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Despite their superior control performance, active vibration control techniques cannot be widely used in some engineering fields because of their substantial power demand in controlling large-scale structures. As an innovative solution to this problem, an unprecedented self-powered active vibration control system was established in this study. The topological design, working mechanism, and power flow of the proposed system are presented herein. The self-powering ability of the system was confirmed based on a detailed power flow analysis of vibration control processes. A self-powered actively controlled actuator was designed and applied to a scaled active vibration isolation table. The feasibility and effectiveness of the innovative system were successfully validated through a series of analytical, numerical, and experimental investigations. The setup and control strategy of the proposed system can be readily extended to diversified active vibration control applications in various engineering fields.

The typhoon-induced vibration characteristics of large wind turbines are significantly different in different travelling stages of typhoons due to the structural complexity of typhoons. Influences of multi-stage typhoon-induced effects on structural safety of wind turbines have not been studied yet. The objective of this paper is to investigate the vibration characteristics of wind turbines in different stages of the typhoon as well as the influencing rules of the structural design standards. For this purpose, a framework was established for predicting multi-stage typhoon-induced effects of large wind turbines, which includes a new typhoon-induced multi-stage wind field simulation method and an advanced multi-body model for large wind turbines. On this basis, aerodynamic loads and dynamic response of large wind turbines during different travelling stages of typhoon were analyzed systematically based on the blade element momentum, multi-body dynamic methods, spectral analysis and data statistics. The working mechanisms of multi-stage effects on vibration characteristics of the large wind turbine were revealed. Finally, an evaluation method of vibration amplification effects for large wind turbines with considerations to multi-stage effects was established. Research results demonstrate that the proposed method can predict vibration characteristics of large wind turbines considering the multi-stage effects efficiently. The multi-stage typhoon-induced effects can influence the value of peak factor and the extremum of wind-induced force and vibration responses of large wind turbines significantly. Conversely, the wind vibration coefficient of structural design was affected slightly. Instead of using a uniform structural design standard for large wind turbines, the influence rule of multi-stage effects on anti-typhoon safety performance was summarized in this paper.

Two types of passive devices, namely, negative stiffness damper (NSD) and inerter damper (ID), have been receiving growing interest in vibration isolation and suppression, because both can produce negative-slope force-displacement relationships that are similar to those associated with active control forces. Despite such a similarity, these two passive dampers possess obvious differences in their mechanical behaviors. This study aims to illustrate the similarity and difference between these two dampers in vibration isolation applications with respect to the H2 and H∞ performance. The comparative study indicates that both dampers can reduce the H∞ norm effectively; the negative stiffness devices can reduce the H2 norm as well, whereas the H2 norm cannot converge under the influence of inerter. This finding explains why a tuned-inerter damper, i.e., an inerter connected in series with a spring with proper frequency tuning, is more commonly adopted in vibration isolation. The pros and cons of both devices were further discussed.

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.

This paper proposes a damage detection method with two phases, namely, localization and quantification, for beam structures subjected to moving load and successfully validates it via a laboratory experiment. Firstly, the discrete wavelet transform (DWT) is applied to decompose the displacement response change induced by a moving vehicle and locate potential structural damages. Then adaptive-scale wavelet finite element model (WFEM) updating is employed to estimate the damage severity in the identified damage regions in a progressive fashion. The elemental scales of WFEM are adaptively changed according to not only the moving vehicle position but also the progressively identified damage regions. Such a method can effectively minimize the number of modeling degree-of-freedoms (DOFs) and updating parameters during optimization. The feasibility and effectiveness of the proposed method is examined through a laboratory experiment with different damage scenarios. The results indicate the proposed method can achieve good consistency between structural modeling, damage scenarios, and load conditions, as well as an optimal tradeoff between damage detection accuracy and efficiency.

