Resumen de Aplicaciones piloto de aleaciones con memoria de forma en estructuras
Benito Mas Gracia, Eva Oller Ibars, Carlos Rodrigo Ribas González, Antoni Cladera Bohigas
The most remarkable properties of shape memory alloys (SMAs) are the superelasticity, shape memory effect and damping. These features open a wide range of possible applications of SMAs in the field of structural engineering. This communication presents a group of significant applications, highlighting the material characteristics which make them attractive.
Most of the applications of SMAs in structural engineering exploit superelasticity effect.
On using SMAs as passive reinforcement, superelasticity enables the reinforcement to yield without showing significant permanent deformations, which is especially relevant in the case of seismic load. Recent research has investigated the feasibility of the SMAs in applications such as concrete beams reinforced with superelastic SMAs, SMA-FRP (fiber reinforced polymers) composite reinforcement for concrete structures, fibers embedded in concrete structures, wide variety of plastic hinges and joints (Figure 1) and damping elements or control devices of the seismic response, among many others. However, SMA passive reinforcement, besides having low elastic modulus compared to steel, can generatebonding problems, as they have been used to date in the form of smooth rebars or plain wires.
Shape memory effect allows the recovery of a predefined geometry by heat treatment.
An example of application is pre-stressed concrete elements. Even though the adherence between SMA wires and concrete is still a technological problem which has yet to be perfectly solved, SMA pre-stressing does not need hydraulic jacks and can be applied at any time during the lifetime of an element, which, undoubtedly, offers new possibilities, such as pre-stressing by phases in order to avoid cracking. What is more, there are no losses due to friction; therefore it could be especially useful when the layout of the pre-stressing is particularly curved. Another application is active confinement of reinforced concrete columns (Figure 2).
The use of SMAs in passive seismic control devices takes advantage of superelasticity, shape memory effect and damping capacity, making it possible to obtain tailor-made devices to fit requirements. The same conceptual idea has been used for bracings for retrofit and damping in structures composed of multiple concrete frames.
