US 21 over Harbor River Bridge Replacement

Photo Credit: Kaze Aerial

The Harbor River Bridge project consisted of replacing the original swing-span bridge over a tidal waterway and navigable channel, which serves as the only means for vehicular access to Harbor and Fripp Islands. The existing bridge was too narrow, structurally deficient and a safety hazard for motorists. The new high-level 3,340′ long fixed-span replacement bridge features two 12′ wide lanes with 10′ shoulders in each direction, providing 90′ of horizontal and 65′ of vertical clearance for river navigation. The new bridge includes 20 spans and 65 feet of vertical clearance over the navigational channel of Harbor River including 167.5-foot spans with Florida BT-78 Beams.

ICE Engineers faced multiple challenges including increased scour potential, seismic design and vessel collision loads, embankment liquefaction and environmental constraints. To compensate for coastal conditions and to increase the structure’s longevity, engineers utilized resources like the 100-year scour profile and impact scenario software to determine the most enduring design. ICE also made many environmental commitments, such as monitoring a bald eagle’s nest and implementing the best management practices for sea turtles and manatees to ensure low impacts to the local ecosystem. ICE provided SCDOT with high quality, efficient design submittals which led to the bridge being successfully completed five months ahead of schedule.

Aggressive Schedule and Complex Needs Led to Design-Build Decision

The bridge has interior bents consisting of prestressed piles supported footings in the overbank regions and oversized drilled shafts in the deeper portion of the channel. The bridge was designed to resist vessel collision loads and required a complex pushover analysis for seismic. The complex bridge design accounted for hurricane wind forces, required a seismic pushover analysis, included vessel collision loads, and accounted for significant long-term scour, while preserving the pristine environmental setting and satisfying environmental permit constraints. ICE also assisted in performing construction support services throughout the construction phase of the project.

Prior to selecting a design-build procurement, a proactive and objective assessment of the project’s unique characteristics was completed by SCDOT to determine the most appropriate delivery method. The aggressive schedule and the project complexity that was established by SCDOT leadership ultimately led to the decision to utilize design-build, as a traditional bid-build delivery would have added an extra time to the schedule. SCDOT utilized its Design-Build unit to administer the project, which included a 13-person team of DBIA-certified professionals as well as support from other DBIA professionals in SCDOT’s Procurement, Legal and Construction offices.

Design-Build Team

Photos