Yandhai Nepean Crossing: Triumph of engineering

After 28 months, Seymour Whyte successfully delivered Australia’s longest single clear-span bridge, measuring 284m in total length with a 200m main span across the Nepean River. The clear-span allows for the 170m required for the river’s heritage rowing course to operate, while providing a safe, shared-user path for pedestrians and cyclists between Penrith and Emu Plains.

The bridge was officially named the Yandhai Nepean Crossing and opened by NSW Premier Gladys Berejiklian and Minister for Western Sydney and Member for Penrith Stuart Ayres last month. In opening the bridge, Minister Ayres thanked the project team from Seymour Whyte “who have set a new standard in construction and engineering excellence.”

Seymour Whyte Regional Manager – Southern Steve Lambert acknowledged that constructing a bridge across such a wide expanse, with just one permanent pier, had presented unique challenges throughout the project duration.

“The bridge was designed as a triangular steel warren truss with curved steel-concrete composite box approach-spans and includes viewing platforms and balconies along the structure. To deliver such a distinctive structure, we worked closely with our client—the NSW Government through Roads and Maritime Services, steel fabricator CIVMEC and launching specialists Freyssinet,” he said.

"It was no easy feat to design, manufacture, transport and incrementally launch all eight 25m x 8m sections of the main span truss—but I am pleased to say the project team did an excellent job.”

Seymour Whyte Project Manager Greg Anderson said the specially designed truss segments were partially manufactured in NSW’s Hunter Region, using 700 tonnes of steel.

"Then, the 25m long segments had to be safely transported across almost 200km to Penrith in Western Sydney. The 8.2m wide loads were the widest ever transported through metropolitan Sydney,” he said.

"The complex traffic management arrangements to the site required months of planning and in-depth coordination with numerous public and private road authorities and logistics providers.”

The truss segments were delivered to a 60m long x 21m high workshop on the eastern bank of the Nepean River for re-assembly and onsite painting works.

The workshop itself—known to bemused locals as ‘The Shed’—was an achievement in temporary works, consisting of a three-bay fabrication facility for the incremental launched truss, that allowed for separation of the fabrication, painting and launching areas. The workshop took 10 months to design and construct, and was utilised for more than half of the project duration.

Another technical challenge that arose was the installation and final casting of the finger and expansion joints on the bridge. As the bridge is orientated east west, the heat effect of the sun not only had a longitudinal thermal expansion effect, elongating the bridge up to 170mm, but it also created a bowing effect on the truss that changed from morning to afternoon.

Mr Anderson said temperature homogeneity of the truss was a critical factor for set-out of the moving parts of the truss, being the bearings and finger joints.

"These conditions made it difficult complete critical activities within the allowed timeframes. To avoid compounding delays, survey setout and conformity works on the steel truss were rescheduled to be done in the early hours of the morning, to avoid seasonal high temperatures, or on cloudy days when the effects of the sun were reduced,” he said.

"This methodology proved effective in achieving the stringent tolerances required under the specification, allowing construction to continue with minimal delay.”

The project was part of a broader plan to improve the existing dual-use path network in the local area, with the provision of an additional 418m of shared pedestrian and cycle route connecting new footpaths into existing networks traversing private properties and Penrith City Council land.

Other works included the construction of retaining walls, piles and piers to support the bridge, reconstruction of a 130m section of Punt Road, adjustments to overhead and underground utilities, provision of lighting, as well as landscaping improvements.

Transporting the 25m long truss segments more than 200km from the Hunter Valley and through Sydney
Transporting the 25m long truss segments more than 200km from the Hunter Valley and through Sydney

 

Launching the bridge from ‘The Shed’
Launching the bridge from ‘The Shed’

 

Aerial view of the bridge being incrementally launched as construction progressed
Aerial view of the bridge being incrementally launched as construction progressed

 

Temporary piers in the water as the bridge was incrementally launched from the eastern bank of the Nepean River.
Temporary piers in the water as the bridge was incrementally launched from the eastern bank of the Nepean River.

 

Seymour Whyte has successfully delivered the Yandhai Nepean Crossing—Australia’s longest single clear-span bridge (photos courtesy of Roads & Maritime Services)
Seymour Whyte has successfully delivered the Yandhai Nepean Crossing—Australia’s longest single clear-span bridge (photo courtesy of Roads & Maritime Services)