experimental study o n size effect of r.c . beam -column ...€¦ · beam-column joints become...

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International Journal of Civil Engineering and Technology (IJCIET)Volume 8, Issue 4, April 2017, pp.

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ISSN Print: 0976-6308 and ISSN Online: 0976

© IAEME Publication

EXPERIMENTAL STUDY OR.C. BEAM

WITHOUT HYBRID

M. Tech Structural Engineering, SRM University,

Department of Civil Engineering

ABSTRACT

The large residual strain energy and the dissipated energy in

shaking by earthquake is a

serviceability. If desired ductility

force (V inelastic) can be much

elastic building (V elastic). Be

stiffness and strength to

Beam-Column joint is essential

joints subjected to large amount of force during

behavior have significant influences on the response of structure.

study was attempted by considering shear lacking beam

made of conventional concrete, fibre reinforced concrete an

concrete under cyclic loading. The experimental

the 1) the progressive propagating nature of failure, implied whenever load

diagram lacks a yield plateau; 2) the need to rationally p

absorption capability and most importantly, 3) the effect size on nominal strength

(i.e., nominal stress at maximum or ultimate load) as well as on ductility and energy

absorption capability. Test results indicate that the provi

fibre and conventional concrete in

effect and Hybrid fibres reinforced concrete specimens indicate the synergy effect.

Keywords: Conventional Reinforced Concrete (CRC); Hybrid

Concrete (HFRC); Steel Fibre Reinforced Concrete (SFRC

effect.

Cite this Article: Sudip Chapagai and G. Premkumar Experimental study on size

effect of R.C. Beam-column joint with and without hybrid fibres under cyclic loading

International Journal of Civil Engineering and Technology

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IJCIET/index.asp 2198 [email protected]

International Journal of Civil Engineering and Technology (IJCIET) 2017, pp. 2198–2209 Article ID: IJCIET_08_04_248

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=4

6308 and ISSN Online: 0976-6316

Scopus Indexed

XPERIMENTAL STUDY ON SIZE EFFECT OF . BEAM-COLUMN JOINT WITH AND

HYBRID FIBRES UNDER CYCLIC LOADING

Sudip Chapagai

Structural Engineering, SRM University, Kattankulathur,Tamil

G. Premkumar

Engineering, SRM University, Kattankulathur, Tamil

The large residual strain energy and the dissipated energy in RC

shaking by earthquake is a key concern for structural safety, sustainabi

desired ductility can be given in the building, the outline

) can be much lower (up to 20%) then the corresponding force in an

). Beam-Column joint should have adequate

oppose the internal forces induced by framing members.

essential zone in a RC moment-resisting frame.

joints subjected to large amount of force during the shaking of ground and its

behavior have significant influences on the response of structure. An

attempted by considering shear lacking beam-column joints. Test specimens

made of conventional concrete, fibre reinforced concrete and hybrid fibre

concrete under cyclic loading. The experimental data was plot and analyzed to study

) the progressive propagating nature of failure, implied whenever load

diagram lacks a yield plateau; 2) the need to rationally predict ductility and energy



Test results indicate that the provision of Hybrid fibre

fibre and conventional concrete in Beam-Column joints follows the principle of size


: Conventional Reinforced Concrete (CRC); Hybrid Fibre Reinforced

Concrete (HFRC); Steel Fibre Reinforced Concrete (SFRC;Ductility; Stiffness; Size

Sudip Chapagai and G. Premkumar Experimental study on size

column joint with and without hybrid fibres under cyclic loading

Journal of Civil Engineering and Technology, 8(4), 2017, pp.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=4

[email protected]

asp?JType=IJCIET&VType=8&IType=4

N SIZE EFFECT OF WITH AND

UNDER CYCLIC

amil Nadu, India.

amil Nadu, India.

structures after

concern for structural safety, sustainability and

can be given in the building, the outline seismic

(up to 20%) then the corresponding force in an

adequate amount of

the internal forces induced by framing members.

