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Cyclic behavior of SMA slip friction damper
Abstract
This paper proposes a new type of self-centering (SC) damper which exploits the shape memory alloy (SMA) bolts and variable friction mechanism, termed the SMA slip friction damper (SMASFD). The theoretical equations governing the force–displacement relationship, the equivalent stiffness and the equivalent viscous damping are first derived. Then, the application potential of such damper is briefly discussed. In the experimental study, the results of the experimental validations of the SMA bolts and the friction mechanism are presented, followed by the results of proof-of-concept test on the fabricated SMASFDs. According to the testing results, the damper exhibited a symmetric tension–compression flag-shaped hysteresis characterized by excellent SC capacity and good damping capability. The prestrain treatment was applied to the SMA bolts in one test, which was found effectively increased the initial stiffness of the damper. To provide a further understanding on the damper and examine the stress and strain demands of the components, high-fidelity finite element models were established for numerical simulations. Both the analytical method and numerical simulation were validated by the experimental data.
... (1) SC dampers and braces (Dolce et al. 2005;McCormick et al. 2007;Zhu and Zhang 2008;Li et al. 2018;Qiu et al. 2022;Hu et al. 2024); (2) SC beam-column connections (Garlock et al. 2005;Wolski et al. 2009;Speicher et al. 2011;Asadolahi and Fanaie 2020); ...
... Figure 25 presents the elevation view of the three-story SC-CBF and SC-CBF-SB. Both the three-story and six-story frames have been adopted in the previous research (Sabelli 2001;Qiu et al. 2022). Table 5 presents the member sizes of the three-story SC-CBF and SB system. ...
... Table 5 presents the member sizes of the three-story SC-CBF and SB system. Other detailed information regarding the frame design can be obtained from the reference (Qiu et al. 2022). Similar to Sect. 8, nonlinear time history analyses of the three-story SC-CBF and SC-CBF-SB under the single ground motion and multiple ground motions were also conducted, and the corresponding results are presented in this Appendix. ...
Seismic-resistant self-centering concentrically braced frames (SC-CBFs) are susceptible to the concentration of inter-story drifts during earthquakes owing to the relatively low energy dissipation ability of braces. To address this limitation, this study proposed a novel solution by designing a strong backup (SB) system to mitigate inter-story deformation concentration in “weak” stories. The proposed SB system consisting of truss members can be attached to the existing SC-CBF through pin connections, forming a system, termed strong backup SC-CBF (SC-CBF-SB), to promote a more uniform distribution of inter-story drifts along the height of the frame and mitigate the weak story behavior. A six-story chevron-braced frame is adopted to investigate the seismic performance of SC-CBF and SC-CBF-SB. Finite element models of SC-CBF and SC-CBF-SB are built. The mechanical characteristics and dynamic responses of the SC-CBF-SB are examined. To comprehensively evaluate the performance of both SC-CBF and SC-CBF-SB, static pushover analyses and nonlinear time-history analyses are conducted. Additionally, incremental dynamic analysis (IDA) is performed to evaluate the responses (particularly drift concentration) of both frame types subjected to increasing seismic intensity levels. Numerical results show that the maximum value of the drift concentration factor (DCF) is around 1.3 and 1.8 for SC-CBF-SB and SC-CBF, respectively, indicating that SC-CBF-SB can effectively mitigate inter-story drift concentration of SC-CBF. Meanwhile, the proposed SB system has a minimal negative impact on the favorable SC ability of the frame.
... Li et al. [30] proposed a self-centering FD by connecting the SMA rods in parallel with the FD, and then the corresponding mechanical tests and parameter analysis were conducted. Chen and Qiu et al. [31,32] developed a self-centering variable FD in which the SMA elements provided the pre-tightening force for variable FD and drove the damper to recenter simultaneously. Zheng et al. [33,34] proposed a self-centering isolator with SMA to mitigate the seismic response of bridges. ...
... According to the literature [32], the mechanical properties of SMA tend to be s after cyclic tensile loading. Therefore, before the test of D-SCFD, the SMA rod with ameter of 4 mm was trained 20 times under equal-amplitude cyclic tensile loading, w made the mechanical properties of the SMA rod stable. ...
... According to the literature [32], the mechanical properties of SMA tend to be stable after cyclic tensile loading. Therefore, before the test of D-SCFD, the SMA rod with a diameter of 4 mm was trained 20 times under equal-amplitude cyclic tensile loading, which made the mechanical properties of the SMA rod stable. ...
Due to their weight, the seismic response control of buildings needs a large-scale damper. To reduce the consumption of shape memory alloys (SMAs), this study proposed a dual self-centering pattern accomplished by the coil springs and SMA, which could drive the energy dissipation device to recenter. Combined with the friction energy dissipation device (FD), the dual self-centering friction damper (D-SCFD) was designed, and the motivation and parameters were described. The mechanical properties of D-SCFD, including the simplified D-SCFD mechanical model, theoretical index calculations of recentering, and energy dissipation performance, were then investigated. The seismic response mitigation of the steel frame adopting the D-SCFDs under consecutive strong earthquakes was finally analyzed. The results showed that a decrease in the consumption of SMA by the dual self-centering pattern was feasible, especially in the case of low demand for the recentering performance. Reducing the D-SCFD’s recentering performance hardly affected the steel frame’s residual inter-story drift ratios when the residual deformation rate was less than 50%, which can help strengthen the controls on the steel frame’s peak seismic responses. It is recommended to utilize the D-SCFD with not too high a recentering performance to mitigate the seismic response of the structure.
... Recently, inspired by the works [22][23][24], the authors proposed a novel SMA damper, which is termed as SMA slip friction (SMASF) damper [25]. In the SMASF damper, the SMA bars do not directly offer SC and damping capability for the device, instead, they serve as nonlinear springs. ...
... where θ f is the angle of the sloped friction plates from the horizontal, as shown in figure 1(b). The analytical equations governing the loading and unloading behaviors of the damper are given as [25]: ...
... Notably, the friction coefficient can be assigned any value in theoretical research. In figure 3, the µ f values are in the range of 0-0.2, which cover the experimental values of 0.11 and 0.15 [25]. However, in practical applications, the actual µ f values should be carefully determined through experimental tests. ...
