Bridging their Way to Success

Structural Design

According to a joint design report from 10 Design and Buro Happold sent to TrafficInfraTech, the bridge is “a cable supported structure with two arches of different sizes supporting the deck by means of hanger cables. The larger arch, of approximately 190m span, crosses the deck diagonally while the smaller arch, of approximately 110m span, runs parallel to, and is offset from, one side of the deck. The arches are connected together under the deck to form one continuous element which touches down at one point in the width of the waterway.”

The deck accommodates three lanes of traffic in each direction and has provision for cyclists and pedestrians. On the south edge, the pedestrian route follows the main deck. On the north side, the pedestrian deck is a separate element, descending to the support point in the width of the channel to create a seating/observation area looking towards Macau.

Structural Elements

Arches are box sections fabricated from stiffened steel plates. Both are flat within their own planes with profiles and cross sections that reflect the distribution of internal forces – curved near the crown where the hanger cables are anchored and straight near the base, thinner at the crown and thicker at the base to resist out-of-plane forces. The larger arch must also resist out-of-balance forces caused by the asymmetric cable configuration.

Deck is a concrete element of constant cross section throughout the length of the bridge, curved in plan to follow the given road layout and in elevation to achieve the necessary clearance over the waterway. “It is supported at 6m centres in the longitudinal direction by pairs of cables and also functions as a tie to the arches to reduce the lateral thrust at the foundation,” says Chan.

Cables are arranged in a fan pattern radiating from the crown portion of the arch. They have dead end anchorages at deck level, and live end anchorages within the arches.

Structural stability: The vertical load of the bridge is carried by the arch system. The lateral load, transverse to the deck and arch, is resisted by the arches acting as cantilevers fixed at the base. The lateral load in the longitudinal direction is resisted by the in-plane stiffness of the arches.

Articulation: “The arches and deck of the other tied arch systems can respond to thermal variation by alteration to their geometry (e.g. curvature of the deck) rather than through lateral translation. This allows their springing points to be monolithic with the foundation without requiring the use of bearing devices at these locations. The deck is a continuous member supported from the hangers, so bearings and movement joints are only required at the ends of the bridge – their specification is no more onerous than for a conventional bridge of similar size,” says Afflek.

Support and Foundation: The tied arch system allows lateral thrust at the base of the arches to be minimised, leading to a simplification of the foundation design. “Foundations will be required under each of the arch springing and abutment to resist vertical and horizontal forces and moments.”

Durability and maintenance: The bridge is designed to last 120 years and is claimed to require minimum maintenance. “The arch is a hollow steel member whose interior will be sealed to mitigate the impact of moisture. Its exterior will be provided with high spec paint protection system appropriate to the environmental condition of the bridge. The deck and sub-structure elements, constructed in concrete, will require minimal long term maintenance. The cables are proprietary products provided with high performance protective systems. The structure will be designed to allow individual cables to be replaced without closing the bridge,” he adds.

Construction: The team has proposed that the bridge be constructed before the channel is fully dug and filled with water. This will allow construction activity to take place in dry condition, minimising complexity. The arch, as was done in Mumbai’s Lalbaug flyover, will be prefabricated and transported in large segments for assembly and erection on the site. The deck will use precast segments joined by insitu concrete.

According to Zhuhai China’s website, Shizimen CBD is conceptualised by the government to make Zhuhai a new urban centre by providing a platform for its international, ecological and regional modern service industry.

10 Design, an international studio of architects and designers was established by 10 founding partners in 2010. A 450,000sqm retail and urban entertainment complex in Zhuhai and the 750,000sqm Danzishi Headquarters District in Chong Qing are two of its current projects being handled by Afflek. Buro Happold, on the other hand, is an independent international body of consulting engineers established in 1976 that specialises in designing and building, infrastructure and environmental projects. The Grand Museum of Egypt (Cairo) and the Louvre (Abu Dhabi) are two of its many current projects.