Xihoumen Bridge: Choosing a Sea-Crossing Structure and Opening in 2009

The road connection between the Zhoushan islands and Ningbo requires a succession of sea crossings. Five bridges form the Zhoushan Archipelago–Mainland Link, with Xihoumen carrying the section between Jintang and Cezi islands. The site faces a deep-water shipping channel and is exposed to summer typhoons and winter monsoons. Route selection, foundation construction, and operating conditions had to be considered together.

CCCC Highway Consultants Co., Ltd. designed the bridge and researched split steel box girders and movable wind barriers. The Zhejiang Zhoushan Island-Link Project Construction Headquarters organized construction. Opening on December 25, 2009, marked the start of traffic service; closure of the main girder before that date was part of construction.

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Nearby Laohushan provided a land site for a bridge tower. Deep water and rapid currents made tower-foundation construction difficult in the channel. The adopted 1,650-meter main span placed towers and anchorages on land, reducing work on deep-water foundations and preserving navigation space below.

The main-cable span arrangement is 578, 1,650, and 485 meters, and the deck uses a two-span continuous suspended system. The layout accounted for seabed conditions, tower locations, and construction risks. The bridge carries four road lanes and provides a navigation clearance of 49.5 meters.

References: [1]

The long-span deck required testing for wind stability. The designers used large-scale sectional models and a full-bridge aeroelastic model in wind tunnels, comparing how the width of a central slot between the steel boxes affected flutter stability. Steel consumption and maintenance requirements were also considered.

The chosen deck consists of split steel box girders with a six-meter gap between them, followed by further full-bridge aeroelastic testing. The central slot changes airflow around the deck, while transverse members make the two boxes work together. The resulting profile reflects the testing and balances wind resistance, steel use, and maintenance.

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Each steel box is 15 meters wide, giving a total width of 36 meters including the central gap. The main cables use galvanized parallel wires with a strength grade of 1,770 megapascals. Material development and construction control support this long-distance load-carrying system. Deck loads pass through the steel boxes and suspenders to the main cables, then to the towers and anchorages.

Sunlight, air temperature, and wind continually change at sea, and temperatures vary along a main cable. Erection surveys therefore required more than a single elevation comparison. Builders monitored cable temperature and local winds, combining prediction and adjustment to control cable profiles and member positions and reduce installation errors caused by environmental changes.

References: [1]

Steel-box sections were transported by ship and lifted beneath the bridge. Deep water, rapid currents, and exposed bedrock made ordinary anchored positioning difficult. Dynamic positioning, reinforced by auxiliary cables connected to the main cables, helped transport vessels hold a suitable lifting position.

The wind stability of an unclosed bridge differs from that of the completed structure, and adding more deck sections does not make every stage safer. The designers’ technical report describes an erection sequence based on the stability of different completion proportions. The extent of erected sections was controlled before typhoon season, and work continued afterward. The main girder closed at the end of 2007, followed by the remaining work needed for opening.

References: [2] [3]

The structural monitoring system entered trial operation at the end of 2009. Anemometers on towers and the deck recorded winds, and dynamic weighing equipment on the southern approach recorded traffic loads. Positioning, displacement, and acceleration instruments observed changes in the main cables, steel boxes, and towers. Distributed acquisition stations transmitted data through industrial Ethernet for retrieval and reporting.

These early measurements established a baseline for later comparisons. Liu Zhiqiang and colleagues noted in their 2010 paper that trucks were not allowed during initial trial operations, so traffic records mainly covered passenger cars and buses. Construction measurement thus developed into daily operational monitoring, with sea-crossing traffic accompanied by vehicle management and maintenance.

References: [3]