Owing to superelastic behavior, shape memory alloy (SMA) has been widely utilized to develop self-centering damping devices. Recently, the authors developed a novel SMA damper, i.e. the SMA slip friction (SMASF) damper. The cyclic behavior of the SMASF damper not only depends on the hysteresis shape factors of SMA bars, but also on the coefficient of kinetic friction and the slope of the friction plates. Hence, the basic working mechanism of the SMASF damper is different from that of conventional SMA dampers. In the early work, the features of the SMASF damper have been revealed by static cyclic loading tests. However, the seismic displacement responses of this novel damper remain unknown. To this end, this paper initiates with a brief introduction of the damper, including the configuration, working mechanism, and testing results. And then, extensive seismic analyses based on single-degree-of-freedom systems were conducted. Based on the constant-strength ductility demand spectra, the displacement responses of the SMASF damper were understood through the comparisons with conventional SMA damper and friction damper. A wide range of fundamental periods, strength capacities and seismic intensity levels were considered. Further, parametric analysis was conducted to assess the effect of the hysteresis shape factors of SMA bars and the coefficient of kinetic friction and the slope of the friction plates. This study also sheds light on the force-based seismic design method for this damper.
... Fateh et al. [23] explored hybrid dampers enhanced by friction mechanisms, showing how steel slit plates improved energy dissipation and seismic performance. Qiu et al. [24] studied shape memory alloy (SMA) slip friction dampers, which exhibited excellent energy dissipation and re-centering capabilities. Additionally, Veismoradi et al. [25] developed self-centering rotational friction dampers, demonstrating their effectiveness in improving overall damping capacity. ...
The research focused on enhancing the seismic performance of steel moment frames using cable braces and a central friction damper. By optimizing the design and pretensioning force of the cable braces, this study aimed to improve the energy absorption and overall behavior of the frames under cyclic earthquake loads. A quasi-cyclic loading test was developed through FE simulations using ABAQUS software, version 2023. To verify the modeling, an experimental test was compared with the numerical modeling, and the numerical results confirmed the accuracy of the experimental data. Results made by modeling in ABAQUS software (version 2023) include the impact of pretensioning force on stiffness and energy absorption, the relationship between pretensioning force and force required to move the target, the increase in absorbed energy with pretension force up to 25%, and the superior seismic performance of frames with rotational friction dampers. This study also highlighted the benefits of using cable braces with a friction damper regarding the symmetry of hysteresis diagrams, cyclic performance, and energy absorption capacity. The amount of pretensioning of the cables affects the energy dissipation capacity. As the pretensioning of the cables increases, the energy dissipation capacity initially increases. However, further increases in pretensioning lead to decreased energy dissipation capacity beyond a certain point. When the percentage of cable brace pretension increases from 2% to 25%, the energy dissipation capacity is enhanced by 2%, and when in the 25–30% range, it stabilizes at around 35%. Energy dissipation capacity decreases for pretensions of more than 30%.
... These findings provide new ideas for improving damping performance in complex systems [10]. Advances in new materials have led to the development of memory alloy (SMA) slip friction dampers and metal dampers with higher energy dissipation efficiency [11,12]. Active damping is generally realized either through the parallel connection of an actuator and a passive damper or by using driving power with active control algorithms. ...
Micro-vibrations during the operation of space remote sensing equipment can significantly affect optical imaging quality. To address this issue, a bellows-type viscous damper serves as an effective passive damping and vibration isolation solution. This paper introduces a bellows-type viscous damper with adjustable damping capabilities, designed for mid- to high-frequency applications. We developed a system damping model based on hydraulic fluid dynamics to examine how different factors—such as viscous coefficients, damping hole lengths, hole diameters, chamber pressures, and volumes—influence the damping characteristics. To validate the theoretical model, we constructed an experimental platform. The experimental results show that the theoretical damping curves closely match the measured data. Moreover, increasing the chamber pressure effectively enhances the damper’s damping coefficient, with the deviation from theoretical predictions being approximately 4%.
... The existing studies have mainly focused on using the super-elastic property of NiTi SMAs to improve the selfcentering property of the structure (the flag-shaped behavior) [16][17][18][19][20][21]. Super-elastic application of NiTi SMAs is usually accompanied with two deficiencies. ...
This study proposes a novel triangular added damping and stiffness (TADAS) damper that uses the shape memory effect of iron-based shape memory alloy (Fe-SMA) to provide a self-centering system to recover the initial shape of a structure after significant inelastic deformation induced by nonlinear response of fused elements, without the need for difficult and expensive replacement procedures of conventional TADAS systems. Unlike most studies which consider simplified uniaxial behavior of Fe-SMAs, the present non-linear finite element simulations cover the full 3D material non-linearity of Fe-SMA component based on the SMA constitutive law to capture both flexural and shear behavior in various coupled thermomechanical loadings, including the mechanical loading/unloading, the heating, and the final cooling (as the recovering process). Simulations performed on a one-bay steel frame for different drift ratios reveal that although the dissipation energy of the new device is at most 10% less than the ordinary one, it enjoys the self-centering property to recover the initial shape of the frame before loading, showing that the proposed damper is an effective alternative to ordinary TADAS yielding dampers to achieve the self-centering characteristics.
... Hyperelasticity coefficients The typical flag-shaped constitutive behaviour of pseudoelastic SMA under isothermal conditions has been modelled through the combination of elasticity (for the austenite phase) and superelasticity (for the martensite phase) using a built-in material model based Auricchio and Taylor's work [24,25]. This model has been widely adopted in the literature and has accurately reflected the mechanical behaviour of Ni-Ti based SMA bars [26][27][28]. The material parameters used to model the superelastic SMA have been extracted from the first load-unload cycle of the experimental stress-strain curve and are presented in table 3. Table 3. Material properties for pseudoelastic SMA. ...
Inter-module connections (IMCs) play a crucial role in the structural behaviour of steel Modular Building Systems (MBSs) by ensuring the vertical and horizontal load-transfer paths between modules, yet existing designs display limited disassembly opportunities and lack damage control features. This study introduces a novel, hybrid demountable IMC comprising bespoke corner fittings, a resilient high-damping rubber core and a shape-memory alloy (SMA) bolt. Proof-of-concept connection tests have been carried out using validated, continuum finite element analysis (FEA) to determine the mechanical behaviour of the proposed IMC with respect to the main deformation modes expected to occur in the joints of tall steel MBSs under the combined effect of vertical and horizontal loading. Main findings show that both the HDR core and the SMA bolt contribute effectively to the overall hybrid response of the IMC under tension and combined compression and shear loading, preventing the formation of significant plastic damage in the MBS’s corner fittings to facilitate reusability of modules.
