Experimental Investigation

of the FRP Strengthening of

Reinforced Concrete Beams

REFERENCES

MSc Civil engineering

Nderim Azemi

Supervisor:

Prof Tiziana Rossetto

UCL Department of Civil, Environmental and Geomatic Engineering, Gower St, London ,WC1E 6BT

The performance of concrete structures will decrease over the time

due to such factors as the local environmental conditions, the quality

of material used and the lack of maintenance. If a structure has

deteriorated significantly there are two possible solutions [2]: the

replacement of the whole structure or the retrofitting of some

structural elements. Replacement of the whole structure can be

economically unviable [1], as well as being hugely disruptive to people

living and working in the area. Retrofitting can lessen these issues,

and is often far less time consuming. Fibre Reinforced Polymer (FRP)

is a composite material which is becoming more widely used in the

retrofitting process, due to, amongst other things, it’s low weight and

speed of application [3]

To study the impact of shear strengthening on the flexural capacity of

reinforced concrete beams.

Assess the shear failure with end de-bonding/rupture of reinforced

concrete T-beams, retrofitted with of Carbon Fibre Reinforced

Polymer (CFRP) sheets.

Assess the flexural failure with the end de-bonding of CFRP

sheets on RC T-beams

Assess the flexural failure with mid de-bonding of CFRP sheets on

RC T-beams

Use an Acoustic Emission (AE) to monitor the different material

performance and fracture mechanisms.

Six reinforced concrete (RC)

T-beams were tested,

designed for two different

failure mechanisms: flexural

failure (BF) and shear failure

(BS). A four-point bending test

was used to assess the

moment and shear resistance

of the test specimens, shown

in figure 1. The strengthened

scheme of the specimen is

shown in figure 2.

So

P/2 P/2

Si

P/2

P/2

L

Group Specimen Strengthening

Area

of FRP

(m2)

CF Control -

BF FRPF -1 1 layer on tension face 0.0795

FRPF -2 1 layer on tension face & U-wrap in both

ends and 4 strips// to tension reinforcement

0.245

CSH Control -

BS FRPSH-1 1 layer on tension face & 6 U-strips in both

ends

0.205

FRPSH-2 1 layer on tension face & 8 U-strips in both

ends

0.225

Distances Configuration of four-point

bending for BF

Configuration of four-point

bending for BC

L (mm) 1500 1500

S0 (mm) 1260 1260

Si (mm) 220 420

The longitudinal reinforcement

was the same for all six

specimens, however the

transverse reinforcement varied.

An example of the T-beam

geometry and configuration is

shown in figure 3. Experimental

Data was collected using two AE

sensors and three LVDT’s, as

shown in figure 4.

1260mm

P/2 P/2

120mm120mm

L5 L6

210mm

Front view

SupportSupport L7

AE Sensor

300mm

AE Sensor

400mm

630mm 210mm

Specimen

fck

(Mpa)

Psh

(kN)

MRd

(kNm)

PM

(kN)

Ultimate

Load

(Exp.), Pf

(kN)

Ultimate

Load (EC2),

Pf (kN)

Failure

Mechanism

(Exp.)

Failure

Mechanism

(EC2)

CF 20.4 57.8 11.4 43.7 39.8 44.5 Shear Flexure

CSH 23.3 44.9 11.5 54.8 36.8 45.5 Shear Shear

FRPF -1 19.6 55.5 12.5 48.1 42.8 49.7 Shear Flexure

FRPF -2 28.1 66.1 13.4 51.5 57.4 50.6 Shear Flexure

FRPSH-1 24.2 35.3 13.5 64.3 38.8 35.3 Shear Shear

FRPSH-2 26.7 49 12.4 59.1 48.3 48.7 shear Shear

44

.5 49

.7

50

.5

45

.5

45

.5

47

.3

39

.8 42

.8

57

.4

36

.8

38

.8

48

.3

C F ( K N ) F R P F - 1 ( K N )

F R P F - 2 ( K N )

C S H ( K N ) F R P S H - 1 ( K N )

F R P S H - 2 ( K N )

ULTIMATE LOAD

Theoretical Max. Load Experimental Max. Load

Specimen Predicted Ultimate

Capacity of the

Specimens

Experimental

Ultimate Capacity

of the Specimens

Over/Underestimated

of Pred. & Exp. (%)

CF 44.5 39.8 10.6

CSH 45.5 38.8 14.7

FRPF -1 49.7 42.8 13.9

FRPF -2 50.5 57.4 -13.7

FRPSH-1 45.5 38.8 14.7

FRPSH-2 47.3 48.3 -2.1

The failure mode observed for all six specimens was shear. Four

specimens retrofitted with the FRP failed in shear with end-

debonding of the CFRP sheets (U-wrap/ strips).

