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An electromagnetic inertial mass damper (EIMD) is an inerter-based damper that can significantly enhance the seismic performance of a frame structure. However, the stochastic seismic analysis of a base-isolated structure (BIS) with the EIMD subjected to earthquake ground motions has rarely been reported. Based on a probabilistic framework, this paper studies the stochastic seismic responses of the BIS with the EIMD subjected to seismic excitations considering three typical soil conditions. The analytical solutions of the response variances of a two-degree-of-freedom (2DOF) BIS-EIMD system are derived considering both stationary and non-stationary seismic excitations. A parametric study on the BIS-EIMD system subjected to stochastic seismic excitations modeled by filtered Kanai-Tajimi spectrum is conducted to investigate the different seismic responses under firm, medium, and soft soil conditions, and the corresponding optimal inertance and damping of the EIMD are obtained by minimizing the stochastic seismic responses of the superstructure or the base floor. The results of the 2DOF BIS-EIMD system indicate that the optimal EIMD achieves comparable control performance under the three soil conditions, but the optimal parameters of the EIMD vary significantly under different soil conditions. Under soft soil conditions, the BIS-EIMD system requires a much larger inertance setting compared with that of the firm and medium soil conditions. A numerical simulation of a seven-story isolated building with an EIMD is conducted considering both artificial seismic excitations and real earthquake ground motions. Numerical results show that the EIMD is capable of significantly suppressing the seismic responses of both the base floor and the superstructure, which is better than that of a conventional viscous damper.

This paper presents the probabilistic seismic demand and fragility analyses of a novel mid-rise large-span cassette structure. A newly designed nine-storey office building in Hunan, China, is selected, and its two different design schemes, namely, a traditional frame structure and a novel cassette structure, are examined using numerical models established on the basis of a shake table test. Based on probabilistic seismic theory, the appropriate intensity measures are firstly studied based on a set of 110 seismic records; and PGV and GeoSaavg, which consider the 3D characteristics of the structure, are selected. In addition, the uncertainty of earthquakes, including spectral characteristics, fault distance and input direction, are considered, and 25 seismic records recommended by the Federal Emergency Management Agency are selected. An incident angle interval of 22.5° is selected to consider the uncertainty in the input directions of real earthquakes. Incremental dynamic analyses are conducted, and the structural responses in every individual input direction as well as in all the directions are studied. Finally, probabilistic seismic fragility analysis is conducted, and the probabilities of exceeding different limit states of the frame and cassette structures is presented. Amongst the studies, the novel cassette design can not only achieve much larger span, but also shows a better, more stable seismic performance. Therefore, the cassette structure may be a better alternative in seismic design.

With increasing transportation speed, the excessive vibrations of high-speed trains (HSTs) have become a critical issue to be solved. This study presents an innovative semiactive suspension system ...

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.

This study presents a new strategy to enhance the seismic performance of self-centering concentrically braced frames (SCCBFs). A hybrid strategy, which combines a SCCBF with a moment-resisting frame or buckling-restrained-braced frame, is first investigated, which show evident reduction in peak deformation demands. This benefit further inspires the design of multi-story pure SCCBFs with the enhanced post-yield stiffness ratio and/or energy dissipation factor directly. Incremental dynamic analyses indicates that the advanced SCCBFs achieve seismic peak deformation control comparable to that of the hybrid systems. Meanwhile, the advanced SCCBFs are nearly damage-free and fully recoverable after significant earthquakes, and thus represents a more favorable strategy from the seismic resilience perspective.

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.