As a new member of the shape memory alloy (SMA) material family, iron-based SMAs (Fe-SMAs) show great potential in seismic applications due to their favorable properties. The thermomechanical behavior of Fe-SMAs has been extensively studied over the past decades. However, the relevant research regarding the use of Fe-SMAs in the community of earthquake engineering is still in an early stage, particularly on their mechanical behavior under cyclic tension–compression loadings. This study conducted a systematic experimental investigation of the cyclic behavior of Fe-SMA bars with a buckling-restrained device, which was cyclically tested under tension–compression loadings. The cyclic properties, such as hysteretic response, recovery capability, fatigue behavior, and fracture behavior were evaluated with varying strain amplitudes and different loading protocols. Test results show that satisfactory hysteretic loops with excellent deformation capability are obtained under cyclic tension–compression loadings. Fe-SMA bars exhibit acceptably stable behavior under multistage loadings. Moreover, they possess unique inherent properties, including moderate shape memory effect, high “post-yield” stiffness, and excellent fatigue behavior, thereby providing a promising solution to develop high-performance seismic devices. These properties are conducive to limit peak drifts, mitigate residual drifts of structures, and withstand long-duration ground motions and strong repeated aftershocks.

A renewed interest in vertical-axis wind turbines (VAWTs), especially straight-bladed VAWT (SB-VAWT), has been observed in recent years. Large-scale VAWTs were briefly explored in the 1980s, but have since been the subject of limited research. Thus, this paper presents a systematic investigation of the structural system of a large-scale SB-VAWT recently developed by Hopewell Holdings Limited of Hong Kong. The structural system, field measurement, finite element (FE) modeling, and model updating of the SB-VAWT is introduced sequentially. The proposed structural monitoring system can successfully identify the modal frequencies of the SB-VAWT below 10 Hz. The structural responses of the SB-VAWT are computed with the updated FE model and the simulated wind loads. The comparison between the computed and measured structural responses in the frequency domain shows satisfactory agreement. The results indicate that the proposed dynamic simulation approach based on a well-designed structural monitoring system can reproduce the structural responses of large-scale SB-VAWTs satisfactorily. This approach will shed light on the future analysis and optimization of this type of structure.

Shape memory alloys (SMAs) show great potential in seismic applications because of their appealing superelastic feature and good energy dissipation capacity. The tensile behavior of SMA wires and bars has been extensively studied over the past decades. However, little attention has been paid to their compressive properties under cyclic loading. Thus, this paper presents a systematic experimental study on the cyclic behavior of superelastic SMA bars with buckling-restrained devices (BRDs) when subjected to tension–compression cycles. The detailed design of BRD is described first. The material properties such as “yield-like” strength, peak strength, self-centering capability, and energy dissipation of typical interest in seismic applications are evaluated with varying strain amplitudes, strain rates, and loading protocols. Test results show that satisfactory and stable flag-shaped hysteretic loops without any strength degradation are obtained in multiple loading cycles under cyclic tension–compression loading. Moreover, the SMA bars exhibit remarkable self-centering capability that is nearly independent of strain rate and loading protocol.

This study systematically investigates the dynamic characteristics of a stay cable with an inerter damper installed close to one end of a cable. The interest in applying inerter dampers to stay cables is partially inspired by the superior damping performance of negative stiffness dampers in the same application. A comprehensive parametric study on two major parameters, namely, inertance and damping coefficients, are conducted using analytical and numerical approaches. An inerter damper can be optimized for one vibration mode of a stay cable by generating identical wave numbers in two adjacent modes. An optimal design approach is proposed for inerter dampers installed on stay cables. The corresponding optimal inertance and damping coefficients are summarized for different damper locations and interested modes. Inerter dampers can offer better damping performance than conventional viscous dampers for the target mode of a stay cable that requires optimization. However, additional damping ratios in other vibration modes through inerter damper are relatively limited.

Metamaterials provide an unprecedented solution for seismic hazard mitigation by blocking seismic wave transmission. This paper investigates the wave attenuation capability of one-dimensional binary seismic metamaterials. Variations in the bandgaps of metamaterials are studied analytically with different material combinations. Results indicate that large contrasts in mass densities and wave velocities between the two constituent materials are desirable in consideration of gap width and central frequency, and increasing the contrast in mass density is relatively more effective. Reducing the filling ratio of the soft and light material is also beneficial to seismic wave attenuation. However, several practical challenges are also highlighted. For example, attenuation of low frequency waves inevitably leads to low global stiffness of seismic metamaterials because the use of soft constituent material is indispensable. Despite enhancement of the attenuation effect in the whole frequency range, material damping weakens the band structure. In addition, the vibration in front of the metamaterial is amplified to a certain degree due to wave reflections. These may present several practical conundrums in the application of seismic metamaterials.

