2017 President, Ian Firth, discusses six structures celebrating 10 year anniversaries in 2017.

This is the final episode of my series on anniversary structures. For those of you who have been following me, you will know that I have been counting down the decades, one per month, since January when I started with 120 year-old structures completed in 1897. Thank you for sticking with me through the year.

2007 saw a number of significant projects in China in preparation for the Beijing Olympics the following year. Another common theme was the replacement of old structures (e.g. Wembley Stadium) or the adaptation of existing structures (e.g. The Smithsonian Courtyard Roof in Washington). And of course there were plenty of bridges, and we pick up a few of those in this short review. There were some really horrible shockers among the bridges that year, but I have resisted the temptation to feature them because I would not be able to restrain my criticism! I have just added a few pictures at the end for you to enjoy.

2007 was, of course, the edge of the precipice as the world plunged into recession the following year, so those that were completed got there just in time. Other projects were not so lucky, with several abandoned by nervous investors, and I know several engineering companies really struggled through the subsequent few years.

So, we reach the end as my Presidential year draws to a close. I hope that you have enjoyed this series.  I have enjoyed putting it together, with the help of several young COWI colleagues in the office who did some of the research, to whom I owe my sincere thanks.

1.Wembley Stadium, London

We start with Wembley, the world-famous football stadium which underwent a major re-build, and now sports an easily identifiable, some would say iconic, steel lattice arch structure. There were a lot of people involved with this project, but the principal designers were the architects, Foster & Partners and Populous, and the engineers, Mott MacDonald, Aurecon and Jacobs (previously SKM).

The old Wembley Stadium, with its familiar landmark twin towers, was one of the most important sports and entertainment venues in Britain. The challenge of reinventing it for a new century was to build on its extraordinary heritage and create a new venue no less magical or memorable than the original. Covering 90,000 seats, standing almost four times the height and covering twice the area of the original, the new stadium structure certainly achieves that, and is one of the largest covered arenas in the world.

The seating bowl is very steep, to keep viewing distances sufficiently short, and the roof slopes upwards towards the centre with drainage at the perimeter. This arrangement restricts the amount of light arriving on the grass, so to improve this the east and west areas have sliding panels that allow morning and evening sun to enter. Unlike a normal football club ground, the number of football events are limited, so to maintain sufficient income the stadium is used for other events and entertainments for which the pitch is often covered for protection. As a result, maintaining sufficiently high quality grass for the playing surface presents some particularly difficult challenges.

The roof structure is rather complex. The arch is aligned east-west and leans to the north so as to avoid casting a shadow on the pitch. It is stabilised by a cable truss which also supports the northern half of the roof which spans on to the perimeter truss. The southern half of the roof has a longitudinal truss, and transverse trusses span to the cable truss. As a consequence of this arrangement, the structure experiences a large number of complex loading patterns which would certainly have given the engineers something to think about in the analysis.

Wembley Stadiun(Image: Richard Johnson via Wikimedia Commons)

The main arch, which is probably one of the most complex and hard to fabricate lattice trusses anywhere, was assembled on site in a horizontal position, and then raised up to it final position just past the vertical using strand jacks and temporary struts up to 100m long. What with the complex arrangement of cable truss, lightweight secondary trusses and a number of other factors, this was a very difficult structure to construct, requiring lots of temporary stabilising steelwork during erection. Indeed there were significant problems and delays during construction, leading to major claims and pain for all concerned, and it remains one of the most expensive stadia anywhere in the world.

2. Smithsonian National Portrait Gallery Courtyard Roof, Washington

The Smithsonian Institution in Washington occupies the former United States Patent Building which was built between 1836 and 1867 and is a fine example of Greek Revival architecture. Now designated as a National Historic Landmark, the building was saved from demolition in 1958 by President Eisenhower who transferred it to the Smithsonian Institution for use as the National Portrait Gallery and American Art Museum.