Electromagnetic damper cum energy harvester (EMDEH) is an emerging dual-function device that enables simultaneous energy harvesting and vibration control. This study presents a novel energy-harvesting adaptive vibration control application of EMDEH on the basis of the past EMDEH development in passive control. The proposed EMDEH comprises an electromagnetic damper connected to a specifically designed energy harvesting circuit (EHC), wherein the EHC is a buck–boost converter with a microcontroller unit (MCU) and a bridge rectifier. The effectiveness of the energy-harvesting adaptive vibration damping is validated numerically through a high-speed train (HST) model running at different speeds. MCU-controlled adaptive duty cycle adjustment in the EHC enables the EMDEHs to adaptively offer the optimal damping coefficients that are highly dependent on train speeds. In the meantime, the harvested power can be stored in rechargeable batteries by the EHC. Numerical results project the average output power ranging from 40.5[Formula: see text]W to 589.8[Formula: see text]W from four EMDEHs at train speed of 100–340[Formula: see text]km/h, with a maximum output power efficiency of approximately 35%. In comparison to energy-harvesting passive vibration control and a pure viscous damper, the proposed energy-harvesting adaptive control strategy can improve vibration reductions by approximately 40% and 27%, respectively, at a speed of 340[Formula: see text]km/h. These numerical results clearly demonstrate the benefit and prospect of the proposed energy-harvesting adaptive vibration control in HST suspensions.

Construction activities often generate intensive ground-borne vibrations that may adversely affect structure safety, human comfort, and equipment functionality. Vibration monitoring systems are commonly deployed to assess the vibration impact on the surrounding environment during the construction period. However, traditional vibration monitoring systems are associated with limitations such as expensive devices, difficult installation, complex operation, etc. Few of these monitoring systems have integrated functions such as in situ data processing and remote data transmission and access. By leveraging the recent advances in information technology, an Internet of Things (IoT) sensing system has been developed to provide a promising alternative to the traditional vibration monitoring system. A microcomputer (Raspberry Pi) and a microelectromechanical systems (MEMS) accelerometer are adopted to minimize the system cost and size. A USB internet dongle is used to provide 4G communication with cloud. Time synchronization and different operation modes have been designed to achieve energy efficiency. The whole system is powered by a rechargeable solar battery, which completely avoids cabling work on construction sites. Various alarm functions, MySQL database for measurement data storage, and webpage-based user interface are built on a public cloud platform. The architecture of the IoT vibration sensing system and its working mechanism are introduced in detail. The performance of the developed IoT vibration sensing system has been successfully validated by a series of tests in the laboratory and on a selected construction site.

This paper proposes novel self-centering (SC) seismic base isolators by utilizing shape memory alloy U-shaped dampers (SMA-UDs) with favorable superelastic behavior. Two different designs, ...

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.

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.

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.

Refereed/Peer-reviewed

Reinforced concrete (RC) wall is a common type of structural component used in high-rise buildings to resist lateral loads induced by earthquakes. RC walls are typically designed and detailed to dissipate energy through significant inelastic responses to meet expected seismic performance under moderate-to-strong earthquakes. However, costly repair or even demolition caused by excessive residual deformation is usually inevitable. Given this deficiency, this study investigates the feasibility of utilizing superelastic shape memory alloy (SMA) bars to achieve self-centering (SC) RC walls. Under this condition, the residual deformation of SC–RC walls is reduced by superelastic SMA with large recoverable strain and remarkable fatigue properties. The mechanical properties of superelastic nickel–titanium bars and SC–RC wall design are described. A numerical SC–RC wall model is developed and validated by comparing the test results. Parametric studies of SC–RC wall systems are then conducted to investigate the effects of axial compressive load ratio, bottom slit length, and lower plateau stress factor of SMA. Results show that the proposed SC–RC walls have excellent SC ability and moderate energy dissipation capacity. The damage regions and levels of the SC–RC wall systems are also discussed.

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.

Many existing reinforced concrete (RC) structures around the world have been designed to sustain gravity and wind loads only. Past earthquake reconnaissance showed that strong earthquakes can lead ...

Long bridge cables are vulnerable to unanticipated large vibrations induced by earthquakes, wind, and traffic loads. The use of various dampers, including inerter dampers (IDs), as an effec...

The comfort of pedestrians on a footbridge is a rather complex problem that has been discussed for a long time. Vibration acceleration is generally accepted as the main controlling factor t...

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.

