Akshay Final Seminar

APPLICATIONS OF SHAPE MEMORY ALLOYS IN CIVIL ENGINEERING SEMINAR REPORT SUBMITTED BY

AKSHAY B H (11152004) GUIDED BY

NIVYA T K H.O.D CIVIL ENGINEERING

BACHELOR OF TECHNOLOGY In CIVIL ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING

COLLEGE OF ENGINEERING THALASSERY (Engineering College Under CAPE, Estd by Govt. Of Kerala) October 21,2017

Seminar report 2017

Applications Of Shape Memory Alloys In Civil Engineering

ACKNOWLEDGMENT “It is not possible to prepare any seminar report without the assistance and encouragement of other people. This one is certainly no exception.” On the very outset of this seminar report I would like to extend my sincere and heartfelt obligation towards all the personages who have helped me in this endeavor. Without their active guidance, help, cooperation and encouragement, I would not have made headway in the seminar report. My sincere thanks to my guide Mrs. NIVYA T K, H.O.D. civil engineering for her constant guidance and encouragement in carrying out this seminar, without whom this success couldn‟t be achieved. I am extremely thankful and pay my gratitude to Asst. Professor SEEMA, civil department for her support in choosing the topic and giving proper guidance. I am also thankful to the Asst. Professors Mrs. THAMARA C and Mrs. REMYA for their support. I also acknowledge with a deep sense of reverence, my gratitude towards my parents and members of my family who has always supported me morally and economically. At last but not the least gratitude goes to all of my friends who directly or indirectly helped me to complete this seminar report. Any omission in this brief acknowledgment does not mean any lack of gratitude. Thanking you, Akshay B H

2 Department of civil engineering

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ABSTRACT Shape Memory Alloy (SMA) materials are widely used in different disciplines and it has substantial potential for civil engineering applications. The unique properties of SMA result in high damping, combined with repeatable re-centering capabilities which can be used in civil infrastructures, especially in vibration control devices. An overview of the Shape Memory Effect (SME) and Pseudo-Elasticity (PE) characteristics of SMA due to thermal or/and stress variation controlled reversible hysteretic phase transformation between Martensite & Austenite is detailed. Also reviews the constitutive modeling of SMA’s, current research using SMA-based devices for civil structures along with established examples while focusing on the disadvantages that may arise.


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CONTENTS 1. INTRODUCTION 2. BASIC CHARACTERISTICS OF SMA’S 2.1.SHAPE MEMORY EFFECT 2.2.PSEUDO ELASTICITY 2.3.DAMPING PROPERTIES 3. STRUCTURAL APPLICATIONS OF SMA IN CIVIL ENGINEERING 3.1.SMA BRACED FRAMES 3.2.SMA DAMPER FOR BRIDGES 3.3.STEEL BEAM COLUMN CONNECTING USING SMA TENDONS 3.4.SMA AS A TENDON IN CONCRETE STRUCTURE 3.5.SMA AS AN EXTERNAL TENSIONING MATERIAL IN CONCRETE STRUCTURE 3.6.REINFORCEMENT 3.7.SMA AS FRP 3.8.SMA AS FIBRES 4.EXPERIMENTAL PROGRAMS ON SMA 4.1.BOND BEHAVIOUR OF SMOOTH AND SAND COATED SHAPE MEMORY ALLOY REBAR IN CONCRETE. 4.2.RC BEAMS REINFORCED WITH SMA REBARS 5. TYPE OF SMA, SUITABLE FOR USE IN CIVIL STRUCTURES 6.CASE STUDY 7. LIMITATIONS 8.CONCLUSION 9.REFERENCES


