Column is a very important load bearing structural element. When column
fails, it does not only cause the collapse of the story where the column exists but may
catastrophically disintegrate the overall structure. In this manner, first story column
should possess sufficient ductility by which the structure should be able to deforms
with large lateral drift, hence, the life safety extendsway beam mechanism develops.
One way to enhance concrete ductility is by using confinement as it eenhance the
stress and strain of concrete. This study proposes new alternative of confining
concrete column by means of external steel ring. Steel ring is employed solely as an
external confinement. Despite the fact that the steel ring does not act as external
reinforcement, however, it improves the ductility, enhances the column capacity,
maintains the cross-sectional area of concrete from premature spalling, and
strengthens the columns.
The preliminary study employed concrete cylinder confined with steel rings.
The cylinder was 300 mm in height and 155 mm in diameter subjected to uniaxial load
according to SNI 03-1974-1990. The study was conducted to investigate the effect of
confinement on the mechanical properties of concrete. The thickness of steel ring was
constant at 2.4 mm. Variation of steel ring volumetric ratio is based on variations in
width (28, 45, and 73 mm) and the clearances between the steel ring (90, 47, and 25
mm). The results were used as the basis to predict the the capacity and ductility of the
reinforced concrete (RC) columns confined with steel rings under cyclic loading.
Eventually, half scale laboratory test was performed to determine the effects of the
external confinement. The test specimen was a RC circular column with height of 1710
mm and diameter of 260 mm. The thickness of steel ring was 6.3 mm, the width of 50
mm and clearances between the steel ring was 80 mm (volumetric ratio of steel rings
was 1.86%). The specimen was subjected to a constant axial load and lateral cyclic in
accordance to ACI 374.2R-13. Three RC circular columns specimens were employed
in the investigation. The first specimen was unconfined column (K0-0,4) and the
second specimen was column confined by steel rings (KT-0.4). Both were under
constant axial load with axial load ratio of 0,4P
. The third specimen was a column
confined by steel ring (KT-0.6) subjected to a constant axial load with axial load ratio
of 0,6P
0
0
.
The preliminary study clearly demonstrates that the steel ring is effectively
confine the concrete, as its stress and strain increases compared to the unconfined
concrete. With steel rings volumetric ratio range was 1.25 to 2.28%, it is found that
the confinement of concrete may be attributed as high confinement level as the
effective confinement index reaches 21.99 while the concrete strength reaches 2.29.
The half scale RC circular columns confined with steel ring exhibit higher ductility,
load carrying capacity and resistance than the unconfined column. The displacement
ductility index of the test specimen K0-0,4; KT-0,4; and KT-0,6 column are 6.33; 8.38;
and 6.82, respectively, while the curvature ductility index of specimen KT0-0,4; KT0,4;
and
KT-0,6
column
are
7.72;
9.72;
and
8.23
respectively.
Keywords:
column,
ductility,
external
confinement,
steel
ring
