The University of Nevada, Reno, announces that its engineers have designed bridge columns made of a flexible concrete reinforced with Nitinol rods to resist collapse during earthquakes. Tests have shown that the columns are able to return to their original shape even after an earthquake as strong as a magnitude 7.5.
Civil engineering professor and researcher Saiid Saiidi has pioneered technology, the result of 15 years of research. Two of the columns are to be used in the construction of a new exit bridge ramp on a section of the busy State Route 99 corridor through downtown Seattle.
“The material in the most critical part of the columns is unique because it’s not actually steel, unlike traditional rebar,” Prof. Saiidi says. “It’s made of an alloy of titanium (44%) and nickel (56%). The material is ‘smart’ because it remembers, as a shape memory alloy, its original shape. If you stretch it or compress it, it goes back to its original length once you let it go. Steel cannot recover its elongation once it gets past certain limits.”
The concrete is known as “engineered cementitious concrete,” or ECC. “The concrete is superior to ordinary concrete because of its high tensile strain capacity that prevents it from falling apart under back and forth action of earthquakes,” says Prof. Saiidi. “There are polyvinyl fibers in the concrete with special coatings that control cracking and maintain the integrity of the material.”
