The project is a road construction project with a length of 6.05 kilometers connecting Hwatae-ri, Nam-myeon, Yeosu-si, Jeollanam-do to Gaedo-ri, Hwajeong-myeon, and is to improve island accessibility by constructing a sea crossing bridge on the unopened section of National Road No. 77 and to revitalize local cultural tourism projects by building beautiful offshore bridges. The project was tendered as an EPC Turnkey project, and we participated in the competitive design as a member of the design consortium with POSCO E&C, and won the competition, and then carried out the detailed design. The project was organized in two packages, of which we participated in the first package, CP1. The CP1 is a project to build two sea-crossing bridges, including the Hwatae-Baekya 1st Bridge and the 2nd Bridge. 

Hwatae-Baekya 1st Bridge was designed as a 611-meter bridge connecting Hwatae Island and Wolho Island, the main bridge is the longest double-tied arch bridge in Korea with a center span of 220 meters, and the approach bridge is an open-type steel composite girder bridge.

The Hwatae-Baekya 2nd Bridge, which connects Wolho Island and Gaedo Island, was planned as a single-span suspension bridge with a main span of 910 meters, with a three-dimensional cable-shape and an A-type tower.

For the Hwatae-Baekya 1st Bridge, the main span bridge was designed as a three-span continuous arch bridge with a 220 meter central span, the longest in Korea. Among the three spans of the arch bridge, a tide arch bridge was applied to the central span, and box-type edge girders, in which the arch ribs of the central span are continuous to the side span edge girders, were applied to the side spans. 

Additional reinforcing arch rib, which serve as a ties, were installed on the piers to reduce the deflection of the side spans and increase the in-plane stiffness of the arch ribs of the center span. This application of double-tie arch bridges greatly improved the seviceability and structural safety compared to ordinary tie arch bridges, making it possible to realize a long-span arch bridge.

In order to ensure the rigidity of the arch with a center span of 220 meters and reduce the deflection of the relatively long 95-meter side span, a new type of arch bridge was required. To achieve this, a new type of three-span continuous tie arch bridge was planned, using the box section of the main arch rib as the main girder for the side span, placing additional arch rib responsible for the tensile force of the bridge, and placing diagonal members connecting the additional arch rib and the main arch rib.

To increase the out-of-plane stiffness of the arch ribs against wind and seismic loads, six transverse struts were installed between the two center-span arch ribs. The center-span girder was planned as an I-type edge tie girder with excellent efficiency against axial tension and in-plane bending moments. Compared to box-type tie girders, I-edge girders are superior in quality improvement, productivity and maintenance as well as steel saving, and high-strength HSB380 steel was used in the design.

A total of 30 PWS hanger cables are installed at intervals of 12m along the bridge axis at the girder anchorages, with each hanger gradually inclined 3 degrees from the center of the span to both piers to create a more dynamic landscape.

The piers, which are substructures, were V-shaped concrete piers that harmonize with the upper arch ribs of a dynamic formative beauty.

The bridge foundation was planned as track-type concrete caisson, which has good applicability and constructability due to the shallow depth of the supporting layer, and excellent quality and environmental properties through pre-production, and exclusion of temporary bridges.