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:
ε
c
24
4
?
ε
c
8
84
24
4
?
18
:
4
8
1
:
k
a
0
:
37
a
k
a
?
ξ
?
d
L
0
:
37
?
0
:
27
?
160
16
:
06 mm
z
s1
d
s1
a
140
16
:
06
123
:
94 mm
z
L
h
a
160
16
:
06
143
:
94 mm
The moment capacity of the strengthened reinforced concrete cross-section is
therefore
61
?
10
3
94
?
10
3
m
Rd
z
s1
?
F
s1d
z
L
?
F
Ld
123
:
94
?
192
:
172
:
2
?
143
:
41
:
85 kNm
=
m
As the moment capacity is greater than the acting moment of 39.18 kNm/m, the design
is veri
ed.
4.5
Accurate analysis
4.5.1 General
The CFRP strip cross-section required was estimated iteratively via the bond analysis for
the concrete element between cracks. That resulted in a strip thickness
t
L
=
1.4mm with
a strip area of approx.
a
L
=
130mm
2
. As according to DAfStb guideline part 1, RV
8.2.1.1 (RV 1), or Section 3.7.1 of this topic, the centre-to-centre spacing may not
exceed
five times the slab depth and only certain strip sizes are available, the following
strip area will be chosen:
t
L
?
b
L
;
single strip
5
?
h
1
:
4
?
80
5
?
160
?
1000
140 mm
2
a
L
?
1m
=
m
a
L
t
L
b
L
100 mm
=
m
4.5.2 Veri
cation of
flexural strength
As with the simpli
ed analysis, this analysis is only carried out for the maximum
moment at mid-span. In the following calculation it is assumed that the reinforcing
steel is yielding and the compression zone of the cross-section is fully utilized.
Therefore, as with the simpli
ed analysis,
the admissible tensile force in the
reinforcing steel is
a
s1
?
f
yk
γ
s
4
:
43
?
10
2
?
500
F
s1d
192
:
61 kN
=
m
1
:
15
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