An innovative approach to identify local anomalies in a structural beam bridge with an instrumented vehicle moving as a sensory system across the bridge. Accelerations at both the axle and vehicle body are measured from which vehicle-bridge interaction force on the structure is determined. Local anomalies of the structure are estimated from this interaction force with the Newton's iterative method basing on the homotopy continuation method. Numerical results with the vehicle moving over simply supported or continuous beams show that the acceleration responses from the vehicle or the bridge structure are less sensitive to the local damages than the interaction force between the wheel and the structure. Effects of different movement patterns and moving speed of the vehicle are investigated, and the effect of measurement noise on the identified results is discussed. A heavier or slower vehicle has been shown to be less sensitive to measurement noise giving more accurate results.

Blade pitch control is a well-developed and widely-used approach in modern horizontal axis wind turbines in operation. However, its application in vertical axis wind turbines (VAWTs) is restricted by the ambiguities in its functional mechanism. A generic formulation that uses five governing parameters to represent the solution space of the optimal blade pitch control is developed through an in-depth analysis of the relationship between blade pitch and the output power of VAWTs. Subsequently, a variable blade pitch automatic optimization platform (VBPAOP) composed of genetic algorithm and computational fluid dynamics (CFD) simulation modules is built to search for optimal blade pitches that can maximize turbine power. A 2D unsteady CFD model is used as a performance evaluation tool because of its high computational efficiency, and its accuracy is validated through wind tunnel experiments prior to its application in optimization. Results show that in a wide range of tip speed ratios (TSRs), the optimized blade pitches can increase the average power coefficients by 0.177 and 0.317, respectively, in two simulated VAWT models with different chord lengths. At stages below the rated TSR, stall-induced torque losses are delayed or even avoided by the proposed optimized pitch control. At stages beyond the rated TSR, energy extraction in the downwind zone is improved due to increased upwind wake velocity.

Direct application of the Kalman filter algorithm to state estimation of civil structures presents a computational challenge due to their high dimensions and complexity. Rewriting dynamic equations using modal coordinates can be an alternative solution to this problem because high modes with minimal contributions to structural responses can be truncated. Although the mode selection is important in accurately estimating the state of civil structures, studies on determining the remaining mode number are limited. Hence, the mode selection method in the Kalman filter for the optimal reconstruction of structural responses is investigated in this study. A modal signal-to-noise ratio (MSNR) is defined as the ratio of the estimated modal response variance to the corresponding estimation error variance. Only modes with MSNR values higher than an analytically derived threshold are selected. A beam structure is numerically investigated to examine effects of excitation amplitude and frequency, measurement noise, and number of sensors on the adaptive mode selection for optimal response reconstruction. Experimental studies using a simply supported overhanging beam also confirm the efficacy of the proposed approach in response reconstruction using multiple types of sensors (including strain gauges, displacement sensors and accelerometers). Both the numerical and experimental results reveal that using all vibration modes or a complete numerical model with all degrees of freedom will reduce the accuracy of response reconstruction.

Electromagnetic dampers (EMDs), which are regarded as an emerging type of dampers, have recently drawn increasing research interests in structural vibration control due to their unique advantages over conventional damper types. Although advanced synthetic impedance and energy harvesting functions of EMDs have been separately investigated, their integration has not been explored to the best of the authors’ knowledge. The major obstacle herein is that the former versatile damper behavior is normally realized by consuming input energy, whereas the latter can only provide pure damping behavior comparable to passive viscous dampers while producing output energy. To fill this research gap, this study proposes a novel H-bridge circuit based EMD (HB-EMD), which allows bidirectional power flow between the EMD and the energy pool, and enables the realization of versatile damper behavior with the salient self-powered feature. The system design, working mechanism, synthetic impedance technique, power analyses, and emulation of various conventional dampers by using HB-EMD, are analytically, numerically, and experimentally examined. Scalability issues of HB-EMD are also discussed to shed light on future large-scale applications.

Ocean waves are an ultra-low-frequency renewable energy source. Various point absorbers have been developed over the past decades as small-sized wave energy converters (WECs). However, realizing tunable and ultra-low frequencies in WECs remains an extremely challenging technological issue. This paper proposes a novel and simple design of a double-mass pendulum (DMP) oscillator whose natural frequency can be conveniently tuned by simply adjusting the positions of two independent masses. Shake table test results successfully illustrated that the tunable ultra-low natural frequency range (0.2–1.4 Hz) can be achieved even in a small-size DMP prototype, which can be hardly achieved in conventional oscillator designs. Subsequently, a small prototype of a point absorber enclosing the DMP-based energy harvester was fabricated and tested in a wave flume under different wave heights and periods. Average output power of nearly 100 mW was captured in the experimental case when the wave period and height were 0.7 s and 0.1 m, respectively. The corresponding power extraction in a large-scale case is predicted to be up to 3.5 kW under wave height of 2 m and wave period of 6 s. The experimental results demonstrated that the proposed DMP oscillator is a promising power extraction device with an appealing tunable ultra-low frequency, which is extremely suitable for WECs, as well as other energy harvesters designed for ultra-low-frequency vibration sources.

