Civil Engineering Reference
In-Depth Information
2200.0
2000.0
1800.0
f: pure compression
1600.0
1400.0
e:
x
=
D
1200.0
d:
x
=
d
1000.0
(
M
n
,
P
n
)
GFRP-reinforced
(
M
n
,
P
n
)
steel-reinforced
800.0
600.0
Compr
ession
controlled failure
400.0
200.0
M
n
(ft-kips)
c: balanced
0.0
0
.0
100.0
200.0
300.0
400.0
500.0
600.0
-200.0
b:
x
= 0
-400.0
Tension controlled failure
-600.0
a: pure tension
Figure 5.6
Interaction diagrams of GFRP and steel RC columns (circular cross section).
Similarly, Figure 5.6 shows the interaction diagrams for the circular
cross section reinforced with the same number of GFRP and steel bars.
The considerations made for the rectangular cross section hold here. It
should be noted that the balanced condition for the GFRP RC column
occurs when the axial force produces tension. This is generally the case
for large values of the reinforcement ratio (ρ
f
≥ 2%).
5.7 STRENGTH-REDUCTION FACTOR FOR
COMBINED BENDING MOMENT
AND AXIAL FORCE
As ACI 440.1R-06 [1] is silent about columns, the method presented herein
to calculate the strength-reduction factor for columns relies on a reliability
analysis study as discussed in detail in Chapter 4. This method aims to
unify the strength-reduction factors of columns and flexural members as a
function of the maximum tensile strain in the reinforcement. The proposed
formulation to compute the ϕ-factor is the following:
ε
ε
ƒ
0.65
≤φ=
1.15
−
≤
0.75
(5.49)
2
fd
ε
f
in Equation (5.49) is the tensile strain taken as positive.
Search WWH ::
Custom Search