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