Electromagnetic shunt damper (EMSD) is an emerging damper type capable of mimicking conventional mechanical dampers using their electrical circuit counterparts. Damping, stiffness, and inertance within mechanical domain can be emulated by resistance, inductance, and capacitance from electrical domain, respectively. In particular, four representative conventional damper types, namely, viscous fluid damper (VFD), viscoelastic damper (VED), inerter damper (ID), and tuned inerter damper (TID), are emulated by an EMSD in this paper, thereby forming EMSD-VFD, EMSD-VED, EMSD-ID and EMSD-TID, respectively. Their control performances when installed in a vibration isolation system are subsequently studied both analytically and experimentally. The behavior of EMSD can be easily tuned by changing the external circuits connected to the electromagnetic damper. Moreover, these four types of EMSDs possess complementary isolation performances across the frequency spectrum, which implies that different optimal circuits should be selected in different frequency bands to achieve the best isolation performance. A broadband vibration isolation technique by automatically switching among sub-circuits integrated in a single circuit board will be a promising future research direction.

Applying signal processing tools on quasi-static moving load induced response to localize damage is extremely promising in the field of structural health monitoring. However, it is still an issue to quantify damage for such methods for the lack of definite correspondence between damage severities and damage indexes they adopted. This paper aims to develop a two-stage method with the ability to quantify structural damages by using the quasi-static moving load induced displacement response. As the displacement response of beam structure caused by quasi-static moving load is in close proximity to displacement influence line (DIL), this paper investigates the correspondence between damage parameters and several DIL related features systematically. Then a damage localization index is defined based on area of the region encircled by the DIL change (DILC) and element (ADE), and a damage quantification equation is established based on the area of the region encircled by the DILC and beam (ADB), respectively. Such a two-stage method can take better advantage of the rich test data provided by moving load test, localize and quantify damage with few sensors rapidly. Numerical and experimental examples are carried out to demonstrate the effectiveness of the proposed method.

Structural damage could be localized through comparing the quasi-static moving load induced response before (taken as baseline) and after damage. However, it is very difficult, if not impossible, to obtain the baseline (information from the undamaged structure) for some structures. On this hand, structural response in damaged state only is not sufficient for such methods. On the other hand, only single type response (acceleration, strain or displacement) is employed for moving load based damage localization, i.e., multi-type response is inefficiently utilized. In this paper, a baseline-free damage localization method for statically determinate beam structures is proposed by using dual-type response (strain and displacement) excited by quasi-static moving load. It makes full use of the property that local damage causes no change on the static strain response of statically determinate beam structures except the damaged regions. The baseline displacement response in undamaged state is estimated through the strain response in damaged state. Then the measured displacement response in damaged state is compared with the estimated baseline displacement response, and the area change of the zone encircled by the displacement response and each sub-region (ADRC) is calculated to localize damage. Only the strain response and the displacement response in damaged state are required, and their comprehensive utilization avoids the need for a baseline. Numerical and experimental studies are conducted to investigate the feasibility, effectiveness, and limitations of the proposed method.

This paper presents the detailed modelling, parametric studies, and optimizations for two recently proposed magnetic negative stiffness dampers (MNSDs). Both dampers are composed of several coaxially arranged permanent magnets and a conductive pipe. The novel MNSDs can efficiently integrate negative stiffness and eddy-current damping in compact and simple configurations. However, the optimal design of MNSDs has never been investigated. Therefore, this paper establishes numerical models for MNSDs, and the accuracy of the model is validated through a comparison with the experimental results. The effects of magnet arrangement and dimensions on the negative stiffness and eddy-current damping characteristics are systematically investigated through parametric studies. The MNSDs are also individually optimized to maximize the negative stiffness and eddy-current damping coefficients. Based on the optimization results, some optimal design formulas are obtained to facilitate the quick design of MNSDs for different vibration suppression applications in the future.

