Damping in Civil Engineering using SMA. The choice of the alloys (CuAlBe and NiTi)

This paper is centered in the required SMA behavior for their application to earthquakes damping in steel structures as in family houses and, also, in damping of stayed cables in bridges. In the earthquakes, the SMA requirements are associated to the relatively reduced number of oscillations. In fact, the earthquake (near one minute with frequencies close to 1 Hz) and the eventual replicas requires that the damper can realize around 1000 cycles of work without relevant changes and, also, that in the time interval between installation and earthquake (one or more decades) not appears changes related to diffusion processes related to meta-stability of the phases modifying the expected behavior of the material. The summer-winter temperature effects also require analysis. Usually, the dampers are situated inside the house and the amplitude of summer–winter wave temperature effects is smoothed.

In the application to stayed cables in bridges the required behavior is substantially different. The working time scale is completely different, eventually the use of damper is immediate after the initial installation and the number of oscillations to be damped is, also extremely higher. In general, successful use of SMA requires a deep and clear knowledge of the effective conditions related to each application and, also, what are the required characteristics of SMA. For instance the use of pre-stressed material that furnishes better behavior in, for instance, damping processes is inappropriate for Cu-based alloys for their ability to stabilize the martensite with time and producing unexpected paths in the phase coexistence trajectories.