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Basic Structural Elements Designs to BS 8110-Part 1:1997
3.0
COLUMN DESIGN
3.1
UNBRACED SHORT COLUMN DESIGN
X-X axis
Y-Y Axis
Y-Y Axis
X-X axis
Figure 3.1: General arrangement
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Basic Structural Elements Designs to BS 8110-Part 1:1997
Reference
Calculations
Out Put
Column is designed as un braced column. Cl.3.8.1.6
Calculation of Column effective height.
BS 8110-1:1997
Effective Length for X-X Plane Bending ( L ex )
L ox -Clear height between end restraints. L ox
= Floor
to Floor Height − Beam along Y direction
L ox
= 3600 − 600 =
3000mm
(Dimension of column for XX axis Bending h = 750 mm and Depth of the Beam along Y direction is 600mm.) Cl.3.8.1.6.2
Hence Top Condition is 1.
BS 8110-1:1997
Ground Beam Depth is 900mm. Hence Bottom Condition -1
Table 3.2
Hence β = 1.2
BS 8110-1:1997
L ex L ex h
= βL ox = 1.2 × 3000 = 3600mm =
3600 750
=
4.8 < 10
Hence Column is short in X-X direction.
Cl.3.8.1.6
Effective Length for Y-Y Plane Bending ( L ey )
BS 8110-1:1997
See Figure 1. L oy -Clear height between end restraints. L oy =Floor to Floor Height-Beams along Y direction
L oy
=
3600 − 600 = 3000mm
Other Design Information
f cu
2
= 30N/mm
Cover to Reinforcement is 30mm. T25 Main bars and T10 Links are to be used.
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Basic Structural Elements Designs to BS 8110-Part 1:1997
Reference
Calculations
Out Put
(Depth of the Beam along X direction is 600mm.) Cl.3.8.1.6.2
Hence Top Condition is 1.
BS 8110-1:1997
Ground Beam Depth is 900mm. Hence Bottom Condition -1
Table 3.2
Hence β = 1.2
BS 8110-1:1997
L ey
= βL oy = 1.2 × 3000 = 3600mm
L ey
=
b
3600 400
= 9 < 10
Hence Column is short in Y-Y direction.
Short Column
Hence column is a short column.
Cl.3.8.1.7
Checks for Slenderness limit of un braced column
BS 8110-1:1997
L oy
= 3000mm
60b = 60 × 400 = 24000 L oy
< 60b
Hence Slenderness Limit is Ok.
Design Loads from SAP 2000 Model
Column is designed for ULS 1 Load Combination.(Critical) N = 5464 kN
Mxx
Myy
Edifice Consultants Pvt.Ltd
=
524 kNm
=
23kNm
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Basic Structural Elements Designs to BS 8110-Part 1:1997
Reference
Calculations
Cl. 3.8.2.4
Checks for Minimum Eccentricity
BS 8110-1:1997
Minimum eccentricity in X-X Plane Bending emin , x
=
0.05h or 20 mm which ever is greater
emin , x
=
0.05 × 750 = 37.5mm
Out Put
Hence minimum eccentricity is 20mm. Hence M min,x
= Ne
min,x
= 0.020 × 5464 = 109.28kNm < 524kNm
Hence Design moment about X-X axis taken as 524kNm. Minimum eccentricity in Y-Y Plane Bending
emin,y
=
e min , x
0.05b or 20mm which ever is greater
= 0.05 × 400 = 20mm
Hence minimum eccentricity is 20mm. Hence Mmin , x
= Ne
min , x
= 0.020 × 5464 = 109.28kNm > 20.3kNm
Hence Design moment about Y-Y axis taken as 109.28kNm.
Reinforcement Design for Column (See Figure 3.2)
h′ = 750 − 30 − 10 −
b′ = 400 − 30 − 10 − Mx h′
=
My b′ Mx h′
=
>
524 697.5
=
109.28 347.5
25 2 25 2
=
697.5mm
=
347.5mm
0.75
=
0.31
My b′
Hence Column is designed for an increased moment about X-X axis.
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Basic Structural Elements Designs to BS 8110-Part 1:1997
Figure 3.2: Column axis convention
Figure 3.3: Reinforcement Detailing of the Column Section
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Basic Structural Elements Designs to BS 8110-Part 1:1997
Reference
Calculations
M′x
= Mx +
7
β =1−
=
7 6
M 2 bh f cu
h
My
N
×
5464 × 10
3
400 × 750 × 30 697.5 347.5
5464 × 10
=
bhf cu
=
b′
524 + 0.3 ×
N
d
′
6 bhf cu
β =1−
M′x
h
Out Put
702.5 750
× 109.28 =
=
6 590 × 10 2 400 × 750 × 30 =
590kNm
3
400 × 750 × 30
=
= 0.29 < 0.3
0.61
= 0.09
0.93
From Appendix D of “Manual for the Design of Reinforced Concrete Building Structures”
ρf y
= 0.42
f cu ρ=
As
As bh
= 0.42 ×
30 460
2
× 400 × 750 = 8217mm
The area of reinforcement should be detailed in as per Figure 8.3. Table 3.25
Checks for Minimum Area of Reinforcement
100A sc bh A sc
=
= 0.4
0.4 × 400 × 750 100
2
= 1200mm
Provided reinforcement satisfied the minimum reinforcement requirement.
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Reference
Calculations
Cl. 3.8.2.4
Checks for maximum area of reinforcement
BS 8110-1:1997
100A sc bh A sc
=
Out Put
=6
6 × 400 × 750
100
= 18000mm
2
Hence provided area of reinforcement is within the maximum allowable.
At Laps At a Lap 8T25 bars are lapped. Hence Total 24 Bars ar e at the cross section (16+8) 2
A sc
= 24 × 491 = 11784mm
A sc
=
11784 × 100 750 × 400
Cl. 3.8.4.6
Checks for Shear
BS 8110-1:1997
Mx N
=
590 5464
= 3.93% < 10%
= 0.11
0.6h = 0.6 × 0.750 = 0.45
Hence a shear check is not required.
Cl.3.12.7.5
Design of Links
BS 8110-1:1997
Largest Compression bar
=25mm
Hence Diameter of the shear link should be larger than 25/4=6mm. Hence T10 Links were provided. Shear Link spacing should be less than 12 times smallest compression bar. (12x20=240mm) But link details required to mitigate seismic effects are stringent than this. Hence shear link details were provided to mitigate the seismic effects.
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Basic Structural Elements Designs to BS 8110-Part 1:1997
Reference
Calculations
Out Put
Design of Links to mitigate Seismic Effects
Detailing of the shear links were done as per “Reinforcement Detailing to mitigate seismic effects “ published by Society of Structural Engineers, Sri Lanka. Column confinement zone depth ( Adjacent to Beams) is greater of (a) 500mm (b)
lo
6
= 500mm
(c) Maximum dimension of column (750mm) Hence Depth of the confinement zone is taken as 750mm. In confinement zones and at laps spacing of links/ cross ties shall be greater of (a) 100mm (b)
Minimum Column Dimension 3
400 3
but greater than 50mm
= 133.33mm > 50mm
Diameter of the links/ cross ties should be greater than 8mm. Hence T10 links at 100mm spacing provided throughout since column bars are lapped at two location between a given floor height.