Reinforced concrete (RC) coupled walls are extensively used as the seismic-resistant structural system of tall buildings in high seismic zones. In RC coupled wall systems, the coupling beams are typically designed and detailed to dissipate energy through large inelastic responses to meet the expected seismic performance under moderate-to-strong earthquakes. However, costly excessive repair or even complete demolition caused by the considerable damage in conventional RC coupling beams is usually inevitable. Such disadvantage of RC coupling beams has increased the interest on replaceable steel coupling beams, which can isolate the damage concentrated in the fuses; thus, these beams are expected to be replaced after a strong earthquake. However, replacing these beams in practice is difficult if considerable residual deformation exists in these replaceable fuses. Therefore, seismic resilience cannot be explicitly guaranteed. For this reason, this study proposes a novel self-centering (SC) steel coupling beam that incorporates superelastic shape memory alloy (SMA) bolts and steel angles. The SC steel coupling beam is composed of two elastic beam segments and one rocking segment. Elastic beam segments are designed by steel beams that connect to the RC walls at both ends of the coupling beam, whereas the rocking segment located in the middle of the coupling beam is controlled by the SMA bolts and steel angles. Two ingenious shear keys are designed between the elastic beam segments and the rocking segment; these shear keys help the SC coupling beam to exhibit centerline-rocking behavior that is free from beam elongation. The working principle of the novel SC steel coupling beam is described first. Then, the cyclic responses of the SMA bolt and the steel angle, which are the two core components in the SC steel coupling beam, are investigated. The seismic performance of the SC steel coupling beam is computationally investigated in consideration of the effects of steel angles and the prestrain in the SMA bolts. Results show that the proposed SC steel coupling beams exhibit excellent SC capability and energy dissipation. Most damage is isolated in the steel angles, which can be easily and rapidly inspected or replaced after earthquakes without operation interruption. Importantly, beam elongation is almost eliminated under cyclic loading. With these advantages, the SC steel coupling beam can provide a promising solution for high-performance coupled wall systems.

Excessive ground-borne vibrations induced by construction activities may pose adverse effects on the surrounding environments. On-site vibration control is typically based on vibration monitoring results at a few selected locations. However, this approach cannot predict vibration intensities at locations other than the monitored points because the locations of vibration sources are usually unknown in vibration assessment processes. The localization of impact sources (e.g., impact piling) becomes a critical problem to be addressed before vibration intensities can be quantified in a broad area instead of at several discrete points. Therefore, this paper develops a two-stage impact source localization method based on wave propagation characteristics obtained in finite element analyses of an infinite half-space soil domain. The localization accuracy of this approach is validated by numerical examples and field experiments on a construction site with ongoing impact piling work. The results indicate that the plan coordinates of the impact sources can be localized with satisfactory accuracy. The variations of the measured vibration intensities along with the distance from the localized impact source are modeled by using an empirical formula. The estimated impact source locations and the obtained empirical formula can jointly extend vibration intensity assessment from the discrete monitored points to the global surrounding area.

This study proposes a performance-based seismic design (PBSD) method for steel braced frames with novel self-centering (SC) braces that utilize shape memory alloys (SMA) as a kernel component. Superelastic SMA cables can completely recover deformation upon unloading, dissipate energy without residual deformation, and provide SC capability to the frames. The presented PBSD method is essentially a modified version of the performance-based plastic design with extra consideration of some special features of SMA-based braced frames (SMABFs). Four six-story concentrically braced frames with SMA-based braces (SMABs) are designed as examples to illustrate the efficacy of the proposed design method. In particular, the variability in the hysteretic parameters of SMAs, such as the phase-transformation stiffness ratio and the energy dissipation factor, is considered in the PBSD method. Accordingly, four SMABFs are designed with different combinations of these hysteretic parameters. The seismic performance of the designed frames is examined at various seismic intensity levels. Results of nonlinear time-history analyses indicate that the four SMABFs can successfully achieve the prescribed performance objectives at three seismic hazard levels. The comparisons among the designed frames reveal that the SMABs with greater hysteretic parameters result in a more economical design in terms of the consumption of steel and SMA materials.