... Various SC strategies have been investigated, e.g. SC connections [16][17][18], braces [19][20][21][22][23][24][25][26], rocking cores [27], walls [28][29][30], and others [31][32][33]. Each of these SC technologies showcases a flag-shaped hysteresis to furnish SC force and alleviate RIDs in structures. ...
... To further enhance the energy dissipation capacity of SMA-based self-centering devices, researchers have begun to explore the development of hybrid devices that combine additional energy dissipation mechanisms with SMAs. These additional energy dissipation mechanisms primarily include frictional damping [36][37][38][39][40], viscoelastic damping [35,[41][42][43], and metal yielding [20,44], among others. For example, Ke et al. [38] developed a novel self-centering damper, mainly consisting of a wedge-shaped friction mechanism and SMA bolts, which utilizes frictional deformation to drive the deformation of SMA bolts, thus achieving self-centering performance. ...
This paper investigates the seismic performance enhancement of steel frame buildings using a novel hybrid self-centering braces (HSBs) under extremely rare earthquake events. The hybrid self-centering brace consists of shape memory alloy (SMA) cables and viscoelastic (VE) dampers. A prototype bracing system is designed and fabricated to explore its basic mechanical behavior and working mechanism under cyclic loading, with a focus on its failure modes under large deformation loading condition. A multi-material mechanical model is developed to capture the mechanical behavior and failure of the HSB. Furthermore, five steel frame buildings with different parameterized HSBs are designed and modeled in OpenSees. Nonlinear dynamic analyses and incremental dynamic analyses are conducted on the five case-study frames using 44 far-field ground motions. The risk-based seismic performances of steel buildings with HSB are evaluated to assess the performance of HSB during extremely rare seismic events. The results show that the hybrid self-centering brace exhibits excellent self-centering and energy dissipation capabilities with the maximum equivalent viscous damping ratio reaching 9.4%. Even under large deformations, VE dampers continue to work effectively after the failure of SMA cables, demonstrating remarkable redundancy. Numerical simulations further reveal that the redundancy of HSB can improve the structural seismic resilience in terms of inter-story drift ratio, residual drift, and floor absolute acceleration. The higher the redundancy of HSB in the case-study frames, the smaller the seismic response and mean annual frequency of exceedance of the engineering demand parameters, thereby indicating a significant improvement in seismic performance.
... The SMA rods combined with a steel core significantly increased the self-centering capacity of the brace and reduced the permanent drift response of the BRBFs. Furthermore, an SMA-based self-centering damper was proposed by Qiu et al. [22]. According to the testing results, the damper exhibited a symmetric tension-compression flag-shaped hysteresis characterized by excellent SC capacity and good damping capability. ...
The major concerns of buckling-restrained braced frames (BRBFs) are the low post-yield stiffness and excessive residual displacement, which can delay the post-earthquake recovery procedure and enhance the repair cost. The current numerical work presents an innovative buckling-restrained brace (BRB) including a reduced-length hybrid core that is attached to a robust steel pipe. The core is laterally supported and consists of a shape memory alloy (SMA) rod inserted into a steel pipe. The paper represents a detailed description of the proposed device. The performance of the proposed BRB is numerically investigated at the component level using the ABAQUS finite element package. Subsequently, the system-level response of the proposed device is investigated by nonlinear static pushover and dynamic time history analyses in the OpenSEES environment. The results demonstrate that the proposed device shows a two-stage yielding mechanism, benefits the combined hysteretic responses of the SMA and the steel cores, and exhibits a stable and symmetric cyclic behavior with a nearly flag-shaped hysteresis. Furthermore, compared with conventional BRBs, the proposed device reduces the maximum inter-story and particularly the problematic residual drift responses of the BRBFs. Additionally, by an increase in the total area of the SMA core, though the maximum inter-story drift response is slightly increased due to the low elastic modulus of the SMA material, the residual drift response of the BRBFs is further decreased.
The tension-only braced frame has been confirmed as an innovative seismic resilient structure. Moreover, the repair procedure after the seismic action is greatly simplified as to only re-tighten the loosening braces by screwing the turn-buckle device. The excellent seismic performance, and the low repair cost refers to its great potential in the massive engineering praxis. Thus, this paper presents experimental and numerical studies on the seismic and post-repair performance of a tension-only concentrically braced steel beam-through frame. Three cyclic loading tests are performed to explore the hysteretic behaviors and failure modes, after re-tightening the tension-only braces. The testing results suggest that the hysteretic patterns are jointly affected by the plastic hinge in the bolted connections of the bare frame and the tension-only braces. The tension-only characteristic results in pinched hysteretic loops oriented towards maximum deformation. The testing frames exhibit excellent ductility, with the resistance degradation of roughly 4.5 % under the drift of 5 %. Moreover, re-tightening the tension-only braces after experiencing maximum drifts of 1 % successfully restores initial stiffness and yield resistance, without significant sacrifice in ductility. This confirms the excellent deformability and repairability of the tension-only braced frame. Additionally, a simplified modeling method based on OpenSees is proposed. In terms of the bolted connections, the Hysteretic-Elastic Parallel model is used to characterize the pinched hysteretic loops with adjustable re-yielding point. The tension-only behaviors is described by the Elastic-Perfectly Plastic Gap model. Furthermore, a new modeling technique for the re-tightening procedure is proposed using element replacement and the initial strain command in OpenSees. Compared to testing results and simulations based on the refined model in Abaqus, the simplified models are validated in terms of hysteretic loops for three loading cases, considering the re-tightening repair, as indicated by low percentage errors for skeleton curves as 4.84 % and yield strength as 6.70 %.
