Course Title: Design of Concrete Structures II

Course Code: CE 3217

Reference Books

1. Design of Concrete Structures” by – Winter & Nilson (7th Edition)

2. Design of Concrete Structures” by – Nilson, David & Dolan (14th

Edition)

3. Design of Prestressed Concrete by T.Y. Lin

4. Pre-stressed Concrete by Krishna RajuCourse Content

• Design of columns under uniaxial and

biaxial loading, introduction to slender

column

• Structural design of footings

• Structural forms

• Introduction to prestressed concrete

• Analysis and preliminary design of prestressed beam sections

Design of Concrete Structures II (CE 3217)

Chapter: Footings

Reference Book: Design of Concrete Structures” by – Nilson, David & Dolan (14th Edition)

Lecture prepared by

Md Nuruzzaman

Lecturer, Department of Civil Engineering

Bangladesh Army University of Engineering and Technology (BAUET)

E-mail: suvo.ruet@gmail.com, md.nuruzzaman@live.edu.my

Phone: +8801719456829

Foundation

A foundation is the element of a structure which connects it to theground, and transfers loads from the structure to the ground.

Footings

1

TYPES OF FOUNDATIONS

Foundation Systems

Shallow Foundation Deep Foundation

Pile Foundation Pier (Caisson)

Foundation

Isolated spread

footings Wall footings Combined

footings

Cantilever or

strap footings

Raft or Mat

foundation

2

Shallow Foundations – are usually located no more than 6 ft below the lowest

finished floor. A shallow foundation system generally used when (1) the soil close the

ground surface has sufficient bearing capacity, and (2) underlying weaker strata do not

result in undue settlement. The shallow foundations are commonly used most

economical foundation systems.

Footings are structural elements, which transfer loads to the soil from columns, walls

or lateral loads from earth retaining structures. In order to transfer these loads properly to

the soil, footings must be design to

• Prevent excessive settlement

• Minimize differential settlement, and

• Provide adequate safety against overturning and sliding.

Types of Footings

Isolated spread footings under individual columns.

These can be square, rectangular, or circular.

Footing

Column

3

Wall footing is a continuous slab strip along the

length of wall.

Footing

Wall

4

Property line

Combined footings support two or more columns. These can

be rectangular or trapezoidal plan.

Combined Footing

Footing

Columns

5

Property line

Cantilever or strap footings: These are similar to combined

footings, except that the footings under columns are built

independently, and are joined by strap beam.

6

Raft or Mat foundation: This is a large continuous footing

supporting all the columns of the structure. This is used when

soil conditions are poor but piles are not used.

Mat or Raft

Footing

Columns

7

Deep Foundations – The shallow foundations may not be economical or even

possible when the soil bearing capacity near the surface is too low. In those cases deep

foundations are used to transfer loads to a stronger layer, which may be located at a

significant depth below the ground surface. The load is transferred through skin friction

and end bearing (Figure below).

Fig. 1(a) Axial Compressive Load transfer in deep foundations

Skin friction

Hard soil/

Bedrock

End bearing

Wf

P

Fig. 1(b) Axial Compressive Load transfer in deep foundations

Skin friction

End bearing (negligible)

Wf

P

8

Fig. 2 Axial Tension Load transfer in deep foundations

Skin friction

Wf

P

Fig. 3 Lateral Load transfer in deep foundations

M V

9

Piles

Piles cap

Column

Piles

Piles cap

Column

Fig. Pile Foundation- (a) Vertical Piles; (b) Battered Piles

(a) (b)

10

Pile Foundation

Column

Pile Cap

Piles

11

Bell

Column

Pier shaft

Pier Foundation (Caisson)

15

Soil Bearing Pressure at base of Footings

A. Concentrically Loaded Footing

P

L

W

Bearing pressure, p = P/A = P/(W x L)

Design of Concrete Structures II (CE 3217)

Chapter: Design of Columns

Reference Book: Design of Concrete Structures” by – Nilson, David & Dolan (14th Edition)

Lecture prepared by

Md Nuruzzaman

Lecturer, Department of Civil Engineering

Bangladesh Army University of Engineering and Technology (BAUET)

E-mail: suvo.ruet@gmail.com, md.nuruzzaman@live.edu.my

Phone: +8801719456829

Columns

Tied Column Spiral Column

Columns

Tied Column Spiral Column

Columns

Columns

Why strength reduction factors are lower in column than beam?

The ACI strength reduction factors are lower for columns than forbeams, reflecting their greater importance in a structure. A beamfailure would normally affect only a local region, whereas a columnfailure could result in the collapse of entire structure.

A basic 𝟇 factor of 0.7 is used for spirally reinforced columns and 0.65for tied columns vs 𝟇=0.90 for most beams.

Columns

Specification for Lateral tie bars

For longitudinal bars upto #10 (32 mm bars), use #3 (10 mm) lateral tie bar.

For longitudinal bars greater than #10 (32 mm bars), use #4 (12 mm) lateral tie bar.

Spacing

S = 16 db

S = 48 dt

S = Least dimension of column

The smallest value is to be selected.

Columns