We are now into relatively recent memory with a selection of structures celebrating their 40th birthday this year. These structures were being built while I was at university studying to become an engineer and some of you reading this may even have been involved in their design or construction - if so I would love it if you would like to comment on this article.

I hope you enjoy this month's selection, which includes some well-known structures and some well-known designers.

1. The Pompidou Centre, Paris

It is always good to start with something well known, and this structure is certainly famous! Names commonly associated with its design include Italian architect, Renzo Piano (also the architect for London's Shard), British architect Richard Rogers (known for London's Lloyds Building), and of course British engineers Peter Rice and Ted Happold, both then at Arup. We must also mention Su Rogers and Gianfranco Franchini, who were also part of the design team. It was the winning entry in a design competition which attracted no less than 681 international entries! (I have won design competitions with long odds before but never that long!)

Pompidou Centre
Image: Wikimedia Commons, Nikolai Karaneschev

The Centre Georges Pompidou, as it is properly known, stands in the Beaubourg area of the 4th Arrondissement in the centre of Paris, so is also commonly known simply as Beaubourg. It is named after Georges Pompidou, the President of France from 1969 to 1974 who commissioned the building, and was officially opened on 31 January 1977.  It is a major modern art gallery, and is also home to a public reference library, sculpture terrace, cinema, performance halls, a bookshop, cafés and a restaurant, all arranged over six levels including a basement. The building is rectangular in plan and occupies half the area of the site — the other half is a public piazza.

The architects had a clear vision of developing a building based on "a large loose-fit frame where anything could happen" as Rice says in his excellent book "An Engineer Imagines". The principle was to provide as much internal flexible column-free space as possible, so most of the structure, circulation and services is on the outside of the building. The long elevation facing the piazza is a circulation zone, with a series of escalators and walkways running full width and enclosed in transparent tubes. The other long elevation, on the Rue de Renard, is a mechanical services zone, containing a forest of colour-coded ducts, pipework, goods lifts and fire stairs. The inside of the building is for art.

The primary structure involves 28 full-height steel columns arranged in two rows, one on each long elevation. This creates 13 structural bays along the building's length, each 12.8m wide. The floors are supported by steel trusses 45m long and 2.85m deep which span across the width of the building and bear on short stubs of 8.2m long cantilevered beams which are pinned to the columns and tied down to the ground at their outer ends.

Pompidou Centre 02Image: Wikimedia Commons, MilénaGranel

Combining a suspended beam and short propped cantilevers is known as a Gerberette solution (after the 19th century German engineer, Heinrich Gerber, who invented it for bridge design), and the Pompidou Centre's short beams are referred to as Gerberettes. They are made of cast steel and each weighs nearly 10 tons. The decision to use cast steel as a major element of the scheme was made early in the design process by Peter Rice, who was looking for a way to 'personalise' the structure, giving it individuality. Each Gerberette passes around the column so that it applies load on each side via two spherical bearings. This arrangement avoids large eccentric forces on the columns, which would otherwise need to be bigger to resist the bending moments.

The columns are also cast steel thick-walled tubes of constant 850mm diameter with wall thickness varying from 85mm thick at the bottom to 40mm at the top. This resulted in a slimmer column than if a standard hollow steel section had been used. Interestingly, the columns are filled with water for fire protection. The nodes of the main trusses are also in cast steel.

The building is well known (and originally derided by some) for its flamboyant and colourful external exposed building services which are mostly accommodated on Rue de Renard side in the 6m space between the glass façade and the vertical tension tie rods of the Gerberettes. The pipes and ducts are colour-coded — blue for air, green for fluids and yellow for electricity, and red is used for circulation elements and safety elements. This colour-coding, together with the clearly expressed external structure, create the building’s distinctive 'information machine' hi-tech style.

2. New River Gorge Bridge, USA

The New River Gorge Bridge is a steel arch bridge 924m long over the New River Gorge near Fayetteville, West Virginia. With an arch span of 518m, the bridge was for many years the world's longest single-span arch bridge (it is now the fourth longest), and with the roadway at 267m above the New River, it is also one of the highest vehicular bridges in the world.

