Crack Pattern

No cracks were observed up to a load level of 50 kips (222 KN) for any of the three bridge decks. However visible top cracks started to occur at a load level of roughly 60 kips (444 KN) for each deck. Figure 14 shows the top cracks at a load level of 100 kips. Negative flexural cracks formed before the positive cracks due to the higher values of negative moments in comparison to the positive moments.

Positive moment flexural cracks at load levels of 100 and 150 kips (444 and 666 KN) for the first bridge deck are shown in Figure 15, where the crack pattern confirms the two way distribution of the load. Further loading led to spreading and widening of the flexural cracks until the formation of the flexural-shear crack at the top surface of the deck close to the middle girder. The formation of the flexural-shear crack led to a sudden drop in the load as previously discussed. However, the flexural-shear crack formed symmetrically on both sides of the middle girder of the first bridge

deck, therefore allowed increase of the load to cause punching shear of both spans. For the second and third bridge decks, the flexural-shear crack occurred on the left side of the middle girder only which allowed the load to increase in the right span causing punching shear at the right span only as shown in Figure 13.