Deflection Profile

The deflection profiles along the longitudinal direction of the three bridge decks are given in Fig­ures 6, 7, and 8, respectively. It should be noted that the deflection profiles are plotted for the final loading cycle only. The deflections shown for each deck represent the residual deflection from previous loading. The deflection profiles for the three bridge decks indicate that the deflection at the edge of the bridge decks was very small. This implies that selection of the length of the model is effective for carrying the total load, and therefore, representative to the actual bridge deck.

The deflection profiles along the transverse direction of the three bridge decks are given in Fig­ures 9,10, and 11, respectively. It should again be noted that the deflection profiles are plotted for the last loading cycle only, therefore residual deflections are shown at the beginning of the loading cycle (zero load). The deflection profiles indicate that the maximum deflection occurred at the mid-span under the applied load. Also, it is clear that the spans failed in punching shear (right span) exhibited less deflection than the spans failed due to flexural as will be discussed in the following sections.

Fig. 7. Longitudinal deflection profile for the second bridge deck.

Fig. 8. Longitudinal deflection profile for the third bridge deck.

Mode of Failure

In general, the behavior was two-way flexural mode followed by development of an arching action supported by membrane forces developed in the bottom layer of the reinforcement. At first peak load of the first bridge deck a sudden drop in the load occurred due to the formation of flexural-shear

Fig. 9. Transverse deflection profile for the first bridge deck.

Fig. 11. Transverse deflection profile for the second bridge deck.

cracks along the top surface of the bridge deck on both sides of the middle girder. Further loading led to the widening of those cracks associated with slight increase in the load resistance until punching failure occurred. Punching failure of both spans occurred simultaneously at a load level of 229 kips (1019 N) and 216 kips (961 N) for the left and right spans, respectively. Figure 12 shows the first bridge deck at the conclusion of the test, where the punching areas under the two loads and the shear cone at the bottom of the left span can be seen clearly.

The behavior of the second bridge deck, reinforced with grade 60 steel using the same reinforce­ment ratio was similar to the first deck. At the peak load of the left span, a sudden drop in the load occurred due to the formation of a flexural-shear crack on the top surface of the bridge deck to the left of the middle girder only (left span only). This drop in the load made the left span incapable to carry higher load equivalent to the punching shear capacity of the deck. The test was terminated due to excessive deflections in the left span. The smooth decrease of the load carrying capacity of the left span reveals that flexural-shear failure was the mode of failure of the left span. The maximum measured load for the left span was 185 kips (823 KN) and a deflection of 2.2 in. (56 mm) prior to termination. Failure of the right span was due to punching shear at a load level of 204 kips (907 KN).

Similar to the second bridge deck the right span of the third deck failed by punching shear prior to the failure of the left span. A flexural-shear crack formed in the left span causing a sudden drop in the load which made the left span incapable to carry more load equivalent to its punching shear resistance. Flexural-shear failure was the mode of failure of the left span as revealed by the smooth

decrease in the load carrying capacity of the load, whereas the right span failed in punching shear at a load level of 203 kips. The test terminated due to excessive deflections in the left span and the maximum recorded load for the left span was 181 kips (805 KN). Figure 13 shows the second and third bridge decks at failure, where the punching area under the actuator in the right span and the flexural-shear crack formed in the left span are clearly visible.