flexural behaviour of coldformed steel - concrete

FLEXURAL BEHAVIOUR OF COLDFORMED STEEL - CONCRETE COMPOSITE BEAMS

By K.Senthil Kumar, 90108512013 M.E., Structural Engg, ACCET, Karaikudi.

Project Guide Prof.M.S.Komala, Head of the department, Dept. of Civil Engg, ACCET, Karaikudi.

OBJECTIVE • The objectives of the experimental investigation were to determine the ultimate flexural strength, deflection,stiffness,energy absorption and ductility characteristics. • The area of tension steel in the conventional RCC beam was computed and it was replaced partially by cold formed steel so as to produce the same tensile force in the composite beam. and effectively bonded with concrete using shear connectors. • Different arrangements of Shear connectors were used and their effects on the mode of failure of beam were studied.

FINITE ELEMENT MODELING OF REINFORCED CONCRETE BEAM AND COMPOSITE BEAM USING ANSYS The objectives of the computer modeling were to:

• Examine the structural behavior RC beam and composite beams. • Establish a methodology for applying computer modeling to RC beam and composite beams.

BEAM DESIGN (100 x 200 x 1700 mm)

RCC Beam

Plate Composite beam with shear connector

CPS1

CPZS

CPAS

CPCS

CPS2

CPIS

Experimental Setup

Experimental Setup

TEST RESULTS AND DISCUSSIONS

Flexural test results Beam First crack Designation load (kN)

Mid span Deflection at First crack load (mm)

Ultimate load (kN)

Mid span deflection at Ultimate load (mm)

RC

18.75

2.18

59.38

17.36

CPS1

22.79

2.27

53.13

18.80

CPS2

21.88

3.00

54.25

25.20

CPZS

23.65

2.98

61.36

24.32

CPCS

22.85

3.40

54.69

29.14

CPIS

25.00

2.21

62.50

22.16

CPAS

24.80

2.54

68.76

32.90

Comparison of Deflections and Ductility Index Mid span Deflection at First crack load y (mm)

Ultimate midspan

RC

2.18

17.36

7.96

CPS1

2.27

18.80

8.28

CPS2

3.00

25.20

8.40

CPZS

2.98

24.32

8.16

CPCS

3.40

29.14

8.57

CPIS

2.21

22.16

10.03

CPAS

2.54

32.9

12.95

Beam Designation

Ductility index D.I =u/y

Deflection u (mm)

Stiffness Beam Designation

Ultimate load (kN)

Mid span deflection at Ultimate load (mm)

Stiffness

N/mm

RC CPS1

59.38 53.13

17.36 18.80

3420.50 2826.06

CPS2 CPZS CPCS CPIS CPAS

53.13 61.36 54.69 62.50 68.76

25.20 24.32 29.14 22.16 32.90

2108.33 2523.03 1876.80 2820.39 2089.96

80

Load Deflection Curve (Mid Span)

70

60

RC CPCS CPAS CPS1 CPIS CPS2 CPZS

Load in kN

50

40

30

20

10

0 0

5

10

15

20

25

Deflection in mm

30

35

80

Load Deflection Curve (Under point load)

70

60


Load in kN

50

40

30

20

10

0 0

5

10

15

Deflection in mm

20

25

80

Load Deflection Curve (250mm from support)

70

60


Load in kN

50

40

30

20

10

0 0

2

4

6

8

10

12

14

Deflection in mm

16

18

20

80

Load-Strain plot(Steel plate)

70

Load in kN

60

50

CPZS CPAS CPCS CPS2 CPS1 CPIS

40

30

20

10

0 0

0.1

0.2

0.3

0.4

Strain

0.5

0.6

0.7

Crack pattern of RC Beam

Mode of failure (RC Beam) • Reinforced concrete beam failed in bending zone . • After the first crack load of 18.75 kN, the reinforcement started yielding and more number of cracks has formed in the bending zone and extended towards the point loads with the increment in loads. • At ultimate load (59.38 kN ) the failure of beam occurred due to crushing of concrete in compression zone.



Crack pattern of CPS1

Mode of failure (CPS1) • Composite beam(CPS1) failed in bending zone . • After the first crack load(22.79 kN) , close minor cracks has formed in the bending region and extended towards the point loads. • After the first crack, local buckling of cold formed steel plate occured. • At ultimate load (53.13 kN ) the failure of beam occurred due to crushing of concrete in compression zone.



Mode of failure (CPS2) • Composite beam(CPS2) failed in bending zone . • After the first crack load(21.88 kN) , cracks has formed in the bending region and extended towards the point loads. • After the first crack, local buckling of cold formed steel plate occured.

• At ultimate load (53.13 kN ) the failure of beam occurred due to crushing of concrete in compression zone.

Crack pattern of CPZS

Mode of failure (CPZS) • Composite beam(CPZS) failed in bending zone . • After the first crack load(23.65 kN) , cracks has formed in the bending region and extended towards the point loads. • At ultimate load (61.36 kN ) the failure of beam occurred due to crushing of concrete in compression zone. • Local buckling of plate was lesser in CPZS.

