A s Bilbao residents watch construction progress on the world’s first all-stainless steel bridge, developments across Europe confirm the growing interest in a host of

architectural applications for the metal. Designed by the late Jose Antonio Fernandez Or-donez, Bilbao’s Abandoibarra Bridge will span the Nervion River, linking the University of Deustro to the famous Guggenheim museum, itself clad in titanium. When finished, the bridge will be 143 meters long and 7.6 meters wide, its all-stainless exterior made of 500 Mt of 20mm-thick hot-rolled quarto plate, in a high-strength duplex grade (international standard: EN10088 1.4362). Completion is scheduled for De-cember 2001. The microstructure of duplex stainless steel gives it even better exterior corrosion resistance than standard austenitic stainless steels, and superior tensile strength, allowing the use of lighter gauges. Supplier AvestaPolarit has given the material on the bridge a life-cycle guarantee of 50 years. Functional and aesthetically pleasing "Over the past 10 years, some of the most striking ar-chitectural designs in the world have been made, not out of bricks and mortar, but stainless steel," reads a

recent AvestaPolarit press release. The text goes on to cite the fin-ishes on the Lloyds Building in London, The Petronas Towers in Kuala Lumpur, the Euro-pean Court of Human Rights in Strasbourg and

the Puerta de Europa twin towers in Madrid, among others. The choice of stainless steel is due to its natu-ral corrosion-resistant properties, ease of fabrication, resistance to surface damage, and to the variety of available surface finishes. The Eurostar Terminal at Waterloo, London, in the UK, uses stainless steel for roofing panels, gutters and supports, to meet long-life design criteria of 125 years with a first maintenance requirement of 25 years. Stainless steel surfaces are generally easy to keep clean, although they do require some attention to maintain their original beauty. On buildings, depending on the grade of steel and where it is used, cleaning need only take place, on average, once every six to twelve months. Duplex and austenitic materials The duplex grades now available create entirely new possibilities in stainless steel architecture and con-struction. Partly austenitic and partly ferritic in struc-ture, they combine the strength of the one with the ductility of the other. Market observers describe archi-tecture as an exciting growth area in the use of these grades, citing the UK examples of the Lowry Centre in Salford, and the Dockland Boating Centre in London, both partly roofed in duplex. Further afield, the stainless-steel roof of the Conference and Exhibition Centre in Hong Kong is light yet strong - and corro-sion-resistant, which is a vital factor in a coastal envi-ronment. Standard austenitic grades (most commonly the 316 family) are ideal for many exterior uses, such as a new glass and stainless steel building in the La Défense business district and the new Charles De Gaulle airport (see front cover picture), both near Paris, France. Corrosion resistance is greatly affected by the presence of molybdenum in this material, only a slight raising of which, say from the usual 2 to 2.5 percent up to 3 percent, dramatically improves per-formance. Above 3 percent, you move into the 317 range, or into duplexes if structural properties are re-quired. Also concerning corrosion, in Sweden, the UK and elsewhere, street lighting columns, traditionally made of reinforced concrete or galvanised steel, are a big

Stainless Steel: A glowing future in Construction by Paul Snelgrove

The first all-stainless steel bridge in Bilbao, Spain (Picture: Courtesy of AvestaPolarit)

Internal stainless steelwork of the La Défense Tower, Paris (Picture courtesy of AvestaPolarit)

A new glass and stainless steel building in the La Defense area of Paris designed by architect IM Pei (picture courtesy of AvestaPolarit)

December 2001 STAINLESS STEEL INDUSTRY 13

issue today for many city councils. Concrete can crack and drop off as the inner metal reinforcement rusts and expands, while steel columns corrode both below ground and above ground when water seeps inside posts and damages the galvanising. In the UK alone, it is estimated that about 3 million outdoor lampposts will need replacing in the next ten years. Many are ur-gent. The industry is promoting the proposition of stainless steel columns that should last 70 years at the very least. Stainless steel seeks acceptance as a structural material Explaining that the industry is working hard to in-crease the structural use of stainless steel, experts affirm that the physical forming of a stainless steel tube enhances the material's mechanical properties (work-hardening), making it actually stronger than car-bon steel. The result requires no coating, painting or maintenance, so stainless steel can be doubly advan-tageous as a strong, lightweight structural member. Already widely used in door- and window-frames, the metal can be folded and shaped into elaborate sec-tions, and ground or brushed for an attractive finish. In

addition, the advantages of stainless steel in terms of fire resistance are not yet fully exploited, and further research is needed to assess the material's true po-tential here. Extensive R&D, centred on the behaviour of stainless steel members and connections, has been carried out in Europe since 1991. The work culminated in the publication of the ENV for Eurocode 3 Design of Steel Structures - Supplementary Rules for Stainless Steels (EC3: Part 1.4). These rules were, however, adapted from carbon steel rules. Since the load-bearing capac-ity of stainless steel members differs from that of car-bon steel members, further research was required to define a new design approach and maximise the cost-effectiveness of stainless steel’s desirable properties in structural uses. A recently completed, partially EC-funded, three-year research project, involving major producers and other organisations from six European countries, is now being followed up by a valorisation project that updates the old design manual for stainless steel. The project will also ensure wide dis-semination of the latest findings (partly through elec-tronic media) among architects and structural engi-neers.

