9
simultaneously at two points by servo-controlled hydraulic actuators specially designed and
fabricated for this study
The maximum applied load (Pmax) was 115 kN (26,000 lb). The minimum applied load
(Pmin) was 9 kN (2,000 lb). Therefore, the fatigue stress ratio (R = Pmin/Pmax) was 0.077. Loading
Initially a quasi-static test was performed at room temperature. Then the testing room
temperature was changed by operating either the refrigeration system for cooling or operating the
heating system for raising the temperature of the room. Once the equilibrium temperature for the
deck was achieved fatigue load cycling was initiated.
Quasi-static load deflection tests were performed at regular intervals. In the quasi-static
test the load was applied at a rate of 1 mm/min. (0.04 in./min) and sensor measurements were
recorded every 3 seconds. Each quasi-static test consisted of a loading and unloading cycle and
was repeated three times, as shown in Figure 7.
5. DISCUSSION OF EXPERIMENTAL RESULTS
Fatigue damage accumulation can induce stiffness degradation of the FRP composite
deck material. Fatigue damage can also lead to residual deformation in the deck and in the deck
girder haunch connections. Thus, the fatigue performance evaluation was based on assessing the
residual stiffness of the deck response and the fatigue damage. Quasi-static load deflection tests
were conducted for damage assessment. The experimental data were analyzed and load
deflection curves were generated.
The FRP deck prototypes did not fail during the loading cycles. However, following the
ten million cycles of loading at two extreme temperatures, degradation of stiffness was observed
(Figure 8 and Figure 9).
The loaddeflection curves for the low temperature, 30C (22F), and the high
temperature, 50C (122F), at the five LVDT locations on the top of each panel and aligned in
the direction perpendicular to girders are shown in Figure 8. The reinforced-concrete deck
(Bridge #1) and the FRP-concrete hybrid deck (Bridge #2) exhibited higher stiffness than the
FRP composite decks (Bridges #3, #4, and #5).
Load deflection curves for each deck prototype for the LVDT position LV-2 before
fatigue cycling, after 2 million load cycles and after 10 million load cycles are shown in Figure
9. The decrease in slope of the load-deflection curves with number of fatigue cycles, indicate
damage accumulation in the decks.
The effects of temperature on the load-deflection response are presented in Figure 10. As
expected, the deck stiffness was reduced at the higher temperature level. The reduction in
stiffness with temperature was more important for the FRP composite decks than for the
reinforced-concrete deck and the FRP-concrete deck. From the maximum loaddeflection curves
(Figure 10), it was observed that the FRP bridge deck fabricated by the VARTM process (Bridge
#3) and the FRP bridge deck fabricated by the pultrusion process (Bridge #4) had significantly
more deflection than that of reinforced-concrete deck (Bridge #1) and the FRPcomposite hybrid
deck (Bridge #2). There was only a relatively small change in deck stiffness between the FRP
bridge deck fabricated by the hand lay-up contact molding process (Bridge #5) and the
reinforced-concrete bridge deck (Bridge #1) at both low and high temperatures.
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