DESIGN OF REINFORCED CONCRETE
UNIVERSITY OF WASIT- COLLEGE OF ENGINEERING
CIVIL ENGINEERING DEPARTMENT
THIRD CLASS
Asst. Prof. Dr. SALLAL RASHID ABID
2017-2018
Design of Reinforced Concrete Lec.1 Introduction
1 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
Design of Reinforced Concrete
Text Books:
1- Design of Concrete Structures (14th
Edition) by: A. H. Nilson; D. Darwin & C. H. Dolan
2- Building Code Requirements for Structural Concrete ACI 318-14
References:
1- Reinforced concrete Design (7th
Edition) by: C. K. Wang , C. G. Salmon & J.A. Pincheira
2- Design of Reinforced Concrete (10th
Edition) by: J.C. McCormac & R. H. Brown
Syllabus:
Syllabus Semester
Introduction 1st
Materials 1st
Flexural Analysis & Design of Beams (Working Stress Design Method) 1st
Flexural Analysis & Design of Beams (Ultimate Strength Design
Method) 1
st
Shear & Diagonal Tension in Beams 1st
Analysis & Design of Torsion 1st
Bond, Anchorage & Development Length 1st
Serviceability: Crack and Deflection 2nd
Analysis & Design of One-way Slabs 2nd
Analysis & Design of Continuous Beams and One-way Slabs 2nd
Analysis & Design of Two-way Slabs 2nd
Analysis & Design of Short Columns: Concentrically and Eccentrically
loaded 2
nd
Analysis & Design Slender Columns 2nd
Units
SI Metric British
Force
N
kN = 1000 N
1 kg = 9.81 N
gm
kg = 1000 g
Ton = 1000 kg
lb
kip = 1000 lb
1 lb = 4.448 N
Length
mm
m = 1000 mm
mm = 0.1 cm
cm
cm = 10 mm
m = 100 cm
in
ft = 12 in (˝)
1 in = 25.4 mm
Stress
Pam
N
Area
ForceStress
2
kPam
kN
2
MPamm
N
2
2cm
gm
2cm
kg
2m
Ton
psiin
lb
2
psiksiin
kip1000
2
MPaksi 895.61
Kilo Pascal = kPa = 103 Pa
Mega Pascal = MPa= 106 Pa
Gega Pascal = GPa = 109 Pa
Tera Pascal = TPa = 1012
Pa
Design of Reinforced Concrete Lec.1 Introduction
2 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
ACI Building Code:
Whenever two different materials, such as steel and concrete, are 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 continuously
revised and improved as a result of theoretical and experimental research accumulates. The
American Concrete Institute (ACI) serves as clearing house for these changes and issues
building code requirements.
Design Philosophy:
Two philosophies of design have long prevalent.
• Working stress method focuses on conditions at service loads.
• Strength design method focuses on conditions at loads greater than the service loads
when failure is imminent.
The strength design method is deemed conceptually more realistic to establish structural safety.
Strength Design Method:
In the strength method, the service loads are increased sufficiently by factors to obtain the load
at which failure is considered to be “imminent”. This load is called the factored load or
factored service load.
The provided strength is computed in accordance with rules and assumptions of behavior
prescribed by the building code and the strength required is obtained by performing a structural
analysis using factored loads.
The “strength provided” has commonly referred to as “ultimate strength”, however, it is a code
defined value for strength and not necessarily “ultimate”. The ACI Code uses a conservative
definition of strength.
Safety Provisions:
Structures and structural members must always be designed to carry some reserve load above
what is expected under normal use.
There are three main reasons why some sorts of safety factor are necessary in structural design.
[1] Variability in resistance.
[2] Variability in loading.
strength required to strength provided
carry factored loads
Fundamentals
Design of Reinforced Concrete Lec.1 Introduction
3 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
[3] Consequences of failure.
Variability of the strengths of concrete and reinforcement.
Differences between the as-built dimensions and those found in structural drawings.
Effects of simplifications made in the derivation of the member resistance.
Primary Elements of Reinforced Concrete Buildings:
Every reinforced concrete building composes of three or more structural elements that should be
designed to resist the different types of loads. The main parts of reinforced concrete buildings
are:
1- Footings
2- Columns
3- Beams
4- Slabs
The beams and slabs work together as one monolithic part referred to as the floor-slab system.
The floor-slab system is mainly the slab with or without; beams, drop panels, and column
capitals as will be explained in following sections. Figure (1) shows the main parts of a
reinforced concrete structure designed for gravity loads.
