•Superelastic shape memory alloy (SMA) cables are comprehensively studied.•Thermal-mechanical characterisations of the SMA material are carried out.•A series of SMA cable specimens are tested under ...various cyclic loading protocols.•A simple yet effective numerical modelling method is proposed for SMA cables.•A prototype bridge employing SMA cables as restrainers is designed and analysed.
This paper reports a comprehensive study on the mechanical behavior, annealing (heat treatment) scheme, hysteretic modelling strategy, and potential seismic application of superelastic shape memory alloy (SMA) cables. The study commenced with the thermal-mechanical characterization of monofilament SMA wires, and in particular, the influence of annealing scheme on the mechanical and phase transformation characteristics of the material was revealed. A series of 7 × 7 SMA cable specimens were subsequently tested at room temperature under various cyclic loading protocols. It is observed, among other findings, that the SMA cables are able to reasonably “scale up” the satisfactory properties of the SMA wires, and the mechanical behavior of the SMA cables may be improved by annealing. Moderate annealing temperature and duration (i.e., 350–400 °C for 15 min) can generally increase the stiffness, energy dissipation, and form setting ability of the SMA cables considered in this study, whereas an overly high annealing temperature tends to compromise these characteristics. Following the experimental study, an effective numerical modelling approach is proposed which reliably captures the basic mechanical behavior of the SMA cables. A model bridge, where SMA cables are adopted as restrainers, is finally designed and analyzed to demonstrate the efficiency of the SMA components for seismic damage mitigation. The analysis result shows that the SMA-cable restrainers can effectively control the peak and residual displacements of the bridge girder, and make the bridge more resilient.
•A new type of self-centering rocking (SCR) bridge pier is proposed.•Superelastic SMA washer springs are the kernel elements for the pier.•Five proof-of-concept tests are carried out on a small-scale ...SCR pier specimen.•A numerical study examining an extended range of design parameters is conducted.•Preliminary design recommendations are given.
The emergence of rocking bridge piers provides the community of civil engineers with a broader vision of next-generation seismic-resilient bridge design. This study introduces a new type of shape memory alloy (SMA) washer spring-based self-centering rocking (SCR) systems which could be an important addition to the existing rocking pier family. The proposed system combines the advantage of the existing rocking pier solution with extra benefits such as simplified construction, excellent fatigue and corrosion resistance, and extra “locking mechanism” which safely prevents the pier from excessive rocking. The working principle of the SCR piers is discussed first, and five tests are subsequently carried out on proof-of-concept SCR pier specimens. This is followed by a further numerical study examining an extended range of design parameters. The SCR pier shows excellent self-centering capability with minimal damage to the pier, which is attributed to the intended gap-opening deformation mode. Moderate energy dissipation is offered by the SMA washer springs, and once they are fully flattened, further drift is provided by the flexural deformation of the pier itself. The SMA washers can be used repeatedly with no need for repair/replacement, and the highly flexible stack pattern caters to different design objectives and requirements. An effective supplementary source of energy dissipation is enabled by installing steel angles at the gap opening interface. The experimental and numerical investigations provide a strong proof of feasibility of this innovative structural system.
•The hysteretic response curves of the fuse connections subjected to cyclic loading were plump.•The fuse angles can concentrate the inelasticity effectively in a wide deformation range.•The retest ...with replaced angles exhibited a similar performance to the initial test.•The fuse connection achieved an initial stiffness close to that of a typical welded beam-to-column connection.
In this study, an innovative replaceable fuse connection for beam members in moment resisting steel frames was proposed. Steel angles are designed as fuse elements for energy dissipation and post-earthquake replacement. The load carrying mechanism of the connection was explored. In order to examine the feasibility of the notion, a total of six full-scale subassemblies of beam-to-column connections were tested. The test parameters that affect the performance of the fuse connection were studied, and the repairability was validated by a retest specimen with replaced fuse angles. Test results demonstrated that the hysteretic response curves of the test connections subjected to cyclic loading were plump, and the fuse angles can concentrate the inelasticity effectively in a wide deformation range. The novel connections equipped with fuse angles can achieve an initial elastic stiffness close to that of a conventional welded beam-to-column connection. In addition, theoretical equations for predicting the elastic stiffness and resistance of the connection were developed, and their sufficiency was validated by test results.
