Civil Engineering Reference
In-Depth Information
4
Example 1: Strengthening a slab with externally bonded
CFRP strips
4.1
System
4.1.1 General
The example presented on the following pages is dealt with in considerable detail to aid
understanding, and in some cases several analysis options are described. It has therefore
something of a textbook character and does not represent the approach that would be
chosen in practice for structural calculations.
Owing to a change of use, a reinforced concrete
floor slab in a residential building needs
to be strengthened. The structure was built in the year 2000 and as-built documents are
available. Externally bonded CFRP strips are to be used as the strengthening system.
The floor slab spans one way and was designed as a simply supported member. It is
assumed that the slab is free to rotate at its supports on the masonry walls. The slab is not
designed to act as a horizontal diaphragm for stability purposes. Dry internal conditions
are assumed. Figure 4.1 shows the structural system requiring strengthening.
4.1.2 Loading
The loads are predominantly static. Three load cases will be investigated for ultimate
limit state design:
-
Load case 1
represents the situation prior to strengthening.
-
Load case 2
is the loading during strengthening. The strengthening measures are
carried out under the dead load of the slab. Existing
fitting-out items will be removed
during the strengthening work.
-
Load case 3
represents the loading situation in the strengthened condition.
Table 4.1 lists the actions of the various load cases for the loads given in Figure 4.1.
Load case 3 governs for designing the strengthening measures. The load combination
for the ultimate limit state and the load combination for the serviceability limit state
under a rare load combination are required for the analyses. These load combinations are
in line with the requirements of DIN EN 1990 [24] together with its associated National
Annex [25]. The following applies for the ultimate limit state (persistent and transient
design situations):
X
X
1
γ
G
;
j
?
G
k
;
j
γ
P
?
P
γ
Q
;
1
?
Q
k
;
1
1
γ
Q
;
i
?
ψ
0
;
i
?
Q
k
;
i
j
i
>
γ
Q
?
q
k
m
2
p
d
γ
G
?
g
1
;
k
g
2
;
k
1
:
35
?
4
3
1
:
5
?
5
16
:
95 kN
=
The load for the serviceability limit state is calculated as follows for a rare load
combination:
X
X
i
>
1
ψ
0
;
i
?
Q
k
;
i
G
k
;
j
P
Q
k
;
1
j
1
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