FATIGUE BEHAVIOR OF NONCOMPOSITE REINFORCED CONCRETE BRIDGE DECK MODELS

The fatigue performance of the AASHTO and Ontario Highway Bridge Design Code (OHBDC) designs for noncomposite reinforced concrete bridge decks was studied on the basis of tests conducted on small-scale physical models. The type of fatigue loading has a profound influence on the fatigue behavior of the decks. Under a moving constant wheel-load, the initial two-way deck slab action changes to a one-way slab action, whereas under a stationary pulsating load the two-way action is maintained until failure. The bridge decks subjected to a stationary pulsating load exhibited a flexural radial cracking; those under a moving constant wheel-load exhibited a flexural gridlike pattern similar to the grid of the bottom steel layer. For a given applied fatigue load level, the decks subjected to a stationary pulsating loading regime exhibited higher fatigue life than those subjected to a moving constant wheel-load. On the basis of an exponential curve fit of the fatigue data in this study, the 2.5 million load cycle deck fatigue strength under a stationary pulsating load ranges between 0.47 and 0.54 P sub u (safety factor against a 2.5 million load cycle fatigue failure of 5 to 12), where P sub u is the measured static ultimate strength. On the other hand, the 2.5 million wheel-load passage deck fatigue strength under a moving constant wheel-load is estimated to be between 0.21 and 0.28 P sub u (safety factor of 3 to 4). If the efficiency of the deck fatigue design is determined by the number of wheel-load passages on the deck at a given moving wheel-load level ratio (P/P sub u) without deck failure, the OHBDC deck design appears to be more efficient than the AASHTO design.