Civil Engineering Reference
In-Depth Information
Using the coefficient
k
a
(for
ε
c
<
2mm/m), which is the result according to Section 3.2,
it is now possible to determine the internal lever arms:
2
c
3
?
2
:
47
2
3
?
ε
4
?
ε
c
2
6
?
ε
4
?
2
:
47
2
6
?
2
:
47
2
k
a
4
?
ε
c
4
?
2
:
47
0
:
39
c
a
k
a
?
ξ
?
d
L
0
:
39
?
0
:
196
?
690
53
:
0mm
z
s1
d
s1
a
653
53
:
0
600
:
0mm
z
L
h
a
690
53
:
0
637
:
0mm
The moment capacity of the strengthened reinforced concrete cross-section is
therefore
M
Rd
z
s1
?
F
s1d
z
L
?
F
LRdL
1338
:
6
?
600
?
10
3
320
?
637
?
10
6
1006
:
9kNm
As the moment capacity is greater than the acting moment of 978 kNm, the design is
veri
ed.
6.5
Bond analysis
6.5.1 Analysis point
According to DAfStb guideline [1, 2] part 1, RV 6.1.3.3 (RV 2), or Fig. RV 6.12, the
analysis should be carried out, as described in section 5.3, at the point at which the CFRP
strip is first required for loadbearing purposes. To do this we determine the point on the
unstrengthened member at which the existing reinforcing steel reaches its yield point
under the loads in the strengthened condition (load case 3). So we must first determine
the bending moment at which the reinforcing steel begins to yield. The tensile force and
the strain in the reinforcing steel for this situation are
30
:
79
?
10
2
A
s1
?
f
yk
γ
s
?
500
F
s1d
1338
:
6kN
1
:
15
f
yd
E
s
435
200 000
2
:
175 mm
=
m
ε
s1
Assuming a compressive strain in the concrete
2mm/m and a compression zone
contained completely within the slab, the compressive force in the concrete can be
expressed as follows according to Section 3.2:
ε
c
>
F
c
b
?
x
?
f
ck
?
α
R
b
?
ξ
?
d
s1
?
f
cd
?
ε
12
ε
c
c
2
ε
c
ε
c
ε
s1
0
:
85
1
:
5
?
ε
12
ε
c
c
1000
?
?
653
?
30
?
2
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