Civil Engineering Reference
In-Depth Information
6
Example 2: Strengthening a beam with near-surface-
mounted CFRP strips
6.1
System
6.1.1 General
Owing to a change of use for a single-storey shed, a reinforced concrete downstand
beam must carry higher loads and therefore needs to be strengthened. As-built
documents with structural calculations to DIN 1045 [94] are available. The downstand
beam, which was designed as a simply supported member, is to be strengthened with
near-surface-mounted CFRP strips. It is assumed that the beam is free to rotate at its
supports. Moderately damp conditions prevail in the building and the loads are primarily
static. Figure 6.1 shows the structural system requiring strengthening and Figure 6.2
shows an idealized section through the beam.
6.1.2 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 beam. Existing fitting-out items will be removed
during the strengthening work.
-
Load case 3
represents the loading situation in the strengthened condition.
Table 6.1 lists the actions of the various load cases for the loads given in Figure 6.1.
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 given by DIN EN 1990 [24] together with its associated National Annex [25]. The
following applies for the ultimate limit state (persistent and transient design situa-
tions):
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
p
d
γ
G
?
g
1
;
k
g
2
;
k
1
:
35
?
30
5
1
:
5
?
5
:
0
122
:
35 kN
=
m
The load for the serviceability limit state is calculated as follows for a rare load
combination:
X
X
G
k
;
j
P
Q
k
;
1
1
ψ
0
;
i
?
Q
k
;
i
j
1
i
>
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