Figure (1) Main parts of reinforced concrete buildings
Design of Reinforced Concrete Lec.1 Introduction
4 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
Design and Construction of Reinforced Concrete Structures:
The sequence of design is the inverse of the sequence of construction. The design starts from the
highest level with slab and beams through columns and ends at the lowest level at the
foundations (footings). On the other hand, the construction starts from the lowest level by
preparing and pouring the footings, followed by the construction of the columns of the first
floor. Then after, the floor-slab system (slab and beams) are cast together as one unit as shown
in Figure (2). And so on for the above floors, until reaching the roof. Figures (3) to (12) illustrate
the construction process of the building shown in Figure (1).
Figure (2) Monolithic slab-beam system
Figure (3) Footings and columns layout
Design of Reinforced Concrete Lec.1 Introduction
5 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
Figure (4) Construction of footings shown in Figure (3) (Note that dowels of columns from
footings should be included in this stage)
Figure (5) Columns of ground floor
Figure (6) Columns of ground floor on footing with tie beams and different shapes of columns
Design of Reinforced Concrete Lec.1 Introduction
6 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
Figure (7) Illustration of beams of ground floor (Note that beams are cast monolithically with
slabs)
Figure (8) Illustration of floor slab of ground floor (Note that beams are cast monolithically with
slabs as one continuous system and that dowels of the above level columns should be included in
this stage)
Design of Reinforced Concrete Lec.1 Introduction
7 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
Figure (9) Columns of first floor
Figure (10) Illustration of floor slab of first floor (Note that beams are cast monolithically with
slabs as one continuous system and that dowels of the above level columns should be included in
this stage)
Design of Reinforced Concrete Lec.1 Introduction
8 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
Figure (11) Columns of second floor
Figure (12) Illustration of roof slab (Note that beams are cast monolithically with slabs as one
continuous system)
Design of Reinforced Concrete Lec.1 Introduction
9 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
Sequence of the Design of Reinforced Concrete Structures:
For ordinary reinforced concrete buildings designed for gravity loads only, the uniformly
distributed load on slabs is transferred from slabs at each level to beams in the same level, from
which the loads are transferred to the columns of that level. The loads are then accumulated
from the higher columns to the lower ones reaching the footings that should withstand the whole
structure load and transfer it to the soil as illustrated in Figure (1).
What Is the Design And What to Design?
The word “design” here means the detailed calculations that lead to the proper cross section
dimensions of the concrete element and the adequate amount and distribution of reinforcing bars
to safely withstand the different types of the applied loads. In addition, the design should assure
that the deformations (deflection and cracks) are safe along the design life of the structure.
Figure (13) Formwork and reinforcement of a slab and an edge beam
Under gravity loads, slabs are mainly designed for flexure and shear. Shear should be carried out
by the concrete section only (except special cases of flat slabs with high punching stresses),
while the flexure is designed to be carried out by both the concrete section and the reinforcing
steel. The amount of required reinforcement depends mainly on the amount of the applied loads
on the slab and hence on the applied bending moment, while the distribution of reinforcement
depends on the boundary conditions, i.e. the degree of restraint at each end of the slab. Figure
Design of Reinforced Concrete Lec.1 Introduction
11 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
(13) illustrates an example of the formwork and reinforcement of a slab panel and its
corresponding edge beam. As shown, the reinforcement of the slab is distributed as a grid of
bars along the two directions.
Beams are designed to resist three main loading types; flexure, shear, and torsion. The flexural
reinforcement are distributed longitudinally as number of bars at the bottom and top of the
section as shown in Figures (14) to (16). To resist shear forces, the beam is reinforced with
vertical bars (U-shape or closed) called “stirrups” as clearly shown in Figure (14) and Figure
(15). On the other hand, resistance of twist from the torsional moment requires both stirrups and
longitudinal bars.
Columns are subjected to axial compression loads with or without bending moments. Therefore,
columns main reinforcement composes of vertical bars distributed either on two sides or on all
sides of the section. Moreover, sufficient lateral reinforcement should be provided to resist any
possible shearing forces. This reinforcement is similar to the stirrups of beams; however, it is
called “ties” instead. Spirals maybe used also as lateral reinforcement in circular columns.
Figures (14) and (16) show the vertical and lateral reinforcement of columns.
Footings are generally designed as slabs with inverted loads. Note that the word footing in this
text lecture refers to shallow foundations only. In general, footing design is not included in this
course. Students are to take lectures to design the different types of foundations in the fourth
class.
Figure (14) Reinforcements of footings, columns, and beams
Design of Reinforced Concrete Lec.1 Introduction
11 Asst. Prof. Dr. Sallal R. Abid Wasit University - Civil Engineering Department.
Figure (15) Reinforcement details of beams.
Figure (16) Picture of the formwork of slab-beam system and the reinforcements of slab, beams,
and a column