Influence line (IL) has emerged as very promising damage indices for bridge damage detection. This study proposed a method to localize and quantify damage in beam structures by estimating section flexibility change from deflection IL (DIL) change. To this end, the relationship between second derivative of DIL change and flexibility change was established. To remove noise interference in measurement, piecewise quadratic functions were used to fit and replace noisy DIL change curves, wherein the coefficients of quadratic function were determined via a sparse regularization method, considering the sparsity nature of damage that typically takes place in only a limited number of elements. The feasibility and accuracy of the proposed method are verified through numerical examples and laboratory experiments. Through four hypothetical damage scenarios of a simply supported beam with one or two damaged locations, its ability to quantify minor damage and its anti-noise robustness were well verified. Finally, a laboratory experiment on a simply supported aluminum beam illustrated that the location and extent of damage could be successfully identified in the single-damage and double-damage cases. The numerical and experimental results indicate that the proposed method is promising for future damage localization and quantification of bridge structures.

Wavelet techniques enable multi-resolution analysis that can represent a function (either field or signal function) in a multi-scale manner. This article presents a damage detection method with dynamically changed scales in both temporal and spatial domains, by taking advantage of the wavelet-based multi-resolution analysis. This method combines a wavelet-based finite element model (WFEM) that employs B-spline wavelet as shape functions and wavelet-based modal identification method to detect structural damage progressively. High-fidelity modal information can be computed or identified with minimized computation cost by lifting the wavelet scales in the wavelet-based finite element model and in signal processing individually according to the actual requirements. Numerical examples demonstrate that the accuracy of damage detection is improved considerably by this lifting strategy during the damage detection process. Besides, fewer degrees of freedom are involved in the wavelet-based finite element model than those of traditional finite element method. The computational efficiency can be improved to large extent and computation resources can be utilized more rationally using the proposed multi-scale approach.

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.

Fiber Bragg gratings (FBGs) have being seen for a growing application in the field of structural health monitoring (SHM) because of their lightweight features. This letter introduces an adaptive SHM sensing system based on the ultrasonic guided wave (UGW) and FBG sensor technology. First, the capability of the proposed SHM sensing system used to detect UGW is demonstrated by the frequency detection of Rayleigh wave that is generated by the piezoelectric transducers with a function generator. Furthermore, a nanosecond pulse laser is utilized to generate Lamb wave on an aluminum plate, while the SHM sensing system is employed to detect the wave in a long distance. Finally, the SHM sensing system is used to locate the source of Rayleigh wave that is created by a pulsed laser. The experiment results show the proposed SHM sensing system is capable of localizing and monitoring the UGW by using four FBG cascaded on a loaded aluminum plate.

Energy harvesting is an emerging technique that extracts energy from surrounding environments to power low-power devices. For example, it can potentially provide sustainable energy for wireless sensing networks (WSNs) or structural control systems in civil engineering applications. This paper presents a comprehensive study on harvesting energy from earthquake-induced structural vibrations, which is typically of low frequency, to power WSNs. A macroscale pendulum-type electromagnetic harvester (MPEH) is proposed, analyzed and experimentally validated. The presented predictive model describes output power dependence with mass, efficiency and the power spectral density of base acceleration, providing a simple tool to estimate harvested energy. A series of shaking table tests in which a single-storey steel frame model equipped with a MPEH has been carried out under earthquake excitations. Three types of energy harvesting circuits, namely, a resistor circuit, a standard energy harvesting circuit (SEHC) and a voltage-mode controlled buck-boost converter were used for comparative study. In ideal cases, i.e., resistor circuit cases, the maximum electric energy of 8.72 J was harvested with the efficiency of 35.3%. In practical cases, the maximum electric energy of 4.67 J was extracted via the buck-boost converter under the same conditions. The predictive model on output power and harvested energy has been validated by the test data.

The dynamic response of a beam under a moving load is a superposition of two components, namely, the moving-frequency component corresponding to the moving load and the natural-frequency component of the beam. This study investigates the closed-form solution of the dynamic response of a damaged simply supported beam subjected to a moving load and examines the effects of the loss of local stiffness on these two components. The study provides deep insights into beam damage detection based on moving load-induced response. Consequently, a simple and intuitive method for damage localization is developed. First, the closed-form solution is derived based on the modal perturbation and modal superposition method. The closed-form solution enables the individual examination of damage-induced changes in moving- and natural-frequency components. The results show that the moving-frequency component is preferred in damage localization. Then, multi-scale discrete wavelet transform is employed to separate the moving-frequency component from the total dynamic response and to subsequently locate the damage. Numerical examples with single or multiple damages are utilized to validate the efficacy of the proposed response computation algorithm and to demonstrate the effectiveness of the corresponding damage localization method. The effects of moving velocity and noise level are carefully studied. In particular, the effects of varying moving velocities and moving vehicular dynamics on damage localization are presented in this paper.