resisting frame. Beam column

the shaking of ground and its

An experimental

. Test specimens

d hybrid fibres reinforced

lot and analyzed to study

) the progressive propagating nature of failure, implied whenever load-deflection

redict ductility and energy



sion of Hybrid fibres, Steel

the principle of size


Fibre Reinforced

Ductility; Stiffness; Size

Sudip Chapagai and G. Premkumar Experimental study on size

column joint with and without hybrid fibres under cyclic loading,

, 8(4), 2017, pp. 2198-2209.

asp?JType=IJCIET&VType=8&IType=4

Sudip Chapagai and G. Premkumar

http://www.iaeme.com/IJCIET/index.asp 2199 [email protected]

1. INTRODUCTION

Beam-Column joints become critical in framed buildings when they are subjected to

horizontal force like wind and earthquake. Based on intensity, the earthquakes at a given

place can be grouped into three classifications, for example, minor, moderate and strong.

Typically, minor earthquakes occur frequently, moderate earthquakes occasionally. But

strong earthquakes occur rarely. Sometimes the probability of occurrence of strong

earthquakes may exceed the life time of the structure. The construction of earthquake

resistance building for these places is too expansive. The earthquake resistant building should

resist the consequence of ground motion; even however they may get damaged extremely yet

would not fail during strong earthquake. Along these lines, wellbeing of individual and things

is accepted in tremor safe structures and accordingly a catastrophe is avoided. This is the

significant target of seismic design codes all through the world. The awareness for proper

design of joints started with the publication of the ACI – ASCE Committee 352 report in

1976 titled “Recommendations for design of beam column joints”. Among the Indian codes

of practice, I.S. code 13920 deals briefly with subject. According to Z.P. Bazant size effect is

defined through a comparison of geometrically similar structures of different sizes, and is

conveniently characterized in terms of the nominal stress σN at maximum (ultimate) load, Pu.

When the σN value for geometrically similar structure of different sizes are the same, we say

there is no size effect. A dependence of σN on the structure size (dimension) is called the size

effect. The size effect in HFRC and SFRC needs to be clarified through the discussion in

paper. Bazant’s size effect law can be defined by equation 1.

σN = ��

�(1 + ƛ�� )� (1)

The unknown constant B and ƛo are empirical parameter to be calculated by iterating linear

statistical regression of the measured maximum loads Pu. The value of ftis determined by 0.7

× √fck MPa (IS 456: 2000), where fck = characteristics compressive strength of concrete, D =

Characteristics size (dimension of geometrically similar specimen and Da = maximum size of

aggregate used (mm).

2. RESEARCH SIGNIFICANCE

The research significance of this paper is that, to the best of writer knowledge, this study is

the first to study of size effect on Beam-Column joint with HFRC and SFRC and the

comparison based on ductility and energy dissipation per unit volume. Using of ultimate

loads, the size effect law is illustrated based on nominal stress log (σN) versus log (d).

3. TEST DATA AND TEST MATERIAL

To study the size effect, geometrically similar beam-column joint of various sizes were

considered. Three types of specimens, to be specific, Beam-Column joint with beam weak in

shear Conventional, SFRC and HFRC were considered. The naming of specimens was done

with initial three latter in order to cover the deficiency type, forth for size and remaining for

type of specimens. For instance, BWSLCS remains for beam weak in shear large

conventional specimen similarly, BWSSHFRCS remains for beam weak in shear small hybrid

fibre reinforced concrete specimen and BWSMSFRCS remains for beam weak in shear

medium steel fibre reinforced concrete specimen. The detail drawings for these specimens are

shown in figure 3. The cross section of the column was chosen smaller then of beam to make

the member as a strong beam weak column. Concrete of characteristic compressive strength

of M40 was used. Three different sizes were adopted viz. for large specimen, column size (L