The decision to enclose the building's grand central courtyard with a glass roof was prompted by a desire to improve the visitor experience and to create one of the largest event spaces in Washington. It was also inspired, no doubt, by the enormous success of the new roof completed in 2000 over the Great Court at the British Museum in London. As at the Great Court, the architect was Foster and Partners, with engineers Buro Happold, and they once again created a beautifully fluid and expressive steel and glass gridshell roof structure.

The roof structure consists of three interconnected vaults, with a diagrid of fins which together form a rigid shell that needs to be supported by only eight columns, thus avoiding the application of extra loads to the historic existing buildings. "Given the importance of the Old Patent Office, the design was wholly driven by a deep respect for the existing building," said Lord Foster. "It was decided that it should not touch the building at any point but instead float above it like a cloud over the courtyard."

Robert and Arlene Kogod Courtyard(Image by Nigel Young/Foster + Partners​)

The enclosed courtyard forms the centrepiece of the building's long-term renovation programme. Visitors can enter the surrounding galleries from the courtyard, and out of museum hours the space regularly hosts a variety of social events, including concerts and public performances.

3. Three Countries Bridge

This bridge crosses the River Rhine between Weil am Rhein in Germany and Huningue in France, and is of huge symbolic significance. The third country of the name is Switzerland which is close on the German side. The design was by Leonhardt Andra und Partner, working with the architect Dietmar Feichtinger.

Weil am Rhein(Image by Wladyslaw via Wikimedia Commons)

With a free span of 230m, it is the longest single span pedestrian arch bridge in the world. It is a tied arch structure, with a very shallow arch rise of 24m, only about a tenth of the span. The arch comprises of the main twin hexagonal section arches which lie in a vertical plane, supplemented by a smaller circular arch on the opposite side of the deck which leans inwards slightly to aid lateral stability.

The bridge was placed just to the north of the line connecting the two public spaces on each bank so as to preserve important views of a historic tower on the French side. The architect was particularly keen to use an arch form rather than the suspension or cable stayed form for the bridge, because of its unifying appearance, visually joining the two sides of the river in a strong sweeping curve. This form also assisted in the construction, as the entire span was pre-assembled about 100m downstream and floated up to the site where it was lifted into place in a single operation. During the floating operation, the span was supported on two large barges, one at each end, placed sideways to provide stability in what is always a challenging operation.

The bridge was the winning entry in a design competition in 2001, and the bridge was completed in June 2007 at a cost of around 9 million Euros.

4. The Living Bridge, Limerick, Ireland

This pedestrian bridge crosses the River Shannon, and was designed by Wilkinson Eyre Architects and Arup. It is a six span structure, with each span being supported on under-slung catenary cables. The whole bridge is on a wide curved plan alignment joining two parts of the University of Limerick campus across the boundary between County Clare and County Limerick.

Particular environmental sensitivities and constraints strongly influenced the design and construction methodology. Maximum use was made of off-site assembly of large components. The design was developed so as to enable complete spans to be lifted into place and thus minimise environmental damage during construction. The curved alignment was also devised to suit the natural river environment, and the span arrangement responds simply to the available locations for suitable foundations within the river, placing supports on the riverbanks and natural islands within the stream.

Living Bridge by Wilkinson Eyre Ros Kavanagh(Image by Ros Kavanagh, Wilkinson Eyre Architects)

The bridge deck is supported from two groups of three under-slung catenary cables. The inclination of the cable planes and the curved alignment naturally produces wide platforms at each pier position which can be used as resting places or spaces for public art.

The term "Living Bridge" derives from the idea to create a new 'living' link between the University's established campus to the south of the River Shannon within County Limerick and its developing annexe to the north of the river within County Clare. At this location, the River Shannon is wide and shallow, fragmented by woodland growth and with extensive floodplains. The environmentally sensitive nature of the site required a solution which would celebrate the 'hidden world' of the river landscape and encourage users to linger as they cross.