New River Gorge BridgeImage: Wikimedia Commons, JaGa

The bridge is part of U.S. Route 19, and its construction marked the completion of Corridor L of the Appalachian Development Highway System. The bridge shortened the gorge crossing time from 45 minutes to 45 seconds, and is crossed by an average of 16,200 vehicles per day.

Designed by the Michael Baker Company and constructed by the American Bridge Company, the bridge is a classic example of a lattice steel trussed arch and is fairly typical for its period. Nowadays, I would like to think that we have learnt the importance of reducing maintenance costs, and a modern equivalent would probably avoid quite so many inaccessible and potentially vulnerable components and connections. But at least the designers thought about the problems of corrosion and inaccessibility for painting, because the bridge uses CORTEN (weathering steel) - a relatively early example of the use of the material at this scale.

The final cost of construction was $37 million, and at the time the bridge was West Virginia Highways Department's largest project in its history.  In 2013, the bridge was listed on the US National Register of Historic Places.

3. Dallas City Hall, USA

This unusual building is the seat of the Dallas municipal government and features wider floors in the upper levels where important people demand bigger offices and narrower floors lower down for ordinary mortals. Designed by architect I.M. Pei, with engineers Robert E. McKee Inc., it is the fifth city hall, replacing the previous Dallas Municipal Building.

Dallas City Hall
Image: Wikimedia Commons, Daquella Manera

After WW2, the City of Dallas’ began planning a new municipal centre, but plans faltered due to excessive costs. Then, after the 1963 assassination of President John F. Kennedy, world opinion turned against the city, so the Mayor made new plans to restore the city's image. The resulting “Goals for Dallas” program included the statement, "We demand a city of beauty and functional fitness that embraces the quality of life for all its people."

This was the start of the movement to create a new modern City Hall and municipal centre. Planning commenced in 1964, and a committee of prominent citizens settled on I.M. Pei to design the new facility. Construction began on June 26, 1972, and the project was completed in three phases, finishing in December 1977.

I.M. Pei’s modernist inverted pyramid design is a response to the space requirements set by the client, with larger upper office floors overhanging the smaller public spaces below. The building slopes at a 34° angle, and provides protection from the weather and the fierce Texas sun. When the mayor reacted to the apparent top-heaviness of the building's shape, three cylindrical pillars that appear the hold up the structure were inserted. These contain stairwells that had originally been concealed within the design, but they only provide visual support - they do not carry load from the building.

The building features in the Robocop movies of the 1980s, as the Headquarters of the OCP company; special effects were employed to make the building appear taller than it is.

4. Palace of Europe, Strasbourg, France

The Palace of Europe (French: Palais de l'Europe) is a building located in Strasbourg, France, that has served as the seat of the Council of Europe since 1977 when it replaced the 'House of Europe'. Between 1977 and 1999 it was also the Strasbourg seat of the European Parliament.

Palace of Europe
Image: Wikimedia Commons, Council of Europe 

The building was designed by the architect, Henry Bernard, who was also responsible for the extraordinary circular Maison de la Radio in Paris. It is a square with 106m long sides and nine storeys high. In the centre is the large fan-shaped Parliament Chamber, known as the hemicycle, with its striking curved radial beams.

Palace of Europe 02Image: Wikimedia Commons, Adrian Grycuk

I have tried to find out more information online about the structure and the engineer but without success.  If anyone out there has some information, please pass it on. Zooming in on the photo, those radial beams look like timber with bolted steel flitch plate joints. They look very skinny, but this is not my field, so hopefully someone out there can enlighten us.

5. Kuwait Towers

The Kuwait Towers are a group of three slender towers in Kuwait City, standing on a promontory reaching into the Persian Gulf. They were the sixth, and last, group in the larger Kuwait Water Towers system of 34 towers (33 store water, one stores equipment), and were built in a style considerably different from the previous five groups. The Kuwait Towers were officially inaugurated in March 1979 and are regarded as a landmark and symbol of modern Kuwait.
Kuwait TowersImages: Wikimedia Commons: Left -  Evan Hemingway, Right - Different Al-Akhawand from Kuwait

As water towers in a desert city, these towers are highly symbolic and have become an icon for the city. They were designed by the Danish architect, Malene Björn, and they received the coveted Aga Khan Award for Architecture in 1980.

