Civil Engineering Reference
In-Depth Information
stresses have been analyzed to determine the effective strain level that can
be attained (Triantafillou 1998):
ε=ε≤
k
0.004
(6.7)
fe
v u
The bond reduction coefficient (
k
v
) is a function of the concrete strength, the ply
stiffness, and the wrapping scheme. This coefficient may be computed based on the
model by Khalifa et al. (1998):
kk L
12
e
(6.8)
k
=
≤
0.75
in U.S. customary units
v
468
ε
fu
kk L
12
e
k
=
≤
0.75
in SI units
(6.9)
v
11,900
ε
fu
where
2/3
f
c
4000
k
=
in lb-in. units
(6.10)
1
2/3
f
c
27
k
=
in SI units
(6.11)
1
dL
d
−
fv
e
forU-wraps
fv
(6.12)
k
=
2
d
−
2
L
fv
e
fortwo bondedsides
d
fv
ACI 440.2R-08 defines
L
e
as the active bond length, which is the length over
which the majority of the bond stress is maintained:
2500
L
=
in lb-in. units
(6.13)
e
(
)
0.58
nt E
f
f
23,300
L
=
in SI units
(6.14)
e
(
)
0.58
nt E
f
f
Even though the
k
v
factor has been validated for a high-shear, low-moment region,
ACI 440.2R-08 reports that it is sufficiently conservative for areas of high flexural
and shear stresses as well as for negative-moment regions.
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