AHSANULLAH UNIVERSITY OF SCIENCE &TECHNOLOGY

Column Design Uniaxial

By-

Sajid Anwar Anik

I.D.- 10.01.03.046

SEC- ADepartment Of C.EPRESTESSED CONCRETE SESSIONAL

Column Design Uniaxial

What is Uniaxial Column?

If the rotation is strictly bound about a single axis only in a column, as the load eccentricity is pure about a single axis.

This can be easily understood by coordinate system . suppose x-y coordinate the center of the column . Now simply if the force is acting on the x-axis only at point P , with zero y co-ordinate , it is uniaxial column.

Some Properties:

• Most of the bars are on tension side . • Use of unsymmetrical pattern of bar is more economical .

Unsymmetrically reinforced column is loaded concentrically , as the load must pass through plastic centroid.

• In a uniaxial reinforced column ,the plastic centroid and geometric center doesn't coincide.

UNIAXIAL SHORT COLUMN DESIGN BY INTERACTION CURCVE (USD) METHOD

Column subjected to eccentric compression

Balanced Failure, eb

Interaction diagram for normal column strength in combined bending andaxial load.

UNIAXIAL SHORT COLUMN DESIGN BY (WSD) METHOD

1. If column controlled by compression eccentricity, e= M/P <= eb :-

• For symmetrical tied column,

eb= (0.67Pgm+0.17)d• For spiral column eb= (0.43PgmDs+0.14t)

• Pg= As/Ag

• m= fy/0.85f’c

Selection of column is done using the relation –

(fa/Fa) + (fb/Fb) <=1, (this is also known as interaction formula.)

Where,fa= P/Ag

Fa= 0.34(1+Pgm)fc’

fb= M/S

S= I/c (c=0.5h)Fb= 0.45 fc’

2. If column controlled by tension, e>eb

Section of column shall be proportioned by using the relation-

M= Mo+ P/Pb (Mb-Mo)

Pb & Mb shall be calculated by using the relation-

(fa/Fa) + (fb/Fb)= 1

=> (Pb/Ag)/Fa + (Pbeb/S)/Fb= 1

For symmetrical tied column: Mo= 0.4 As fy (d-d’), As is tensile steel.

For spiral column: Mo= 0.12 Ast fy Ds, Ast is total steel.

THANK YOU