Shape Memory Alloy (SMA) cables have emerged as promising materials for self-centering devices owing to its remarkable self-centering ability and good energy dissipation capacity. However, the impact of SMA cables on the mechanical behavior of hybrid self-centering devices, particularly concerning pre-tension forces, has not been extensively explored through experimentation. In light of this, this study takes the recently proposed hybrid self-centering brace (HSB) as an example, which comprises Viscoelastic (VE) dampers and SMA cables in parallel, to further investigate its mechanical behavior through in-depth experimental tests. Firstly, the configuration and working mechanism of the HSB are elucidated, and the formulas for calculating its mechanical parameters are derived. Then, three HSB specimens are designed and manufactured, each possessing different parameters for SMA cables but identical parameters for VE dampers. Next, cyclic loading tests are carried out to examine the hysteretic responses of these three HSBs. The focus is on revealing the influence of different quantities and pre-tension forces of SMA cables on the mechanical behavior of HSB, as well as examining the loss of pre-tension force in SMA cables during the testing process. The research findings demonstrate that the working mechanism of HSB is experimentally validated, and that training contributes to achieving more stable mechanical behavior in HSB. HSB exhibits excellent recoverability, with the hysteretic curves overlapping substantially in two identical loading tests, with a maximum decrease of only 8.6 % in various mechanical properties. The greater the quantity and pre-tension force of SMA cables, the higher the initial stiffness and activation force of HSB, while the transition stiffness and residual deformation are smaller. Trained HSB specimens show a noticeable reduction in pre-tension of SMA cables in the first cycle of subsequent cyclic loading, averaging around 28 %, which shall be carefully considered in the future applications of HSB.
Abstract: This paper reports an experimental and analytical investigation on a novel self-centering damper. The damper is characterized by a multistage energy-dissipation mechanism, which is desirable for multi-performance-based seismic designs. The conceptual design, working mechanism, assembling process and hysteretic performance of the proposed damper are presented. The fundamental mechanical behavior of each component of the damper was examined experimentally. Then a series of cyclic tests of damper specimens was conducted, focusing on the influence of the preload of the shape-memory alloy (SMA) bolts, the SMA bolt type, and the sloping angle of the wedge-shaped friction plates on the damper performance. An analytical model is proposed for quantification of the hysteretic behavior of the damper. The test results showed that the damper specimens exhibited the expected multistage energy-dissipation characteristics and stable flag-shaped hysteretic curves with full self-centering behavior. A good energy dissipation capacity with an equivalent viscous damping (EVD) of about 20% was
observed, which basically was consistent over the entire loading stages. The overall behavior of the damper was related closely to the aforementioned test parameters, indicating that the damper performance can be adjusted flexibly according to various seismic design requirements. The analytical predictions and the test results of the damper were in good agreement, indicating that the developed analytical model can be used confidently by engineers for the design of the developed damper.
This paper presents coupled structures based on a nonlinear hysteresis friction damper subjected to harmonic forces for vibration suppression. The steady-state responses of the structures are obtained by the Runge–Kutta method and the harmonic balance method, which describe the hysteretic nonlinearity of friction dampers and exhibit their attenuation performance. The forced response is well controlled by the normal force applied to the friction damper, and the amplitude and frequency of the resonance peaks can be varied within a certain range by changing force magnitude. The time-averaged vibrational power is calculated to show the total input power and power dissipated by each element. The results indicate that the friction damper participates in the energy dissipation in the frequency band around the resonance frequency, thereby enabling high-amplitude vibration filtering. The vibration power flow analysis shows that the normal force for the friction element can be designed to reduce vibration transfer. These results confirm that such friction dampers have the potential to be designed to be adjustable and meet different vibration control objectives.
This study explores comparative seismic performance of a shape memory alloy (SMA)-only device, a friction damper, and a hybrid self-centering device. The self-centering device considered in this study, named as superelastic friction dampers (SFDs), is a hybrid damper operating on a mechanism where SMA cables and frictional components are arranged in parallel. A detailed description of the device and an experimental characterization of mechanical behavior are presented first. Then, an 8-story archetype steel frame building is designed and modeled with each seismic protection device (SMA-only, hybrid self-centering, and friction only). To enable comparative performance assessment, each device is designed to have similar initial stiffness and the same maximum force at design displacement. Nonlinear time history analyses are conducted using a total of 44 ground motion records. The results are evaluated to compare performance of each frame design at design-basis and maximum considered earthquake hazard levels. Next, a risk-based seismic hazard demand analysis framework that involves comprehensive incremental dynamic analyses is employed for further assessing the performance of each system. The experimental results validate the parallel working mechanism of SMA cables and frictional components in the SFD, with 90% of the damper deformations recovered. Comparative analysis of seismic responses demonstrates the excellent performance of the SFDs in reducing interstory drift ratio, residual interstory drift ratio, and absolute acceleration responses. Furthermore, fragility analysis and risk-based seismic hazard assessment further reveal that the SFDs provide a well-balanced combination of energy dissipation capability and self-centering ability, thereby enhancing the seismic resilience of structures.
In this study, a novel passive hybrid damper based on combinations of shape memory alloy (SMA), steel and glass fiber-reinforced polymer (GFRP) was introduced. The hysteretic properties of both SMA and steel and reversibility effect of both SMA and GFRP rods provide a superior passive damping device to dissipate large amounts of input excitation energy besides superior re-centering characteristics. A series of experiments to achieve material properties were carried out with the aim to incorporate accurate properties of triple materials utilized in analytical model. The non-dominated sorting genetic algorithm II was applied to evaluate the quantity of proportionality for each material used in the device, in terms of increasing energy absorption, improving reversibility and reducing manufacturing costs. Then, the optimal damper was constructed and tested based on results obtained from analytical modeling. The results showed the high efficiency of proposed hybrid damper to attain mentioned multi-objective goals. Subsequently, the application of damper in a prototype structure was investigated. The results of the analyses showed that the use of the damper has a significant effect on reducing seismic effects. Therefore, the damper can be used as a superior low-cost device in a retrofitting program for various types of structural systems in new and existing deficient buildings in earthquake-prone regions.
