BEHAVIOUR OF CONCRETE ENCASED BUILT-UP STEEL CONCRETE COMPOSITE

COLUMNS WITH ANGLE SECTIONS

ByS.Amudhalingam (0271101)

Under the guidance of

Tmt.V.M.Shanthi

Lecturer in Civil Engg (Sel.Grd)

INTRODUCTIONCOMPOSITE COLUMNSEXPERIMENTAL PROGRAMMEANALYTICAL PROGRAMMERESULTS GRAPHSCONCLUSIONSBIBLIOGRAPHY

PRESENTATION OUTLAY

GeneralSteelSteel and concreteand concrete

Concrete is efficient in compression and steel Concrete is efficient in compression and steel in tensionin tension

Concrete encasement restrain steel against bucklingConcrete encasement restrain steel against buckling

Protection against corrosion and fireProtection against corrosion and fire

Steel bring ductility into the structureSteel bring ductility into the structure

COMPOSITE COLUMNS

Definition

Composite columns are compressive members in which steel section acts compositely with concrete. So that, both steel and concrete resist the compressive force.

abc

bcy

y

z

tfh hc

cz

b

y

z

h = hc

b = bc

d

c

y

z

b

y

z

t

t

h

b ed

t

y

z

fd

t

y

z

cy

cz

twtf

tw tw

h = hc

b = bc

tf

TYPES OF COMPOSITE COLUMNS

OBJECTIVE OF THE PROJECT

To study the behaviour of built-up steel concrete composite columns with angle sections under axial load and Uniaxial bending (two eccentricities) To study the effect of Fibre reinforced concrete and Additional reinforcement.

To find the moment interaction curves for the built-up sections for ANGLE sections.

TYPES OF SECTIONSTypes of

specimensDimensions of

the sectionsHeight of the specimens

Types of Variation

Built up Angle

sections

20×20×3 mm (3 nos)

890mm Angle sections with

Conventional concrete

Built up angle

Sections

20×20×3 mm (4 nos)

890 mm Angle sections with

Fibre reinforced concrete

Built up Angle sections

20×20×3 mm (4 nos)

890 mm Angle sections with

Additional reinforcement

BUILT UP ANGLE SECTIONWITH SINGLE LACING

EXPERIMENTAL PROGRAMME MATERIAL PROPERTIES

Cement _ Ordinary Portland Cement (43 grade) Fine Aggregate – Passing through 4.75 mm

sieve Coarse Aggregate – 6 mm Water – Potable Water Steel – Cold rolled Steel

Sections of 3mm thickness

MIX DESIGN - IS METHOD

1 : 1.67 : 2.71 : 0.45

Concreting

Composite columns

Built-up sections

1:1.67:2.71:0.45

Curing

ANALYTICAL PROCEDURE PLASTIC RESISTANCE OF THE ENCASED SECTIONS

Pp =Aa fy /a +c Ac fck / c

Aa, Ac = Area of steel and concrete

fy = Yield strength of steel

fck = characteristic compressive

strength of cube

c =strength coefficient

MAXIMUM MOMENT OF RESISTANCE OF THE SECTION

Mmax = PyZpa +0.5PckZpc

Py = Yield strength of steel

Pck = characteristic strength of concrete

Zpa,Zpc = plastic section modulus for steel and concrete section

ANGLE SECTION

Sl.no

Types of loading

First crack

load in KN

Maximum load in KN

T/E % of increase

Maximum deflection in mm

T/E Position

Theoretical

Experimental

Theoretical

Experimental

1 Axial 360 406 718 0.565 12.91 1.64 1.78 0.91 L/2

2 Eccentricity @15mm 320 406 584 0.695 18.5 1.82 1.96 0.89 L/2

3 Eccentricity @20 mm 370 372 430 0.84 0.6 2.02 1.99 0.96 L/2

ANGLE SECTION WITH REINFORCEMENT

Sl.no

Types of loading

First crack

load in KN

Maximum load in KN

T/E % of increase

Maximum deflection in mm

T/E Position

Theoretical

Experimental

Theoretical

Experimental

1 Axial 480 435 758 0.574 42.6 2.24 2.36 0.92 L/2

2 Eccentricity @15mm 640 354 656 0.539 46.1 2.59 2.89 0.86 L/2

3 Eccentricity @20 mm 446 435 647 0.672 32.8 2.86 3.04 0.79 L/2

ANGLE SECTION WITH FIBRE REINFORCED CONCRETE

Sl.no

Types of loading

First crack

load in KN

Maximum load in KN

T/E% of

increase

Maximum deflection in mm

T/E Position

Theoretical

Experimental

Theoretical

Experimental

1 Axial 618 376.72 694 0.5428 45.72 2.82 3.12 0.79 L/2

2 Eccentricity @15mm 430 376.72 543 0.693 31.7 3.14 3.32 0.74 L/2

3 Eccentricity @20 mm 526 376.72 532 0.708 29.2 3.35 3.64 0.71 L/2

RESULTS AND DISCUSSIONS

Load Deflection graph for angle section under axial load

0

50

100

150

200

250

300

350

400

450

0 0.1 0.2 0.3 0.4 0.5 0.6

Deflection in mm

Load

in K

N

l/4 x direction

l/2 x direction

3l/4 x direction

l/4 y direction

l/2 y direction

3l/4 y direction

Load deflection graph for Angle section under e - 15mm

0

10

20

30

40

50

60

70

80

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

Delfection in mm

Load

in K

N l/4 x

3l/4 x

l/2 x

Load and Deflection of angle section with 20mm eccentricity

0

50

100

150

200

250

300

350

400

0 0.5 1 1.5 2 2.5 3

Deflection in mm

Load

in m

m l/4 x direction

l/2 x direction

3l/4 x direction

Load deflectiongraph for angle section with additional reinforcement under axial load

