© 2019 JETIR April 2019, Volume 6, Issue 4 ...5. C2R2 62.3 61.9 65.95 % 60.25 63.15 Due to wrapping...

© 2019 JETIR April 2019, Volume 6, Issue 4 www.jetir.org (ISSN-2349-5162)

JETIR1904O79 Journal of Emerging Technologies and Innovative Research (JETIR) www.jetir.org 482

EFFECT OF CORNER RADIUS ON SHEAR

STRENGTH OF CFRP WRAPPED RC BEAM:

AN EXPERIMENTAL APPROACH

Sanjay G. Makwana1, Prof. Payal H. Andharia2 1P.G. Student, Applied Mechanics Department, L.D. College of Engineering, Ahmedabad, Gujarat, India.

2Assistant Professor, Applied Mechanics Department, L.D. College of Engineering, Ahmedabad, Gujarat, India.

Abstract: Reinforced concrete beams can be effectively strengthened in shear using externally bonded carbon fiber reinforced

polymer. Effect of corner radius on FRP wrapped RC columns has been done, but the same effect consideration has not been

included for beam strengthening. In this work, study has been conducted to know the effect of CFRP sheets on the strengthening of

the RC beams having different corner radii. There are total fifteen RC beams to be casted for this study with different configuration

of CFRP strips. Three specimen will be Control section. There are six among fifteen beams which have 5 mm corner radius, while

other six beams have 25 mm corner radius. The testing of these beams will be carried out under 2 point loading system. The results

shows that there is an improvement in strength of beams having 25 mm corner radii than the beams having 5 mm corner radii.

Key Words: CFRP, Shear Strength, Corner radius

I. INTRODUCTION

Over the time, different kinds of techniques are used to retrofit existing structures by applying external confining stresses. The

FRP can be applied through three methods (i) EBR (Externally Bonded Reinforcement) method (ii) NSM (Near Surface Mounted)

method (iii) ETS (Embedded through Section) method. In this research EBR method is applied. In recent years, externally bonded

fiber reinforced polymer (FRP) composites has been used and become popular for the repair and retrofitting of RC structures. Due

to high stiffness to weight ratio, flexibility in design, non-corrosiveness, ease of application, these material has great potential in

becoming a substitute to concrete jackets and steel jackets. Significant number of studies has been done on shear strengthening of

the RC beams, but the behaviour is not completely understood. Behaviour of FRP wrapped RC beam is depended on the wrapping

configuration, section changes and wrapping method.

Sharma S. et. al. [1] have done research on strengthening of FRP wrapped RC columns with different corner radii. They have

casted 15 columns of size 125mm x 125mm x 1200mm. They have taken 2 corner radii as 5 mm and 25 mm. 6 columns were of 5

mm corner radii with one and two layer of GFRP. Other 6 beams had same configurations with 25 mm corner radii. They have

concluded that as corner radius increases the performance of specimens were increased. Yousef et. al. [2] have done influence of

corner radii on FRP wrapped columns. They have taken 4 different corner radii. They have concluded that due to increase in the

corner radius, the stress concentration at corner starts decreasing. Pham et. al. [3] have done research on strengthening of RC beams

with taking different beam section. They have modified the section of the beams by changing flat soffit of the beam with arch type

soffit having radius as 125mm. They have concluded that the modified section can improve the performance and delay the

debonding of FRP.As corner radius increases, the performance of the FRP wrapped RC columns starts improving [4-10]. So, effect

of corner radius on FRP wrapped RC beams has not been researched. Therefore, this study aims to know the effect of corner radii

on FRP wrapped RC beams as well as on configurations.

