Design of concrete structure.

Course No. : CE-2106 Credit : 0.75
Course Title : Design of Concrete
Structures-I (Sessional)
Topic : Reinforced Concrete Column

Presented by :
Group : B 1-1
Department of Civil Engineering
Dhaka University of Engineering & Technology, Gazipur.
Md. Mehedi Hasan - 161065
Md. Tayeb Hasan - 161066
Md. Momin Ali - 161067
Md. Rabeul Awal - 161068
Md. Mehedi Hasan Shamim - 161069
Md. Helal Sarker - 161071
M M Alamgir Hossain - 161072
Faysal Ahmed - 161073
Md. Morshed Alam - 161074

Presented to :
Dhaka University of Engineering & Technology, Gazipur.
Dr. Md. Khasro Miah
Professor
Suman Mia
Assistant Professor
Md. Tarek Hasan
Lecturer

Objectives
❑ To know the arrangement of RCC Column.
❑ To know about design specification .
❑ To know about the characteristic of Column .

★ Definition of column (BNBC-6.3.2.1) :
A primarily compression member, which may
or may not be designed to carry simultaneous
flexural forces, shall be termed a column.
● Normally columns carry heavy
compressive loads.
● Columns are used in concrete and steel
buildings.
What is column ?

CLASSIFICATION
(On The Basis of Shape)
1. Square Section
2. Rectangular Section
3. Circular Section
4. T Section
5. L Section

CLASSIFICATION
(On The Basis of Reinforcement)
Tied Spiral Composite Combination

Concentrically
Loaded
Eccentrically
Loaded
1. Concentrically Loaded
Column -resultant load acting
in center
2. Eccentrically Loaded Column-
resultant load does not acting
in center
I. Uniaxial column -
acting one axis
II. Biaxial column -
acting both axis
CLASSIFICATION
(On The Basis of Load)
BiaxialUniaxial

EFFECTIVE LENGTH OF COLUMN
Effective length of column is defined as height
between the point of contraflexure of the buckled i.e.
between two floors basically.
No. End condition of column Effective length
01. Both ends pin ended 1.O L
02. Both ends fixed 0.5 L
03. One end fixed and the other end
pinned
0.707 L
04. One end fixed and the other end
free
2.0 L

BUCKLED MODE FOR
DIFFERENT END CONNECTIONS

BNBC Code 8.3.5.1 specifies :
❑ Tied column: minimum size-12 inch or
300 mm
❑ Spiral Column: minimum size of dia-12
inch or 300 mm
❑ The ratio of the shortest cross-sectional
dimension to the perpendicular dimension
shall not be less than 0.4
SIZE OF COLUMN

Function of longitudinal bar in column
• To resist any tension that might develop due to
bending caused by transverse load, eccentric load of
the moments.
• To reduce the effect of creep and shrinkage due to
sustained loading.
• To prevent or delay sudden collapse.

MINIMUM LONGITUDINAL BARS OF COLUMN
(According to BNBC – 6.3.6.3)
1.Minimum of 6 bars in circular arrangement enclosed
by spiral reinforcement.
2.Minimum of 4 bars in rectangular arrangement
enclosed by ties reinforcement.
3.Minimum of 3 bars in triangular arrangement
enclosed by ties reinforcement

Amount of Reinforcement
(According to BNBC - 6.3.6.1)
1% to 6% in main bar
(According to ACI -10.6.1.1)
1% to 8% in main bar

MINIMUM SPACING FOR LONGITUDINAL BAR
(According to BNBC - 8.1.6.3)
★ 1.5 times of bar diameter or
★ 1.33 times of coarse aggregate size or
★ 25 mm (1 inch)
Largest value is used for spacing.

FUNCTIONS OF TIES
★ To hold the longitudinal bars in position
★ To prevent the highly stressed
★ To prevent buckling

RULES OF TIE ARRANGEMENT
(According to ACI Code:10.7.6.1)
Lateral Tie Longitudinal Bar
#3 or 10 mm <=32mm
#4 or 12 mm >=36mm
★ Maximum 4 bars are used if longitudinal
bars are bundled.
★ Lateral ties should not be less than 10mm.

MINIMUM SPACING FOR TIES
(According to ACI Code:25.7.2.1)
★S = 16*dia of longitudinal bar
★S = 48*dia of lateral bar
★S = Least lateral dimension of column
smallest value is used for spacing.
Minimum spacing for spirals (ACI:25.7.3)
★Pitch = 1.0 inch to 3.0 inch
(25mm to 75mm)

• Covering in contact with earth : 3 in or 75mm.
• If shuttering is used, covering in contact with earth : 2.5 in
or 62.50mm.
• ( According to BNBC- 8.1.7.2 )
• When concrete surface not exposed to weather or in
contact with ground the minimum cover is 30 mm to
40 mm or minimum 1 inch
MINIMUM COVERING FOR COLUMN

LAPPING
Lapping means overlapping of two bars side by side to.
Lapping is usually done where minimum bending stress
is encountered.
Lapping length = 48*dia of main bar

HOOP LENGTH & SPACING
Web reinforcement provide at support section (using largest value)
1. l0 = L/6 (L= clear height between two floors)
2. l0 = maximum dimension
3. l0 = 18 inch
Spacing of tie bar (using smallest value)
1. S = 8*dia of main bar
2. S = 24*dia of tie bar
3. S = 0.5*maximum dimension
4. S = 12 inch

BUNDLE BAR
( According to BNBC-8.1.6.8 )
★ Groups of parallel reinforcing bars bundled to act as a single unit shall be
limited to four.
★ Bundled bars shall be enclosed within stirrups or ties.
★ Where spacing limitations and minimum concrete cover are based on bar
diameter, a unit of bundled bars shall be treated as a single bar of a diameter
derived from the equivalent total area.

FAILURE MODE OF COLUMN
1.LONG COLUMN
Long columns fail by buckling

2.INTERMEDIATE COLUMN
• Intermediate columns fail by a
combination of crushing and buckling

3.SHORT COLUMN
• Short columns fail by crushing

Design of concrete structure.

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