Bridges

The Karapiro Gully Bridge is the longest bridge to be constructed as part of the Cambridge section of the Waikato Expressway in New Zealand and will service four lanes of traffic. The new bridge spans over the Karapiro Gully with a total length of 200 m, consisting of four 50 m long equal spans and is 24 m wide. This paper describes the design development, final design key aspects and technical challenges for the design of the Karapiro Gully Bridge. Due to the nature of the steep slopes and depth of the gully, the majority of the substructure is located on the gully floor. Slender reinforced concrete columns up to 35 m tall support the superstructure. The gully is comprised of loose sand which liquefies during a seismic event and requires the bridge to be piled down to 40 m below ground.A weathering steel superstructure was adopted as the deep gully would cause future access and maintenance to be complicated and difficult. The main girders are post-tensioned to the pier crossheads to create a moment connection between the substructure and superstructure, creating a slender sway-frame. The design was refined to create a constructible yet efficient final structure which accommodated the challenging construction constraints of the Karapiro Gully.