Crack pattern of CPCS

Mode of failure (CPCS) • Composite beam(CPCS) failed in bending zone . • After the first crack load(24.80 kN) , cracks has formed in the bending region and extended towards the point loads. • At ultimate load (54.69 kN ) the failure of beam occurred due to crushing of concrete in compression zone. • Local buckling of plate was more than other composite beams.

Crack pattern of CPIS

Crack pattern of CPIS

Mode of failure (CPIS) • Composite beam(CPIS) failed in bending zone . • After the first crack load(25 kN) , cracks has formed in the bending region and extended towards the point loads.

• At ultimate load (62.50 kN ) the failure of beam occurred due to crushing of concrete in compression zone. • Local buckling of plate occured only in flexure zone.

Crack pattern of CPAS



Mode of failure (CPAS) • Composite beam(CPAS) failed in bending zone . • After the first crack load(21.88 kN) , cracks has formed in the bending region and extended towards the point loads. • At ultimate load (68.76 kN ) the failure of beam occurred due to crushing of concrete in compression zone. • Local buckling of plate was lesser in CPAS than other composite beams.

CONCLUSIONS • The Composite beam(CPAS) has the highest load carrying capacity of 68.76 kN. This is 1.15 times the load carrying capacity of RCC Beam.

• The composite beams (CPIS & CPZS) had a ultimate load carrying capacity which is 5 percent more than the RCC beam. • The ultimate load carrying capacity of composite beams (CPS1,CPS2 & CPCS ) is less than RCC beam by 10 percent.

• Detailing of Shear connector in alternate pattern(CPAS) gives more bonding between plate and concrete. • The ultimate load carrying capacity of the composite beam with plate (CPAS) higher than that of control beam(RC) . • Stiffness of composite beam (CPAS) was lesser than RC. • Composite beam (CPAS) undergoes more deformation than conventional reinforced concrete beam .

• A better ductility performance seen from the test results of composite beam(CPAS) compared with RCC beam . • CPAS shows an overall better strength and ductility than the composite beams (CPS1,CPS2,CPCS,CPZS,CPIS).

FINITE ELEMENT MODELING OF REINFORCED CONCRETE BEAM AND COMPOSITE BEAM USING ANSYS The objectives of the computer modeling were to:

• Examine the structural behavior RC beam and composite beams. • Establish a methodology for applying computer modeling to RC beam and composite beams.

FEM of beams using ANSYS Concrete • Solid65 element is used to model the concrete. • This element has eight nodes with three degrees of freedom at each node – translations in the nodal x, y, and z directions. • This element is capable of plastic deformation, cracking in three orthogonal directions, and crushing.

Reinforcing steel • A Link8 element is used to model steel reinforcement. • This element is a 3D spar element and it has two nodes with three degrees of freedom – translations in the nodal x, y, and z directions. • This element is also capable of plastic deformation.

Cold formed Steel Plate • An eight-node solid element, Solid45, was used for the steel plate. • The element is defined with eight nodes having three degrees of freedom at each node -translations in the nodal x, y, and z directions.

MODELING FULL-SIZE REINFORCED CONCRETE BEAM Categories Types of Elements Concrete Reinforcement Steel Cold formed steel Material properties Concrete Reinforcement Steel Cold formed steel Model Descriptions Modeling Approach Size of the Beam Boundary Conditions Left End Right End

ANSYS Model SOLID65 (Nonlinear) LINK8 (Nonlinear) SOLID45 (Nonlinear) E=5000Fck ,=0.25 E=2 x10^5 , =0.3

Full-size model 100 x 200 x1700 mm All DOFs restrained

• An important step in finite element modeling is the selection of the mesh density. • A convergence of results is obtained when an adequate number of elements is used in a model.

• Therefore, in this finite element modeling study a convergence study was carried out to determine an appropriate mesh density.

• • •

• • • • •

• • •

REFERENCES 1. Johnson, R.P.(1975). “Composite Structures of Steel and Concrete”, Volume I – Blackwell Scientific Publication, London. 2. . N. Kottiswaran, R. sundararajan, Behaviour of thin walled cold formed steel concrete composite beams”Proceedings of National Seminar - REDECON 2005, Pg 373 -381. 3. Richard P. Nguyen,” Thin-Walled, Cold-Formed Steel Composite Beams” Jornal of structural engineering ,Vol. 117, No. 10, October 1991, pp. 2936-2952. 4. IS 456: 2000, “Code of Practice for plain and Reinforced Concrete” – Bureau of Indian Standards,New Delhi. 5. IS 11384-1985, “Composite Construction in Structural Steel and Concrete”, Bureau of Indian Standards, New Delhi. 6. IS: 801(1975) “Code of Practice for the use in Cold-Formed light gauge steel structural members in general Building Construction”, Bureau of Indian Standards, New Delhi. 7. IS 3935-1966, “Code of Practice for Composite Construction”, Bureau of Indian Standards, New Delhi. 8. BS 5950-3.1:1990, “Code of Practice for design of simple and continous composite beams ”. 9. Workshop on Steel –Concrete composite structures, Anna university, Chennai, 2000.

Thanks to • Friends,Faculties of ACCET and my family members. • Narayanan,Asst.Prof,Mech dept,ACCET. • Kay Pee Engineering,Coimbatore. • Ammayappa welding works.