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1.INTRODUCTION The name shape memory implies that it remembers its original formed shape. The superelastic behavior exhibited by shape-memory alloys help material to totally recover from large cyclic deformations, while developing a hysteretic loop. Due to its hysteretic behavior and excellent re-centering capability, SMA can be used in a wide variety of civil engineering applications. The other key features of SMA’s include high strength, good fatigue and corrosion resistance, high damping capacity, temperature-dependent Young’s modulus, ability to undergo large deformations, and availability in many possible shapes and configurations. SMA’s have two main phases which have different crystal structures. One is called martensite that is stable at low temperatures and/or high stresses and the other austenite, which is stable at high temperatures and/or low stresses. Austenite, also named as the parent phase, generally has a cubic crystal structure while martensite has a less-ordered crystal structure. Austenite phase provides more stiffness than that of Martensite and civil engineers can leverage the variation in stiffness depending upon temperature & stress. It is seen that structural steel is much stiffer than NiTi and that the martensitic yield strength of NiTi is lower than its austenitic counterpart. However, the most important characteristic of NiTi is its outstanding ability to recover from strains up to about 8%, without residual deformations, while showing a mechanical hysteresis. This provides the material with unique energy dissipation and re-centering capabilities.Over the past two decades, SMA’s have been widely investigated for their possible application in civil engineering structures. Latest applications of SMA’s in civil engineering along with established examples while also focusing on the limitations in application is disussed under this report.


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2.BASIC CHARACTERISTICS OF SMA’S

SMA’s have two unique properties, The Shape Memory Effect (SME) which is the phenomenon that the material returns back to their original shape upon heating and the Pseudo-Elasticity (PE) which is the phenomenon that the material can undergo a large amount of inelastic deformation and recover after unloading. These properties are the result of reversible phase transformations between the austenite phase and the martensite phase. In the stress-free state, an SMA is characterized by four transition temperatures such as martensite start temperature Ms, martensite finish temperature Mf, austenite start temperature As and austenite finish temperature Af. At a temperature below Mf, the SMA exhibits the SME

and

at

a

temperature

above

Af,

the

SMA

exhibits

the

PE.

Figure 1: Stress-strain diagrams of NiTi SMA, (a) SME; (b) PE; (c) Ordinary plastic deformation 2.1.Shape Memory Effect

Shape memory effect (SME) is a unique characteristic of SMA that exhibits thermo-elastic martensitic phase transformation. It is the ability of SMA material to recover its original shape after being deformed through a thermal cycling. Through training, the material has the ability to memorize a very specific physical configuration or shape in either the martensite or austenite phase, which is called one-way shape memory (Fig. 1a). Also it is possible to train the material, such that it memorizes two different configurations or shapes in martensite and austenite phases, which is called two-way shape memory. The key to the SME is the build-up of residual stress fields within the SMA, by deforming the material plastically, and then these stress fields control the phase transformation.For example if a straight bar of austenitic phase SMA is allowed to cool below the phase transition temperature, the crystalline structure will change to martensite. If the bar is 6 Department of civil engineering

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subsequently deformed by bending, and then reheated above the transition temperature again, it will return to its original straight configuration as shown in figure 3.

Figure 2: Materials crystalline arrangement during Shape Memory Effect

Figure 3: Demonstration of shape-memory effect


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2.2.Pseudo Elasticity

Pseudo-Elasticity (PE), also known as super-elasticity, is described as the recovery of large strain as a result of the stress-induced martensitic phase transformations under constant temperature. When T>Af, SMA is in its austenite phase. If a sufficiently high stress is applied to the material in the austenite phase, the SMA transforms into the detwinned martensite. When the load is released, a reverse transformation to the austenite state takes place, which results in complete shape recovery and a substantial hysteretic loop (Fig. 1b). However, if the temperature is below Af but above As, there will be only a partial shape recovery. Also, if the temperature in the austenite phase exceeds the maximum temperature at which martensite occurs, Md, the material is stabilized in the austenite phase and the martensitic transformations cannot be induced by an applied load, thus the PE of SMA is completely lost (Fig. 1c). 2.3.Damping Property