II. EXPERIMENTAL PROGRAM

2.1 Test Specimens

Table 1 Specifications of RC Beams

Column b (mm) L (mm) r (mm) No. of Specimen Configuration

CB 125 1200 0 3 Nil

C1R1 125 1200 5 3 Vertical Strips

C1R2 125 1200 25 3 Vertical Strips

C2R1 125 1200 5 3 U wrap

C2R2 125 1200 25 3 U wrap

(a)

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(b)

(c)

(d)

Figure 1 Configuration Details (a) Vertical strips with 5 mm corner radii (b) Vertical strip with 25 mm corner radii (c) U-wrap

with 5 mm corner radii (d) U-wrap with 25 mm corner radii

2.2 Material Properties

2.2.1 Concrete

All the beams were prepared using M25 grade of concrete. Based on the IS code mix design, mix proportion is given below in

table 2.

Table 2 Mix Proportion for Concrete Mix

Material Cement Water Fine Aggregates Coarse

Aggregates

Mass (kg/m3) 383.16 209.92 691.19 1223.63

Mass (kg) 50 27.4 90.2 159.7

Proportion 1 0.55 1.80 3.19

2.2.2 CFRP Sheet

In this experimental study, unidirectional carbon fiber fabric has been used. CFRP sheets are applied over RC beams using

epoxy system having two parts, resin and hardener. Properties of the CFRP sheets are given below in table 3.

Table 3 CFRP Properties given by the manufacturer (12k UD 300GSM)

Areal

Weight

Thickness Tensile

Strength

Tensile

Modulus

Ultimate

Elongation

Fibre

Density

Sheet

Width

300 gm/m2 ±

5 gm/m2

0.168 mm 3000 N/mm2

(Minimum)

220 – 240

Gpa

1.25 - 1.60 % 1.78 gm/cm3 500 mm

2.3 Casting of RC Beams

15 RC beams with a cross section of 125 mm x 125 mm and 1200 mm length have been casted. The corner radius were taken

as 0 mm, 5 mm and 25 mm. The beams have reinforcement as 4 numbers of 10 mm dia. bars in longitudinal direction and 8 mm

dia. bars spaced at 500 mm in transverse direction. The beam design is based on IS 456:2000 [13]. Use of stirrups spacing at 500

mm c/c is used to make RC beam shear deficient. To provide 25 mm round corner radius, special wooden formwork is to be prepared

as shown in fig. 2 below. Before placing the concrete in the wooden formwork, oiling is done.

(a) (b)




(c) (d)

Figure 2 (a) Reinforcement detailing of RC beam (b) Special formwork for beam having 25 mm corner radii (c) Formwork with

cage (d) Section of casted RC beam having 25 mm corner radii

2.4 CFRP Wrapping

For CFRP wrapping, the specimens have to be washed, so that the dust particle are eliminated. The two part epoxy system was

prepared having resin ad hardener. Then epoxy was applied on the specimen. After 5-10 minutes, the carbon fiber fabric has to be

applied on the epoxy coated surface of the RC specimen. Another coat of epoxy is to be applied on the fabric. The care has been

taken that, any kind of voids can be eliminated which may affect the strength due to debonding of the fabric. The fabric was applied

in the transverse direction.

Figure 3 CFRP wrapping process

2.5 Test Procedure

The test was carried out on UTM (universal testing machine) having capacity of 2000 kN. The specimens were placed on the

two point load assembly. The span was taken as 1000mm and the load span was taken as 400 mm. The deflections were measured

at two points, at mid span and at under load. The dial gauges were used to measure the deflection. The test setup is shown below in

fig. 4.

Figure 4 Test setup on universal testing machine




III. RESULTS AND DISCUSSION

3.1 Ultimate load carrying capacity

Ultimate load carrying capacity of each specimen and the percentage increase of strengthened beam over unstrengthened one is

given in Table 4.

Table 4 Results of test

Sr.

No.

