Civil Engineering Reference
In-Depth Information
6.5.3 Bond resistance
First of all, the bond length of the near-surface-mounted CFRP strip is required
to determine the bond resistance. The bond length is the result of the analysis
point in Section 6.5.1 minus the distance of the strip from the centre of the support. To
make it easier to cut the slot, the distance of the strip from the edge of the support is
specified as 200mm. According to Figure 6.1, the distance from the edge of the
support to the centre of the support is another 200mm. The bond length available is
therefore
l
bL
x
a
L
1710
200
200
1310 mm
To determine the bond strength, the maximum bond stress in the adhesive and the
maximum bond stress in the concrete are required according to DAfStb guideline [1, 2]
part 1 Eqs. (RV 8.13) and (RV 8.14), using the variables from Section 6.1.3:
s
q
f
Gtk
τ
bGk
k
sys
?
2
?
f
Gtk
2
?
f
Gck
?
f
Gtk
f
Gck
?
f
Gtk
s
q
30
2
mm
2
τ
bGk
0
:
8
?
2
?
30
2
?
90
?
30
90
?
30
24 N
=
p
38
p
f
cm
27
:
7N
=
mm
2
τ
bck
k
bck
?
4
:
5
?
The design value of the bond stress is now calculated with the long-term
effect coef
cients and the safety factor according to DAfStb guideline [1, 2] part 1
Eq. (RV 8.12):
1
γ
BE
?
min
1
1
:
3
?
min
1
1
:
3
?
12
9
:
23 N
=
mm
2
τ
bGk
?
α
bG
τ
bck
?
α
bc
5
27
:
7
?
0
:
85
24
:
0
?
0
;
τ
bLd
The tensile force per strip that can be anchored via the composite action between CFRP
strip and concrete member can be calculated for
l
bL
>
115mm to DAfStb guideline part
1 Eq. (RV 6.56):
70
?
?
0
:
95
p
a
r
a
r
F
bLRd
b
L
?
τ
bLd
?
26
:
2
0
:
065
?
tanh
l
bL
115
4
?
?
p
50
50
70
4
F
bLRd
20
?
9
:
23
?
26
:
2
0
:
065
?
tanh
1310
115
0
:
95
34
:
44 kN
?
?
The edge distance of the strip
a
r
here is such that it is also equal to the centre-to-centre
spacing of the strips. The spacing and edge distance chosen in this way also comply with
the requirement according to DAfStb guideline part 1, RV 8.2.1 (see Section 5.7 of this
book).
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