SMA used for damping can be both martensitic as well as austenitic. The damping comes from either martensite variations reorientation in the martensitic material or from stressinduced martensite in austenitic material. When an SMA specimen is subjected to a cycle of deformation within its superelastic strain range, it dissipates a certain amount of energy without permanent deformation (Fig. 4a). This results from the phase transformation from austenite to martensite during loading and the reverse transformation during unloading, ensuring a net release of energy. When an SMA is loaded in the martensite phase, it yields at a nearly constant stress after initial elastic deformation and displays strain hardening at larger strains. When unloaded, there remains some residual strain at zero stress. This martensitic composition of SMA’s generates a full hysteresis loop around the origin (Fig. 4b). Thus, martensite SMA dissipates a much higher amount of energy compared with that of austenite SMA because of its larger hysteresis loop. But it has no re-centering capability like the austenitic SMA. In the martensite phase under tension – compression cycles, the maximum stress attained in compression has been found to be approximately twice that in tension (Fig. 2b). Although superelastic SMA dissipates less energy than martensitic SMA, its advantage is that it can still dissipate a considerable amount of energy under repeated load cycles with negligible residual strain.


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Figure 4: Typical stress – strain curve of SMA under cyclic axial stresses: (a) superelastic

SMA; (b) martensite SMA

3.STRUCTURAL APPLICATIONS OF SMA’S

IN CIVIL

ENGINEERING 3.1.Sma Braced Frames

Several studies have considered the use of SMA’s as diagonal braces in frame structures. The frame structures deform under excitation, SMA braces dissipate energy through stressinduced martensite transformation (in the superelastic SMA case) or martensite reorientation (in the martensite SMA case) as shown in Fig. 3a. The effectiveness of using large diameter NiTi bars as a bracing system for steel structures and compared the SMA braces with buckling-restrained steel braces is carried out. Th e outcome of numerical studies showed that SMA bracing systems can satisfactorily limit the inter-story drifts in steel buildings and significantly reduce the residual drifts.

Figure 5: (a) SMA braced frame 9 Department of civil engineering

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3.2.Sma Damper For Bridges

(a)

(b

(c)

Fig 6:(a) Schematic of the setup of SMA restrainer for a simple-supported bridge; (b) Schematic of the SMA damper for a stay-cable bridge; (c) Schematic of the SMA isolation device for elevated highway bridges;

Several studies have been carried out to investigate the possibility of using SMA as unseating prevention devices on multiple span bridges to overcome some of the limitations of traditional devices such as steel cable restrainers, steel rods, and shock transmission units.The schematic of SMA restrainer setup for simple supported bridge is shown in Fig. 6a. Both superelastic and martensite SMA’s can be used as damper elements for bridges. Theoretically studied the vibration mitigation of a combined cable-SMA damper system which can be used on a stay-cable bridge (shown in Fig. 6b). The dynamic responses of the SMA damped cable were simulated as it vibrated at its first mode or at its first few modes respectively. They stated that the proposed superelastic SMA damper can suppress the cable’s vibration in both cases. For highway bridges, Comparative simulations of the SMA isolation system (shown in Fig. 6c) and a conventional isolation system were conducted with three excitation levels. For small excitation level, the SMA isolation system firmly links the pier and the deck, while the relative motion emerges in the case of the conventional system. For a medium excitation level, the SMA bar undergoes a stress-induced martensitic transformation so that the soft stiffness allows a relative displacement comparable to that of the conventional isolation


Seminar report 2017


system. At severe loading, the SMA bar enters an elastic range of martensite and the maximum displacement is one-fifth as much as that of the conventional isolation system. The comparison shows that the damage energy of the bridge with the SMA isolation system is smaller than with the conventional system. 3.3.Steel Beam Column Connecting Using Sma Tendons

Several studies have been conducted on SMA beam-column connectors. SMA connectors have been designed to provide damping and tolerate relatively large deformations and found to be most effective in controlling structural response under high levels of seismic intensity.When experimentally evaluated the performance of partially restrained steel beamcolumn connections using martensitic SMA’s,it was observed that the SMA connections were able to recover 76% of the beam tip displacement.

Fig 7:(a) Schematic of the SMA isolation system for buildings ; (b) Schematic of the SMA spring isolation device ; (c) Schematic of a bell tower using SMA anchorage retrofitting.

