## 3 Experimental Program
The ultimate strengths of the UHPFRC were 140, 30, and 8 MPa in compression, flexural, and direct tension, respectively, while its modulus of elasticity was 50 GPa. Using the available force-control hydraulic actuator system, the experimental program tested two precast FDDPs supported over a twin-steel girder bridge. The first precast FDDP system was tested under constant amplitude fatigue (CAF) loading, followed by increasing static loading to collapse. To collapse, the second precast FDDP system was tested under incremental step fatigue loading of variable amplitude (VAF). Table 2 presents a summary of fatigue-tested slab configurations. The constant-amplitude fatigue test is intended to examine whether the jointed slab can accommodate a minimum of two million cycles of fatigue loading without significant damage as an acceptance criterion per the Canadian Highway Bridge Design Code [2]. After the fatigue testing, the slab was statically loaded to collapse to determine its ultimate load-carrying capacity and compare it with the design wheel load for ultimate limit state design. The variable amplitude fatigue load test is meant to obtain fatigue test data to assist in developing a fatigue prediction model. Figure 2: Details of steel twin-girder system supporting the precast FDDPs. The actuator system generates sinusoidal harmonic force, \(p_{t}=p_{avg}+p_{o}\sin 2\pi t\), where \(p_{avg}=p_{static}\) is the average load of the maximum and minimum load, \(p_{o}\) is the amplitude of applied load, \(f\) is the frequency of the applied load, and \(t\) is the time. Before performing the fatigue tests, a flexural crack was initiated at the bottom of the tested slab by applying the fatigue test. The fatigue test was initiated at the bottom of the tested slab by applying the fatigue test to the test. The fatigue test was initiated at the bottom of the tested slab by applying the fatigue test to the test. a static load equal to three times the applied wheel load for serviceability limit state design per CHBDC (SLS\({}_{1}\) = 87.5 kN \(\times\) 1.4 \(\times\) 0.9 = 110.25 kN). The 87.5 kN equals the heaviest wheel load in the CHBDC truck, multiplied by 1.4 to include the dynamic load allowance (DLA) and 0.9 as the fatigue limit state design load factor. This load is three times SLS\({}_{1}\) = 110.25 \(\times\) 3 = 330.75 kN. The footprint of the wheel load on the top surface of the tested slab measured 600 mm wide by 250 mm long, and it was decided to locate it just beside the edge of the joint, as depicted in Figure 2c. The constant amplitude fatigue (CAF) loading was applied under force control with a sinusoidal shape to represent the fatigue limit state (FLS) load specified into the CHBDC as FLS = 87.5 \(\times\) 1.4 \(\times\) 1.0 = 122.5 kN at the frequency of 4 Hz for 4 million cycles. To prevent rattling of the test setup under cyclic loading, the loading cycle started with a 15 kN applied load that increased by 122.5 kN. Thus, the sinusoidal cyclic CAF ended up with a loading range of upper and lower absolute values of 137.5 kN and 15 kN, respectively, with a sample rate of 20.013 Hz. Figure 5a shows the CAF loading history applied to the test specimens. A static load test at 1.5 times the applied FLS load (i.e., 122.5 kN \(\times\) 1.5 = 183.75 kN) was performed every 250,000 cycles to assess the degradation of the jointed slab due to fatigue loading. The force-control monotonic test had a ramp segment shape at a loading and unloading rate of 5 kN/min. and 10 kN/min, respectively, collecting data points every 0.049967 s, per Table 3. After the 4 million cycles of CAF loading, the FDDP system was monotonically loaded to collapse using a 1300 kN capacity hydraulic jack. The resulting ultimate load was compared to the CHBDC factored design load that was taken as P\({}_{\text{f}}\) = 87.5 \(\times\) 1.4 \(\times\) 1.7 = 208.25 kN, where 87.5 kN is the heaviest wheel load in the CHBDC  
Figure 4: Panel-to-girder connection of the precast FDDP.