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312
IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 3
Experimental analysis of reinforced concrete columns strengthened with self-compacting concrete
and connectors
as the second pair of connectors approaches the centre of the
column. However, both columns failed abruptly by uncoating of
the strengthening concrete.
Column P8, which had three pairs of connectors, revealed the
greatest failure load of all the columns tested. Nevertheless, de-
spite having two more pairs of connectors, the strength increase
between P5 and P8 reached only 4%. The highest increase ob-
tained by testing this model was a change in failure mode, from
ductile failure to strengthening concrete crushing, similarly to the
failure mode shown by monolithic reference column P2, thus meet-
ing the central aim of this work.
b) Displacements
Figure 12 shows horizontal displacements that took place in the po-
sition of the R3 dial indicator for all the columns tested. All strength-
ened columns showed less inclined curves than reference columns
P1 and P2, suggesting that strengthening results in smaller dis-
placements. The original reference column P1 showed the biggest
displacements, whereas strengthened column P8 had the smallest
displacements.
Columns P3, P4 and P5 were strengthened with only a pair of con-
nectors, placed in different positions. As shown in Figure 12, the
location of the connector may influence the horizontal displace-
ment of the models used; the further the connector stands from the
center (P5), the smaller the displacement on the loads near failure.
Columns P6A and P7 with two pairs of connectors reveal (Figure
8) that the ability to move was increased in relation to the rein-
forced columns with only one pair of connectors, letting P6A show
a final displacement close to the displacement shown by mono-
lithic reference column P2. For this, reinforcement with two pairs
of connectors, maintaining the first pair of connectors in the same
position used in column P5 and varying the position of the second
pair of connectors, reveals that the further away the second pair is
from the center, the greater the displacement of the model.
c) Strains
Figure 13 shows load curves x strain of the reinforcement under
the greatest tension of all the columns assayed. With the excep-
tion of columns P2 and P5, face reinforcement was under tension
on all the remaining columns; this tension was requested since the
beginning of the test. For columns P2 and P5, the steel only began
to be submitted to tension from 280 kN and 400 kN loads onwards,
respectively. Of the reference columns, only column P1 reached
steel yield strain value. Column P2’s curve shows a tendency to
reach yield strength.
Columns P3, P4 and P5, strengthened with a single pair of con-
nectors, failed to reach the reinforcement’s yield strain. As it can
be observed in Figure 9, the closer to the centre the pair of connec-
tors is, the greater the strains of the reinforcement on the tension
column face. Columns P6A and P7, strengthened with two pairs
of connectors, showed yielding of the tension face reinforcement.
These columns show very similar strain values, but P6A shows
the greatest strain. We observed that, by placing the first pair of
connectors in the position used in column P5 and then a second
pair of connectors in an intermediary position in relation to the first,
strain values of the tensed reinforcement increase considerably.
Furthermore, in case of using two pairs of connectors, the closer
to the centre the second pair of connectors is, the lower the strain
value produced by the tensed reinforcement; this is the opposite
situation to that of columns with only a single pair of connectors.
Column P8, which was strengthened with three pairs of connec-
tors, showed a final steel strain similar to that observed for mono-
Table 2 – Failure loads and modes of all columns
sub
str
P : Failure load; ƒ and ƒ : Compression strength of substrate and strengthening concrete, respectively, on the day of failure
u
c
c
sub
str
testing; E e E : Elasticity modulus of substrate and strengthening concrete, respectively; e : Initial eccentricity; D : Maximum
c
c
initial
max
horizontal displacement; e : Final eccentricity = e + D ; max and max: Maximum strain of tension steel and of compressed
final
initial
max s
c
concrete, respectively;
e
= 2.42 mm/m: for ø = 10.0 mm; = 3.0 mm/m (ACI 318M-02); = 3.5 mm/m (NBR 6118/2003); EA: Steel
y
u
yield; EC: Concrete crushing; DR: Uncoating of strengthening concrete; column P6 malfunctioned during tests and an analysis
was performed for its replacement by P6A.
e
e
e
Column
P
u
(kN)
sub
ƒ
c
(MPa)
str
ƒ
c
(MPa)
sub
E
c
(MPa)
str
E
c
(MPa)
e
initial
(mm)
D
max
(mm)
(mm)
(mm/m)
(mm/m)
Failure
mode
P1
140
42.3
-
26.3
-
60.0
25.3
85.6
-3.3
2.7
EA
P2
450
42.3
-
26.3
-
42.5
17.7
60.2
-2.2
4.6
EC
P3
390
41.9
41.1
26.1
34.5
42.5
7.8
50.3
-1.7
2.9
DR
P4
470
42.0
41.6
26.2
34.9
42.5
7.5
50.0
-1.4
2.4
DR
P5
500
42.1
42.0
26.2
35.3
42.5
7.0
49.5
-0.8
2.1
DR
P6
370
42.2
42.3
26.3
35.5
42.5
11.6
54.1
-2.0
1.7
DR
P6A
430
37.8
33.4
26.5
26.7
42.5
14.0
56.0
-4.5
2.0
DR
P7
480
38.5
35.0
26.8
28.2
42.5
9.3
51.3
-4.3
-
DR
P8
520
38.2
34.5
26.7
27.7
42.5
4.8
47.3
-2.3
3.8
EC
e
final
e
max
s
e
max
c