Experimental study on size effect of R.C. Beam-column joint with and without hybrid fibres under

cyclic loading


x B x D) were 1500 mm x 120mm x 120mm and that of beam size (L x B x D) were1500mm

x 120mm x 150mm similarly, for medium specimen, column size (L x B x D) were 1200mm

x 96mm x 96mm and that of beam size (L x B x D) were 1200mm x 96mm x 120mm and for

small specimen, column size (L x B x D) were 960mm x 77mm x 77mm and that of beam

size (L x B x D) were 960mm x 77mm x 96m. For large specimen, four numbers of high

strength deformed bars (Yield strength 500 MPa) of 10mm diameter was used as

reinforcement in column and that of beam with lateral ties of 8mm diameter high strength

deformed bars (Yield strength 500 MPa) at 75mm c/c spacing were used in the special

confinement part of column and 8mm diameter high strength deformed bars (Yield strength

500 MPa) at 100mm c/c spacing were used in remaining part of column and that of beam

further 20 mm clear cover were used. The diameter of reinforcing bars, development length,

length of confinement part, cover of reinforcement was scale down properly. Ordinary

Portland cement of grade 53, fine aggregate passing through IS 4.75mm sieve, coarse

aggregate passing through 12.5mm, 0.5mm diameter crimped steel fibre (aspect ratio of 40),

Polypropylene fibre (aspect ratio of 1200) and potable water were used for all geometrically

similar beam-column joint of different sizes. A constant water-cement ratio of 0.4 was used

for mix proportion design. The amount of material for concrete mixes is given in Table 1.

Mix proportion while Steel fibre and polypropylene fibres were added to concrete at a volume

fraction of 1%.

1) Beam column joint specimen 2) Hydraulic Jack

2)Hydraulic Jack 4) Dial Gauge 5)Loading Frame

Figure 3a Anchorage of Beam Bars in an Exterior

Joints

Figure 3b Experimental Test Set – up

Ld + 10 Ø

Ld +

10

Ø

3

2

4

5 5

5



Figure 3c Typical Reinforcement Drawing of Tested Beam-Column Specimen

Figure 3d Typical Experimental Setup of Beam column joint Specimen

0.1

2

10 mm Ø

8mm Ø@100mm c/c

8mm Ø@100mm c/c

0.12

10 mm Ø

SECTION B - B SECTION A - A

8mm Ø@100mm c/c

8mm Ø@100mm c/c

0.4

5

0.12

0.1

5

0.1

5

0.12

8mm Ø@75mm c/c 1.50

8mm Ø@100mm c/c

1.5

0

AA

B

B


cyclic loading


Figure 3e HFRC specimen after

failure

Figure 3f SFRC specimen after

failure

Figure 3g Conventional concrete

specimen after failure

Table 1 Quantity of materials in various concrete mixes

Mix da

(mm) Cement (kg/m3)

Fine aggregate

(kg/m3)

Coarse aggregate

(kg/m3)

Water (kg/m3)

Steel fibre (%)

PP fibre (%)

Conventional

concrete

12.5 437 663 1221 181 - -

HFRC 12.5 437 663 1221 181 0.8 0.2

SFRC 12.5 437 663 1221 181 1 -

Note: Steel fibres were added by volume of concrete and PP fibres were added by weight of cement.

3.1. Casting and testing of specimens

Plywood moulds were used for casting of specimens; rebar was fabricated in bar bending

yard and placed it inside the mould. Mix proportion amount of cement, sand, water, hybrid

fibre and steel fibre were mixed thoroughly, mixes were poured in to mould and through

compaction were done. After 24 hours of casting, specimens were demoulded and cured

under wet jute bags for 28 days. A constant axial load of 30kN, is about 50% of axial capacity

of column (large specimen) was maintained to the column by hydraulic jack for holding the

specimen in position. A hydraulic jack of 500 kN capacity was used to apply load on beam.

