete can be obtained by measuring the strains under
RCD 502 Reinforced Concrete Design
increments of loading on a standard cylinder.

𝑓
𝐸
𝑓
𝑆𝑡𝑟𝑒𝑠𝑠
𝐸 =
𝑆𝑡𝑟𝑎𝑖𝑛 0.45𝑓

𝜀 4
The ACI Code, Section 19.2.2.1, gives a simple formula for calculating the modulus of elasticity of normal and
lightweight concrete considering the secant modulus at a level of stress, 𝑓 , equal to half or 0.45 of the specified
concrete strength, 𝑓 ,

(a) For values of 𝑤 between 1440 and 2560 kg/m3

𝐸 = 𝑤 . 0.043 𝑓 (𝑖𝑛 𝑀𝑃𝑎)

b) For normal-weight concrete, 𝑤 is approximately (2320 kg/m3)

𝐸 = 4700 𝑓 (𝑖𝑛 𝑀𝑃𝑎)

RCD 502 Reinforced Concrete Design

Typical Concrete Stress-Strain Curves in Compression

1 psi = 0.007 MPa

Poisson’s Ratio, n , is the ratio of the transverse to the longitudinal strains under axial stress within the elastic
range.

n ~ 0.15 to 0.20 Usually use n = 0.18

5

Types of compression failure

There are three modes of failure.

1. Under axial compression concrete fails in shear.
2. The separation of the specimen into columnar pieces
by what is known as splitting or columnar fracture.
1. Combination of shear and splitting failure.

Tensile Strength Mc 6M
fr = = 2 RCD 502 Reinforced Concrete Design

 Tensile strength ~ 7% to 11% of 𝑓 I bh

 Modulus of Rupture, 𝑓 for deflection calculations, use:
P unreinforced
concrete beam
𝑓 = 0.62 𝜆 𝑓 ACI (19.2.3.1)

𝜆 is in accordance with 19.2.4

𝜆 = 1.0 for normal weight concrete fr

6
𝜆 = 0.75 for light weight concrete Mmax = P/2*a
Tensile Strength (cont.)
 Splitting Tensile Strength, fct
 Split Cylinder Test

RCD 502 Reinforced Concrete Design

2𝑃
𝑓 =
𝜋𝑙𝑑

(Not given in ACI Code) 7

Shrinkage and Creep

 Shrinkage: Due to water loss to atmosphere (volume loss).

 Plastic shrinkage occurs while concrete is still “wet” (hot day, flat work, etc.)

 Drying shrinkage occurs after concrete has set

 Most shrinkage occurs in first few months (~80% within one year).
 Cycles of shrinking and swelling may occur as environment changes.
 Reinforcement restrains the development of shrinkage.

RCD 502 Reinforced Concrete Design

o Shrinkage is a function of
o W/C ratio ( Higher w/c ration causes greater shrinkage )
o Aggregate type (the smaller aggregate the greater shrinkage)
o Volume/Surface Ratio
o Type of cement : The finer the cement, the greater the expansion under moist conditions.
o Admixtures: increasing the water requirement increases shrinkage.
o size and shape of the specimen.

8
 Creep
 Deformations (strains) under sustained loads.
 Like shrinkage, creep is not completely reversible.

P
dL, elastic
L dL, creep

RCD 502 Reinforced Concrete Design

 Magnitude of creep strain is a function of all the above that affect shrinkage, plus
 magnitude of stress
 age at loading

 Creep strain develops over time…

 Absorbed water layers tend to become thinner between gel particles that are
transmitting compressive stresses
 Bonds form between gel particles in their deformed position.

Shrinkage:
1. Definition: Shrinkage is the reduction in volume of concrete as it dries and cures.
2. Cause: It primarily occurs due to the loss of moisture from the concrete, which causes it to
contract.
3. Timing: It happens soon after the concrete is placed and continues for a period of time as it
dries.
4. Effect: It can lead to cracking if not properly managed.

