Bridges, Tunnels and other Transportation Structures
Throughout the nation due to the transportation needs exceeding available conventional funding, tolled express lanes have been recognized as a cost-effective alternative to improve mobility and enhance economic development. This paper discusses the structural and construction solutions for the I-75 Express Lanes in South Florida, specifically Ramp H-4 in the segment A/B corridor.
The segment A/B corridor is the largest and more complex of the 4 segments comprising the I-75 Express Lanes project in South Florida. One of the key ramps in the Segment A/B corridor is Ramp H-4. Ramp H-4 is an elevated ramp crossing over the I-75 southbound general-purpose lanes and connecting the southbound express lanes built in the existing median to a southbound exit on the west side of the HEFT. This traffic movement was accommodated by a 595 ft-long, three spans continuous, steel twin tub curved girder bridge with a 30’-1” roadway width.
The flyover ramp accommodated a S-curve roadway alignment and super-elevation transitions and required intermediate supports capable of clearing and straddling the southbound general-purpose lanes. The intermediate supports resulted in C-shape piers and a 115’-0” integral straddle bent cap.
The bridge structure required extensive finite element modeling to correctly evaluate the structural behavior of the system due to its complex geometry and variable support stiffness. To efficiently design the main bridge structural elements according to AASHTO specifications, calibrations and validations between the FEM and a grid model were performed which resulted in satisfactory matching of deflection, moment, and shear. Additional analysis was performed to account for the biaxial stresses caused by the combined effects of the longitudinal and transverse bending between the tub girders and the straddle bent cap.
The structural solutions incorporated careful consideration of the steel detailing, fabrication, and transportation. Bolted splices and high load multi-rotational bearing fixities were strategically located and selected to ease erection and provide handling flexibility.
This paper will provide discussion of complex structural and construction solutions in a design-build environment.