Abstract:
ABSTRACT
A hybrid double skin tubular members (DSTM) consist of three
composite materials in one section, include fiber reinforced polymer (FRP)
tube out ward, steel tube in ward and concrete in between. These three
materials give the member unique properties like protect column from
harsh environment, reduce amount of concrete by presence of inner steel
tube that allowed to the passage of services. Therefore, consider
sustainable structure element, as well as rising strengthening of members
and excellent corrosion resistance.
This study presents experimental program include 24 columns with two
types of circular columns, concrete filled FRP tube (CFFT) and double
skin tubular column (DSTC), with dimensions 100 mm*310 mm that
divided into five groups which constructed and testing under axial
compressive load till failure. With variables, numbers of layers of outer
FRP tube, compressive strength of mortar, ts/d ratio and ds/d ratio of inner
steel tube.
The experimental results showed that the mortar was effected
confinement in the hybrid DSTC led to very ductile behavior of stress
strain relationship, the number of outer FRP layers was the most effective
parameters on DSTCs behavior. The nominal confinement ratio was
affected by thickness of outer FRP tube and compressive strength of
concrete inside DSTCs. By increase number of layers of outer FRP tube
from 1 to 2 and 3) layers, the strength enhancement ratio increasing by
II
(48%, 72% and 155%), the enhancement of axial strain increasing by
(114%,123% and 274%) and the ductility rising by (149%,183% and
266%). When increasing mortar compressive strength from 45 to (50, 55
and 60) MPa, the strength enhancement ratio was about (50%, 40%, 41%
and 48%), enhancement of axial strain decreasing by (215%, 164%, 157%
and 114%) and the ductility decreasing by (174%, 160%, 167 and 149%).
By using ts/d ratio of inner steel tube from 0.015 to (0.02 and 0.03), the
strength enhancement ratio decreases by (48%, 38% and 41%), the
enhancement axial strain increase by (114%, 126% and 134%) and the
ductility was about (149%, 137% and 150%). By increase ds/d ratio of
inner steel tube from 0.25 to (0.32, 0.38 and 0.48), the strength
enhancement ratio decreased by (61%, 53%, 50% and 48%), the
enhancement of axial strain was about (191%, 167%, 130% and 114%) and
the ductility decreasing by (223%, 176%, 146% and 137%). When the ds/d
ratio decrease the behavior of specimens similar to the behavior of CFFT.
By compared between CFFT and DSTC the enhancement ratio is
approximately more in CFFT than DSTC, and presence of inner steel tube
in DSTC is supported to concrete in order to less press concrete on outer
FRP tube.