The extended Kalman filter (EKF), as a popular tool for optimally estimating system state from noisy measurement, has been used successfully in various areas over the past several decades. However, classical EKF has several limitations when applied to structural system identification; thus, researchers have proposed a number of variations for this method. The current study focuses on using EKF for real-time system identification and damage detection in civil structures. An improved EKF approach, called moving-window EKF (MWEKF), is proposed in this paper after a discussion on the problems associated with the application of classical EKF in time-variant systems. The proposed approach uses the moving-window technique to estimate several statistical properties. MWEKF is more robust and adaptive in structural damage detection compared with classical EKF because of the following reasons: (1) it is insensitive to the selection of the initial state vector; (2) it exhibits more accurate system parameter identification; and (3) it is immune to the inaccurate assumption of noise levels because measurement and process noise levels are estimated in this approach. The salient features of MWEKF are illustrated through numerical simulations of time-variant structural systems and an experiment on a three-story steel shear building model. Results demonstrate that MWEKF is a robust and effective tool for system identification and damage detection in civil structures.

Seismic-resisting, multi-story steel frames with self-centering braces (SCBs) are numerically investigated through pushover and incremental dynamic analyses. The seismic performance of self-centering braced frames (SC-BFs) is systematically compared with that of buckling-restrained braced frames (BRBFs), with emphasis on high-mode effect. The concentration of inter-story drift in the upper part of the buildings is more significant in SC-BFs than in BRBFs as a result of this effect. This high-mode effect strengthens with the increasing intensity of ground motions. Parametric studies indicate that increasing the post-yield stiffness ratio and/or energy dissipation capacity can successfully improve the seismic performance of SC-BFs, particularly in terms of limiting the high-mode effect. SC-BFs with enhanced post-yield stiffness and energy dissipation capacity exhibit relatively uniform inter-story drift ratios and reduced record-to-record variability in seismic performance.

This study is devoted to the experimental validation of the multi-type sensor placement and response reconstruction method for structural health monitoring of long-span suspension bridges. The method for multi-type sensor placement and response reconstruction is briefly described. A test bed, comprising of a physical model and an updated finite element (FE) model of a long-span suspension bridge is also concisely introduced. The proposed method is then applied to the test bed; the equation of motion of the test bed subject to ground motion, the objective function for sensor location optimization, the principles for mode selection and multi-type response reconstruction are established. A numerical study using the updated FE model is performed to select the sensor types, numbers, and locations. Subsequently, with the identified sensor locations and some practical considerations, fiber Bragg grating (FBG) sensors, laser displacement transducers, and accelerometers are installed on the physical bridge model. Finally, experimental investigations are conducted to validate the proposed method. The experimental results show that the reconstructed responses using the measured responses from the limited number of multi-type sensors agree well with the actual bridge responses. The proposed method is validated to be feasible and effective for the monitoring of structural behavior of long-span suspension bridges.

Given their inherent unique superelasticity, the use of shape memory alloys (SMAs) to build seismic-resistant self-centering devices has presented attractive prospects in the field of earthquake resilience. This work investigates the mechanical behavior of superelastic SMA angles subjected cyclic loading. The deformation mechanism in superelastic SMA angles is elaborated first. Subsequently, experimental investigations of SMA angles are conducted using different loading protocols. Various mechanical properties, such as strength, self-centering and energy dissipation capabilities, are evaluated under varying loading amplitudes. Testing results show SMA angles can exhibit satisfactory flag-shaped hysteresis loops under multiple loading cycles. Different measures, such as the training process or the inclusion of reversed compressive cycles, can stabilize the hysteresis loops effectively and minimize the strength degradation and residual deformation in the repeated cycles. The cyclic behavior of the SMA angles is also simulated by using the finite element method to complement the observation and understanding obtained from the experiments. The proposed SMA angles are expected to offer an effective self-centering function to engineering structures toward earthquake resilience.

