Civil Engineering Reference
In-Depth Information
Using the coefficient
k
a
(for
ε
c
>
2mm/m), calculated according to Section 3.2, it is
now possible to determine the internal lever arm
z
s1
:
8
ε
c
24
8
0
:
26
24
k
a
4
?
ε
c
26
0
:
34
4
?
0
:
a
k
a
?
ξ
?
d
s1
0
:
34
?
0
:
28
?
653
62
:
6mm
z
s1
d
s1
a
653
62
:
6
590
:
4mm
As the internal lever arm roughly corresponds to the assumed lever arm, the resistance of
the reinforced concrete cross-section at the position of the acting moment is
M
Rk
;
0
z
s1
?
F
s1
590
:
4
?
406
:
5
?
10
3
240 kNm
The prestrain for the concrete therefore amounts to
ε
c,0
=
0.26mm/m, and for the
reinforcing steel
ε
s1,0
=
0.66mm/m.
6.4 Veri
cation of
flexural strength
In the following calculations it is assumed that
five strips are required for strengthening.
The total strip cross-section is therefore
200 mm
2
A
L
n
L
?
t
L
?
b
L
5
?
2
?
20
When strengthening a member by means of near-surface-mounted CFRP strips, the slot
dimensions must satisfy certain requirements, which in
uence the effective structural
depth of the strips. According to DAfStb guideline [1, 2] part 3 section 4.4.1 (3), the
depth of each slot in the concrete is
t
s
c
Δ
c
dev
The allowance
Δ
c
dev
is made up as follows according to Section 5.2:
Δ
c
dev
Δ
c
tool
Δ
c
slot
Δ
c
member
1
2
2
5mm
With a concrete cover
c
20mm, which is exactly
the same as the strip width
b
L
. The effective structural depth of the CFRP strip according
to DAfStb guideline [1, 2] part 1 Eq. (RV 6.53) depends on the depth of the slot and is
=
25mm, the ensuing slot depth is
t
s
=
700
b
L
2
20
2
d
L
h
t
s
20
690 mm
The maximum strain that may be assumed in the design is determined from DAfStb
guideline [1, 2] part 1 Eq. (RV 6.52) using the characteristic tensile strength of the strip
f
Luk
, the safety factor for strip failure
γ
LL
and the coefficient
k
ε
:
f
Luk
γ
LL
?
E
L
2400
1
:
2
?
170
?
10
3
ε
LRd
;
max
κ
ε
?
ε
Lud
κ
ε
?
0
:
8
?
9
:
41 mm
=
m
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