A bridge never too far Thursday, 24 May 2018

Engineers Australia Fellow and 2017 John Connell Gold Medal winner, Ken Wheeler, has revealed some of the challenges he overcame in the design of Sydney’s Anzac Bridge.

The University of Sydney alumnus, now a consultant, graduated with a Bachelor of Engineering (Civil) in 1976 and a Master of Engineering Science in 1984. He has enjoyed a 40-year career, one of its many highlights his involvement with the iconic bridge.

Spanning 345 metres with 120-metre high diamond-shaped pylons, Anzac Bridge is now 22 years-old and the longest of its kind in Australia. The eight-lane bridge is made of reinforced concrete and is a cable-stayed structure.

“We were a small group tasked with designing a new form of bridge incorporating innovative structural concepts and employing state-of-the-art methods of construction,” Wheeler said.

“The initial preferred design option was a 200-metre main span-balanced cantilever, concrete box girder bridge with the two main V-shaped piers in the water.

However, the alignment of the new Anzac Bridge was close to a set of submarine high voltage electrical cables, Wheeler revealed, which crossed Blackwattle Bay and serviced Sydney’s CBD.

“It was determined that the integrity of these submarine cables was at an unacceptable risk should there be a ship collision with the main bridge piers,” he explained.

So, the decision was made to move the piers out of the water and lengthen the span beyond the range of a balanced cantilever bridge and into the range of a cable-stayed bridge. But there were many challenges associated with this.

Wheeler said the team needed to incorporate new technologies such as analysis methods and stay-cable technology (materials, corrosion protection, installation) into the design. The team also had to come to grips with learnings around what had and had not previously worked on similar projects overseas – such as effects of rain and wind vibration of the cables near the end of construction.

“Under conditions of moderately light winds with coincident rain, the stay-cables started to vibrate and the movement of the cables could be alarming to the bridge user,” Wheeler revealed.

“This was a phenomenon only recently observed in some Japanese bridges and we needed to quickly understand the causes and how this could be controlled.”

These days, this type of vibration can be easily controlled by adding dampers to the cables or incorporating a spiral bead on the outside of the cable ducting to drain away the rain, according to Wheeler. Both solutions were incorporated into the Anzac Bridge.

Ken Wheeler led the design of Melbourne’s Bolte Bridge and the main spans of Brisbane’s Gateway Bridge. He also managed the construction engineering of the cable-stayed Centennial Bridge over the Panama Canal and the Phu My Bridge in Vietnam. Wheeler is leading the multi-disciplined design team on Bangladesh’s Padma Multipurpose Bridge, which is under construction.


Image: Padma Multipurpose Bridge. Source: Government of Bangladesh