Civil Engineering Reference
In-Depth Information
Accordingly, the ultimate confined concrete axial load, replacing that of Equation
(7.1), is
(
)
φ= φ
P
0.85
0.85
f
AA
−
+
0.85
f
(
AAAf
−
)
+
(7.16)
n
cce
c
st
ccf
g
c
st
y
lf
/ is greater than 0.08, the Lam
and Teng (2003a) model described in Section 7.2.1 is used with the proper
f
cce
and
f
ccf
for the core and the cover, respectively. In this case, the ultimate compressive
strain (ε
ccu
) is assumed to be different in the core and cover, which is determined by
substituting
f
lf
or
f
le
for
f
l
in Equation (7.8). Accordingly, the slope (
E
2
e
) of the core
will also be different from the slope of the cover (
E
2
f
). On the other hand, when
ff
For the combined confinement effect when
ff
lf
/ is less than 0.08, the Mander model described in Mander, Priestley, and Park
(1988) is used with the proper
f
cce
and
f
ccf
for the core and the cover, respectively. The
minimum ultimate compressive strain (ε
ccu
)—between that of Equations (7.8) and
(7.9) using
f
lf
for the case of FRP and that of the energy approach corresponding to
the fracture of the first hoop (Mander et al. 1988) for the case of transverse steel—is
selected. So in this case, the peaks of the curves for the core and cover take place
at different strains (ε′
cce
and ε′
ccf
) corresponding to the different strength values for
the core and the cover (
f
cce
and
f
ccf
), and the ultimate strain (ε
ccu
) is also different for
both the core and the cover. This procedure has been programmed into the software
“KDOT Column Expert” developed by the author and coworkers and described in
two references (Abd El Fattah 2012; Rasheed et al. 2012).
7.2.4 C
ombineD
C
onFinement
oF
Frp
anD
t
ranSverSe
S
teel
in
r
eCtangular
S
eCtionS
The
f
l
expression given by Equation (7.7) is replaced with the two lateral pressures
along the
x
- and
y
-axes as formulated by Al-Rahmani and Rasheed (2014) to account
for the contribution of FRP and transverse steel in confining the core and the cover
in the
x
- and
y
-directions, as seen in Figure 7.4.
2
nt E
h
ε
+ρ
f
f
fe
f
=
k
kf
(7.17)
flxe
e
exyh
b
c
r
c
f
flxf
f
flxe
h
h
c
h
b
b
FIGURE 7.4
Effective horizontal pressure of confined rectangular section. (Courtesy of
Al-Rahmani and Rasheed [2014].)
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