Creep:
1. Definition: Creep is the gradual deformation of concrete under a constant load over time.
2. Cause: It results from the long-term effects of stress on concrete, even after the initial shrinkage
has stabilized. RCD 502 Reinforced Concrete Design
3. Timing: It occurs over a longer period, often months or years, as the concrete continues to
deform under sustained loads.
4. Effect: It can cause long-term deflection and deformation in structural elements.

In summary, shrinkage is about volume reduction due to drying, while creep is about long-term
deformation under constant stress.

10
Steel Reinforcement

1. General
Standard Reinforcing Bar Markings

ACI – Appendix B – Steel Reinforcement Information

RCD 502 Reinforced Concrete Design

11

2. Types of steel reinforcement

 The modulus of elasticity of steel is equal to 200 000 Mpa
 Steel grade 60 ASTM A615 and ASTM A706
 The main difference between steel A615 and A706 is more ductile and they both have the same yield strength
 Grade 40: 𝑓 = 40 ksi = 280 Mpa
 Grade 60: 𝑓 = 60 ksi = 420 Mpa
 Grade 80: 𝑓 = 80 ksi = 560 MPa
 Grade 100: 𝑓 = 100 ksi = 700 Mpa
 Based on ACI 318-19, the ratio of actual tensile strength to actual yield strength, minimum: 1.10 for steel A615
and 1.17 for steel A706
RCD 502 Reinforced Concrete Design

3. Stress versus Strain

 Stress-Strain curve for various types of steel
reinforcement bar.

Typical stress – strain curve of reinforcing steel 12

DEAD LOAD:
Definition. Dead loads consist of the weight of all materials of construction incorporated
into the building including, but not limited to, walls, floors, roofs, ceilings, stairways,
built-in partitions, finishes, cladding, and other similarly incorporated architectural and
structural items and fixed service equipment, including the weight of cranes and material
handling systems. ( 3.1.1 ASCE 7-22 )
Weights of Materials and Constructions. In determining dead loads for purposes of
design, the actual weights of materials and constructions shall be used, provided that in
the absence of definite information, values approved by the Authority Having Jurisdiction

RCD 502 Reinforced Concrete Design

shall be used ( 3.1.2 ASCE 7-22 )

Weight of Fixed Service Equipment. In determining dead loads for purposes of design,
the weight of fixed service equipment, including the maximum weight of the contents of
fixed service equipment, shall be included. The components of fixed service equipment
that are variable, such as liquid contents and movable trays, shall not be used to
counteract forces causing overturning, sliding, and uplift conditions. ( 3.1.3 ASCE 7-22 )

Can Be Uncertain…. pavement thickness Earth fill over an underground structure

13

• Brick wall: w = thickness of the bricks x unit weight of bricks + thickness of plastering
x unit weight of plain concrete.
• Tiles: w = thickness of each layer x unit weight of the layer

Unit weights
Reinforced concrete: 25kN/m3
Plain concrete: 23kN/m3 Dead loads may be classified into:
Masonry stone: 27kN/m3 Self-weight: own weight
Concrete blocks: 15kN/m3 Superimposed dead load: mechanical, plumbing,
Fill under tiles:18kN/m3 electrical… etc.
Plastering: 23kN/m3 RCD 502 Reinforced Concrete Design

Examples
• Brick wall: w = 200 mm bricks+ 20 mm plastering + 20 mm plastering: w =
3.62kN/m3
• Brick wall: w = 100 mm bricks+ 20 mm plastering + 20 mm plastering: w =
2.42kN/m3
• Tiles: 30 mm marble tiles + 20 mm plain concrete + 10 mm plastering at
bottom surface of slab: w = 3.3kN/m3 14
LIVE LOAD: A load produced by the use and occupancy of the building or other structure
that does not include construction or environmental loads, such as wind load, snow load, rain
load, earthquake load, flood load, or dead load

RCD 502 Reinforced Concrete Design

15

Flood Loads: Chapter 5 ( ASCE 7-22): Structural systems of buildings or other

structures shall be designed, constructed, connected, and anchored to resist flotation,
collapse, and permanent lateral displacement due to the action of flood loads associated
with the design flood
Snow Loads: Chapter 7 ( ASCE 7-22) Structural systems of buildings or other structures
shall be designed, constructed, connected, and anchored to resist flotation, collapse, and
permanent lateral displacement due to the action of flood loads associated with the design
flood

