We are now well into recent memory with a selection of structures celebrating their 30th birthday this year, and I suspect that some of my readers were directly involved in some of them, so I had better be careful what I say!

I have been counting down the decades, one per month, since January when I started with 120 year-old structures completed in 1897, and we are getting close to the end when we will finish with a flourish in December with 10-year old structures.  I hope you have been following me this far and have enjoyed learning a bit about some interesting structures along the way.

This month there were a lot of bridges and not so many notable buildings to choose from, so it is a bit bridge-focussed. But I have selected a few projects as usual, and you will probably recognise some of them and the names of some of the designers.

1. Bac de Roda Bridge, Barcelona

I really have to start with this one. The name Santiago Calatrava is familiar to most engineers, not just those involved in bridge design, but it wasn't always so. This bridge in Barcelona was his first bridge commission and whatever you think about it, the design certainly made people sit up and take notice. It certainly made a big impression on me when I first saw pictures of it. Starting with this project, Calatrava has opened the eyes of designers to all sorts of new possibilities, and while not everyone likes his work, and many of his more recent designs have been heavily criticised, there is no question that he has changed the way many people think about bridge design.
 
Pont Bac de Roda
Image: Ralf Roletschek, commons.wikimedia.org

The bridge was planned as part of a larger development in preparation for the 1992 Olympics in Barcelona, and it functions as both a symbolic and physical connection between two previously disjointed districts, Sant Marti and Sant Andreu, which were separated by railway lines into a new station. The city planners wanted an icon that would breathe new life into this part of the city, and so while they could have had a much less costly crossing of the railways they set out to build something noteworthy and that is certainly what they got.

This is a steel through-arch bridge with a main span of 46m. The arches support the edges of the roadway between them and also the edges of the pedestrian platforms each side. These platforms widen towards the middle to create a broad pedestrian viewing area with spaces to rest and admire the views. (Why anyone particularly wants to do this over a busy railway is beyond me but never mind!)
 
Pont Bac de Roda
Image: Josep Bracons, commons.wikimedia.org

There are not two but four arches, arranged in two pairs, with the two outer ones leaning against the two inner vertical ones to provide stability. This enables the base of the arches to come to a point where they don't need to transfer moment. It also avoids the need for any stabilising elements crossing over the roadway between the arch pairs. Instead of single cables or bars as hangers to suspend the deck, Calatrava has used pairs of hangers, which for me adds unnecessary clutter. A cleaner appearance would have been possible using single hangers only.

Among the more successful features of the bridge are the concrete supports and underside of the deck in the approaches, and the way the generous wide staircases at each corner are integrated with the outer, inclined arches. I don't have close-up photos of these – I'm afraid you will just have to go to Barcelona to see it for yourself!

2 Sunshine Skyway Bridge, USA

This very famous cable stayed bridge crosses Tampa Bay in Florida and was designed by the well-known designers Eugene Figg Jr and Jean Muller. The cable stayed section is 1.2km long, with a main span of 367m, and is the centrepiece of a 7km crossing of the bay.

It stands alongside the site of an earlier bridge which was built in 1954 but partially destroyed by a ship which hit one of its supporting piers during a storm in 1980. 35 people died as a result of that accident, which saw a 370m long section of the bridge girder plummet into the bay along with six cars, a truck and a Greyhound bus.

The incident led to world-wide toughening of ship impact design standards and is one of those episodes that designers look back on as a step change in design practice. As a result, the new bridge is characterised by very large vessel protection structures or "dolphins" around the base of the bridge piers. These serve the purpose of protecting the piers but look absolutely horrendous!

The new bridge was constructed by the American Bridge Company, at a cost of $244m. It has a single plane of stays along the centreline and so requires a torsionally stiff box girder for the deck. The bridge is formally named as the Bob Graham Sunshine Skyway Bridge after a former state governor. Apparently he was inspired by a visit to the Brotonne Bridge in France to suggest its cable stayed form to the Sunshine Skyway designers. Who knows, but there are certainly marked similarities.

Sunshine Skyway Bridge

Image: Robert Neff, commons.wikimedia.org

The bridge has experienced problems of corrosion in the precast segmental columns of the approach viaducts, leading to repair works in 2003 and 2004. But a potentially greater problem is that its 55m navigation clearance is no longer sufficient for some of the larger vessels wishing to pass underneath, so maybe some time there will be a third, higher, bridge at this location. Who knows?

The new bridge was recently closed during Hurricane Irma due to sustained wind speeds of over 40mph but no damage has been reported.

3 Roof of Montreal Olympic Stadium, Canada

This unusual and ill-fated membrane roof system was installed on the Montreal Olympic stadium in 1986-87. The stadium itself was built in 1976 for the summer games that year, but it was completed without its roof at the time. The construction of the tower and membrane roof was delayed in August 1986 by an explosion and fire, which turned out to be the first of a series of unfortunate accidents and disasters that have subsequently plagued the structure. The kevlar roof was finally completed in April 1987.

The design was for a folding membrane which retracted up into the tower in order to open the roof of the stadium.  The system was very complex, and in hindsight it is easy to see why this was always going to be a roof with big challenges.  The tower contains the housing for the roof membrane when it is open, and also acts as an observation platform.

In June 1989, the membrane lining ripped forcing evacuation of about 8,000 people, and in June 1991 the roof split during a wind storm, leaving a hole of 30 metres by 15 metres. Then a few months later in September 1991, a 55 tonne beam crashed to the ground, resulting in the closure of the stadium for 94 days.  Thankfully, no-one was hurt.  In January 1998, the roof was damaged by ice, resulting in snow and water falling onto the floor and forcing cancellation of two Rolling Stones concerts. With all of these and various other disasters, the moving roof was finally replaced by a fixed one in 1998.
 