Connections of different structural components are more likely to get damaged on occurrence of earthquake. SMA connectors have been designed to provide damping and resist relatively large deformations. The SMA anchorages were made of Nitinol SMA rods in 20-30 mm diameter and steel bars. The results obtained from the loading test and numerical simulation shows that SMA rods were very effective in dissipating energy and reducing the vibration of building under severe seismic ground motion. It was observed that, in comparison to the accumulated deformation and residual strain in ordinary anchorage, the SMA anchorage can


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recover their original shape after cyclic loadings. Resistance performance of SMA connectors was kept same to prevent plastic deformation and damage in the structural columns. Martensite SMA tendons were used as a primary load transferring elements in steel beamcolumn connection. Based on load test results of full-scale model it was concluded that the connection exhibits stable and repeatable hysteresis for rotation up to 4% and the SMA tendon was able to sustain up to 5% strain without any permanent damage. 3.4.Sma As A Tendon In Concrete Structure

In concrete members shape memory alloy bars or cables can act as tendons. Studies presented the use of SMA as a tendon in concrete members. SMA tendons have several advantages over conventional steel tendons. There are no frictional losses due to development of uniform tension force along the total length of the tendon during initiation of shape memory effects. It is very suitable for curved concrete member or where tendon profile is much curved. Using SMA prestressing tendon, there is no need of anchors. This can be used for tensioning extremely thin concrete members. 3.5.Sma As An External Tensioning Material In Concrete Structure

The deficit in load bearing capacity and the risk of large deformation occurs in concrete structures due to increase in load and time dependent effects of concrete. With age of the concrete structure, it often develops cracks that lead to shortening in its service life. Adding external tensioning element is a well accepted strategy today for countering such problems in concrete structures. Materials like steel and Fiber Reinforced Plastic (FRP) are commonly used for these purposes. In comparison to these materials, SMAs have the ability of being stressed without any tensioning devices, like hydraulic jacks etc. After mounting and anchoring of martensite SMA along the external surface of structure, they need to be heated to initiate shape memory effect. As deformation recovery is restrained due to anchorage with structure, a tension force builds up. Corrosion resistant Fe-Mn-Si-Cr rods were used to enhance the shear resistance of a cracked region of a reinforced concrete bridge girder. Resistance heating was applied at a current of 1000Ampere. 3.6.Reinforcement

SMA’s are particularly beneficial for construction in seismic regions.If SMA is used as reinforcement, it will yield when subjected to high seismic loads but will not retain significant permanent deformations. 12 Department of civil engineering

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3.7.SMA as FRP

SMA-FRP reinforcing bars behave in a ductile manner and are capable of dissipating energy.It was found that SMA-FRP bars have more potential to improve the ductility and energy dissipation capability of concrete structures compared to conventional FRP bars. 3.8.SMA As Fibres

Due to the propagation of micro-cracks, strength of concrete decreases.This may be prevented by using prestrained SMA wires that are embedded in the concrete matrix.Upon activation, these wires regain their original shape, and consequently, initial compressive stresses are transmitted to the concrete matrix.

.

Fig 8:SMA APPLICATIO


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4.EXPERIMENTAL PROGRAMS ON SMA 4.1.Bond Behaviour Of Smooth And Sand Coated Shape Memory Alloy Rebar In Concrete.

The experimental program conducted in this study involved a series of 56 push out test specimens (concrete cylinders) with different parameters. Push out test was selected since it was simple to conduct .Ni – Ti SMA rebar (nitinol) has been used as reinforcement to investigate the bond behaviour.4different concrete mixes were evaluating the effect of concrete compressive strength on the bondbehavior of SMA rebar.

Fig9:Test setup for bond behavior SMA rebar with concrete


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Fig.10Specimens (smooth) (a) before testing, (b) after testing and (c) inside view

The results from 56 pushout tests lead to the following conclusions: 1.The stress – slip curve of SMA rebar can be divided/idealized into four stages: elastic stage, ascending stage, linearly descending stage and residual stage.