Vibration-based electromagnetic energy harvesters involve an apparent coupling effect between the dynamics of mechanical structures and electric circuit. Such a coupling effect complicates the impedance optimization of energy harvesting circuit in the design of energy harvesters. The classical impedance matching, which ignores the coupling effect, becomes inapplicable. This paper proposes a unified overall impedance optimization strategy for the harvesting circuit to achieve the maximum output power and power efficiency, and such a unified strategy is applicable to a number of cases with different structural complexity, different types of excitations, and different levels of coupling effects between mechanical and electrical systems. By converting the mechanical structures of single-degree-of-freedom (SDOF) and multiple-degree-of-freedom (MDOF) energy harvesters into equivalent circuit models, the electro-mechanical coupling is simplified as the coupling effect inside an electric circuit. This conversion provides insight into the overall impedance optimization framework from the pure electric circuit perspective. Different optimal impedance values of energy harvesting circuits under different excitation types (harmonic and random) are derived within the proposed overall impedance optimization framework. The optimal impedance values for the maximum output power depend on the circuit dynamics, structural characteristics, and excitation types. Meanwhile, the optimal impedance values for the maximum power efficiency are related to the inherent damping of the structure and transducer but independent of excitation types. Numerical simulations of various cases were conducted, including resonant, non-resonant, and random excitation, in the SDOF and MDOF harvesters. Simulation results successfully validate the effectiveness and accuracy of the proposed overall impedance optimization strategy for enhancing the harvesting performance of vibration-based electromagnetic energy harvesters.

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.

An electromagnetic damper cum energy harvester (EMDEH), which consists of an electromagnetic damper (EMD) connected to an energy harvesting circuit (EHC), aims to suppress structural vibrations by harvesting the vibration energy of structures. Maintaining a steady equivalent resistance of an EHC is often desirable for achieving the target performance of vibration control and energy harvesting functions; however, it remains an unresolved challenge in the EHC design. This study proposes an improved version of EMDEH with a specially designed EHC, a buck–boost converter with a low-power microcontroller unit (MCU). Compared with the existing EMDEH using an EHC with a fixed duty cycle, the improved version employs the MCU to adjust the duty cycle based on the feed-forward signal so as to continuously maintain a nearly constant resistance characteristic of the EHC. The effectiveness of the proposed EHC was validated through numerical simulations and experimental tests. A prototype of the improved EMDEH was installed in a 135 m-long bridge stay cable and tested under harmonic excitations of different levels. An output power of 200 mW and a nearly constant resistance of the proposed EHC were observed in this full-scale experiment. The results of this study show how the use of a MCU in a feed-forward controlled EHC benefits the performance of a dual-function EMDEH with respect to its simultaneous vibration control and energy harvesting performance.

This study uses 2.5D large eddy simulations (LES) and wind tunnel experiments to investigate aerodynamics of high-solidity straight-bladed vertical axis wind turbines (SBVAWTs). The experimental setup and numerical simulation strategy of a high-solidity SBVAWT are first introduced. The self-start performance of the high-solidity SBVAWT is then assessed. The aerodynamic forces acting on the rotating high-solidity SBVAWT are computed by 2.5D LES method, and the numerical results are compared to those from the wind tunnel experiments. The numerical and experimental results indicate that the high-solidity SBVAWT has a good self-start capability. The results also indicate that 2.5D LES method can provide satisfactory prediction to the aerodynamic forces, especially for the straight blade in the upwind zone. Flow characteristics of the high-solidity SBVAWT with different tip speed ratios (TSRs) are finally analyzed, and the mechanism of variation of aerodynamic forces in one rotational circle is revealed. By comparing the flow characteristics of the high-solidity SBVAWT with the moderate-solidity SBVAWT, it is observed that high solidity introduces complex flow field and the aerodynamic force curves of the high-solidity SBVAWT are different from those of the moderate-solidity SBVAWT.

Taking advantage of the unique multi-scale and localization features of wavelet finite element model (WFEM), this study proposes a novel progressive damage detection approach. Dynamic equations of beam-type WFEM are first derived using the second-generation Hermite multiwavelet as shape functions. Then the procedure of WFEM-based progressive damage detection is elaborated, in which sub-element damage can be gradually identified through the model updating process with an objective function that combines measured frequencies and mode shapes. The scales of wavelets can be adaptively enhanced or reduced during the progress according to actual damage scenarios. Hence, the proposed approach can effectively minimize the number of degrees of freedom (DOFs) in WFEM, as well as the number of unknown variables to be updated. Numerical examples of a simply supported beam and a single-story frame are simulated with different damage scenarios. The results demonstrated that the proposed multi-scale WFEM-based damage identification approach could progressively identify the location, extent and severity of damage. Compared with the traditional method, the proposed method involves fewer DOFs and updating parameters in structural models, and fewer sensors in modal tests, and thus would considerably improve the efficiency of damage identification.