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

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.

Support settlement and cable slippage of a long-span suspension bridge may occur when it is subjected to extreme events. The evaluation of effects of support settlement and cable slippage on the remaining capacity then becomes important before making a retrofitting decision. However, it is difficult to conduct such an evaluation on the prototype bridge. This paper therefore presents experimental and numerical studies to examine the effects of support settlement and cable slippage on the structural performance of a long-span suspension bridge through a testbed, which include a laboratory-based model and an updated finite-element (FE) model. Four support settlement cases are experimentally studied with two on anchorage settlements and two on tower settlements. Main cable slippage at the top of towers is then investigated experimentally in two opposite directions. Both support settlement cases and cable slippage cases are also simulated using the corresponding FE model, and results are compared with ...

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.

An adaptive-scale damage detection strategy based on a wavelet finite element model (WFEM) for thin plate structures is established in this study. Equations of motion and corresponding lifting schemes for thin plate structures are derived with the tensor products of cubic Hermite multi-wavelets as the elemental interpolation functions. Sub-element damages are localized by using of the change ratio of modal strain energy. Subsequently, such damages are adaptively quantified by a damage quantification equation deduced from differential equations of plate structure motion. WFEM scales vary spatially and change dynamically according to actual needs. Numerical examples clearly demonstrate that the proposed strategy can progressively locate and quantify plate damages. The strategy can operate efficiently in terms of the degrees-of-freedom in WFEM and sensors in the vibration test.

This paper presents a new approach for detecting ultrasonic generated by a laser in the confined ablation regime, utilizing an adaptive fiber Bragg gratin (FBG) sensing system. A nanosecond pulsed laser is used for generating ultrasonic wave in aluminum specimen with water-confined layer. Experimental measurements demonstrate that the amplitudes of Rayleigh wave in the confined ablation regime are unexpectedly 8 times larger than the ones in direct ablation regime when the incident laser intensity is about 0.12×109 W/cm2. It is shown that confinement of the surface with a waterconfined layer provides an effective method of enhancing amplitude of laser-induced ultrasonic waves in the target material about an order of magnitude. These results indicate that the possibility of applying the laser-based FBG ultrasonic sensing system in nondestructive testing (NDT) and structure health monitoring (SHM) within special structural materials of high-speed train

Stay cables are vulnerable to excessive vibration because of their inherently low damping properties. Described in this paper is an experimental investigation of the vibration control perfo...

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.

This study employs a novel beam-type wavelet finite element model (WFEM) to fulfill an adaptive-scale damage detection strategy in which structural modeling scales are not only spatially varying but also dynamically changed according to actual needs. Dynamical equations of beam structures are derived in the context of WFEM by using the second-generation cubic Hermite multiwavelets as interpolation functions. Based on the concept of modal strain energy, damage in beam structures can be detected in a progressive manner: the suspected region is first identified using a low-scale structural model and the more accurate location and severity of the damage can be estimated using a multi-scale model with local refinement in the suspected region. Although this strategy can be implemented using traditional finite element methods, the multi-scale and localization properties of the WFEM considerably facilitate the adaptive change of modeling scales in a multi-stage process. The numerical examples in this study clearly demonstrate that the proposed damage detection strategy can progressively and efficiently locate and quantify damage with minimal computation effort and a limited number of sensors.

Bridge inspections reveal that severe corrosion and fatigue are the main failure mechanisms of bridge stay cables. This paper presents an empirical modelling of the long-term deterioration process of steel wires in cables with consideration of the simultaneous occurrence of uniform corrosion, pitting corrosion and fatigue induced by a combined action of environmental aggression and cyclic loading. Accelerated corrosion experiments are conducted to determine the different corrosion levels of high-strength steel wires, and time-dependent statistical models are developed to quantify uniform and pitting corrosion depth. Corrosion-fatigue process of steel wires is subsequently simulated using the corrosion models and cyclic stress obtained through cable force monitoring data. The mechanical properties of corroded steel wires, including yield stress, ultimate stress, ultimate strain and modulus of elasticity, are experimentally characterised, and the statistical models are established through regression analysi...