Montreal Olympic Stadium
Image: Bobjagendorf, commons.wikimedia.org

So this is a building with a chequered history, and the roof structure is certainly uniquely recognisable and has not been without its challenges.

4. Arab World Institute Building, Paris

Institut du Monde Arabe
Image credit: Institut du Monde Arabe - Fessy

This is a striking steel framed building structure with an elaborate and beautiful steel and glass façade. It was designed by Jean Nouvel, in collaboration with Architecture Studio, and was a project that established him as one of the world's great architects. Engineering was by French firm SETEC.
 
The Arab World Institute is an organization founded in Paris in 1980 to research and disseminate information about the Arab world and its cultural and spiritual values. The Institute was established as a result of a perceived lack of representation for the Arab world in France, and seeks to provide a secular location for the promotion of Arab civilization, art, knowledge, and aesthetics. The building was constructed from 1981 to 1987 with funds from both the League of Arab States and the French government, with the total cost of the building being around 230 million Euros.

Institut du Monde Arabe 02
Image credit: Institut du Monde Arabe - Rambaud

In contrast to the curved surface on the river side, the southwest façade is an uncompromisingly rectangular glass-clad curtain wall. A metallic screen behind the glass façade contains 240 photo-sensitive motor-controlled apertures, or shutters. These provide a characteristic motif and act as a sophisticated brise soleil.  The shutters automatically open and close to control the amount of heat and light entering the building, creating an interesting internal space with filtered light reminiscent of Islamic architecture. The project received an Aga Khan Award for Architecture in 1989.

5. Rama IX Bridge, Bangkok, Thailand

The Rama IX Bridge has a main span of 450m which was the second longest cable stayed span in the world (second only to the Alex Fraser Bridge in Vancouver) when it was completed in 1987. It remains the longest span with a single plane of stays on the centreline of the bridge. The design was by the German engineer Helmut Homberg, who was also responsible for the Queen Elizabeth 2 bridge across the Thames at Dartford. 

The bridge carries six lanes of expressway traffic across the Chao Phraya River in Bangkok, Thailand. It has a wide, torsionally stiff steel box girder (necessary because of the central plane of stay cables) with an orthotropic steel deck, and in addition to the 450m main span it has two 166m side spans. The steel pylons rise to a height of about 90m and are supported on concrete piers and piled foundations. It was the first cable-stayed bridge in Thailand.

Rama IX Bridge
Image: Chalit Manipalviratn, commons.wikimedia.org

The bridge was named in honour of King Bhumibol Adulyadej and was opened on his birthday in 1987. The original colour scheme, with white pylons and black cables, was replaced in 2006 with an all yellow scheme considered to be more representative of the king.

6. Hamm Railway Bridge, Germany

Another interesting and slightly unusual structure, the Hamm Railway Bridge crosses the Rhine between the Düsseldorf district of Hamm and the Neuss district of Rheinparkcenter in the German state of North Rhine-Westphalia.  Design was by Dyckerhoff & Widmann and Hein Lehmann.
 
Hamm Railway Bridge 01
Image: Johann H. Addicks, commons.wikimedia.org

The bridge consists of a Warren truss girder within a tied arch arrangement, and at first sight you can't help wondering why you need both the truss and the arch. Maybe if the truss was just a little deeper it could have spanned on its own without the arch. Or maybe if the arch was just a little stronger and stiffer the deck could have been a simpler, lighter and shallower structure. But there is a technically and aesthetically logical reason, as well as a historically rational explanation for this unusual form. The technical reason is that the truss is structurally and visually continuous over the adjacent side span (see the photo below). The truss depth is governed by the side span and is constant throughout to provide visual consistency, so the arch is simply stiffening and strengthening the longer main span. For the historical rationale we have to go back a few years.

Hamm Railway Bridge 02
 Image: qwesy qwesy, commons.wikimedia.org

The original Hamm Railway Bridge at this site was a double-track bridge built in 1870 and named the König-Wilhelm-Brücke ("King William Bridge") after the Prussian King William I. It was a wrought iron arch supporting a three-span truss. (Can you see the relevance?)  It also had towers at the ends, both for architectural decoration and also as an expression of the military security of the bridge in the event of a war.  Later, the increase in train traffic led to the construction of a second, parallel, double-track bridge just 32 m upstream in 1911. It was built with the same three spans and a similar but more contemporary iron truss arch. As with the older bridge, there were also bridge towers, but they were larger and stronger. Immediately after commissioning the new bridge, the old bridge was upgraded, so that by November 1912, there were two almost identical arch-truss bridges next to each other providing four tracks across the river, with only the bridge towers differing significantly.

During the Second World War, the German Wehrmacht blew up all the Rhine bridges in Düsseldorf, including the Hamm Railway Bridges, to slow down the advance of the allies from the west in March 1945. After the war, the northern bridge was repaired, but not the southern one, reducing the crossing to only two tracks once again. It was not until the construction of the east–west S-Bahn line in 1984 that the there was a strong need to restore the Hamm Railway Bridge to four tracks again. 

I am sure that the designers of the new bridge chose to reflect the character and heritage of the old bridges in its structural form, deliberately keeping the arch-supported truss as a modern expression of the original concept, although now with a longer navigation span to accommodate busier river traffic and larger vessels. 

The new two-span bridge has a main tied-arch span of 250m and a side span of 135m. The Warren truss is continuous throughout and fully welded. The bridge has two tracks within the truss structure and a single track on both sides outside the truss. 

 

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