The retrofitted specimens with the FRP, showed an increase in

capacity which varied from 7 -30%, depending on the configuration

of the FRP strengthening scheme. Increase in stiffness and

cracking decrease was observed too..

The onset development of debonding was accurately determined

using Acoustic Emission (AE)

Figure 1: Four-Point Bending Test Configuration for Group BF and BS

Figure 2: Summary of Strengthened Specimens with CFRP Sheets

Figure 3: Geometry and Configuration of Steel

Reinforcement Details of BF Specimens

Figure 4: : Locations of the LVDTs and AE Sensors

Figure 4: Load-Deflection Graph for the BF Group Specimens Figure 5: Load-Deflection Graph for the BS Group Specimens

Figure 6: Ultimate Capacity for the Theoretical and Experimental Data Figure 7: Over/Underestimated of the Predicted

and Experimental Ultimate Capacity

Figure 8: FRPF -1 T-beam: (a) AE Hit Transient Frequency and Force

vs. Displacement Related to Materials Mechanism Graph; (b)Total

Number of Hits within the Frequency Range Normalized by AE Hits

(a)

(b)

Figure 9: FRPF -1 T-beam: (a) Force vs. Displacement AE and Hit

Transient Frequency Related to Shear and Tensile racks; (b)Total

Number of Hits within the Frequency Range Normalized by AE Hits

for the Shear Movement and Tensile Cracks Mechanism

(a)

(b)

Figure 10: FRPF -1 T-beam: Ratio of Average

frequency and Rise Time AmplitudeFigure 11: Comparison of Experimental and Theoretical data for six

tested specimens under four point bending

1260mm

P/2 P/2

520mm 220mm 520mm

120mm120mm

1500mm

100mm

50m

m1

30m

m

180m

m

50mm 50mm

200mm

2 Ø 10mm

4 Ø 6mm

6 Ø//150mm

FC

(a)

(b)

(a)

(b)

0

100

200

300

400

500

600

700

800

900

1000

0.00 0.10 0.20 0.30

Av

era

ge

Fre

qu

ency

(k

Hz)

Rise Time/ Amplitude (ms/V)

Tensile crack

48%

Shear crack

52%

Figure 8: FRPSH -2 T-beam: (a) AE Hit Transient Frequency and Force

vs. Displacement Related to Materials Mechanism Graph; (b)Total

Number of Hits within the Frequency Range Normalized by AE Hits

Figure 9: FRPSH -2 T-beam: (a) Force vs. Displacement AE and Hit

Transient Frequency Related to Shear and Tensile racks; (b)Total

Number of Hits within the Frequency Range Normalized by AE Hits

for the Shear Movement and Tensile Cracks Mechanism

[1] Hollaway, L.C. and Leeming, M. eds., 1999. Strengthening of reinforced concrete structures: Using Externally-bonded FRP composites in Structural and Civil Engineering. Woodhead Publishing Limited, Cambridge,

England.

[2] Obaidat, Y, T., (2011). Structural Retrofitting of Concrete Beams Using FRP - Debonding Issues. Doctoral Thesis, Lund University, Sweden.

[3] Teng, J.G., Chen, J.F., Smith, S.T., Lam, L. and Jessop, T., 2003. Behaviour and strength of FRP-strengthened RC structures: a state-of-the-art review. Proceedings of the Institution of Civil Engineers, Structures and

Buildings, 156(1), pp.51-62.

1. INTRODUCTION

2. AIMS & OBJECTIVES

3. METHODOLOGY

4. CONCLUSION

4. RESULTS & DISCUSSION