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TRANSCRIPT
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