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Raftsundet Bridge Project

Aas-Jakobsen Bridge Page

"Structural Engineering International", May 1999 (Great article and pictures)

structurae: Raftsundet Bridge

PROJECT OVERVIEW

The Raftsundet Bridge with a main span of 298m and a total length of 711m, was the longest concrete cantilevered span in the world when the cantilevers were joined at June 24^th 1998. The bridge was opened for traffic at November the 6^th the same year. The structure is exposed to a severe wind climate with a design gust wind speed of almost 60 m/s. The surrounding alpine topography with high mountains raising up to 1000m above sea level, creates fluctuating wind forces of large magnitude on the bridge. The dynamic wind climate severely affects the slender columns and the bridge beam. The main span is constructed in high strength lightweight aggregate (LWA) concrete LC60 and the side spans and piers in normal density (ND) concrete C65. The bridge is high level, providing a ship channel of 45 x 180 m.

Raftsundet Bridge is a part of the ferry free mainland connection for the Lofoten islands. The Lofoten islands are located north of the Arctic Circle in the county of Nordland in Northern Norway.

Owner: Public Roads Administration, Nordland (PRAN)
Contractor: AS Anlegg
Architects: BOARCH A/S
Designer (EOR): Aas-Jakobsen (Information on this page kindly provided by them)

 

Contract award, design: 1995
Contract award, construction: 1996
Construction completed in 1998

Tender price (1996): US$14.3 mill
Total project cost (1996) US$16.2 mill

Materials:

• LWA-concrete in main span: LC60

• ND-concrete in side spans and piers: C65

• Tendons: 140 mm² strands S_0.2=2800–3300 kN

Spans: 86+202+298+125= 711 m
Width overall: 10.30 m
Ship Channel: H x W = 45 x 180 m

In 1991 PRAN arranged an architectural competition to find the most favorable bridge design for this particular location. The competition was open for all kinds of bridge types, but the topography and the actual range of span lengths favored a concrete cantilevered bridge or a cable stayed bridge. Several bridge designs were proposed, notably with cantilevered or cable stayed bridges. The jury decided that a concrete cantilevered bridge proposed by Aas-Jakobsen A/S with a continuous horizontal curve best could fit into the local topography. Cost estimates of the two bridge types clearly favored the concrete cantilevered bridge, which was then chosen by PRAN for construction.

The structure is fully continuous, with flexible twin piers and large foundations to solid rock on dry land. Expansion joints are provided at each abutment. Compared to a design with ND-concrete C65 in the main span, the savings were in the order of US$ 0.4 mill. Auxiliary piers were required to stabilize the free-standing pier/balanced cantilevers during construction.

Construction methods

The following construction methods were a basis for the detailed design:

• Piers by self-climbing forms

• Cantilevers by cast-in-place segments of varying lengths, max 5.0 m

Because of the severe wind climate at the bridge site, wind measurements were necessary to establish reliable design parameters to describe the dynamic wind field. Dr.Ing. A. Aas-Jakobsen AS was engaged by PRAN to plan and perform the detailed wind measurements including evaluation of the dynamic wind parameters to be used in the detailed design of the bridge. Three independent wind sensors were mounted on a 30m high mast at different levels. The wind-sensors consist of three-axial propellers measuring the momentary wind velocity in three orthogonal directions in space simultaneously. The data were recorded 5 times every second for mean wind speeds higher than 10m/s.

Click on picture for overview.