The tallest tower is 185m high with two spheres and the second is 140m high with only one. Each of the two big spheres contains 4500 cubic metres of water, and the tallest tower also supports a rotating restaurant and other recreational facilities.

The third tower contains no water but only supports the lighting system to illuminate the other two – an expensive lighting column!

They are constructed in reinforced and pre-stressed concrete, with the spheres covered in coloured, enamelled steel pieces brought from China. The total cost of the towers was USD 16.5m.

They were badly damaged during first gulf war (1990-91) but repaired in 2012, following which their re-opening was celebrated with an extravagant fireworks festival.

6. Citigroup/Citicorp Centre, New York

The Citigroup Centre is an office tower in New York City on 53rd Street between Lexington Avenue and 3rd Avenue in midtown Manhattan, built in 1977 as the HQ of Citibank. It is 279m tall and one of the ten tallest skyscrapers in New York, with 59 floors comprising 120,000m² of office space. The building is one of the most distinctive in New York's skyline, thanks to its 45° angled top, and was designed by architect Hugh Stubbins and structural engineer, William LeMessurier. The building is currently owned by Boston Properties, and was renamed 601 Lexington Avenue in 2009.
Citigroup CentreImages: Wikimedia Commons: Left - Pablo Costa Tirado, Right - Public Domain

The Citigroup Center was always going to be an engineering challenge, and due to a design oversight and changes during construction, the building was found to be structurally unsound when first built.
The building had to accommodate the site of a pre-existing Lutheran church in one corner, so the solution was to use massive columns in the centre of each side instead of more conventionally at the corners. This resulted in 22m long cantilevers in the corners of the building, providing enough space at the northwest corner for the church. To help accomplish this, LeMessurier employed a system of stacked load-bearing braces, in the form of inverted chevrons. Each chevron is designed to distribute loads due to wind to the centre and then down to the ground via the massive columns.

However, the original design only considered wind blowing perpendicularly onto each of the four faces of the building in turn, which was all that was required by the New York building code. Such winds would normally represent a worst loading case in a conventional building and a structural system designed to handle them should generally cope with wind from any other angle. Thus, the engineer did not specifically calculate the effects of a diagonal wind blowing onto the corners of the building. In June 1978 (after the building was completed), a conversation with a civil engineering student at Princeton University prompted a review, so LeMessurier recalculated the wind loads on the building, this time including wind on the diagonal. This recalculation revealed a substantial increase in the load at the chevron brace connection joints due to wind.

Furthermore, the original design for the chevron braces used welded joints, but during construction the contractor had been allowed to use bolted joints instead to save costs – a change that was made without the knowledge of LeMessurier although somehow approved by his firm without reference to him. The combination of the increased load for a diagonal wind and the weaker chevron joints meant that the bolts could potentially fail catastrophically at a relatively low wind speed calculated to occur on average once in 55 years. As a result the building was in critical danger, particularly as the problem was identified at the beginning of the hurricane season so action was required quickly.

LeMessurier persuaded Citicorp to repair the building, and for the next three months work proceeded at night to weld 50mm steel plates over each of the critical bolted joints, almost unknown to the general public. Six weeks into the work, a major storm (Hurricane Ella) was heading for New York. With the city only hours away from an emergency evacuation, and the joint reinforcement only half-finished, Ella thankfully turned and veered out to sea, allowing the work to be completed without incident. As a precaution, Citicorp did work out emergency evacuation plans with local officials for the immediate neighbourhood but these were thankfully not needed.

Because nothing happened as a result of the errors, the danger was kept hidden from the public for years until it was publicized in a lengthy article in The New Yorker in 1995.  LeMessurier was criticised for insufficient oversight of the change from welded to bolted joints, for not informing the endangered neighbours, for actively misleading the public about the extent of the danger during the reinforcement process, and for not informing other engineers about the issue for almost 20 years. However, his act of alerting his client to the problem in his design is sometimes cited as an example of ethical good practice!
Incidentally, the building also has a tuned mass damper at the top to reduce movements due to wind, and was the first skyscraper in the United States to feature a tuned mass damper.

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