CFRP-prestressed scale-model bridge design was fatigue
tested to 7 million cycles at 60% ultimate load, with
negligible e€ects on the stress levels and dynamic char-
acteristics of the bridge [12].
2.3. Tendon strength characterization
Manufacturer-supplied strength data for two leading
CFRP prestressing products were included in Ref. [18].
Using these data, ratios of guaranteed-strength to ulti-
mate-strength were computed to be 0.67 for Leadline
(by Mitsubishi Kasei, Japan) and 0.81 for CFCC (by
Tokyo Rope, Japan). This discrepancy suggests that
there is not a consistent methodology in use by di€erent
tendon manufacturers to establish characteristic
strength values.
2.4. Gripping and hold-down issues
Because FRP tendon materials lack the ductility of
prestressing steel, it has found been necessary to develop
new grip/anchor designs for FRP tendon tensioning.
FRP tendon anchorage technology was reviewed in 1993
[19]. Reusable wedge-type grips have been developed for
some speci®c FRP prestressing products [14,19]. Potted-
end anchorage has been demonstrated using a variety of
organic resins and cementitious materials as grout
[16,19,20]. Pretensioned CFRP tendons have been used
in draped con®gurations, although in one project, con-
ventional small-radius steel rollers were found to cause
splitting of the tendons [21]. The steel rollers were re-
placed with large-radius polymer guide channels as a ®x.
The issue of safety in the face of grip failures has been
raised as new gripping technology is being applied in the
®eld [9].
2.5. Transfer length
Careful tests of transfer length have been performed
for selected FRP prestressing products [7,13]. No un-
usual behavior was discovered compared to steel ten-
dons, though the characteristic transfer lengths di€er
from steel. Because there is variability in FRP tendon
composition and surface deformations, the transferlength must be determined for the speci®c product under
consideration.
2.6. Thermal expansion mismatch
The coecient of thermal expansion (CTE) values for
concrete and steel are similar, approximately 10 ´ 10ÿ6
/°C
for concrete and 11 ´ 10ÿ6
/°C for steel. For an epoxy-
matrix CFRP tendon, typical longitudinal and transverse
CTE values are in the neighborhood 70 ´ 10ÿ6
/°C and
30 ´ 10ÿ6
/°C, respectively. Temperature will a€ect bend-
ing stress levels, and concerns about concrete cracking
due to transverse expansion of the reinforcement have
been raised. A concern over beam end splitting was ad-
dressed in one ®eld application by the addition of helical
FRP reinforcements in the end regions [21]. The e€ects of
thermal expansion mismatch have been studied both
analytically [22] and experimentally [22,23] for the case of
unprestressed FRP rebar.
2.7. Ductility concerns
FRP tendons lack the ductility under extreme loading
exhibited by steel. Thus, a CFRP-prestressed beam may
simultaneously provide greater ultimate load capacity
and lower energy absorption than a similar steel-pre-
stressed design. Tendons have been distributed over a
large range of eccentricity values to achieve progressive
failure [14]. Recent work has advanced the ability to
predict the de¯ections of CFRP-prestressed beams
during progressive tension cracking, including load
cycling [24].
3. Prestressed bridge beam test program
Two 12.19 m long AASHTO Type 2 beams were
designed, fabricated, and tested to destruction in four-
point bending. The two beams shared the same geo-
metric con®guration for prestressing tendons and shear 复合材料高强度混凝土桥梁英文文献和中文翻译(2):http://www.youerw.com/fanyi/lunwen_17287.html