Shape memory alloys (SMAs) are a class of alloys that possess numerous unique characteristics. They offer complete shape recovery after experiencing large strains, energy dissipation through hysteresis of response, excellent resistance to corrosion, high fatigue resistance, and high strength. These features of SMAs, which can be exploited for the use in control of civil structures subjected to seismic events, have attracted the interest of many researchers in structural engineering over the past decades. This article presents an extensive review of seismic applications of SMAs. First, a basic description of two unique effects of SMAs, namely shape memory and superelastic effect, is provided. Then, the mechanical characteristics of the most commonly used SMAs are discussed. Next, the material models proposed to capture the response of SMAs in seismic applications are briefly introduced. Finally, applications of SMAs to buildings and bridges to improve seismic response are thoroughly reviewed.

Seismic Response Control Using Shape Memory Alloys: A Review

Performance-based seismic design of self-centering steel frames with SMA-based braces

Summary
Given their excellent self-centering and energy-dissipating capabilities, superelastic shape memory alloys (SMAs) become an emerging structural material in the field of earthquake engineering. This paper presents experimental and numerical studies on a scaled self-centering steel frame with novel SMA braces (SMAB), which utilize superelastic Ni–Ti wires. The braces were fabricated and cyclically characterized before their installation in a two-story one-bay steel frame. The equivalent viscous damping ratio and ‘post-yield’ stiffness ratio of the tested braces are around 5% and 0.15, respectively. In particular, the frame was seismically designed with nearly all pin connections, including the pinned column bases. To assess the seismic performance of the SMA braced frame (SMABF), a series of shake table tests were conducted, in which the SMABF was subjected to ground motions with incremental seismic intensity levels. No repair or replacement of structural members was performed during the entire series of tests. Experimental results showed that the SMAB could withstand several strong earthquakes with very limited capacity degradation. Thanks to the self-centering capacity and pin-connection design, the steel frame was subjected to limited damage and zero residual deformation even if the peak interstory drift ratio exceeded 2%. Good agreement was found between the experimental results and numerical simulations. The current study validates the prospect of using SMAB as a standalone seismic-resisting component in critical building structures when high seismic performance or earthquake resilience is desirable under moderate and strong earthquakes. Copyright © 2016 John Wiley & Sons, Ltd.

Shake table test and numerical study of self‐centering steel frame with SMA braces

Analytical prediction of the seismic behaviour of superelastic shape memory alloy reinforced concrete elements

Results from 18 large-scale tests of steel bracing members are presented to examine their inelastic buckling and fracture behavior as related to the seismic design of concentrically braced frames. The brace specimens include square hollow structural shapes (HSS), pipe, and wide-flange sections. The effect of various parameters, including width–thickness and slenderness ratios, cross-section shape, loading history, loading rate, and grout fill on the performance of these braces is investigated. Among these parameters, loading history, width–thickness ratio and slenderness ratio are shown to have the largest influence on brace ductility. The test data suggest that for some HSS and pipe specimens, current seismic design provision limits on maximum width–thickness ratios may not provide sufficient ductility for seismic design. Effects of loading rate are found to be insignificant, and the grout fill is shown to provide a modest improvement in cyclic ductility. Measurements of brace stiffness, tensile strength...

Experimental Investigation of Inelastic Cyclic Buckling and Fracture of Steel Braces

The use of special concentrically braced frames has increased since the 1994 Northridge and 1995 Hyogoken-Nanbu Earth- quakes. However, past performance suggests limited ductility and energy dissipation in braced frame systems due to buckling of conventional braces. In order to address this limitation, three- and six-story concentrically braced frames with superelastic shape memory alloy SMA braces are studied to evaluate their seismic performance in comparison to traditional systems. SMAs are unique metallic alloys that have the ability to undergo large deformations while reverting back to their original undeformed shape providing recentering capabilities to the braced frame. Detailed analytical models of the frames with SMA braces are developed and two suites of ground motions are used to evaluate the structures with respect to interstory drift and residual drift. The results suggest that the SMA braces are effective in limiting interstory drifts and residual drifts during an earthquake, in part, due to the recentering nature of superelastic SMAs.

/pdf/seismic-assessment-of-concentrically-braced-steel-frames-5etpun8fjw.pdf

Seismic Assessment of Concentrically Braced Steel Frames with Shape Memory Alloy Braces

Superelastic NiTi shape memory alloy (SMA) wires and bars are studied to determine their damping and recentering capability for applications in the structural control of buildings subjected to earthquake loadings. These studies improve the knowledge base in regard to the use of SMAs in seismic design and retrofit of structures. The results show that the damping properties of austenitic SMAs are generally low. However, the residual strain obtained after loading to 6% strain is typically <0.75%. In general, it is shown that large diameters bars perform as well as wire specimens used in non-civil-engineering applications. The results of a small-scale shake table test are then presented as a proof of concept study of a SMA cross-bracing system. These results are verified through analytical nonlinear time history analysis. Finally, a three-story steel frame implementing either a traditional steel buckling-allowed bracing system or a SMA bracing system is analyzed analytically to determine if there is an advantage to using a SMA bracing system. The results show that the SMA braces improve the response of the braced frames.

Seismic Vibration Control Using Superelastic Shape Memory Alloys

This paper presents and compares two different uniaxial constitutive models for superelastic shape-memory alloys (SMAs), suitable to study the dependence of the stress-strain relationship on the loading-unloading rate. The first model is based on the inclusion of a direct viscous term in the evolutionary equation for the martensite fraction and it shows how the material response is bounded between two distinct rate-independent models. The second model is based on a rate-independent evolutionary equation for the martensite fraction coupled with a thermal balance equation. Hence, it considers mechanical dissipation as well as latent heat and includes the temperature as a primary independent variable, which is responsible of the dynamic effects. The ability of both models to reproduce the observed reduction of damping properties through the modification of the hysteresis size is discussed by means of several numerical simulations. Finally, the capacity of the constitutive equations to simulate experimental data from uniaxial tests performed on SMA wires and bars of different size and chemical composition is shown.

/pdf/numerical-and-experimental-evaluation-of-the-damping-tzuwetpyt0.pdf

Numerical and Experimental Evaluation of the Damping Properties of Shape-Memory Alloys

Pan-Alpine glacier phenology reveals lowering albedo and increase in ablation season length

This study analyzed the challenges and benefits of the identification and promotion of a long-distance cycleway in high mountain areas with the aim of promoting Alpine eco- and geo-tourism. We also investigated the role of e-biking in discovering local geodiversity and geoheritage in a sustainable way. In particular, we focused on the path from Bormio to the Forni Glacier (Upper Valtellina, Italy), analyzed within the framework of the “E-bike” Interreg project. We performed a detailed analysis to select the points of environmental–geological interest (POIs), with a focus on geoheritage sites to increase the knowledge of the natural heritage of the area. Since these sites are widespread in the study area, within the frame of the “E-bike” project, we selected only the most exemplary ones, covering a wide spectrum of attractions, from a moving geosite (i.e., landslide) to a paradigmatic example of the effects of climate change (glacier). The “E-bike” path represents in its entirety a great opportunity to visit mountain and high-mountain landscapes, even for inexperienced mountain bikers, and to enjoy places rich in naturalistic and cultural values. Our interdisciplinary approach allows visitors to identify the sites of interest and export the structure of the project in different environmental and human contexts.

/pdf/the-role-of-e-bike-in-discovering-geodiversity-and-1s29bq96.pdf

The Role of E-Bike in Discovering Geodiversity and Geoheritage

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