Winner: The Supreme Award for Structural Excellence and the Award for Tall or Slender Structure

The British Airways i360

Structural Designer: Jacobs

Principal Contractor: Hollandia Infra b.v.

Main Contractor: Nardo Hoogendijk

Architect: Marks Barfield

Location: Brighton, UK

Project description: British Airways i360 is the world's tallest moving observation tower. It carries 200 passengers in a circular glass viewing pod, which rises slowly from beach level to a height of 138m. The tower is 162m high and only 3.9m in diameter (holding the Guinness Record for the "world's most slender tower"). The tower was delivered by barge directly to the beach and erected by a novel "top-down" method without the use of cranes. It features purpose-designed perforated cladding to minimise vortex shedding and sloshing liquid dampers to limit wind-induced dynamic movements.

Judge's comments:

“The steel tower is clad in perforated aluminium Expamet sheet, which cleverly reduces the wind forces on the tower, allowing it to be so slender. To help still further in resisting any dynamic movements when the wind is blowing, the tower has another trick up its sleeve. It hides 78 containers on the inside of the tower, each filled with Australian water, positioned perfectly to help resist movements which the tower might otherwise want to make under wind gusting.

“Another innovation lies in the manner in which the tower was constructed. It comprises 17 ‘cans’, each weighing between 50 and 100 tonnes, which were jacked up one by one in a top-down method of construction by using a jacking frame. This avoided the use of unfeasibly large cranes, and ensured that all construction occurred safely at ground level. And you’ll be happy to know that over 60 per cent of the energy used to lift the pod each time is recovered on its descent. A remarkable feat of engineering.”

Winner: The Award for Long Span Structures

San Mames Football Stadium Cable Roof Extension

Structural Designer: Idiom

Principal Contractor: INBISA and PFEIFER

Architect ACXT-IDOM (IDOM Group)

Location: Bilbao, Spain

Project description: During the summer break of 2016, the roof of San Mames football stadium in Bilbao, Spain, was upgraded with the aim of improving the spectators’ comfort on rainy days. The selected solution, an innovative double-layer cable-roof extension designed by IDOM, increased the roof span by 13m to 23m, minimised the required reinforcements on the original roof, and enabled a record construction time without any disruption to football games.

Judge's comments:

“The extension of the San Mames football stadium roof in Bilbao is a triumph of structural engineering in several different ways. Arising from a need to improve spectator comfort on rainy days, a new lightweight, translucent 4,700sq m oculus of ETFE-clad roofing has been delicately poised within the existing stadium roof opening. The new structure extends the cantilevered distance of the original roof by between 13m and 23m, resulting in maximum projections of up to 75m.

“The structure comprises an oval prismatic truss compression ring of structural steel linked by radial cables to a two-layer internal cable tension ring. The total weight of the roof extension structure, including the compression ring, purlins and reinforcement of the existing cantilevered roof, is around 500 tonnes, while the cable system and connections add a further 180 tonnes.

“The entire roof extension structure was assembled, lifted into position and sequentially tensioned in a period of just two months during the stadium’s summer closure period.

“The engineering design relied heavily upon the ability to accurately predict the complex non-linear interaction between the existing cantilevered roof and the new cable net. This required the development of a 3D BIM model and the non-linear computer analysis of the new and existing structures, supplemented by wind tunnel testing, CFD modelling and wind-driven rain simulation, and the use of a 1:30 scale operating mock-up of the roof to simulate and assess the complex processes of lifting and tensioning the new structure without overstressing the existing roof.”

Winner: The Award for Structural Transformation

The Design Museum

Structural Designer: Arup

Principal Contractor: Mace

Fit-out Contractor: Willmott Dixon

Architect: OMA and Allies & Morrison

Location: London, UK

Project description: Arup provided a radical engineering solution to enable the successful re-invigoration of the Grade II* Listed Commonwealth Institute exhibition building, creating a new home for the Design Museum.

The sophisticated solution involved strengthening and then retaining the building’s 2,000-tonne (55m x 55m) roof and primary structure by temporarily suspending it 20m above ground, supported entirely by temporary works. This enabled the replacement of the existing façade and internal structure and the creation of a significant new basement covering the entire building plan. The building’s amazing transformation has continued to entice and delight visitors since opening in November 2016.

Judge’s comments:

“Used frequently in the 1960s and 70s, hyperbolic paraboloid roofs are smoothly curving in shape, but are formed from a series of straight pieces.

“The copper-covered hyperbolic paraboloid roof of the Grade II* listed Commonwealth Institute exhibition building, originally constructed in 1962, weighs 2,000 tonnes and measures some 55m x 55m – the same area as 15 tennis courts. It was strengthened and then supported on temporary supports, in its original position some 20m above ground. Then its walls and floors were demolished. Below the temporarily supported roof, new basement and floor structures were constructed, ultimately being built up to provide permanent support for the roof. The roof is very thin – so damage to it could be caused if movements in the temporary supports exceeded a tiny + or – 5mm.

“Particularly impressive is the way in which the risks associated with supporting such a large fragile roof so high in the air were dealt with, by initial painstaking investigation, the design of strengthening and analysis of various scenarios, for example, the supports moving after initially being set up.”

Winner: Construction Integration

The Taichung National Theater

Structural Designer: Arup

Principal Contractor: Lee Ming Construction Co.

Architect: Toyo Ito & Associates

Location: Taichung, Taiwan

Project description: The Taichung National Theater is one of the most structural ambitious spaces constructed in recent decades. The main structure, a free-form, doubly curved, reinforced concrete shell, is a single continuous surface. It is an innovative combination of a sophisticated construction technology and local knowledge and craftsmanship. Taiwan has the highest seismic loads, and the engineering team used advanced analysis and optimisation processes to deliver a robust structural design and a highly optimised structure to keep the project on budget.

Judge's comments:

“The Taichung National Theatre houses an opera house with 2009 seats, a playhouse with 800 seats and a small theatre space with 160 seats. Its construction has transformed Taichung through the creation of a cultural hub in the city.

“The free-form, doubly curved, reinforced concrete shell is an astonishing built form, unlike any other, with its sweeping curves and folds. A new construction method was developed to achieve this, allowing complex forms to be constructed off-site and then brought together on site without the need for traditional form-work. As the site is severely seismic, the engineers employed methods of analysis more commonly used for nuclear power stations.

“This is a tour de force of engineering, using advanced analytical techniques to deliver a building that that will undoubtedly inspire people who experience its complex and unexpected form in pursuit of culture.”