Civil Engineering Reference
In-Depth Information
Fig. 7.2
Ultimate strain
ju
in the CF sheet depending on the rounding radius
R
c
for reinforced and
plain concrete compression members
ε
always
finished with a lap. Owing to the disintegration of the concrete microstructure
caused by the large deformations in the concrete, a loss of bond with the concrete surface
must be assumed in the region of the lap. This means that the lap, without the help of the
concrete, must be able to transfer the tensile force acting on one layer of the CF sheet.
Therefore, the long-term and environmental in
uences that reduce the load-carrying
capacity must be considered in the design. In the DAfStb guideline [1, 2] this is achieved
by multiplying together the reduction factors for temperature
α
T
, moisture
α
F
, fatigue
α
E
and permanent loading
α
Z
as proposed by
Franke
and
Deckelmann
[108] for cold-curing
epoxy resin adhesives. The value [
k
3
]
=
0.7 recommended for
α
T
in the DAfStb
guideline [1, 2] was taken from the work of
Franke
and
Deckelmann
[108]. In the
case of conventional applications in buildings, moisture and fatigue stresses can be ruled
out, which means the system coefficients [
k
4
] and [k
5
] can be recommended for the
factors
α
F
respectively, taken as 1.0 in each case. A time of about 34 h, which is
adequate for the ultimate limit state, has been verified experimentally for the ratio
α
E
and
α
Z
equal to the system coefficient [
k
6
]
0.75, which agrees with the results of the tests
on epoxy resin concretes carried out by
Rehm et al.
[107]. This can also be seen in Figure
7.3, which compares the scatter given by
Rehm et al.
[107] with tests [129] carried out at
the Technische Universität München.
Owing to the
=
much higher level of stress compared with
the un-strengthened condition, the strain in the CF sheet resulting from the creep-
induced longitudinal deformation
ε
cc
of the reinforced concrete column, which in turn
canonlybepartiallydissipatedbythecreepof the laminating resin, is also considered
-
in some circumstances
-
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