ure tests, where specimen sizes were relatively
strain was observed at high-temperature testing,
small (see Table 13). Thus, the variability of the
from which the creep parameter results match
properties appeared to be size dependent, with
Mosallam and Chamber's (1995) published values
larger sizes having less variability. The results also
for commercially available, pultruded FRP WF
showed directional variability (anisotropy) both
beams: p = 9.72 and q = 0.298. These results, how-
in the compression and tension tests.
ever, did not follow Findley's classical creep equa-
The presence of a small amount of moisture in
tion, possibly because of the scatter in the data. If
RPC tends to increase the compressive strength
the tests had been continued over a longer time,
and decrease the flexural strength (see Table 13).
a more discernible creep strain might have devel-
The exact mechanism of this phenomenon is not
oped. The data at room temperature and low tem-
clear, but is possibly related to nonhomogeneity
perature did not show any trend of increasing;
in the moisture distribution and the resulting
therefore, they were not analyzed with Findley's
stresses through the cross section of the speci-
equation. It must be noted that Findley's theory
mens.
applies very well to viscoelastic polymers, but in
A comparison of Tables 7b and 7c shows that
composites, when the stress is applied in the
for the RPC, low temperature has the most sig-
fiber direction, the behavior is not totally vis-
nificant effect on its mechanical properties. The
coelastic. In fact, with a higher volume fraction
strain at failure decreased significantly, as
of glass fibers oriented in the load direction, the
expected, indicating a tendency toward more
creep in FRP composites is not expected to be a
brittleness. Simultaneously, the stiffness (modu-
problem.
lus) and strength increased dramatically.
The application of FRP in breakaway couplers,
Relating the mechanical properties of the RPC
although attractive at first, actually presents seri-
to the design of guardrail posts or blockouts is
ous problems if the design is a "one-to-one"
not straightforward, because the analytical design
replacement of steel couplers. The FRP coupler
is too complex. The relationship depends not only
failures (Fig. 71a and b) in fiber-reinforced com-
on the material properties and structural response
posites are strongly direction oriented, and the
of the rails and posts, but also on the restraining
failure mechanism is controlled by the fiber arch-
forces of the soil. It also includes dynamic effects,
itecture. In order to have a clean, transverse, shear
large displacements, stiffness, yield strength, and
break in a necked-down breakaway coupler made
the inelastic behavior of all materials in the sys-
with FRP composites, the fiber architecture has
tem, the final goal of which is to redirect errant
to be developed and designed properly. The design
vehicles and other traffic to safety. Experience and
must force the failure to be induced by inter-
knowledge are the key factors in designing the
laminar or interfacial bond failure in the trans-
system; therefore, highway engineers rely on trial
verse direction to the bolt, without reducing the
and error in evaluating candidate systems by
longitudinal strength to withstand wind and ice
crash testing.
loads. Further research and design development
For a large-scale application of RPC in high-
through microstructural analysis of composites
way structures or in civil engineering, two things
are needed to accomplish this. The composite
are needed: (1) nationally acceptable, standard-
breakaway coupler in this case would have to be
ized test methods to ensure consistency in qual-
precast rather than machined from the commer-
ity from the suppliers, and (2) additional research
cially available bar stocks.
and tests to assess performance under prolonged
Crushable plastic cushions to protect vehicle
stress, wider ranges of temperature, and cyclic
occupants from side impacts with roadside fixed
periods of heat, cold, and dampness. The FHWA
objects is another potential application for FRP
approved RPC blockouts, which when used by
composites and plastics for highway safety struc-
some State DOTs, can provide valuable field data
tures. This investigation was confined only to a
for such assessments and evaluations.
conceptual design, shown in Figure 74. The
The quickest implementation of FRP compos-
design requires three rubber gaskets, and one end-
ites in civil engineering is FRP rebars for con-
cap to be molded with either rubber or polyure-
crete reinforcement. The present study evalu-
thane. The inner FRP facing would be cast or ma-
ated with the creep behavior of FRP rebar at
chined with a slot to accept the leaf springs. In
low-temperature, room-temperature, and high-
making the sandwich hubs for the body and cap
temperature conditions using a deadweight load-
cushions, additional machining for groove cut-
ing system. Only a very small trend of increasing
ting in the foams would be needed. Assembling
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