Ahsanullah University of Science & Technology

Department of Civil Engineering

Pre-stressed Concrete Lab

Imtiaz Ahmed TilokID: 10.01.03.048

4th Year; 2nd Semester Sec : A

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Column Design: Biaxial

Column is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member.

The biaxial bending method discussed permit rectangular column to be designed or analyzed if bending is present about only one of the two principal axes of section.

Axial compression is accompanied by simultaneous bending about both principle axes of the section.

It occurs in corner columns of building.

Fig: Biaxial bending plus compression

From this figure, we get:

Equivalent Eccentricity of column load

(a) Concentrically loaded column (b) Eccentrically loaded column

Fig: Column subject to eccentric compression

(a)loaded column(b)Strain distribution at section a-a(c)Stress and forces at nominal strength

Nominal load,

Nominal moment,

Balanced Failure, eb

Fig: Interaction diagram for nominal column strength in combined bending and axial load

Interaction Curve

Interaction diagram for compression plus biaxial bending

(a) Uniaxial bending about y axis(b)Uniaxial bending about X axis(c)Biaxial bending about diagonal axis(d)Interaction surface

Methods : There are three types of method.1.Load Contour Method2.Reciprocal Load Method3.Computer Analysis For Biaxial Bending Of Columns.

Load Contour MethodWhere

Where,

Reciprocal Load Method

Fig: Interaction surface for the reciprocal load method

• The 12×20 in column shown in fig is reinforced with eight no.9 bars arranged around the column perimeter, providing an area Ast=8 in². A factored load Pu of 255 kips is to be applied with eccentricities

=3in, =6in.

material strengths are ƒ’c = 4 ksi and ƒʏ= 60 ksi.

Check adequacy by trial design using

a. Reciprocal load method

b. Load contour method.

EXAMPLE: DESIGN OF COLUMN FOR BIAXIAL BENDING

Problem Figure:

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