Cyclic load was applied to the end of the beam, beam was loaded up to first increment, then

unloading and reloaded to the next increment of load and this increment system of loading

was continued for each specimens. Dial Gauge were used to measure the deflection of beam.

Load was applied 50 mm distance from the free end of the beam. Totally four cycles were

imposed, load steps chose was increment of 2kN to ultimate load carrying capacity of beam-

column joint.

3.2. Results and Analysis

The recorded data were plotted to find size effect of beam column joint indicated by Bazant

law, energy dissipation, ductility gain due to HF and SF, percentage gain in ultimate load

carrying capacity due to HF and SF etc. comparisons of results were made between

conventional, HFRC and SFRC as far as all previously mentioned properties.



4. ULTIMATE LOAD CARRYING CAPACITY OF SPECIMENS

The ultimate load carrying capacity of conventional, steel fibre (1%) and Hybrid fibre (0.8%

S.F. and 0.2% P.P.) specimens were obtained and presented in Table 2. The ultimate load

carrying capacity of steel fibre and Hybrid fibre presented in Table 2 show an increase of

about (20 to 40%) in ultimate load as compared to the corresponding conventional specimen.

The increase in ultimate load of fibre specimens may be due to following reason. As and

when the micro cracks develop in the matrix, fibers intercept the cracks and prevent them

from propagating in the same direction subsequently the cracks may prompts deviation way

which take more vitality for further propagation, thus resulting about higher load carrying

capacity of concrete members. (Ganesan and Indira 2000).

Table 2 Ultimate Load Carrying Capacity of Specimens

Conventional Specimens

HFRCS SFRC

Name of Specimen

Ultimate Load

carrying capacity

(kN)

Name of Specimen

Ultimate Load

carrying capacity

(kN)

Name of Specimen

Ultimate Load

carrying capacity

(kN)

BWSSCS

BWSMCS

BWSLCS

26.0

32.0

42.0

BWSSHFRCS

BWSMHFRCS

BWSLHFRCS

35.0

44.0

54.0

BWSSSFRCS

BWSMSFRCS

BWSLSFRCS

32.0

40.0

48.0

4.1. Measure of ductility

A quantitative measure of ductility is arrived from load-deformation curve. This is obtained

by the horizontal distance between the origin and point of intersection of tangent drawn from

load deflection curve. The ratio of the ultimate deformation to the deformation at the initial

yielding can give the measure of ductility and it is also called ductility ratio or displacement

ductility may be in the strain rotation, curvature or deflection.

Ductility ratio µ = ��

��(��) Ductility is always depends on the material property. The fibre reinforced concrete

specimens show higher ductility then corresponding conventional specimens’ addition of

fibres links the cracking consequence and delayed the development of first crack. The gain in

ductility due to SFRC and HFRC varies from 30% to 50%. The ductility factor of

conventional, SFRC and HFRC for small specimen is the maximum and it decrease as the

specimen size increase as shown in figure 4b. This is an indication of existence of size effect.

The hybridization of fibres possesses more ductility then steel fibre. The gain in ductility due

to HFRC with corresponding SFRC varies from 14% to 21% this is an indication of synergy

effect.


cyclic loading


Figure 4a Typical Comparison of envelop curve

Figure 4b Comparison of ductility of HFRC, SFRC and Conventional specimens

4.2. Lacks a yield plateau

Based on load- deflection diagrams, one may distinguish two basic types of structural failure:

Plastic and brittle. The typical characteristics of plastic are that the structure develops a single

degree of freedom mechanism such that the failure in various part of the structure proceeds

simultaneously in proportion to a single parameter. Such failures are manifested by the

existence of a long yield plateau on load deflection plot. If the load deflection diagram lacks

such a plateau the failure is not plastic but brittle. The absence of plateau implies the

existence of softening in the material due to fracture, cracking or other damage. This further

implies that failure process cannot develop a single degree of freedom mechanism but

consists of propagating of failure zone throughout the structure; the failure is non-

simultaneous and propagating.

