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Shear behaviour of lightweight concretebeams strengthened with CFRP composite
Al-Allaf, MHF, Weekes, L and Augusthus Nelson, L
http://dx.doi.org/10.1680/jmacr.17.00488
Title Shear behaviour of lightweight concrete beams strengthened with CFRP composite
Authors Al-Allaf, MHF, Weekes, L and Augusthus Nelson, L
Type Article
URL This version is available at: http://usir.salford.ac.uk/id/eprint/47134/
Published Date 2019
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1
SHEAR BEHAVIOUR OF LIGHTWEIGHT CONCRETE BEAMS 1
STRENGTHENED WITH CFRP COMPOSITE 2
3
4
5
6
7
8
9
10
11
12
Figure 1: Beams reinforcement details 13
14
300mm
200mm
5 D16
Section A-A
600mm
150 mm 150 mm
1700 mm
600mm
300 mm
P P
A
A
2
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
Figure 2: Strengthening detail 30
31
Closed-shaped CFRP strips
BL/N-UST samples
BL/N-CST samples
150 mm 150 mm
1700 mm
100 mm 150 mm
300 mm
P P
20 mm
U-shaped CFRP strips
150 mm 150 mm 1700 mm
100 mm 150 mm
300 mm
P P
3
32
33
34
35
36
37
38
39
40
41
42
43
Figure 3: Details of test set-up 44
45
600 mm 600 mm
300 mm Steel box
Steel abutment 200x100x25 mm
Steel plate
200x100x25 mm steel plate Steel column
I - steel beam (spreader beam)
Supports rollers
500 mm
150 mm 1700 mm
Reaction frame
Hydraulic jack
Load cell
3750 mm
150 mm
RC beam
1500 mm
4
46
47
48
49
50
51
52
53
Figure 4: Position of strain gauges attached to the central bottom steel bar (plan view and all 54
dimensions are in mm) 55
56
Left end
Strain Gauge (FLA-6-11)
250 150 150 150 150 150 150 150 150 250 300
LS1 LS2 LS3 LS4 LS5 LS6 LS7 LS8 LS9 LS10
Right end
200
5
57
58
59
60
61
62
63
64
Figure 5: Position of CFRP strips and strain gauges (all dimensions are in mm) 65
66
200
P P
350
500
75
75
75
75
SF1 SF2 SF3 SF4 SF5 SF6
SG1
SG2
SG3
SG4
SG6
SG7
SG8
SG9
SG5
SG10
SG11
SG12
SG13
SG14
SG15
SG16
SG 17
SG18
6
67
68
69
70
71
72
73
Figure 6: Location of the LVDTs underneath the test samples 74
75
250 mm
300 mm
P P
250 mm
1000 mm
LVDTs (L) LVDTs (R)
LVDTs (C)
7
76 Figure 7: (a) Comparison of the shear strength gained due to CFRP reinforcement and (b) 77
increase in the maximum deflection at failure compared with the control sample 78
79
80
81
0
0.5
1
1.5
2
2.5
BL/N BL/N-UST BL/N-CST
Shea
r st
ren
gth
gai
ned
du
e to
CFR
P
LWC samples
NWC samples
0
0.5
1
1.5
2
2.5
3
BL/N BL/N-UST BL/U-CST
Incr
ease
in t
he
max
imu
m d
efle
ctio
n
ove
r th
e co
ntr
ol s
amp
le
LWC samples
NWC samples
Control samples
U-wraps
Closed-wraps
Control samples
U-wraps
Closed-wraps
(a) (b)
8
82
83
84 Figure 8: Comparison of load-deflection of LWC and NWC samples 85
86
0
50
100
150
200
250
300
350
400
0 5 10 15 20
She
ar f
orc
e (
kN)
Mid-span deflection (mm)
BN-UST
BN-CST
BL-UST
BL-CST
BL
BN
9
Figure 9: Failure mode of samples (a) BL, (b) BN, (c) BL-UST, (d) BN-UST, (e) BL-CST and 87
(f) BN-CST 88
89
(a)
(c)
(e) (f)
(d)
(b)
CFRP
debonding CFRP
debonding
CFRP
rapture
CFRP
rapture
10
Figure 10: (a) Light micrograph of lightweight concrete sample, (b) SEM micrograph of 90
lightweight aggregate, (c) SEM micrograph of reacted area of lightweight aggregate, (d) SEM 91
micrograph of reacted area of lightweight aggregate and cement paste, (e) SEM micrograph of 92
lightweight aggregate and (f) SEM micrograph of cement paste 93
(b)
(c)
(a)
Lightweight
aggregate(Black)
(f) (e)
Macro crack
(d)
Reacted area
(Orange)
Cement Paste
Reacted area
(Orange)
Cement Paste
11
Figure 11: (a) Light micrograph of normal weight concrete sample, (b) SEM micrograph of 94
normal weight aggregate and cement paste, (c) SEM micrograph of normal weight aggregate and 95
(d) SEM micrograph of normal weight aggregate and cement paste 96
97
(a)
(c)
(b)
(d)
Normal weight aggregate
Cement Paste
12
98
99
100
Figure 12: Strain profile along longitudinal steel reinforcement of specimen (a) BL-CST and (b) 101
BN-CST 102
103
13
104
105
Figure 13: Internal forces in a failed concrete strengthened beam strengthened with CFRP 106
107
𝜃
𝑉𝑓3
𝑉𝑓2
𝑉𝑓1
𝑉𝑅
Critical shear crack
𝑉𝑓3 𝑉𝑓2 𝑉𝑓1
𝑉𝑅
Free body diagram
14
108
109
110
Figure 14: Estimated shear contribution of (a) BL-UST, (b) BL-CST, (c) BN-USL and (d) BN-111
CST 112
0
50
100
150
200
250
300
350
400
0 50 100 150 200 250 300 350 400
She
ar c
on
trib
uti
on
(kN
)
Applied shear force (kN)
CFRP shear contribution
Total shear capacity
0
50
100
150
200
250
300
350
400
0 50 100 150 200 250 300 350 400
She
ar c
on
trib
uti
on
(kN
)
Applied shear force (kN)
CFRP shear contribution
Total shear capacity
0
50
100
150
200
250
300
350
400
0 50 100 150 200 250 300 350 400
She
ar c
on
trib
uti
on
(kN
)
Applied shear force (kN)
CFRP shear contribution
Total shear capacity
0
50
100
150
200
250
300
350
400
0 50 100 150 200 250 300 350 400
She
ar c
on
trib
uti
on
(kN
)
Applied shear force (kN)
CFRP shear contribution
Total shear capacity
(a) BL-UST (b) BL-CST
(c) BN-UST (d) BN-CST
𝑉𝑐 = 149.82 kN
𝑉𝑓 = 68.56 kN
𝑉𝑐 = 148.53 kN
𝑉𝑓 = 118.61 kN
𝑉𝑐 = 164.3 kN
𝑉𝑓 = 84.1 kN
𝑉𝑐 = 161.1 kN
𝑉𝑓 = 159.7 kN
