DESIGN OF CONCRETE BRIDGE DECKS. FINAL REPORT

The static ultimate strength, fatigue life and failure mode of reinforced concrete highway bridge deck slabs supported on steel girders is determined by testing small-scale deck models under static, fixed pulsating and moving constant wheel-load. The specimens included a 1/6.6 scale bridge model of a 50-ft long prototype bridge deck (with a girder spacing of 7 ft and a slab thickness of 8.5 in.) and a 1/3 scale panel model of a portion of the deck. Both isotropic (steel ratio of 0.3% in both directions in each face - Ontario bridge design code) and orthotropic (steel ratio of 0.7% in longitudinal and 0.35% in transverse direction in each face - AASHTO code) reinforcing arrangements were considered. For the isotropically reinforced decks (43% reduction in steel content compared to the AASHTO design) a safety factor against static ultimate strength equal to 17.5 was determined. The moving wheel-load resulted in far shorter fatigue life than the pulsating load, especially for the orthotropically reinforced decks. The failure mode was punching rather than flexure. Under the fixed pulsating load a radial fan-shaped cracking pattern formed at the bottom surface of the deck, while under the moving wheel-load cracking followed the location of the bottom bars (grid form) indicating flexural debonding prior to punching. Under the AASHTO design prototype load of 20.8 kips the measured maximum steel stress is less than 3 ksi. Under either static or fatigue laoding the reinforcing steel may yield just before deck failure (punching).