Civil Engineering Reference
In-Depth Information
s
w
spacing of links or pitch of helical reinforcement in longitudinal direction ofmember
Δ
p
decrease in transverse compression as a result of different areas of influence of
confining reinforcement according to Equation 7.7
ρ
wy
transverse reinforcing steel ratio according to Equation 7.14
ε
ju
assumedultimate strain inCFsheet usedas conning reinforcement aroundmember.
2
3
!
2
s
2
?
D
c
4
5
f
cc
f
c
k
?
E
jl
?
ε
ju
ρ
wy
?
f
wy
Δ
p
(7.13)
D
2
?
t
w
;
eff
D
c
ρ
wy
(7.14)
2
?
E
L
?
t
L
D
E
jl
(7.15)
where:
E
L
modulus of elasticity of surface-mounted CF sheet relative to
fibre cross-section
t
L
theoretical thickness of
fibre cross-section in CF sheet
t
w,eff
thickness of smeared con
ning reinforcing steel according to Equation 7.16.
A
sw
2
?
s
w
t
w
;
eff
(7.16)
where:
A
sw
total bar cross-section of effective confining transverse reinforcement per link or
one complete winding of helical reinforcement.
The above equations for compressive strengths
f
cc
and
f
c
*
take into account the various
areas of influence of the confinement in the form of CF sheet and reinforcing steel in a
practical way. To do this, the concrete compressive stresses acting in the effective
con
ned area within the con
ning reinforcing steel are distributed over the entire cross-
section. At the same time, the effects of the individual steel links or helical reinforcement
at a certain spacing/pitch in the longitudinal direction of the compression member are
also taken into account through the theoretical notion of the parabolic arc according to
Sheikh
and
Uzumeri
[125].
However, only the effect of the con
ning CF sheet is used when de
ning the longitudinal
strain
ε
cc
in the con
ned concrete upon failure of the
fibre-reinforced material.
7.4 Load-Carrying Capacity of Member
Most of the experimental studies of the load-carrying capacity of compression members
with a wrapping of CF sheet were carried out on concrete cylinders with a height-to-
diameter ratio of about 2 : 1. With fixity at both ends, which must be assumed for the
majority of the tests, this corresponds to a slenderness ratio
λ
=
4. Therefore, the design
approaches for the load-carrying capacity derived from these tests are only valid for
members with similar geometrical conditions, i.e. small slenderness ratios. However,
considerably greater slenderness ratios are found in practice; ratios between 20 and
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