Fig. 11. Load – slip curves for pushout test of smooth SMA rebar. 15 Department of civil engineering

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2. The bond strength of both smooth and sand coated SMA rebar is significantly influenced by the concrete strength, bar diameter and embedment length but is independent of concrete cover. 3. The application of sand coating increased the bond strength between concrete and SMA rebar by developing friction and interlocking forces in addition to the adhesion mechanism. 4. The coarser the sand size, the more is the improvement in bond strength. 5. The surface roughness of SMA rebar significantly affects the failure pattern as well as the bond strength . 6. Concrete with smooth SMA rebars resulted in simple push out failure whereas sand coated rebars resulted in splitting failure. 4.2.RC BEAMS REINFORCED WITH SMA REBARS

A concrete beam reinforced with shape memory alloys (SMA) wires was tested and compared with a conventionally reinforced concrete (RC) beam.For the tests, NiTi (Nickel/Titanium) wires approximately 4.3mm in diameter were used to reinforce the underside of a concrete beam with a span of 1.14m.The surfaces of the SMA wires were sand-blasted

and

coated

with

quartz

sand

using

an

epoxy

adhesive

Figure 12.Beam reinforced with SMA wires in the test set-up


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5. TYPE OF SMA, SUITABLE FOR USE IN CIVIL STRUCTURES However, not all the SMAs have the potential for being used in civil structures due to requirement of special mechanical properties, the specific temperature conditions in civil structures and last but not the least the cost involvement. Fe-Mn-Si-X alloys are low cost SMA with high superelastic properties and good shape memory effects. Comparing the market price of Ni and Ti on the one side and Fe, Mn, Si, Cr on the other side and consider their ratio, it will be a factor of about 8 to 12. So, in terms of cost an iron based SMA could only be a small fraction of that NiTi SMA. The studies shows that Fe-based SMA like FeMn-Si-X, Fe-Ni-C and Fe-Ni-Co-Ti also referred to as shape memory steel or Ferrous SMA have the potential for use in civil structures. The shape memory effects in Fe-Mn-Si containing sufficient amount of Mn were detected in 1982 by Sato et al.. In last decades FeMn-Si based alloys with several additional alloying elements were developed and tested. With lots of research work, the poor shape memobehavior was improved. It was found that 60% to 65% ratio of iron in Fe-Mn-Si-X alloys combine low cost with high strength and high Young’s modulus. Corrosion behavior similar to that of stainless steel was achieved by Li. H.J., with addition of 10% chromium and nickel.It was found that addition of Al, C, Co, Cu, N, Nb, NbC, V, VN, and ZrC improves shape memory effect. There is a wide scope of research towards uses of low-cost SMAs for initiating large-scale applications like civil structures. Low-cost SMA has been successfully implemented in bridge rehabilitation,Ni-Ti for the damping of seismic load successfully. Cu-Zn-Al for torsion, bending and tension dampers incorporated in bracings. Because of better workability and lower cost of ferrous SMAs, these are more attractive than Ni-Ti SMA’s for use in civil structures.


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6.CASE STUDY 6.1.Retrofitting Of The Basilica Of San Francesco At Assisi, Italy

The superelastic behavior of SMA has attracted the attention of civil engineers. Its major field of application is retrofitting structures in an earthquake design. Graesser E.J successfully used Ni-Ti SMA for damping of seismic loads. A real scale application of a superelastic SMA device is the earthquake resistant retrofit of the Basilica San Francesco at Assisi, Italy. The historic gable was connected with the main structure by device using SMA rods.The Ni-Ti SMA rods were subjected to tension, although they were designed to take tension and compression forces.Earthquake induced vibrations may cause severe damage in particular to historical buildings, like the Basilica of San Francesco at Assisi.The Basilica was restored after being strongly damaged by an earthquake of 1997.The structural interaction of the basilica’s transept south gable with the main structure needed to be modified.

Figure 13. Shape memory alloy device 6.2. Retrofitting Of The Bell Tower Of The Church Of Sangiorgio At Trignano, Italy

Another project was executed to retrofit the earthquake resistant bell tower of the Church of San Giorgio, Italy. Steel tendons were added to increase its tilt resistance with intermediary superelastic SMA devices to act as load limiters to prevent the masonry from compression failure.Experts proposed increasing the position stability of Simply Supported bridges in earthquake prone regions through connection between the bearings of the bridge and the bridge deck slab using superelastic bars.Seismic upgrade of the bell tower of the Church of San Giorgio at Trignano became necessary after being struck by a 4.8 Richter magnitude earthquake in 1996 and represents one of the first known applications of SMAs to civil engineering.Retrofit design of the 17 meters tall masonry tower was carried out under the framework of the ISTECH project.After a 4.5 Richter magnitude earthquake with the same


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epicenter in 2000, subsequent investigations of the retrofitted bell tower found no evidence of damage .

