BergerWorld: 2nd Quarter 2008

Louis Berger and Berger/ABAM (B/A), in cooperation with J.A. Brennan Associates, were retained by the Japan Highway Public Corporation to develop an aesthetic design for the Ohmi-Ohdori Bridge, which gracefully spans a beautiful valley overlooking the Diado River in the Shiga Prefecture Nature Park, leading travelers into the Kansai District on the New Tokyo to Osaka Meishin Expressway. The challenge was to carefully integrate the new twin bridge into a mountainous region, characterized by small, steep peaks and densely covered mixed vegetation.

The Team first collected input from local communities, government and other stakeholders to identify options that would ensure harmony between the bridge and the region's existing buildings and landscape. Following exploration of the site, research of Japanese culture, architecture and landscape, and extensive public outreach and discussions, the Team developed several design concepts, including one that would emphasize the

idea of a gateway between Tokyo and Osaka; a second that would reflect traditional Japanese architectural forms; a third that would emphasize the dynamic seismic forces at work in the earthquake-prone area; and a fourth that would emphasize the connection and integration of the bridge into the natural surrounding landscape. In the end, the latter concept, Bridge in Flight, was selected as the most desirable and fitting solution. This concept also emphasized the region's famed Shigaraki pottery and the Japanese love for nature and birds. With its light, rhythmic span, the Bridge in Flight gives the impression that the structure is floating over the valley. The sculptural transition between pier column, girder and tower consists of two scalloped, concrete forms with a one-meter-deep reveal, emphasizing the tapered shape of the pier.

The completed 550-meter-long Ohmi-Ohdori Bridge's super-quality concrete ensures high resistance to severe earthquakes and its corrugated steel webbing with a concrete deck and external cantilever cables weigh less than a traditional concrete web bridge. The extradosed design of the cables also reduces potential visual impacts as it allows for the cabling to be situated lower, reducing the height of the main tower and allowing the bridge to act as a cross between a girder-constructed bridge and a traditional cable-stayed bridge. The bridge deck features a unique "web box" design, which includes two extra supports inside the bridge deck to sustain its large width.

Under the direction of Fred Berger, chairman, the Team included Manfred Zinserling, senior project manager; Jim Guarre, senior bridge engineer; and Tanja Wilcox, landscape architect.