This study proposed a novel V-bracing system equipped with a laterally layered friction damper (LLFD), which can supplement the shortcomings of conventional vibration control systems and is applicable to existing reinforced concrete (R/C) buildings. A material test was used to evaluate the material performance and energy dissipation capacity of this LLFD. Pseudo-dynamic testing was conducted on two-story frame specimens based on an existing R/C building with non-seismic details to verify the seismic retrofitting effects of applying the LLFD V-bracing system to existing R/C frames, i.e., the restoring force characteristics, energy dissipation capacity, and seismic response control capacity. Based on the results of the material and pseudo-dynamic tests, restoring characteristics were proposed for the non-linear dynamic analysis of a building (frame specimen) retrofitted with the LLFD V-bracing system. A non-linear dynamic analysis was conducted based on the proposed restoring force characteristics, and the results obtained were compared with the pseudo-dynamic test results. Finally, for evaluating the commercialization potential of the LLFD V-bracing system, a non-linear dynamic analysis was conducted on an existing R/C building with non-seismic details retrofitted with the system. The seismic retrofitting effect was verified by examining the seismic response load and displacement characteristics, energy dissipation capacity, and damper load and displacement response before and after seismic retrofitting. The study results showed that the R/C frame (building) with non-seismic details exhibited shear failure at a design basis earthquake scale of 200 cm/s2; however, light seismic damage could be expected for a frame (building) retrofitted with the LLFD V-bracing system. At a maximum considered earthquake scale of 300 cm/s2, insignificant seismic damage was also anticipated, thereby verifying the validity of the newly developed LLFD V-bracing system.
The utilization of shape memory alloys (SMAs) to reinforce steel structures has been proven to be an efficient and reliable method, the structural strengthening needs can be met without the need for tensioning equipment by activating the SMAs to generate restoring stresses. This paper firstly introduces the properties of SMA, and then presents the latest research progress, opportunities and challenges of SMA in the field of steel structural reinforcement, both in terms of basic components and applications. In terms of components, the construction forms and working mechanisms of Fe-SMA strips, SMA/CFRP composite patches and SMA dampers are introduced. On this basis, the application of SMA in steel structures reinforcement is introduced, and its effect is analyzed from three aspects: crack restoration, seismic retrofitting and structural strengthening. Finally, the results of the current research are summarized and the shortcomings are analyzed, hoping to provide a reference for the research of SMA in the field of steel structures reinforcement.
Shape memory alloys (SMAs) gained increasing attentions from the perspective of seismic protection, primarily because of their excellent superelasticity, satisfactory damping and high fatigue life. However, the superelastic strain of SMAs has an upper limit, beyond which the material completes the austenite to martensite phase transformation and is followed by noticeable strain hardening. The strain hardening behavior would not only induce high force demand to the protected structures, but also cause unrecoverable deformation. More importantly, the SMAs may fracture if the deformation demand exceeds their capacity under severe earthquakes. In the case of installing SMA braces (SMABs) in the multi-story concentrically braced frames (CBFs), the material failure would lead to the malfunction of SMABs and this further causes building collapse. The friction mechanism could behave as a “fuse” through capping the strength demand at a constant level. Therefore, this paper suggests connecting the SMAB with a friction damper to achieve a novel brace, i.e. the SMA-friction damping brace (SMAFDB). A proof-of-concept test was carried out on a homemade specimen and the test results validated the novel brace behaves in a desirable manner. In addition, to explore the seismic response characteristics of the SMAFDB within structures, a six-story CBF equipped with SMAFDBs was designed and compared against those incorporated with SMABs or friction damping braces (FDBs) at the frequently occurred earthquake (FOE), design basis earthquake (DBE) and maximum considered earthquake (MCE). The comparative results show the SMAFDB is superior to the counterparts. Under the FOE and DBE ground motions, the SMAFDBs successfully eliminated residual deformations as the SMABs do, and achieved identical maximum interstory drift as the FDBs. Under the MCE ground motions, the SMAFDBs not only well addressed the brace failure problem that was possibly encountered in the SMABs, but also better controlled residual deformation than the FDBs.
This study proposes a new type of self-centering damper equipped with novel buckling-restrained superelastic shape memory alloy (SMA) bars. The new solution aims to address some critical issues related to degradation and loss of superelasticity observed in existing tension-only SMA-based self-centering devices, and in addition, to encourage enhanced material utilization efficiency. The cyclic tension-compression behavior of individual SMA bars is experimentally studied first, and subsequently, two proof-of-concept self-centering dampers are manufactured and tested. A simple yet effective numerical model capturing the flag-shaped response of the dampers is then established, and a preliminary system-level analysis is finally conducted to demonstrate the effectiveness of the proposed damper in structural seismic control. The individual SMA bar specimens show asymmetrical flag-shaped hysteretic responses with satisfactory self-centering capability and moderate energy dissipation. Through a specially designed configuration, the proposed damper shows desirable symmetrical and stable hysteretic behavior, and maintains excellent self-centering capability at 6% bar strain. The system-level dynamic analysis indicates that the dampers, as a means of retrofitting, could effectively reduce both the peak and residual inter-story drift ratios of a six-story steel frame. In particular, the mean residual inter-story drift ratio is reduced from over 0.5% to below 0.2% under the maximum considered earthquake, implying elimination of necessary structural realignment even after strong earthquakes.
With the goal to assess its effectiveness in structural vibration suppression under strong seismic excitations, this paper experimentally investigates shaking table tests of a new superelastic shape memory alloy friction damper (SSMAFD). The damper consists of pre-tensioned superelastic shape memory alloy (SMA) wires and friction devices. The main function of SMA wires is to provide re-centering capacity, while the integrated friction devices provide the most energy dissipation. With the inherent damping property, the superelastic SMA wires also provide energy dissipation. In the shaking table tests, a scaled-down building structure were used as the subject for vibration control and several representative seismic signals as well as white noise motions were used as the inputs. Comparative studies of dynamic behaviors, i.e. story displacements, interstory drifts and story accelerations, of the structural model with and without SSMAFD under seismic loading were performed. The experimental results demonstrated that the SSMAFD was effective in suppressing the dynamic response of the building structure subjected to strong earthquakes by dissipating a large portion of the energy. In addition, with the re-centering capacity of the proposed damper, the structure was able to undergo strong earthquakes without remarkable residual drift under different seismic loads.
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.