5. Tacoma Narrows Bridge, USA

I include this because, to a bridge engineer, the name Tacoma Narrows immediately conjures up images of the famous film of  'Galloping Gertie' as the original suspension bridge was called, wildly oscillating in a strong wind and finally collapsing in very dramatic fashion.

It was designed by Leon Moisseiff who we met back in May when I was looking at 80-year old structures completed in 1937. The Tacoma incident was in 1940, and it was where we learnt all about the aerodynamic response of slender spans, leading ultimately to the modern streamlined box girder which was first used on the Severn Bridge in 1966.

But it is now in fact two suspension bridges, not one. The replacement for Galloping Gertie - a suspension bridge with a somewhat heavier and stiffer truss girder - was completed in 1950. Then, in 2007, the adjacent span was completed, and is the one whose 10th birthday we are celebrating here.

Tacoma Narrows Bridge 2009(Image by Lderendi via Wikimedia Commons). The 1950 bridge is on the right, the 2007 bridge on the left.

The two suspension bridges span the Tacoma Narrows strait of Puget Sound in Pierce County, Washington, USA, and connect the city of Tacoma with the Kitsap Peninsula. They both carry State Route 16 over the strait; the older bridge carrying westbound traffic and the new one carrying eastbound traffic. Tolls are charged on eastbound traffic only.

At the time of their construction, both the 1940 and 1950 bridges had the third-longest spans in the world, behind the Golden Gate and George Washington bridges. Today, the 1950 and 2007 spans are the fifth-longest in the USA and only the 43rd-longest in the world.

6. The National Aquatics Centre (the Water Cube), Beijing

This famous building, constructed for the Beijing Olympics in 2008, is a highly complex steel space frame and the largest ETFE-clad structure in the world. It is claimed that the thin ETFE foil cushions, which were supplied and installed by Vector Foiltec, achieve a 30% decrease in energy costs compared to equivalent traditional glass cladding.

The National Aquatics Centre (the Water Cube), Beijing(Image by Allen Watkin via Wikimedia Commons)

Engineered by Arup, with the China State Construction Engineering Corporation, the architect was PTW Architects, with China Construction Design International. The design is based on the idea of soap bubbles, and the wall geometry and structural arrangement was developed from the theory of the Weaire-Phelan structure via a complex optimisation programme written by Arup. The true Weaire-Phelan structure, in which the edge of each cell is curved, was adapted to form a structural support system in which each beam/strut is straight so as to better resist axial compression. The resulting optimised system results in exterior cladding made of four thousand ETFE cushions, some over 9m across, with seven different sizes for the roof and fifteen for the walls.

One of the main challenges in this ambitious project was to optimise the design of the 22,000 steel beams and struts, under a complex set of loading conditions, where every single component needed to be as light as possible to minimise steel tonnage. Minimum weight is critical in long span roof structures - the roof spends a lot of its strength simply holding itself up – and particularly in high seismic zones.  One of the key questions was whether to design the roof with compact sections to behave plastically under seismic loads, or whether to use stiffened slender sections to behave elastically under the loads. After extensive structural analysis, Arup decided on a solution which adopted compact sections to take advantage of plastic ductility under extreme seismic loading.

The structure had a capacity of 17,000 during the games that is now being reduced. Although called the Water Cube, the building is really a rectangular box (cuboid) 178m² and 31m high. The structure's popularity has spawned several copycat structures throughout China.

7. And finally…

I promised you a few shockers to finish off with, so true to my word here is the Zhivopisny Bridge, Moscow whose arch seems to be the wrong way round and rather heavy (and red!), and the Lianxiang bridge (also called Lianchen bridge) in Xiangtan, China, which can't seem to make up its mind whether it is a cable stayed or an arch bridge. Both were also completed in 2007.

Zhivopisny Bridge(Image by Daryona via Wikimedia Commons)

Lianxiang bridge(Image by Freeman Joe via Wikimedia Commons)


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