Beam Name Ultimate Load Carrying

Capacity (kN)

Average Ultimate Load

Carrying Capacity (kN)

% Increase over

control beam

1. CB 36.20 37.30 -

35.30

40.40

2. C1R1 51.70 52.35 40.35 %

55.05

50.30

3. C1R2 58.50 58.32 56.36 %

57.30

59.15

4. C2R1 60.9 59.55 59.65 %

58.75

59.05

5. C2R2 62.3 61.9 65.95 %

60.25

63.15

Due to wrapping of CFRP, the increment of ultimate load carrying capacity has been shown in each wrapped RC beam. The

ultimate load carrying capacity is increased by percentage ranging from 40.35 % to 65.95%. The percentage increase of the beams

C1R1, C1R2, C2R1 and C2R2 are 40.35%, 56.36%, 59.65% and 65.95% respectively as compared to CB (Control Beam). Due to

corner radius, the increase in ultimate load of C1R2 is 11.4 % in comparison with C1R1. Increase in ultimate load of C2R2 is 3.94%

in comparison with specimen C2R2. This comparison shows that, there is increase in ultimate load as we increase the corner radius.

Also it shows that, the increase in ultimate load in U-wrap configuration, is not that significant as in vertical strip configuration. It

may be due to number of corners used in wrapping.

3.2 Load vs. Deflection

The load vs. deflection diagram is plotted for mid-span deflection and under load defection for all the RC beams.

(a) (b)

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30

Lo

ad

(k

N)

Deflection at Midspan (mm)

C1R1 C1R2

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

Lo

ad

(k

N)

Deflection under Load (mm)

C1R1 C1R2




(c) (d)

(e) (f)

Figure 5 Comparison of Load vs. Deflection curve of different specimens.

In fig. 5(a), the comparison of load vs. mid-span deflection graph of vertical strip configured RC beam having corner radii 5

mm and 25 mm is given. It shows that the ductility in specimen having 25 mm corner radius is more than the specimen having 5

mm corner radii. Similarly in fig. 5(b), the comparison of same specimens as above is done with deflection under the load, which

also shows the C1R2 is more ductile than the C1R1.

In fig. 5(c) and 5(d), the U-wrapped RC specimen are compared for load vs. mid-span deflection and under load deflection

respectively, having different corner radii. Similar behaviour is shown as above configurations. Also in U-wrapped specimens, it is

shown that specimen with higher corner radii is more ductile.

Fig. 5(e) and 5(f) are comparison of all the five configuration for load vs. mid-span deflection and under load deflection

respectively.

3.3 Failure Modes

Failure modes of different specimen is given below from fig. 6 to fig. 10. Crack propagation is seen in control beam but in CFRP

wrapped beam it is difficult to notice continuity of cracks. The debonding sound is heard while applying loading. Also at some

points the FRP have been teared apart.

Control Beam (CB) failure is given in below fig. 6. This specimen failed in shear manner. Diagonal crack under load is seen at

sides.

(a) (b)

Figure 6 Failure in CB

Failure of specimen with vertical strips having corner radii 5 mm is given in below fig. 7. This specimen failed in shear under

loading point. Out of 3 beams 2 were failed in shear under point load and 1 beam was failed in flexural manner under point load.

0

20

40

60

80

0 5 10 15 20 25 30

Lo

ad

(k

N)

Deflection at Midspan (mm)C2R1 C2R2

0

20

40

60

80

0 5 10 15 20 25 30 35 40

Lo

ad

(k

N)

Deflection under Load (mm)C2R1 C2R2

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30

Lo

ad

(k

N)

Deflection at Midspan (mm)

CB C1R1 C1R2

C2R1 C2R2

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35 40

Lo

ad

(k

N)

Deflection Under Load (mm)

CB C1R1 C1R2

C2R1 C2R2




(a) (b)

Figure 7 Failure in C1R1

Failure of specimen with vertical strips having corner radii 25 mm is given in below fig. 8. This specimen failed in flexural

manner at mid span. All the 3 beams of this configuration have failed in flexural manner.

(a) (b)


Failure of specimen with U wrapping having 5 mm is given below in fig. 9. This specimens failed in shear manner under loading

point. All the 3 beams were failed in shear manner having shear crack under point load.