RCD 502 Reinforced Concrete Design

Rain Loads: Chapter 8 (ASCE 7-22): Each portion of a roof shall be designed to

16
sustain the load of all rainwater that will accumulate on it, assuming all drainage systems
are blocked. ( ASCE 7-22) for more details.
Seismic Loads: Chapter 11-23 ( ASCE 7-22): Every structure and portion thereof,
including nonstructural components, shall be designed and constructed to resist the effects
of earthquake motions as prescribed by the seismic requirements of ASCE7-22.

𝑉 = 𝐶 .𝑊
where
V = Seismic base shear
Cs = The seismic response coefficient
W = The effective seismic weigt

RCD 502 Reinforced Concrete Design

Wind Loads: Chapter 26-31 ( ASCE 7-22): Buildings and other structures, including the
main wind force resisting system (MWFRS) and all components and cladding (C&C)
thereof, shall be designed and constructed to resist the wind loads determined in accordance
with Chapters 26 through 31.

17

Code of Practice:
Design engineers typically follow guidelines known as codes of practice, which are
established by various organizations to ensure public safety. These specifications outline
the minimum standards required but are not intended to limit the creativity or innovation
of engineers.
Codes of practice generally detail requirements for design loads, allowable stresses,
material quality, construction methods, and other aspects of building construction. In the
United States, a key standard for structural concrete design is the Building Code
Requirements for Structural Concrete, known as ACI 318 or the ACI Code. This class’s
design examples are primarily based on this standard. RCD 502 Reinforced Concrete Design

Other important codes and material specifications in the U.S. include the International
Building Code (IBC), the American Society of Civil Engineers’ standard ASCE 7, and the
American Association of State Highway and Transportation Officials (AASHTO)
specifications. Additionally, standards from the American Society for Testing and
Materials (ASTM), the American Railway Engineering Association (AREA), and the
Bureau of Reclamation, Department of the Interior, also play a role in guiding engineering
practices.
18
DESIGN PHILOSOPHY AND CONCEPTS

• The design of a structure may be regarded as the process of selecting the proper
materials and proportioning the different elements of the structure according to state-
of-the-art engineering science and technology.

• In order to fulfill its purpose, the structure must meet the conditions of safety,
serviceability, economy, and functionality. This can be achieved using design
approach-based strain limits in concrete and steel reinforcement.

• The actual loads, or working loads, are multiplied by load factors to obtain the factored

RCD 502 Reinforced Concrete Design

design loads. The load factors represent a high percentage of the factor for safety
required in the design.

• According to the limit state design, reinforced concrete members have to be analyzed
with regard to three limiting states:

1. Load-carrying capacity (safety, stability, and durability)

2. Deformation (deflections, vibrations, and impact)
3. Formation of cracks
19

Required Strength: required internal forces to be resisted by using load combinations

(like Mu)
Purpose of load factors:
• To account for inaccuracy in load calculations.
• To account for slight variations in loads during the lifetime of the structure.
• To account for variability in structural analysis.

RCD 502 Reinforced Concrete Design

20
Nominal Strength: strength of a member or a section calculated in accordance with
provisions and assumptions of the strength design method of code ( like Mn)
Design strength: Strength reduction factor X Nominal Strength (like ∅Mn)

∅ = 0.9 flexural – tension controlled Purpose of the strength reduction factors

∅ = 0.75 shear • To allow slight variations of material strengths.
∅ = 0.75 torsion • To allow slight variations in dimensions.
• To allow inaccuracies in the design equations.
∅ = 0.65 axial − tied columns
∅ = 0.75 axial − sprial columns • To reflect the degree of ductility.
•

RCD 502 Reinforced Concrete Design

To reflect the importance of the member in the
structure.

strength required to 
strength provided   
 carry factored loads 
21