Districtwide Load Rating

Districtwide Load Rating

Client: FDOT D6

Location: Districtwide

Contract Delivery:  TWO

Services Provided:

  • Load Rating

As a subconsultant, BPA performed the Load and Resistance Factor Rating (LRFR) evaluations of two precast segmental bridge structures for the FDOT District 6. Built in the 1980’s, these are considered “first generation segmental” bridges. Both structures were erected using the balanced cantilever method and are post-tensioned longitudinally and transversely with internal tendons, making them distinctive structural systems with unique post-tensioning features.

The Turnpike NB Ramp over I-75, known as Ramp I, is a 2,124 ft long, eleven-span single cell box girder. Ramp I is the first curved precast segmental in the State and uniquely features a quarter-span flexural hinge. The second bridge is Ramp D, located on the north side of the I-75/SR 826 interchange. This is a 396 ft long, three-span, twin single-cell box girder bridge connected with a longitudinal cast-in-place closure.

Due to the structures’ unique structural characteristics, refined analysis of the live load carrying capacity was required, as well as consideration of posting avoidance measures. The structural analysis involved discretizing the top and bottom slab as well as webs in shell finite elements, in addition to imposing essential boundary conditions. Further, the structural model considered all relevant deformations, material properties, curved geometry, time-dependent effects, step-by-step erection sequence, and analyzed their multiple statistical systems, typical of these bridges. The rating was conducted in the longitudinal and transverse directions considering the design, legal, and permit trucks, as well as emergency vehicles. The structural model accounted for the effects of floating lanes, lane permutations, and emergency vehicles mixed with legal trucks for posting avoidance. Service and strength limit ratings were also generated.