Stainless steel for ar-chitects "Handrails and parapets were rare 20 years ago, but have become almost standard nowadays," ex-plains Thomas Pauly of Euro-Inox, the European stainless steel market development association. "Interior cladding is a big growth area as well, be-ing easily maintained and attractive. The extension to London’s Jubilee Line subway, for example, uses it extensively," he adds. Architects tend to worry about fingerprint soiling, but very robust em-bossed and pattern-rolled finishes exist which are less sensitive to fingerprints. These are much used for ele-vators and escalators in stations, hotels and airports. "Stainless steel has both practical and decorative merits and elevators and escalators are amongst the biggest markets for flat products," says Mr. Pauly. Stainless steel facades in architecture go back to the 1950s. The electricity substation at the Elephant and Castle traffic circle in London dates from that time and, despite pollution, is still in fine condition. “Now we can make stainless steel facades at the same cost as with other materials, so there is huge development potential,” Mr. Pauly points out. Stainless steel roofing has been around for 30 years, but is set to grow. There is an obvious trend towards metallic materials on buildings, especially for decorative purposes, and a swing back from the “disposable architecture” philoso-phy to greater construction quality and durability. “With stainless steel you don’t get corrosion, even un-der difficult circumstances, and whatever you combine it with it won’t corrode, so its durability is exceptional,” says Mr. Pauly. Ecologists like it, too, since stainless steel is neutral to the environment and does not result in noxious substances getting into the water table. Switzerland, Austria and parts of France and Ger-many have a long tradition of metallic roofing, and the architects in these Alpine areas readily use stainless steel. There are two approaches. One is the welded stainless steel roof, which is a 100-percent watertight solution, useable on a flat roof, and the other is the conventional standing seam roof, which can be built by any roofing contractor. “This is now a very large, potential market throughout Europe, which we are try-ing hard to promote,” underlines Mr. Pauly. Stainless steel in tunnel and road applications Tunnel linings are an interesting growth area. Alpine countries use it a lot, often in short tunnels, which can use up to 300 metric tons of stainless steel. An inter-esting projection could be made from this about the quantities of stainless steel involved in the new tunnel just agreed between France and Italy, which will be one of the longest in Europe. The most popular grade for tunnels would be 316, but there is potential for higher alloy grades, depending on the corrosion con-ditions. Road tunnels have the problem of exhaust gases and de-icing salt, so high chromium and nickel

Wall cladding at Souhwark station (picture courtesy of EuroInox)

The exterior at North Greenwhich Station (picture courtesy of EuroInox)

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grades, maybe with up to 25 percent chromium, are needed. Another important growth area is in reinforcement bars for concrete structures, like bridges and lighting columns. Everywhere you see the need for expensive refurbishment work on structures often only 30 years old. Carbon steel in concrete tends to corrode, espe-cially if the concrete coverage is under 5 cm. Exhaust gases and de-icing salt get in. In the U.S., highway authorities automatically specify stainless steel for certain applications in bridges and tunnels. Their high-ways are privatised, so they look at a 40-year or more lifetime horizon. The extra cost of stainless steel bars is vastly outweighed by lower maintenance costs over the complete lifetime. "Gradually, life-cycle costing awareness is gaining ground in Europe, and that, plus a growing ecological orientation, is making people more conscious of long-term benefits," Mr. Pauly says. "Reinforcement bars are standard products and have huge potential in these applications," he adds. Where there’s fire or water, there's stainless steel Repair and relining of chimneys is also a fairly big market, especially in countries and at times when a major move from solid fuel to oil or gas is afoot. The necessary reduction in chimney diameter, to avoid condensation, is quickly and cheaply achieved by in-stalling a thin stainless steel inner sleeve in the exist-ing chimney. This was a big German market after re-unification, and there is still constant demand for refur-bishment solutions. Another growth area for stainless steel, related to con-struction, is plumbing, for which there are now new regulations in Europe, where the use of other metallic materials can be restricted. In some areas, such as parts of Scotland, northern France, Germany and Sweden, for example, there have been corrosion problems due to a lowering of pH values in the water down to about 6.5. Above 7 it is alkaline, below 7 it is acid. European bodies, laboratories and regulators now have a program to approve a different material, and stainless steel is the only metallic material that can be used unconditionally. Swimming pool linings Again according to Mr. Pauly, today, about 150 large, public pools in Europe are lined with stainless steel, using a technology developed in Austria. In fact, the two market leaders for this are Austrian companies. The idea spread quickly in Germany, and between the two countries there are about 120 to 130 such lined pools. This is a very interesting repair solution, espe-cially outdoors, since you can leave water in the pool, or make repairs during the winter. You have no con-

Stainless swimming pool at a health club in Holmes Place, Kingston, manufactured and installed by Invarmex (UK) Nottingham.

crete cracks to patch in the case of leakage, and old pool tiles can be left under the stainless steel skin. "Many pools built in the 1960s and 1970s are nearing the end of their lifetime, and we are trying to carry this technology to France, the UK and elsewhere," Mr. Pauly says. Growth on two fronts The inexorable growth in the use of stainless steel falls, it seems, into two categories. One is that of ap-plications where stainless steel substitutes for other materials. Domestic chimneys, formerly with mainly ceramic or plastic solutions, are an example of the first case, as are railings. The other growth category is through increased demand for finished products that use stainless steel. Stainless steel cladding in eleva-tors, for example, has grown due to refurbishment of subway stations and the increasing number of high-rise buildings and shopping malls. Of the two catego-ries, Euro-Inox predicts that promoting “substitution” applications is the principal opportunity for what will surely be a bright future for stainless steel.

December 2001 STAINLESS STEEL INDUSTRY 15

Copyright British Stainless Steel Association, December 2001