•The novel structure showing the partially self-centring behaviour was proposed.•A spectral energy factor model for the system was developed based on the lognormal distribution assumption.•The ...sufficiency of the energy factor model was justified.
To achieve a delicate balance between self-centring behaviour and energy dissipation, it was proposed to develop the damage-control steel frame equipped with shape memory alloy (SMA) connections and ductile links showing the partially self-centring behaviour. This paper examined the inelastic seismic demand of the novel structure, and the emphasis was given to the spectral energy factor of the system subjected to near-field earthquake motions. Based on single-degree-of-freedom (SDF) systems representing the novel structure and a near-field earthquake database, nonlinear spectral analyses were performed considering a wide range of structural period and hysteretic parameters, and more than 25 million energy factors were obtained. The probabilistic characteristics of the energy factors were examined in detail. The analysis database confirmed that the energy factors were sensitive to structural period and hysteretic parameters. In addition, a right-skewed distribution feature of the energy factors was observed. Thus, a spectral energy factor model for damage-control steel frames equipped with SMA connections and ductile links was developed using the lognormal distribution model. Nonlinear regression analyses were conducted to develop a series of prediction equations. The good agreement between the histograms of the energy factor and predictions by the regression equations confirmed the adequacy of the proposed model. The proposed model was eventually applied to evaluating the damage-control behaviour of a prototype structure under near-field earthquake motions, and the sufficiency of the model for assessing the structural damage-control behaviour from a statistic perspective was confirmed.
Shape memory alloys (SMAs) are nowadays promising candidates for seismic engineering applications because of their ability to undergo reversible deformations and to dissipate energy when subjected to ...cyclic loading. This paper presents an experimental study of the cyclic performance of extended end-plate connections connected using SMA bolts instead of normal high strength bolts in the connections. The basic concept is to concentrate the earthquake-induced deformation into the connection, such that a ‘superelastic’ hinge can be formed via the elongation of the SMA bolts. Eight full-scale tests were conducted including seven extended end-plate connections with SMA bolts and one conventional extended end-plate connection with normal high strength bolts. The SMA connection specimens were shown to have excellent recentring abilities and moderate energy dissipation capability with an equivalent viscous damping up to 17.5%. The stiffness and strength of these connections mainly fell into the semi-rigid and partial-strength categories, respectively. The ductility, which was governed by SMA bolt rupture, was found to be dependent on the net threaded-to-shank area ratio of the bolts, where a lower ratio led to earlier bolt fracture over the net threaded cross-section. On the other hand, the conventional extended end-plate connection with High Strength bolts was shown to have good energy dissipation capability and ductility but with considerable permanent deformation. To enable a further understanding of the SMA connections, preliminary numerical models were established and validated by the test results. Based on the results of the tests and the numerical investigations, preliminary design considerations for such connections are given.
•Seven extended end-plate connections with shape memory alloy bolts were tested.•The connection specimens have excellent recentring abilities.•Moderate energy dissipation capability was observed for the specimens.•The equivalent viscous damping of up to 17.5% was recorded.•SMA bolt fracture was observed as the failure mode.
•A novel Fe-Mn-Si alloy U-shaped damper with excellent LCF resistance is proposed.•Both the monotonic and cyclic loading material tests are conducted.•Experimental study on 30 U-shaped dampers is ...conducted.•A combined kinematic/isotropic hardening model is used to simulate the Fe-Mn-Si alloy.•Finite element models are established and validated through comparisons against test results.
This study presents a new type of Fe-Mn-Si alloy U-shaped dampers (FMS-UDs) that exhibit extraordinary low cycle fatigue (LCF) performance. The basic material properties of Fe-Mn-Si alloy were first evaluated by a series of material tests considering both the monotonic and cyclic loading schemes, where normal carbon steel specimens were also tested for comparison. After the material tests, a total of 30 U-shaped dampers were examined, considering various parameters such as material type, geometry, loading direction and strain rate. Following the experimental program, finite element models were established to help interpret the test result. The material tests showed that Fe-Mn-Si alloy exhibited non-obvious yield plateau and moderate strain hardening under monotonic loading. Spring-back phenomenon, non Masing behavior, and excellent LCF performance were generally observed under cyclic loading. The damper tests showed that the FMS-UDs exhibited slightly “narrower” hysteresis responses compared with normal steel dampers. The LCF life and the total energy dissipation of the FMS-UDs are up to 7 times that of their steel counterparts, depending on the parameters considered. From a modeling point of view, the hysteretic behavior of the Fe-Mn-Si alloy could be adequately captured by a combined kinematic/isotropic hardening model. By using the calibrated parameters from the material tests, the hysteresis behavior and stress distribution of the FMS-UDs can be well represented. Critical locations which are prone to fatigue failure of the FMS-UDs were accurately captured by the numerical model, and the predictions agree very well with the test results.