0

100

200

300

400

500

600

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Deflection in mm

Load

in K

N

l/4 x direction

l/2 x direction

3l/4 x direction

l/2 y direction

Load - Deflection for angle-sectionwith additional reinforcement under 15 mm eccentricity

0

50

100

150

200

250

300

350

400

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Deflection in mm

Load

in K

N l/4 x direction

l/2 x direction

3l/4 direction

Load - Deflection graph for angle section with additional reinforcement under 20 mm eccentricity

0

100

200

300

400

500

600

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

Deflection in mm

Load

in K

N l/4 x direction

l/2 x direction

3l/4 x direction

Load - deflection graph for fibre reinforced angle section under axial load

0

100

200

300

400

500

600

700

0 0.5 1 1.5 2 2.5

Deflection in mm

Load

in K

N l/4 x direction

l/2 x direction

3l/4 x direction

l/2 y direction

Load - deflection for fibre reinforced angle section under 15 mm eccentricity

0

100

200

300

400

500

600

0 0.5 1 1.5 2 2.5

Deflection in mm

Load

in K

N

l/4 x direction

l/2 x direction

3l/4 x direction

Load - deflection for fibre reinforced angle section under 20 mm eccentricity

0

50

100

150

200

250

300

350

400

450

500

0 0.5 1 1.5 2 2.5 3

Deflection in mm

Load

in K

N

l/4 x direction

l/2 x direction

3l/4 x direction

Moment curvature for Angle section with Fibre reinforced concrete under e-15mm

0

1

2

3

4

5

6

7

0.000000 0.000001 0.000002 0.000003 0.000004 0.000005

Curvature in Radians

Mom

ent i

n K

N.m

Moment curvature of Angle section with Fibre reinfroced Concrete under e-20mm

0

2

4

6

8

10

12

0.000000 0.000020 0.000040 0.000060 0.000080 0.000100 0.000120

Curvature in radians

Mom

ent i

n KN

.m

Moment curvature for Angle section with reinforcement under e-15mm loading

0

1

2

3

4

5

6

0.000000 0.000002 0.000004 0.000006 0.000008 0.000010 0.000012 0.000014 0.000016

Curvature in radians

Mom

ent i

n K

N.m

Moment Curvature diagram for Angle section with reinforcement under e-20mm

0

1

2

3

4

5

6

7

8

9

0.000000 0.000010 0.000020 0.000030 0.000040 0.000050 0.000060 0.000070 0.000080 0.000090 0.000100

Curvature in radians

Mom

ent i

n K

N.m

Moment curvature for Angel section with 15 mm eccentricity

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0.000000 0.000002 0.000004 0.000006 0.000008 0.000010 0.000012 0.000014

Curvature in radians

Mom

ent i

n K

N.m

Moment curvature for Angle section with e-20mm

0

1

2

3

4

5

6

7

8

0.000000 0.000020 0.000040 0.000060 0.000080 0.000100 0.000120

Curvature in radians

Mom

ent i

n K

N.m

Comparison of Max.Deflection for various specimens

0

100

200

300

400

500

600

0 0.5 1 1.5 2 2.5 3

Defl ec ti on i n mm

Angle under axial load Angle under e-15 mm

Angle under 20 mm Angle r einf or ced under axial load

Angle r einf or ced under e-15mm Angle r einf or ced under e-20mm

Fibr e angle section under axial Fibr e angle under e-15mm

Fibr e angle under e-20mm

LOAD MOMENT INTERACTION DIAGRAM FOR ANGLE SECTION

0

50

100

150

200

250

300

350

400

0 1 2 3 4 5 6

MOMENT IN kN-M

LOAD

IN k

N

C

D

B

A

Mpl Mmax

Pp

Pc

0.5Pc

M

P

CONCLUSIONS Steel elements are not yielding throughout the

complete loading condition. Instead, concrete material failure occurred at a load level close to the maximum axial load.

Failure occurred by crushing of the concrete at the compression face of the cross section.

The maximum load was attained without any distortion of the built-up section or slip between steel and concrete elements.

The composite column will take more loads and the bare steel skeleton will fail by elastic instability at lower load value.

The concrete can be relied upon to transfer the shear between the steel element and concrete.

Experimental load carrying capacity is more than the theoretical load carrying capacity .

when eccentricity is more, variation in the prediction of load carrying capacity is more. When eccentricity is less, variation is also less. This concludes that the theoretical is conservative

The deflections obtained experimentally compared satisfactorily with theoretical values.

Theoretical solution slightly underestimated the value of the collapse load.

No significant torsional displacement could be detected at mid height of the column.

Among all the specimens, built-up angle section with fibre reinforced concrete is found to take more load.

SCOPE OF THE FUTURE STUDY Experimental study on behavior of composite column with

different cross-sections can be carried out.

In this thesis work, baby chips were used as coarse aggregate. Study can be done by varying sizes of coarse aggregate.

The study can be extended to slender composite columns.

The effect of shear connectors can be studied for future work.

Using cold formed and hot rolled steel sections, various other shapes can be carried out and tested.

REFERENCES

Furlong R.W. “Strength of steel encased concrete beam-columns”,

Journal of Structural Division, ASCE,1967:93(ST5):pp 115- 130.

N.E.Shanmugam,B.Lakshmi “State- of – art – report on composite

columns”, Journal of Constructional Steel Research.

Munoz , “Biaxially loaded concrete-encased composite columns”,

Journal of Structural engineering,ASCE,1997,pp1576- 1585.

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