Shape memory alloys (SMAs) are special materials with a substantial potential for various civil engineering applications. The novelty of such materials lies in their ability to undergo large deformations and return to their. undeformed shape through stress removal (superelasticity) or heating (shape-mernory effect). In particular, SMAs have distinct thermomechanical properties, including superelasticity, shape-memory effect, and hysteretic damping. These properties could be effectively utilized to substantially enhance the safety of various structures. Although the high cost of SMAs is still limiting their use, research investigating their production and processing is expected to make it more cost-competitive. Thus, it is expected that SMAs will emerge as an essential material in the construction industry. This paper examines the fundamental characteristics of SMAs, the constitutive material models of SMAs, and the factors influencing the engineering properties of SMAs. Sorne of the potential applications of SMAs are discussed, including the reinforcement and repair of structural elements, prestress applications, and the development of kernel components for seismic devices such as dampers and isolators. The paper synthesizes existing information on the properties of SMAs, presents it in concise and useful tables, and explains different alternatives for the application of SMAs, which should motivate researchers and practicing engineers to extend the use of SMAs in novel and emerging applications.
A novel hybrid frictional metallic passive damper is introduced in this study. The Piston Hybrid Frictional Metallic Damper (PHFMD) is equipped with friction pads and steel variable-width strips as energy dissipating parts. These parts are put in the final assembly of the damper with the aid of connectors and rigid parts. The PHFMD characterizing parameters have been determined based on comprehensive experiments. At first, a setup is designed to test the response of friction pads at different clamping torque. The experimental data approves the applicability of the pads in terms of the stability of their hysteretic response. At the second stage, cyclic loads have been applied to three different PHFMD specimens. These specimens are specially designed to exhibit single-phase (PHFMD-A and PHFMD-B) and dual-phase (PHFMD-C) response when subjected to displacements. In the case of dual-phase response, the first phase’s capacity will be activated in case of wind or light to moderate earthquake excitations. In case of severe earthquakes, the full capacity of the dual-phase damper will be mobilized to mitigate earthquake impact on the structure. The experimental results approve the significant performance of the dampers in fulfilling design goals. The performance parameters include the achievable cumulative displacement, dissipated energy, and effective equivalent viscous damping ratio. It is observed that all the specimens have endured accumulated displacement of over 2000 mm (reaching near 4000 mm for the PHFMD-C specimen) while dissipated a significant amount of energy. The specimens also have demonstrated significant viscous damping ratios in the range 45–55%. None of the dampers has shown any degradation or damage when subjected to standard loading protocol. In order to provide a means for the analysis, FE models of dampers have also been developed. Comparison of FE results and experimental data show remarkable agreement. Finally, FE-verified analytical relations are provided for the design purposes of single-phase and dual-phase PHFMDs.
Post-tensioned hybrid coupled wall system has desirable seismic characteristics including self-centering capability and tolerance for large nonlinear displacements with limited damage. In this study, the behavior of concrete coupled wall subassemblies with post-tensioned steel coupling beam was experimentally evaluated. In this system, the coupling beam is not embedded into the walls, and the coupling of the concrete walls is accomplished by post-tensioning the steel coupling beam to the walls using unbonded post-tensioning strands. Steel angles and friction dampers were used at the beam-to-wall connection region for energy dissipation. In the first series of tests, a friction damper with different values of the clamping force was tested under two different loading frequencies. In the second series, seven quasi-static cyclic tests were conducted on 2/3-scale subassemblies of the post-tensioned hybrid coupled wall system. The test specimens included a control specimen without energy dissipation device, a specimen with steel angles and four specimens with friction dampers. In addition, one of the tested specimens with dampers was re-tested to investigate the structural behavior and residual capacity of the system during a strong aftershock. The test parameters included the type of energy dissipation device, the initial stress of post-tensioning strands and the amount of damper normal force. The test results show that the subassemblies equipped with friction dampers exhibit excellent lateral stiffness, strength, ductility and energy dissipation and are capable of withstanding large nonlinear cyclic deformations up to the drift of 8%, without residual displacements and without significant damage to the system. Whereas the subassembly equipped with steel angles provide lower energy dissipation capacity and because of the low-cycle fatigue fracture of angles, energy dissipation and load carrying capacities of the specimen decrease significantly.
A novel self-centering cable brace (SCCB) with friction devices is developed to improve the seismic performance of existing RC frame structures. This paper presents the structural configuration and the theoretical load-displacement relationship of the SCCB. Cyclic loading tests are conducted to show the effectiveness of the SCCB, and a numerical model is established and validated based on the test results. A parametric analysis is made to investigate the influence of tendon stiffness and friction on hysteretic performance of the SCCB. Nonlinear dynamic analyses are further carried out on a nine-story RC frame, which is seismically deficient and enhanced with buckling restrained braces (BRBs) and SCCBs respectively for comparison. Inter-story and residual inter-story drifts, base shear forces, load-axial elongation relationships and self-centering indexes of the bare and strengthened frames are obtained and compared. It is found that both the SCCBs and BRBs increase the seismic capacity, while the SCCBs can reduce the maximum story drifts more significantly and have much less residual story drifts than BRBs.
This paper presents a novel type of self-centering energy dissipative device equipped with superelastic shape memory alloy (SMA) ring springs. The fundamental mechanical behavior and analytical solutions for individual SMA rings are first presented, which is followed by a detailed introduction of the working mechanism and fabrication process of the proposed device. Two prototype specimens, varying in the size of their SMA rings, are tested, where the stiffness, strength, self-centering capability, and energy dissipation characteristics are examined in detail. In particular, the behavior of the devices under repeated rounds of testing is evaluated to understand their resistance to strong aftershocks or multiple earthquakes. The specimens are shown to exhibit flag-shaped load-deformation hysteretic behavior with excellent self-centering capability and satisfactory energy dissipation with an equivalent viscous damping ratio of up to 20%. Due to a preload applied to the SMA ring springs, the devices have an initial yield resistance of around 90 kN and initial stiffness of approximately 225 kN/mm. No damage to any component of the devices is observed, although certain degradations of the yield resistance are exhibited. To effectively capture the key behavior of the devices, a design model is finally proposed that is shown to be in good agreement with the test results. Some limitations of the proposed model are also identified.
