November 1998

B-2 Bridge

By Technology Review

Since the end of the Cold War, California's defense complex has scurried to beat swords into plowshares-and now bombers into bridges. With $6 million from the Federal Highway Administration, engineers at the University of California at San Diego (UCSD) plan to erect a 150-meter bridge out of advanced composite materials of the type originally designed for the B-2 bomber. The four-lane span, to arc over Interstate 5 near campus, will be the longest bridge ever built from composite materials, says Gilbert Hegemier, a project leader at UCSD. The 3-year project will also serve, he hopes, as the "technical driver for what we think is a new industry." Polymeric matrix composites, made by impregnating fabrics woven from high-strength carbon threads with an epoxy such as vinyl ester, have a stiffness-to-weight ratio 10 times that of the steel used in construction. That means easier-to-handle materials that could push the limit on long-span bridges and allow speedy erection of buildings.