The load-deflection envelopes up to failure for three bridge decks are given in Figure 5. It should be noted that deflection plotted in Figure 5 is measured at the center of the respective deck span directly under the applied load. It is readily apparent from Figure 5 that the first bridge deck reinforced with MMFX steel using the same reinforcement ratio as used for the actual bridge exhibited smaller deflection in comparison to the other two bridge decks. Due to the use of higher reinforcement ratio in the first bridge deck, stiffness was higher than the other two decks; this could also be due to the higher compressive strength of the concrete used for the first deck. Despite the lower reinforcement ratio used for the third bridge deck (33% less than the first two decks), it was capable of sustaining the same load as the second bridge deck of the Grade 60 steel. This behavior is attributed to the utilization of the higher tensile strength of MMFX steel. The slight increase of the deflection measured
Fig. 6. Longitudinal deflection profile for the first bridge deck.
for the third bridge deck in comparison to the second deck is possibly due to the slight reduction of the modulus of elasticity of MMFX steel at high stress levels. According to the AASHTO LRFD Bridge Design Specifications (1998), the design tandem consists of a pair of 25 kips (111 KN) axles. Therefore, at a load level of 25 kips (111 KN), which is less than the cracking load; the deflection at service load was almost identical for the three bridge decks.