Marine structures, as key elements in the global energy network, constantly are subjected to harsh environmental
loading conditions. Therefore, reliable yet efficient structural control mechanisms are required to ensure
their safe functionality and structural stability. In the present work, a novel hybrid structural control element for
marine structures has been designed in which the superelasticity effect of shape memory alloy (SMA) and
damping controllability of magnetorheological fluid (MRF), as smart materials, have been combined. The novel
system does not require huge external energy for activation and in addition, the system has the ability to be
tuned for variable loading conditions. To show the functionality of the proposed control system, the performance
of a simplified marine structure equipped with the present novel control system is evaluated by simulating the
response of a sample structure under three scaled ground motions, namely, Christchurch, Imperial Valley,
Parkfield. The results are compared to structures with the SMA-based system and structures with the MRF-based
control system. It is observed that the present hybrid SMA-MRF control system significantly improves the performance
of marine structures under seismic loadings.
Steel moment-resisting frames are popular structural systems used extensively around the world. However, conventional column base connections are vulnerable to large residual deformation after strong earthquakes. By contrast, shape memory alloys (SMAs), which are high-performance metallic materials, can experience large strains and still recover their initial shape through either heating (shape memory effect) or unloading (superelastic effect). The superelastic behavior of SMAs is appealing to the earthquake engineering community because of the material's excellent self-centering (SC) and energy dissipation capabilities. In this paper, a novel type of steel columns equipped with NiTi SMA bolts was introduced and its potential for achieving earthquake resilience were investigated. Structural details of the column base and mechanical properties of the SMA bolts were described first. Subsequently, an analytical model of the SC column for different limit states and the corresponding design procedure were presented. The seismic behaviors of two steel column specimens were experimentally tested to investigate the effects of the initial prestrain in the SMA bolts and the axial compressive force in the column under cyclic loading. Results showed that the steel columns equipped with SMA bolts exhibited satisfactory and stable flag-shaped hysteresis loops with excellent SC and moderate energy dissipation capabilities. More importantly, SMA bolts with prestrain could still be tightened after removal of lateral force. Therefore, the proposed SC column could achieve seismic resilience design that requires no (or minimal) repair even after strong earthquakes and remains highly functional for aftershocks or future earthquakes. In addition, the analytical model was verified through a comparison with test results obtained at key limit states.
Allowing a wall to rock and uplift during a seismic event can cap the forces and minimize the postevent residual damage. Slip friction connections comprised of flat steel plates sliding over each other have been experimentally tested as the hold-down connectors in timber shear walls and performed well in terms of the hysteretic behavior and the energy dissipation rate. However, the main disadvantage of these joints is the undesirable residual displacements. In recognition of this fact, a novel type of friction joint called a resilient slip friction (RSF) joint is proposed. The innovative configuration of this joint provides the energy dissipation and self-centering behavior all in one compact package. This paper describes the large-scale experimental test conducted on a rocking cross-laminated timber (CLT) wall with RSF joints as the hold-down connectors. Additionally, a series of capacity equations are presented and validated by comparing the analytical results with the experimental data. The results confirmed that this technology has the potential to provide a robust solution for seismic-resilient structures.
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.
A review of permissible residual deformation levels is undertaken in light of the increased interest in performance-based seismic design and self-centering systems. Permissible residual deformation levels are considered based on functionality, construction tolerances, and safety. Values are defined based on a review of past structural engineering research, post-earthquake reconnaissance, current building codes, and research in the field of psychology. The findings show that there are only a limited number of studies that measured residual drift levels of structures after an earthquake and correlated these to actual damage levels. In general, construction tolerances remain at or below 0.003 rad depending on the type of structural system and material being considered. This value is below the residual drift levels at which non-structural systems start to lose functionality. Research in the field of psychology has also shown that the lower limit at which people can sense an inclination is approximately 0.005 rad above which extended periods of inclination can cause headaches and dizziness. In order to verify these findings and provide further quantitative results, floor inclinations and column tilt of an occupied 40 year old structure are investigated. These results combined with those obtained through the extensive literature review suggest that 0.005 rad is an important engineering index in terms of permissible residual deformation levels.
Although Ni–Ti has been recognized as a promising type of shape memory alloys (SMAs) for seismic response mitigation devices in civil structures, its temperature-dependent mechanical behavior prevents its practical use in cold temperature environment. This study experimentally characterizes the cyclic properties of monocrystalline (also known as single-crystal) Cu–Al–Be SMA wires. The emphasis is put on those properties of common interest in seismic applications, e.g. “yield” stress, energy dissipation capability, stabilization of hysteretic shapes (also known as training effect), sensitivity to loading frequency and ambient temperature, large-strain fatigue, and so on. The testing results of another two types of SMA wires, namely Ni–Ti and polycrystalline Cu–Al–Be wires, are also presented for comparison. The monocrystalline Cu–Al–Be specimens show great superelastic strain of up to 23%. Insignificant degradation of transformation stress or accumulation of residual deformation is observed with increasing number of loading cycles. Meanwhile, their cyclic properties show minimal sensitivity to the variation of applied loading frequency or ambient temperature. The tested specimens maintain stable superelasticity down to −40 °C. Compared with Ni–Ti SMAs, the monocrystalline Cu–Al–Be SMA wires are found to be superior in both superelastic capacity and cold-temperature performance and have comparable performance in terms of fatigue, training effect and energy dissipation. Moreover, these wires also have significantly higher superelastic capacity than polycrystalline Cu–Al–Be or other copper-based SMAs. This experimental study proves that monocrystalline Cu–Al–Be SMA has good potential for seismic applications, which is particularly favorable in outdoor environment with cold winter. Additionally, the hysteresis of monocrystalline Cu–Al–Be wires exhibits remarkable dependence on strain amplitude and complex internal loops. This fact necessitates the future development of more sophisticated constitute models for their complex superelastic behavior.
A half-scale interior beam-column connection incorporating superelastic nickel-titanium shape memory alloy (SMA) tendons was designed, fabricated, and tested to assess the feasibility of such a connection in a moment-resisting frame. This connection was compared to three other connections utilizing tendons made of steel, martensitic nickel–titanium, and superelastic nickel–titanium paralleled with aluminum. The connections with steel and martensitic nickel–titanium tendons rapidly lost their stiffness after being cycled beyond their elastic drift levels. The two tests with the superelastic nickel–titanium tendons showed significant recentering capabilities; they recovered a large portion of the post-elastic drift and showed promise for a material-based recentering moment connection. This novel connection was intended as a proof of concept that can be further developed in terms of practicality, ease of installation, and cost.