This paper comprehensively discusses the behavior and failure risk of self‐centering braced frames suffering tendon fracture. The fundamental mechanism of tendon failure in self‐centering braces ...(SCBs) is first introduced, followed by the design and analysis of a series of prototype buildings with different tendon materials and brace configurations. Assuming a normal distribution of tendon fracture strain, the dynamic behavior of the frames is then assessed by a suite of ground motion records, covering both far‐field and near‐fault ones. The collapse and residual deformation fragilities of the frames are further evaluated, and the study ends with a risk assessment considering a 50‐year service period. Among other findings, the study indicates that tendon fracture tends to increase the peak interstory drift, especially for the structure with smaller tendon fracture strains. Tendon fracture also compromises the self‐centering capability significantly, although there is no obvious statistical correlation between tendon fracture and the peak floor acceleration. The probability of collapse and that of exceedance of certain residual drift both increase evidently when tendon fracture is considered. The failure probabilities are closely related to the available deformability of the SCBs, where dual‐core SCBs show less sensitivity to tendon fracture. The probability of collapse of the considered frames over 50 years of service increases from 1.25‐2.12% to 3.58‐6.52% when tendon fracture is considered. Considering a residual drift threshold of 0.5%, the probability of exceedance of the same structures over the same life span increases from 1.78‐3.54% to 5.46‐9.71%.
Shape memory alloys (SMAs) are smart metals featuring either superelastic effect or shape memory effect. While current emphasis on the civil engineering application of SMA is mainly given to dampers ...and isolators, recent research has been directed to superelastic SMA bolts or tendons for recentring connections. However, available information on the mechanical shear response of SMA bars is still inadequate. Consequently, this knowledge barrier can cause significant uncertainties when such components are intended to resist shear action. In this respect, this paper presents an experimental study on SMA bars subject to cyclic direct-shear actions, and uniaxial tensile tests were also undertaken on the bars of similar sizes for comparison. Key results including stress–strain/force–displacement hysteretic response, recentring ability, and energy dissipation are discussed in detail. The results show sound recentring and moderate energy dissipation/damping capabilities of the bars under cyclic tension below a strain level of 3 %, but beyond this the properties start to degrade. The SMA bars with a smaller diameter seem to perform better than those with a larger diameter. On the other hand, the cyclic direct-shear performance of SMA bars is generally unsatisfactory with poor recentring, energy dissipation, and damping characteristics. Therefore, the direct use of SMA bars subject to shear loading is undesirable. For both tension and shear tests, fracture of the bars within the threaded area is the most typical failure mode, which should be minimised in future applications to ensure a ductile response of seismic resistance devices. Recognising both advantages and potential shortcomings of the SMA bars, an innovative recentring connection type is proposed, and the preliminarily findings indicate that such connections are feasible.
•Use of stainless steel components (SSC) against progressive collapse is proposed.•FE models (with fracture simulation) were developed for FEP and WA connections.•Effectiveness of SSC against ...progressive collapse was assessed by parametric study.•With SSC, the collapse resistance of the connections can be enhanced by 30–109%.
With the use of ductile stainless steel bolts and hot-rolled sections/plates as critical connection components, the progressive collapse resistance of bolted beam-to-column connections may be effectively enhanced at relatively low costs. To verify the viability of this concept, a comprehensive numerical study is performed to investigate the collapse-resisting performances of flush end-plate (FEP) and web angle (WA) connections equipped with stainless steel components. Through a detailed parametric study with various connection configurations and structural layouts, it is proved that the use of stainless steel components can produce remarkable enhancement to the collapse resistance of the connections. The average increase in dynamic load capacity is 30% for FEP connections using stainless steel bolts instead of carbon steel bolts. This average ratio can be as large as 109% for WA connections with the use of stainless steel bolts and web angles. These results clearly demonstrate the great potential of using stainless steel components in steel connections for collapse-resisting purposes. Similar concepts may be naturally applied in many other scenarios where the ductility of a few critical components controls the robustness of the entire system.
