Sustainability of civil infrastructure using shape memory technology

Abstract

The last few decades have clearly demonstrated the vulnerability of our civil infrastructure systems to problems like aging, natural, and man-made hazards including earthquakes, hurricanes, blasts, etc. The conventional materials such as steel and concrete have proven to be limited in terms of their ability to withstand the extreme demands imposed on them by modern societies. The limitations in currently used construction materials combined with the consistently growing population worldwide present new challenges and demands for researchers in the field of structural engineering. Hence, there is an urgent need for new materials that are capable of extending the service life of structures with minimal or no need for maintenance or repairs against natural and man-made hazards. Shape memory alloy (SMA) is a class of “Smart Materials” that have recently emerged as potential construction material with unique thermomechanical properties, namely shape memory effect and superelasticity. Two applications of SMAs in civil structures are discussed in this paper. The first application involves the use of SMA in performing seismic rehabilitation of RC bridge columns that lack flexural ductility. In this application, SMA is used in the form of thermally prestressed spirals that can apply large active confinement pressure to the columns at their plastic hinge regions to improve their flexural ductility. The experimental results of large scale shake table tests performed on two RC columns, one of which is retrofitted with SMA are discussed. The results demonstrate the great ability of SMA spirals in mitigating the damage even under strong levels of ground shaking. The second application focuses on utilizing superelastic SMA fibers as reinforcement for polymeric composite bars. The newly developed composite material is named SMA–Fiber Reinforced Polymer (SMA–FRP), and is studied as seismic reinforcing bars for moment resisting concrete frames. The results of nonlinear time history analysis prove that using SMA–FRP bars at the plastic hinge regions of the frames helps significantly in limiting the residual drifts and enhancing the energy dissipation of the frames.