(a) (b)


Failure of specimen with U wrapping having 25 mm is given below in fig. 10. This specimens failed in flexural manner at mid-

span. There were cracks in CFRP also. All the 3 specimen of this batch have failed in same manner.

(a) (b)





IV. CONCLUSIONS

The below conclusions are drawn from this experimental work.

The results clearly shows that, there is an enhancement in performance of specimen with CFRP wrapping in terms of ultimate

load carrying capacity and ductility.

The percentage increment in CFRP wrapped beams in comparison with control beam is ranging from 40.35 % to 65.95 %.

U-wrapped beams have shown better performance than the vertical strips wrapped beams in terms of load carrying capacity.

As we increase the corner radius, increase in load carrying capacity is attained. In, U-wrapped beam the percentage increase in

load carrying capacity is less than the vertical strips wrapped beam. That may be due to difference of number of corners taking

part in wrapping.

The specimens which have 25 mm corner radii have performed better than the 5 mm corner radii in terms of failure. Most 25

mm corner radii beams have failed in flexure and similarly most 5 mm corner radii beams failed in shear.

REFERENCES

[1]. Sharma S.S.; Dave U.V.; Solanki H. (2013), “FRP Wrapping for RC Columns with Varying Corner Radii” Procedia

Engineering, 220-229.

[2]. Yousef A. (2007), “Influence of edge sharpness on the strength of square concrete columns confined with FRP composite

laminates” Composites: Part B 38, 640-650.

[3]. Pham T.M. and Hao H. (2016), “Behavior of fiber-reinforced polymer-strengthened reinforced concrete beams under static

and impact loads” International Journal of Protective Structure, 3-24.

[4]. Yang X., A.M.ASCE; Wei J.; Nanni A., F.ASCE; and Dharani L.R. (2004), “Shape Effect on the Performance of Carbon Fiber

Reinforced Polymer Wraps” Journal of Composites for Construction, 444-451.

[5]. Li A., Assih J.; and Delmas Y. (2001), “Shear Strengthening of RC Beams with Externally Bonded CFRP Sheets” Journal of

Structural Engineering, 374-380.

[6]. Cao S. Y.; Chen J. F.; Teng J. G.; Hao Z.; and Chen J. (2005), “Debonding in RC Beams Shear Strengthened with Complete

FRP Wraps” Journal of Composites for Construction, 417-428.

[7]. Adhikary B.; M.ASCE, and Mutsuyoshi H. (2004), “Behavior of Concrete Beams Strengthened in Shear with Carbon-Fiber

Sheets” Journal of Composites for Construction, 258-264.

[8]. Manuel Silva A.G. (2011), “Behavior of square and circular columns strengthened with aramidic or carbon fibers”

Construction and Building Materials 25, 3222–3228.

[9]. Wang L.M., Wu Y.F. (2007), “Effect of corner radius on the performance of CFRP-confined square concrete columns: Test”

Engineering Structures 30, 493-505.

[10]. Razavi M.; Sam A.R.M.; Ahmad Y., and Koushfar K. (2013), “Behavior of Different Shape of Concrete Prism Strengthened

with FRP Material under Compressive Axial Load” Australian Journal of Basic and Applied Sciences, 203-212.

[11]. Al-Tersawy S.H. (2013), “Effect of fiber parameters and concrete strength on shear behaviour of strengthened RC beams”

Construction and Building Materials 44, 15-24.

[12]. Zhang Z.; Hsu C.T. (2005), “Shear Strengthening of Reinforced Concrete Beams Using Carbon-Fiber-Reinforced Polymer

Laminates” Journal of Composites for Construction, 158-169.

[13]. IS 456: 2000 Plain and reinforced concrete-code of practice

[14]. IS 10262: 2009 Concrete Mix Proportioning – Guideline

[15]. IS: 2386 (part III) – 1963 “Methods of Test for Aggregates for Concrete”


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