Stainless steel bridges - Combining Aesthetics, Function and Sustainability

By Kristina Osterman

Nickel Institute

Utilitarian design has its own aesthetic, though often engineers grapple with the tension between economics and the desire to build structures that are compatible with the surrounding environment."

When the environment is as historic and beautiful as Italy's, aesthetic choices assume new importance. If the existing harmony is not to be disrupted, consideration must be given to modern engineering requirements as well as to the preservation of historical buildings and the surrounding environment.

Siena and Padova

Stainless steel bridges recently built in the Italian provinces of Siena and Padova offer a beautiful illustration of how structures can be made to blend in with their surroundings. Crossing rivers and railways, the fluid arcs of these bridges create a refined and delicate impression.

The Chianti region, situated midway between Florence and Siena and famous for its wine, has some of the most beautiful countryside in Italy. Siena's provincial capital, which goes by the same name, is surrounded by olive groves and the vineyards of Chianti. Perched on three hills with winding alleyways, steep steps, and historic landmarks, it is one of the most beautiful cities in Tuscany. Few towns rival its beauty. In addition to vineyards and olive trees, Siena is noted for its harsh rock formations, captivating coastline, and nature reserves.

It is largely for aesthetic reasons that the municipality of Siena chooses to use stainless steel in many of its infrastructure projects. City planners have taken advantage of the unique properties offered by lean duplex stainless steels.

Although duplex grades are mainly associated with industrial applications, duplex Uranus® 35N (S32304), produced by ArcelorMittal-Industeel in France, was recently used to build a bridge in Siena. Consisting of 23% chromium and 4% nickel, this lean duplex grade has excellent atmospheric corrosion resistance - equivalent to that of 316L (S31603). S32304 is about twice as strong as S31603, is easily fabricated and is highly resistant to fatigue. The bridge's stainless steel tubular arcs, which consist of some 110 tons of S32304 will require minimal maintenance.

Duplex S32304 was also used in the recent construction of a bridge in the province of Padova. Other parts of this bridge have an external sheathing of AISI 304 (S30400) stainless steel which again, translates into minimal maintenance.

Designing for the environment

Metallic bridges are typically designed and built to last 100-200 years, so durability is essential. Decision-makers are well aware that choosing the right materials can ensure long-term cost-efficiency. The use of stainless steel in construction guarantees corrosion resistance and durability while satisfying sustainability criteria.

Using duplex stainless steel, in particular, helps ensure environmental sustainability. It is 100% recyclable and does not degrade. Stainless steel in infrastructure construction not only offers life-cycle cost advantages over other materials, it enables the design of sophisticated creations that please even the most demanding eye.

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