LAST November, the world's longest swing span bridge was opened over the Suez Canal, 20 km north of Ismailia, by President Mubarak of Egypt.

The El Ferdan Swing Bridge, as it is called, is the fifth to be constructed over the Suez Canal. Over the years, the Suez Canal has been widened and deepened and, today, ships with water draughts of up to 18 m can pass through it.

At the site of the El Ferdan Bridge, the canal was recently dredged to a depth of 27 m and its width increased to 320 m. Widening of the canal necessitated a record-breaking bridge span of 340 m. When closed, the bridge has an overall length of 640 m.

Design and construction was effected by an international consortium with a strong local input. Halcrow Group was appointed as principal technical adviser in May 1996 by the Egyptian National Railways (ENR) in its quest to re-establish a rail link across one of the world's busiest and most important shipping channels. The design and building contract was awarded in July 1996 to a consortium comprising Krupp Stahlbau and Krupp Fordertechnik of Germany, Besix of Belgium and Orascom of Egypt.

"Every time the bridge is closed across the canal, a physical rail link is established between Africa and Asia," says Halcrow's project director, Roger Buckby. "The bridge may not be the most elegant of structures, but one cannot help but be impressed by the shear scale of the structure and the way in which it swings across the canal like a gentle giant. We are very proud to have been principal technical adviser to ENR for the design and construction of this world-beating span and to have been part of the team that has seen it develop from a general arrangement drawing to a fully operational structure."

Nick Fuchs, project manager, says: "Seeing 13,200 tonnes of bridge swinging silently and smoothly to create a link across a major waterway is truly spectacular."

El Ferdan restores the former railway bridge over the Suez Canal that linked Cairo to the Sinai until 1967. The new bridge will ultimately link with new rail connections northeastwards to El Arish and Rafah at the border with Israel and southwest to Sharm El-Sheikh.

The structure comprises a double cantilever swing bridge with piled concrete foundations for the pivot piers supporting a steel truss superstructure. The 12.6 m wide truss is 60 m high at the pivot reducing to 15 m at mid-span and the orthotropic steel deck carries a single railway track and two road lanes. The pylons are supported by conventional bridge bearings on 17.1 m diameter rim bearings at each of the pivot piers. At each rim bearing, there are 112 tapered rollers running on machined roller tracks. The rollers are connected by radial arms to a central pivot and the tracks are profiled to ensure an even distribution of load between rollers.

The operating system for the bridge is a key feature. The electro-mechanical operating mechanism enables the bridge to rotate through 90 degrees in 15 minutes. The overall opening time from requesting permission including release of parking locks, rotation, and locking and establishing continuity of railway signalling takes 30 minutes.

Power for bridge operations is from diesel generators with backups and a connection to the national grid system is also available. The generators drive two 45 kW motors at each rim bearing. Similar motors drive the locking bars at the midspan and abutment locations. The locks provide partial continuity at mid-span and, by use of roller guides, can cope with substantial mis-alignment of the bridge ends that might arise from environmental effects.

The bridge is capable of being operated with a single motor at each bearing in the event of motor failure but with an extended operating time. Drive, control, braking, jacking and span locking systems are designed for the arduous desert conditions.

Design was in accordance with ENR specifications, augmented where necessary by German and UK standards, says Fuchs.

Particular design issues included canal bank stability; aerodynamics, both of the whole structure and individual members; seismic analysis; load distribution in the rim bearing; and fatigue effects on the rollers. For the mechanical and electrical items, the design concentrated on operating system logic and fail-safe provision, motors, brakes and locking mechanisms.

Construction

Of the 10,500 tonnes of structural steelwork (grade St 52) used in the structure, some 4,000 tonnes have been fabricated in Germany, with the remainder fabricated in Egypt in accordance with international quality control procedures.

Site clearance and removal of munitions started on the West Bank in July 1997. The truss is fully welded with pre-assembly carried out on both east and west banks. The bridge was erected parallel to the canal bank using crawler cranes and the balanced cantilever method. A temporary transverse support was provided to resist wind effects. On completion of each truss, including surfacing, trial rotations took place to adjust the level at the central joint. Only then could the final approach works, abutments and locking heads be completed.