High Performance Dampers for Bridgesby Reginald DesRoches,
Abstract: A multi-disciplinary research study investigates the use of shape memory alloys as seismic dampers in bridges. Shape memory alloys are a class of alloys that display several unique characteristics, including Youngs modulus-temperature relationships, shape memory effects, and high damping characteristics. Unlike plastically deforming metals, the nonlinear deformation is metallurgically reversible. Nitinol can have two forms: martensite, and austenite. When the material is in its martensitic form, it is soft and ductile and can be easily deformed. In its austenitic form, it is quite strong and hard (similar to Titanium). The NiTi material has all these properties, their specific expression depending on the temperature in which it is used. Below the martensite finish temperature, Mf, the material has the shape memory effect the strain can be can be recovered by heating the specimen. At a temperature above the austenite finish, Af, and below Md the maximum temperature to strain induce martensite, stress-induced martensite is formed (known as the superelastic effect). At an operating temperature above Md, the material is austenitic and undergoes ordinary plastic deformation, with very high strength. Shape memory alloys possess several characteristics that make them desirable for use as a passive energy dissipation in structures. These characteristics include: (1) hysteretic damping; (2) highly reliable energy dissipation based on a repeatable solid state phase transformation; (3) excellent low- and high-cycle fatigue properties; and (4) excellent corrosion resistance. In this study, the SMA dampers exhibiting the shape memory and the superelastic effect are investigated as dampers in bridges.
Subject Headings: Smart materials | Damping | Temperature effects | Deformation (mechanics) | Alloys | Bridges | Strain
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