This tutorial/survey paper: (1) provides a concise point of departure for researchers and practitioners alike wishing to assess the current state of the art in the control and monitoring of civil engineering structures; and (2) provides a link between structural control and other fields of control theory, pointing out both differences and similarities, and points out where future research and application efforts are likely to prove fruitful. The paper consists of the following sections: section 1 is an introduction; section 2 deals with passive energy dissipation; section 3 deals with active control; section 4 deals with hybrid and semiactive control systems; section 5 discusses sensors for structural control; section 6 deals with smart material systems; section 7 deals with health monitoring and damage detection; and section 8 deals with research needs. An extensive list of references is provided in the references section.
Measurements of instantaneous coefficients of friction and associated motions during start-up at a planar contact are presented for four different lubrication conditions. The various patterns of transient behavior are discussed. Difficulties in interpreting static friction coefficients during rapidly applied tangential loads are described in relation to the motion data. It is shown that a molybdenum disulphide grease yields a friction characteristic that is quite different from either dry or boundary lubricated conditions in the presence of liquid lubricants. Transition distances from a static or maximum initial friction to kinetic conditions are examined and found to be considerably longer than had been previously found for concentrated contacts.
A recent study has shown that residual drifts after earthquakes that are greater than 0.5% in buildings may represent a complete loss of the structure from an economic perspective. To study the comparative residual drift response of special moment-resisting frames (SMRFs) and buckling-restrained braced (BRB) frames, buildings between 2 and 12 stories in height are designed according to ASCE 7-05 and investigated numerically. This investigation includes pushover analyses as well as two-dimensional nonlinear time-history analyses for two ground motion hazard levels. The two systems show similar peak drifts and drift concentration factors. The BRB frames experience larger residual drifts than the SMRFs; however, the scatter in the residual drift results is large. Expressions are proposed to estimate the residual drifts of these systems as a function of the expected peak drifts, the initial recoverable elastic drift, and the drift concentration factor of each system. When subjected to a second identical earthquake, both framing systems experienced larger-than-expected drifts when an initial drift greater than 0.5% was present. DOI: 10.1061/(ASCE)ST.1943-541X.0000296. (C) 2011 American Society of Civil Engineers.
Buildings designed according to modem seismic codes are expected to develop a controlled ductile inelastic response during major earthquakes, implying extensive structural damage after a design level earthquake, along with possibly substantial residual deformations. To address this drawback of traditional yielding systems, a new bracing system that can undergo large axial deformations without structural damage while providing stable energy dissipation capacity and a restoring force has recently been developed. The proposed bracing member exhibits a repeatable flag-shaped hysteretic response with full recentering capabilities, therefore eliminating residual deformations. The mechanics of this new system are first explained, the equations governing its design and response are outlined, and one embodiment of the system, which combines a friction dissipative mechanism and Aramid tensioning elements, is further studied. Results from component tests, full-scale (reduced length) quasi-static axial tests, and quasi-static and dynamic seismic tests on a full-scale frame system are presented. Experimental results confirm the expected self-centering behavior of the self-centering energy dissipative (SCED) bracing system within the target design drift. Results also confirm the validity of the design and behavior equations that were developed. It is concluded that the proposed SCED concept can represent a viable alternative to current braced frame systems because of its attractive self-centering property and because the simplicity of the system allows it to be scaled to any desired strength level.
Two families of passive seismic control devices exploiting the peculiar properties of shape memory alloy (SMA) kernel components have been implemented and tested within the MANSIDE project (Memory Alloys for New Seismic Isolation and Energy Dissipation Devices). They are special braces for framed structures and isolation devices for buildings and bridges. Their most important feature is their extreme versatility, i.e. the possibility to obtain a wide range of cyclic behaviour — from supplemental and fully re-centring to highly dissipating — by simply varying the number and/or the characteristics of the SMA components. Other remarkable properties are their extraordinary fatigue resistance under large strain cycles and their great durability and reliability in the long run. In this paper, the working mechanisms of the SMA based devices are outlined and the experimental tests carried out to verify the above-mentioned properties are extensively described. Copyright © 2000 John Wiley & Sons, Ltd.
This study evaluates the properties of superelastic Ni–Ti shape memory alloys under cyclic loading to assess their potential for applications in seismic resistant design and retrofit. Shape memory alloy wire and bars are tested to evaluate the effect of bar size and loading history on the strength, equivalent damping, and recentering properties of the shape memory alloys in superelastic form. The bars are tested under both quasistatic and dynamic loading. The results show that nearly ideal superelastic properties can be obtained in both wire and bar form of the superelastic Ni–Ti shape memory alloys. However, the wire form of the shape memory alloys show higher strength and damping properties compared with the bars. The recentering capabilities based on residual strains are not affected by section size. Overall, the damping potential of shape memory alloys in superelastic form is low for both wire and bars, typically less than 7% equivalent viscous damping. Cyclical strains greater than 6% lead to degradation in the damping and recentering properties of the shape memory alloys. Strain rate effects are evaluated by subjecting the shape memory alloys to loading rates representative of typical seismic loading. The results show that increased loading rates lead to decreases in the equivalent damping, but have negligible effects on the recentering properties of the shape memory alloys.
Shape-memory alloys show features not present in materials traditionally used in engineering; as a consequence, they are the basis for innovative applications.A review of the available literature shows a dearth of computational tools to support the design process of shape-memory-alloy devices. A major reason is that conventional inelastic models do not provide an adequate framework for representing the unusual macrobehavior of shape-memory materials.The present work focuses on a new family of inelastic models, based on an internal-variable formalism and known as generalized plasticity. Generalized plasticity is adopted herein as framework for the development of one- and three-dimensional constitutive models for shape-memory materials.The proposed constitutive models reproduce some of the basic features of shape-memory alloys, such as superelasticity, different material behavior in tension and compression, and the single-variant-martensite reorientation process.For isothermal conditions the implementation of the model in a finite-element scheme and the form of the algorithmically consistent tangent are discussed in detail.Numerical simulations of typical tests performed on shape-memory materials (e.g. uniaxial loading, four-point bending and three-point bending tests) are presented and compared with available experimental data.Based on the overall developments, it appears that the proposed approach is a viable basis for the development of an effective computational tool to be used in the simulation of shape-memory-alloy devices.
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