4.3. Energy Absorption capability

The area under the entire load deflection diagram represents the energy that the structure will

absorb during failure. Plastic limit analysis can give no information on the post-peak decline

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Lo

ad i

n k

N

Deflection in mm

BWSHFRCS

BWSSHFRCS

BWSMHFRCS

BWSLHFRCS

0

1

2

3

4

5

6

7

8

Small Medium Large

Duct

ilit

y F

acto

r

Size of Specimens

Conventional SFRC HFRC



of load and the energy dissipation in this process. According to plasticity, the load is constant

after the peak and the energy absorption theoretically unlimited. So some form of fracture

mechanics is sure to happen. The gain in capacity due to hybrid fibre is show very

impressive. The plot of graph between Cumulative energy per unit volume and drift angle as

shown in figure 4c & figure 4d indicate that gain in energy of small specimens has highest

value and largest specimen has lowest value for all three cases (Conventional, HFRC, SFRC).

This is an indication for existence of size effect.

Figure 4c Cumulative energy dissipation per unit volume for conventional specimens

Figure 4d Cumulative energy dissipation per unit volume for HFRC specimens

0

1

2

3

4

5

6

7

8

0 1 2 3 4

Cum

ula

tive

ener

gy d

issi

pat

ion i

n

kN

-m

Drift Angle

Conventional

BWSSCS

BWSMCS

BWSLCS

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5 6

Ener

gy d

issi

pat

ion c

apac

ity i

n

kN

-m

Drift Angle

Hybrid Fibre

BWSSHFRCS

BWSMHFRCS

BWSLHFRCS


cyclic loading


4.4. Size effect

The size effect consists of the nominal strength σ N with size D. There are various possible

plots showing special aspects of size effect, but the most widely used is bi-logarithmic plot in

which σ N plotted versus log D. The parameters for exploring the size effect are presented on

Table 3. The value of tensile strength of concrete ft was calculated with reference to IS 456

(2000): and was taken as 4.427 N / mm2.

Table 3 Parameters for size effect plot

Name of Specimen

Ultimate Load

carrying capacity

(kN)

Stress (N /mm2)

Depth of Specimen, D in mm

Log(D / D0)

Log(σ N / B f t)

BWSSCS

BWSMCS

BWSLCS

BWSSHFRCS

BWSMHFRCS

BWSLHFRCS

BWSSSFRCS

BWSMSFRCS

BWSLSFRCS

26.0

32.0

42.0

35.0

44.0

54.0

32.0

40.0

48.0

3.52

2.78

2.33

4.33

3.47

2.67

4.73

3.62

3.00

96

120

150

96

120

150

96

120

150

1.982

2.079

2.176

1.982

2.079

2.176

1.982

2.079

2.176

0.09989

0.20241

0.27813

0.29196

0.06410

0.16898

0.00972

0.10550

0.22014

Figure 4e Bi-logarithmic plot for Hybrid fibre specimens

The bi-logarithmic plot of HFRC specimens is shown in figure 4e. It is observed from the

graph that the presence of indication of size effect and it is closely supports the Bazant’s size

effect law. The conventional and steel fibre specimens also show the similar trend of graph.

-0.2

-0.15

-0.1

-0.05

0

0.05

1.95 2 2.05 2.1 2.15 2.2

log (

σN

/ B

ft)

log (D / D0)

Hybrid fibre

BWSHFRCS



Figure 4f Bending Stress versus Displacement plot of conventional specimens

Figure 4g Bending Stress versus Displacement plot of Steel fibre specimens

The plot between Bending stress versus Displacement indicate that stresses for smallest

specimens show highest value at all level of displacement, thus this also support the existence

of size effect in beam column joint.

