The Rose Fitzgerald Kennedy Bridge, located in Ireland, is a ground-breaking segmental structure with an iconic design, the longest post-tensioned all concrete extradosed span in the world of its kind. As part of the N25 New Ross Bypass scheme, the bridge serves to enhance connectivity between Wexford and Waterford, spanning the River Barrow, a wide tidal river. The bridge’s all concrete design aims to blend harmoniously with the surrounding landscape while providing a durable and low-maintenance structure.

The bridge features a three-tower extradosed design, with all three towers having different heights and the central tower being the tallest rising 27m (88ft) above deck level. The proportions of the bridge follow the golden ratio, and the cable arrangement forms a harp configuration with shallow angles for the cables. The four central spans have lengths of 95- 230-230-95m (3 I 1-754-754-311ft) and the difference in height between the two ends of the bridge result in the difference in tower heights, creating a unique rhythm that addresses the road’s continuous climb.

The bridge’s cables are arranged in a clean and elegant manner as a single plane of cables located in the center of the 21m (69ft) wide deck with two lanes of traffic in each direction. Cable sizes vary from 109 to 121 strands at shallow angles varying from 9 to 11 degrees due to the longitudinal slope of the deck. The deck is slender, with a 3.5m (11.5ft) deep section (span/depth ratio of 1/65) at midspan, 8.5m (28ft) over the central tower (span depth ratio of 1/27) and 6.5m (21.5ft) over the side towers (span depth ratio of 1/35).

The design of the bridge was done to Eurocodes and focuses on maximizing durability and minimizing long-tem1 maintenance. Extensive analyses were conducted to ensure the structure’s resilience and robustness against extreme events such as ship impact, fire, and wind. The presence of the central plane of cables in the extradosed configuration presented challenges in the transverse flexural design of the deck, which required careful consideration and detailing of reinforcement and transverse post-tensioning.

Sustainable design principles were integrated into the project, aiming to reduce the embedded carbon footprint, and utilizing locally sourced materials. High-strength concrete, up to 80MPa (12ksi) and ground granulated blast-furnace slag (GGBS) were used to optimize the structure’s strength and durability. Stainless-steel reinforcement was used in the central tower to ensure a long design life in a tidal zone.

Full section form travelers were used to construct the main spans, with a combination of in situ and precast elements used. The main box was cast in situ with precast slabs used in the outer inclined webs that support the cantilevers. Internal steel struts were used at the cable locations to optimize the transverse flexural behavior. Constructing the main spans in this method allowed a minimization of environmental impact on the river and impacts on the navigational channel as no support towers were required. The approach spans were built using a falsework truss for the central box and a wing traveler for the cantilevers which were poured in a second stage.

The asymmetry in height between the central and lateral towers led to a balanced cantilever construction of 140m (459ft) from the central tower, which is a world record in extrados concrete construction.

The construction of the central tower cantilevers posed significant challenges due to their asymmetry, shallow cables, and relatively shallow structural depth. State-of-the-art analysis techniques were employed to predict the behavior of the structure during construction, and the bridge proved to be flexible with substantial deflections as it neared closure. Despite the complexity of the form traveler cycle which included reinforcement placement, concreting, precast panel installation and multiple stressing operations, a cycle of 8 days was achieved at peak production. The whole construction took 42 months from foundations to road opening.

The bridge is equipped with a comprehensive structural health monitoring system to continuously measure bearing reactions, displacements, cable forces, and strains. This monitoring system aids in the maintenance and upkeep of the structure. Final construction cost was around $95,000,000 which represents a cost per square foot of approximately $450, a competitive cost for a world record breaking concrete segmental extradosed bridge with an iconic tower arrangement.

The Rose Fitzgerald Kennedy Bridge stands as a remarkable engineering feat, seamlessly blending aesthetics, functionality, and sustainability. It has greatly improved connectivity, reduced congestion, and enhanced the lives of residents in the area, while also being a visually striking landmark in Ireland.