Civil Engineering Reference
In-Depth Information
this minimum spacing there are also enhanced requirements regarding the distance of a
strip from the edge of a member.
The DAfStb guideline specifies the minimum spacing
a
L
for near-surface-mounted
CFRP strips by way of Equation 5.13, which is based on the diameter
of the steel
reinforcing bars running parallel to the CFRP strips, the clear spacing
a
s
of these steel
reinforcing bars, the maximum aggregate size
d
g
and the strip width
b
L
:
ϕ
d
g
for
a
s
2
?
ϕ
a
L
(5.13)
b
L
for
a
s
>
2
?
ϕ
This minimum spacing is necessary because where individual near-surface-mounted
CFRP strips are too close together, one conceivable failure mode involves the strips
together with the concrete cover become fully detached from the member (see [27]). The
DAfStb guideline therefore includes the rules of [29], which are based on similar rules
for internal steel reinforcing bars according to [27]. The final criterion for a minimum
distance between CFRP strips is guaranteeing being able to cut the slots without
damaging the member, which is also the case with the limits specified above.
A minimum edge distance is necessary because of the risk that the edge of the concrete
member could break away if the spacing between a CFRP strip and the free edge of a
member is too small and also the risk of damage to the edge of the concrete when cutting
the slots. This minimum edge distance is speci
ed in the DAfStb guideline by way of
Equation 5.14. This approach was in the detailing rules of an earlier approval [29] and is
based on [27].
d
g
2
?
b
L
a
r
max
(5.14)
The DAfStb guideline contains another requirement regarding the edge distance for the
case where CFRP strips are being bonded to the soffit and the side face at the same time.
This is because strips meeting along an edge cause a higher stress in the concrete at this
corner.
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