4.5. Stiffness Degradation

Beam- column joint subjected to cyclic loading stiffness gets diminished for each of the three

cases. The decrease of stiffness on joints subjected to forward and backward loading, internal

bonding strength get reduced and the initiation of micro-cracks will sometimes lead to the

deformation of materials. It is important to determine the nature of stiffness degradation in

joints, the following procedure was used. The slope of line joining the origin and peak load of

first cycle represents the secant stiffness of first cycle again slope of line joining the origin

and peak load of second cycle represents the secant stiffness of second cycle. This procedure

was adopted for all the other cycles to determine the secant stiffness for each cycle and the

plots are given in figure 4h. With reference to this figure that as the number of cycles

increases, stiffness decreases. Figure show that all types of specimens have similar effect on

first cycle thus adding of steel fibre and Hybrid fibre does not have any significant effect on

the first cycle. The fact explanations of this is for the first cycle micro-crack would not have

propagate and hence fibres were not viable because of absence due to absence of

development of micro cracks as the number of cycles increases the micro cracks get

propagated and the fibre which are seated indiscriminately position may occupy these cracks

0

40

80

120

160

200

240

0 20 40 60 80

Ben

din

g s

tres

s N

/ m

m2

Displacement in mm

Conventional

BWSLCS

BWSMCS

BWSSCS

0

50

100

150

200

250

300

0 20 40 60 80 100

Ben

din

g s

tres

s N

/ m

m2

Displacement in mm

Steel fibre

BWSLSFRCS

BWSMSFRCS

BWSSSFRCS


cyclic loading


and situated as a scaffold across these cracks. This activity will prevent additionally

propagating of cracks and will result higher energy demand for debonding and pull out of

fibres in the vicinity of cracks, during this process ultimate load carrying capacity of joint

with Hybrid fibres and steel fibre is much higher as compared to corresponding conventional

specimens.

Figure 4h Stiffness degradation of all tested specimens

5. CONCLUSIONS

In this present study, 9 quantities of geometrically similar beam column joints specimens

were tested. Load deflection curve were plotted, various graph like load deflection curve,

stiffness curve, cumulative energy dissipation per unit volume curve, bi-logarithmic curve,

bending stress versus displacement curve were plot to study the relative improvement in

various property such as ductility factor, energy dissipation etc. due to Steel fibre and Hybrid

fibres with respect to size effect. Based on the interpretation of results the accompanying

conclusion can be drawn:

1. The bi-logarithmic plot for all Conventional, Steel, Hybrid fibres specimen follow the size

effect law purposed by Bazant.

2. The gain in energy dissipation per unit volume due to Hybrid fibres and Steel fibreare more as

compare to corresponding Conventional specimens and also follow the existence of size

effect.

3. The gain in ductility due to Hybrid and Steel fibre increase with compare to corresponding

Conventional specimens and also follows the size effect.

4. There was considerable gain in initial stiffness due to Hybrid and Steel fibre with compare to

corresponding Conventional specimens.

5. The fibres used in Hybrid form perform better composite.

6. There is a synergy effect in the hybrid fibres system.

7. As a consequence of hybridization it had the capacity to capture cracks and hence

significantly increment the energy absorption characteristics.

8. The cumulative energy per unit volume of joint at every drift angle follows the existence of

size effect.

0

0.5

1

1.5

2

2.5

0 1 2 3 4 5

Sti

ffnes

s kN

/ m

m

Cycle

Stiffness Degradation

BWSSCS

BWSSSFRCS

BWSSSFRCS

BWSMCS

BWSMSFRCS

BWSSHFRCS

BWSLCS

BWSLSFRCS

BWSLHFRCS



9. The gain in ultimate load carrying capacity of Hybrid fibres concrete joints is more than the

corresponding steel fibre and conventional specimens.

6. ACKNOWLEDGEMENTS

The author like to express sincere appreciation to SRM University, Department of Civil

Engineering, SRM University,teachers, friends and Lab staffs.

REFERENCES

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