Higher Level Evaluation of a Reinforced Concrete Slab Bridge

In New Mexico, many reinforced concrete slab (RCS) bridges provide service on interstates I-10, I-25, and I-40. The load rating for this type of bridge largely depends on the live-load moment in the slab. Consequently, the objective of this study was to determine a more accurate value for the equivalent strip width using higher level evaluation techniques. A continuous RCS bridge was evaluated starting with an AASHTO load and resistance factor rating analysis. A diagnostic test was then conducted to measure live-load strains which showed that the slab stiffness fit within cracked and gross section behavior. Furthermore, slab moments from finite element analysis agreed reasonably well with experimental moments derived using the average of the cracked and gross section modulus. From refined analysis, the equivalent strip widths for positive moment were 26.1 and 22.1% greater than those calculated by the AASHTO approximate method for the exterior and interior spans, respectively. The refined widths for negative moment were greater than AASHTO by 13.1 and 11.1%. This increase in the equivalent strip width reduced the live-load effects, which proportionally increased the rating factors.