Crumbling infrastructure is a worldwide problem

THE first bridges were likely to have been built by early man shoving a fallen tree across a stream. Since then, construction techniques have come on a bit—from wood to stone, wrought iron and then steel. In the 20th century, reinforced concrete appeared. Concrete is an immensely strong material, especially when coupled with steel. But the sudden collapse of the Morandi bridge in Genoa this week (pictured), with a tragic loss of life, adds to the concern of civil engineers that many bridges around the world which use reinforced concrete are deteriorating faster than was expected.The Genoa bridge is based on a design called a cable-stayed bridge, although it is a somewhat unusual variant. Such a bridge uses one or more towers, from which run cables that support the deck of the bridge. This is different from a suspension bridge, such as the Golden Gate Bridge in San Francisco, in which the cables holding up the deck are suspended vertically from a main cable anchored at either end of the bridge. Cable-stayed bridges are widely used, mainly for spans shorter than those crossed in one go by a suspension bridge.