Figure 14.St. Giorgio bell tower

7.LIMITATIONS The price of the SMA’s is high in comparison to the conventional civil engineering construction materials. However, a significant reduction in the price of SMA has occurred over the last decade, recently developed Iron based SMA's are quite cheaper than traditional NiTi, sometimes by ten folds. Fe-Mn-Si-X alloys are an example of a potentially low cost SMA. SMA’s can be heated by using electric current for actuation. But short activation times in the range of seconds are not possible for large cross sections. A high capacity power supply with a current of several hundred Ampere can reduce activation times considerably. This may incur greater costs when setting up the actuator and keeping up the high temperature state for long time.Another difficulty regarding the application of SMA is the machining of large diameter bars using conventional equipment, due to its hardness. The welding of SMA’s is often difficult.


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8.CONCLUSION This paper presents a review of the basic properties of SMA such as the SME and the PE. The ability to change shape by application of heat can be used to move objects. If recovery is resisted, the SMA generates force that is useful as an actuator which can be activated by electrical Joule heating. Thus many applications are possible. Numerous analytical and experimental studies point toward the feasibility and superiority of SMA based devices over conventional methods for seismic protection.The main characteristics of such devices are high energy dissipation and recentering capabilities. In particular, the recentring capability of SMAs can be very efficient in reducing the cost of repairing and retrofitting of various structures. Other prospective use of SMAs is in prestressing, which can help the structure to actively accommodate additional loading or remedy prestress losses over time. Although there has been substantial research work on civil structures utilizing SMAs, the short and long-term deflection behavior of concrete flexural members with SMAs are yet to be investigated through experimental program.It is observed that phenomenological models are more adequate for civil engineering applications because they are simple and easy to incorporate in finite element programs and are not computationally demanding.


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9.REFERENCES

1. Civil Engineering Application of Shape Memory Alloys -M. G. Rashed1*, R. Ahsan2 and B. Islam3,October 2014 2. Review of Shape Memory Alloys applications in civil structures, and analysis for its potential as reinforcement in concrete flexural members Debbarma.S.R1, Saha.S2 1,July 2015 3. Application Of Shape Memory Alloys In Civil Engineering: Past,Present And FuturEMasoud Motavalli, Christoph Czaderski, Andrea Bergamini and Lars Janke 4. Alam, MS; Youssef, MA and Nehdi, M. 2007. Utilizing shape memory alloys to enhance the performance and safety of civil infrastructure: a review. Canadian Journal of Civil Engineering, 34(9): 1075-1086. August 2014 5. Auricchio, F; Fugazza, D and Desroches, R. 2006. Earthquake Performance of Steel Frames With Nitinol Braces. Journal of Earthquake Engineering, 10(Special 1): 45 – 66. Auricchio, F and Lubliner, J.January 2015. 6. Shape-memory-alloys: macromodelling and numerical simulations of the super-elastic behaviour. Computer Methods in Applied Mechanics and Engineering, 146: 281 – 312,August 2013 7. Desroches, R and Smith, B. 2003. Shape memory alloys in seismic resistant design and retrofit: a critical review of their potential and limitations. Journal of Earthquake Engineering, 7(3): 1-15.,2014 8. Dolce, M; Cardone, D and Marnetto, R. 2001. SMA re-centering devices for seismic isolation of civil structures. Proceedings of SPIE 2001. 4330: 238 – 249. Newport Beach, CA: SPIE.,2012 9.Goo, B and Lexcellent, C. 1997. Micromechanics-based modeling of two-way memoryeffect of a single crystalline shape-memory-alloy. Acta Materialia, 45: 727 – 737,july 2010


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