The Powerful, The Strong, The Fast/A Bridge to a Composite Future; Extreme Engineering; Scientific American Presents; by Netting; 2 Page(s)

A barrage of natural and man-made forces threaten bridges, from the imperceptibly slow degradation of salt water, corrosive soils and heavy traffic to the sudden catastrophic destruction of earthquakes. Southern California mercilessly serves up all these onslaughts, challenging the creativity, imagination and ingenuity of structural engineers. One of these technological visionaries is Frieder Seible, chair of the department of structural engineering at the University of California at San Diego. During the next two years, Seible and his team, along with the California Department of Transportation, will undertake an ambitious project to fabricate the world's longest cable-stayed bridge having main structural members built from fiberglass, carbon and other unorthodox construction materials.

Designed to connect two sections of the U.C.S.D. campus, the bridge will stretch 450 feet (140 meters) over Interstate 5. In place of sober concrete and impassive steel, much of the 60-footwide structure will begin as filaments of glass, carbon or goldtoned aramid (a lightweight polyamide material). The delicate black or translucent strands, which look like pieces of yarn made of thousands of twisted fibers, hardly seem capable of supporting the weight of a four-lane bridge. But their delicacy belies hidden properties. According to Seible, these composite materials can be up to five times lighter and stronger than structural steel (the actual strength depends on fiber orientation). Just as important, the materials are largely inert. Unlike steel, they do not corrode in the presence of moisture or salt, nor do they suffer from water seepage that can freeze and enlarge cracks in concrete.