Constructing an Icon: the Sheikh Zayed Bridge

Described as the world’s most complex bridge structure, the Sheikh Zayed Bridge in Abu Dhabi is undoubtedly one of the top construction engineering feats of our time. Zaha Hadid – an architect renowned for her radical, deconstructivist architecture – designed the bridge for the Abu Dhabi government.

In silhouette, the unique shape of the Sheikh Zayed Bridge is a sweeping sinusoidal waveform. Two continuous arch strands mirror one another, first passing through the center of the road decks and then dipping under and outside the decks. The decks appear as ribbons through the length of the crossing.

Construction of the bridge is currently in progress by Archirodon Construction, with assistance from Buckland & Taylor Ltd., which is the erection engineering consultant. The capital cost of the project is AED 840 million (€161.5 million). The bridge is expected to be completed in 2010. High-Point Rendel (HPR) – having performed extensive structural design and analysis of the bridge since inception – is supervising the construction on behalf of the Municipality of Abu Dhabi City.

Erection of the Sheikh Zayed Bridge has been difficult, with increases in structural design time, construction and budget. The construction sequence changed multiple times due to constructability issues and delays in the delivery of fabricated steelwork.

A hybrid structure composed of organic shapes, the bridge presented engineering challenges at every step in the process. Virtually every piece of the bridge was uniquely designed and engineered. All spans are supported differently. The HPR team reanalyzed the entire bridge virtually every time a change was made. Design changes included widening the deck after construction had begun, due to the incorporation of a new slip road.

“The structure twists and element sizes vary in three dimensions, with few surfaces being truly horizontal or vertical,” said Michael Davies, HPR assistant resident engineer. “Such an unusual shape causes unusual force effects beyond those that are normally dealt with and required a rigorous three-dimensional analysis to determine those force effects.”

To perform the extensive ongoing analysis required to investigate problems and find solutions, HPR chose to use Bentley’s RM Bridge software.

“When establishing the primary model properties, [the software’s] pre-processor functionality proved extremely adept at dealing with the complex geometry and the continually changing section sizes throughout the structure,” said Davies.

The main support structure is continuous through the bridge, making the locked-in forces from the sequence of construction an important consideration.

“These locked-in forces had to be continually reassessed during construction due to changes in the sequences, enforced by actual construction program constraints,” said Davies.

A 4-D stepped analysis of the bridge enabled engineers to consider all types of nonlinearity for construction stages and long-term effects. Using 4-D, engineers also assessed the stress distribution within the structure to ensure compliance with design requirements.

The Sheikh Zayed Bridge incorporates a seismic isolation system to reduce the forces required to connect the deck to the support structure. Engineers used RM Bridge to perform dynamic analyses for seismic effects, including both multimodal and time-history analyses. From this they were able to derive the parameters for the design of the seismic isolation system.