A renewed interest in vertical axis wind turbines (VAWTs) has been seen recently. Computational fluid dynamics (CFD) is regarded as a promising technique for aerodynamic studies of VAWTs. In particular, 2D unsteady Reynolds-averaged Navier–Stokes (URANS) is commonly adopted, although past studies on VAWTs revealed the limited accuracy of 2D URANS. This paper investigated the feasibility and accuracy of three different CFD approaches, namely 2D URANS, 2.5D URANS and 2.5D large eddy simulations (LES), in the aerodynamic characterization of straight-bladed VAWT (SBVAWT), with a focus on the capability of the 2.5D LES approach in CFD simulation of high angle of attack (AOA) flow. The 2.5D model differs from a full 3D model in that only a certain length of blades is modeled with periodic boundaries at the two extremities of the domain. The applications of these three approaches were systematically examined in the aerodynamic simulations of a single static airfoil and a 3-blade SBVAWT at different rotating speeds. Their capabilities to predict the aerodynamic forces were evaluated through a comparison with the wind tunnel results obtained by other researchers, with particular attention to high AOA flow beyond stall. Among the three methods, 2.5D LES yielded the best agreement with the experimental results in both cases. Detailed examinations of simulated flow field revealed that 2.5D LES produces more realistic 3D vortex diffusion after flow separation, resulting in more accurate predictions of aerodynamic coefficients in static or dynamic stall situations. It is noteworthy that 2.5D LES cannot capture the effect of tip vortex and vertical flow divergence in VAWTs, which used to be regarded by some researchers as the major cause of overprediction of VAWT power in 2D URANS. In this study, the considerably improved results achieved by 2.5D LES imply that the poor accuracy of URANS method is mainly due to its inherent limitation in vortex modeling. In general, 2.5D LES showed good agreement with experimental results at a relatively low tip speed ratio (TSR), but only fair agreement at a high TSR. Compared with the other two approaches, 2.5D LES is regarded as a more promising and effective CFD tool for investigating the aerodynamic characteristics of VAWTs, particularly their self-starting features corresponding to very low rotation speeds.

This paper proposed and validated a self-powered vibration control and monitoring (SVCM) system which consists of a pendulum-type tuned mass damper (TMD), a rotary electromagnetic (EM) device, an energy harvesting circuit (EHC) and a wireless smart sensor (WSS). As the key element in the system, the regenerative electromagnetic TMD (EMTMD) is able to convert vibration energy of structures to electrical energy, and thus plays dual functions, namely, vibration mitigation and energy harvesting. With the aid of EHC, the electrical energy can be further stored and used to power WSS that closely monitor structural vibration responses. The feasibility of the proposed SVCM system was validated via shaking table tests, in which a single-degree-of-freedom (SDOF) structural model equipped with the SVCM system was tested under random excitations. The functionality of the SVCM system was discussed with regard to the vibration control, energy harvesting and vibration monitoring performance. The experimental results revealed that the proposed regenerative EMTMD device can provide regenerative and economical power to WSS. The harvested power reaches about 312.4 mW under random ground motions with root-mean-square (RMS) acceleration equal to 0.05 g. Meanwhile, the comparison shows that the peak magnitude of the frequency response function of structural displacement is reduced by 10 dB with the aid of the EMTMD. This study demonstrates that the SVCM system provides a novel and promising solution to the power supply problem associated with wireless sensing technology, and will stimulate the integration of vibration control and monitoring system.

Over the past decades, the research on structural vibration control has mainly focused on ‘energy dissipation’ strategy using various dampers for hazard mitigation. This paper proposes a novel application of linear motion electromagnetic (EM) devices, termed linear EM dampers hereinafter, for both vibration damping and energy harvesting. The kinetic energy caused by earthquakes, wind or traffic loads is not only dissipated by EM dampers, but also stored by energy-harvesting electric circuits connected to EM dampers. The green and regenerative energy output may provide an alternative power supply to portable and wireless devices at remote sites. This paper presents a theoretical and experimental study of linear EM dampers connected with four representative circuits. The dynamic characteristics of linear EM dampers, including parasitic damping, EM damping, energy conversion efficiency and output power, are modeled and discussed systematically in each case. The modeling is further verified by a series of dynamic testing of a small-scale linear EM damper, which is cyclically tested on a MTS machine at different frequencies and amplitudes. A good match between the modeling and testing results clearly demonstrates that the described model can predict the performance of the linear EM damper and energy harvesting circuit very well. The promises and challenges of using EM dampers in future civil infrastructure for both vibration damping and energy harvesting are discussed based on the outcome of this study.