Civil Engineering Reference
In-Depth Information
0
:
3
?
b
w
20
b
w
40
α
(3.62)
EI
S
;
A
?
EI
S
;
B
EI
S
;
A
EI
S
;
B
EI
s
;
g
;
α
b
0
:
4
2
?
(3.63)
Accordingly, the contact pressure for
limit case
α
b
=
0.8
is given by Equations 3.64 to
3.66. This results in the lengths
l
3
=
20
+
t
LW
and
l
4
=
2
l
3
. The crack width for CFRP
strips is then
w
=
0.35.
48
?
EI
s
;
g
;
α
b
0
:
8
l
4
26 400
?
EI
s
;
g
;
α
b
0
:
8
11 000
?
l
3
F
u
;
4
?
w
2
(3.64)
2
:
4
?
EI
s
;
g
;
α
b
0
:
8
!
EI
s
;
g
;
α
b
0
:
8
4583
?
l
3
EI
s
;
g
;
α
b
0
:
8
w
2
w
1
?
0
:
1
(3.65)
EI
S
;
A
?
E
S
I
S
EI
S
;
A
E
S
I
S
EI
s
;
g
;
α
b
0
:
8
2
?
(3.66)
3.4
Shear force analyses
3.4.1 Shear strength
The DAfStb guideline [1, 2] states that the analyses of DIN EN 1992-1-1 [20] together
with its National Annex [21] must be carried out to assess the shear strength. It has been
shown in tests [11, 54] (q.v. [84]) that these analyses can also be used for strengthened
members in the building stock. However, externally bonded reinforcement may not be
counted as part of the longitudinal reinforcement ratio in Equation 6.2a of DIN EN
1992-1-1 [20].
In members with externally bonded
flexural strengthening, debonding due to offset
crack edges caused by the shear force can take place additionally in the case of high
stresses in the tension and compression members of the truss assumed for carrying the
shear force. For this reason, the guideline includes Equation 3.67, specifying a limit
value above which the externally bonded CFRP strips have to be wrapped with
externally bonded shear links:
V
Ed
?
σ
sw
V
Rd
;
max
mm
2
75 N
=
for ribbed shear links
(3.67)
25 N
=
mm
2
for plain shear links
The given limits are based on modelling and a subsequent parametric study in [57] (q.v.
[85]). The shear link stress included in Equation 3.67 can be calculated by rearranging
Equation 6.8 or 6.13 from DIN EN 1992-1-1 [20], as Equation 3.68 illustrates:
V
Ed
σ
sw
(3.68)
A
sw
=
s
?
z
?
cot
θ
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