Numerous long-span bridges have been built throughout the world in recent years. These bridges are progressively damaged by continuous usage throughout their long service life. The failure of local structural components is detrimental to the performance of the entire bridge, furthermore, detecting the local abnormality at an early stage is difficult. This paper explores a novel damage detection method for long-span bridges by incorporating stress influence lines (SILs) in control charts, and validates the efficacy of the method through a case study of the Tsing Ma Suspension Bridge. Damage indices based on SILs are subsequently proposed and applied to hypothetical damage scenarios in which one or two critical bridge components are subjected to severe damage. The comparison study suggests that the first-order difference of SIL change is an accurate indicator for location of the damage. To some extent, different levels of damage can be quantified by using SILs incorporating with X-bar control chart. Results of this study indicate that the proposed SIL-based method offers a promising technique for damage detection in long-span bridges.

To ensure bridge safety and functionality under in-service conditions, detecting local abnormalities of a long-span bridge at the early stage is always a desirable but challenging task. Stress influence lines (SIL) or its derivatives are recognized as very promising indices for damage detection. Compared with bridge global responses (such as displacement and acceleration), stress/strain can be more conveniently measured and is often more sensitive to local damages. This paper explores a novel damage localization approach by synthesizing SIL measurements from multiple locations, in which Dempster-Shafer data fusion technique is utilized. Compared with the measurement from a single sensor, more reliable damage-related information with the improved sensitivity and capability in damage localization can be obtained by synthesizing the measured SILs from a number of sensors. The effectiveness of the proposed method is validated through a numerical case study of the Tsing Ma Suspension Bridge. Different hypothetical scenarios, including single-damage case, double-damage, and no-damage cases, are considered in the validation. The comparison with the damage detection results using single-sensor data clearly indicates that the data fusion technique effectively enhance the consistency in the information (e.g., damage-induced structural change) and minimize non-consistent information (e.g. “noise” effect) from multiple sensors installed close to damage. The increasing number of sensors benefits the damage detection results. Excellent damage detection accuracy can be achieved, if different types of bridge components are properly selected for the monitoring. Therefore, it is promising to use the proposed approach in this study in the damage localization of real-world long-span bridges. Parametric studies are conducted to examine the effects of parameter selections and noise levels in this approach.

Many metropolitan cities suffer from a shortage of land supply, which results in new development in areas with high building density. Construction activities, particularly piling processes, may generate excessive ground-borne vibrations. The nearby sensitive people, facilities and buildings (e.g. hospitals and healthcare institutions) are often vulnerable to such excessive vibrations. However, the impact of construction-induced vibrations on sensitive medical equipment is rarely discussed. The vibration limits commonly adopted by the construction industry are mainly with regard to structural safety, which are considerably greater than the tolerable limits for sensitive medical equipment. This case study evaluates the potential effect of ground vibrations induced by piling activities on sensitive medical equipment. The ground-borne vibrations induced by two piling methods are quantified by field measurements. The indoor floor vibrations are simulated using building models. The vibration limits for a large number of sensitive items of medical equipment are established through questionnaires to the manufacturers. The potential risk to the functionality of the concerned equipment is illustrated by comparing the tolerable vibration limits with the predicted vibration levels.

Base isolators are commonly used to protect highway bridges from severe seismic damage. A novel self-centering isolator based on superelastic shape memory alloy (SMA) has been proposed to be installed between the piers and decks of highway bridges. This paper systematically evaluates the seismic performance of SMA isolators via the incremental dynamic analysis (IDA) of a prototype highway bridge with SMA isolators. The multi-span reinforced concrete highway bridge and the corresponding SMA isolators are designed according to an ad hoc displacement-based design (DBD) approach. The seismic analyses are conducted under different seismic intensity levels using the computation program DRAIN2DX. IDA results indicate that the SMA isolators can effectively protect the superstructure of the highway bridge and minimize the post-earthquake residual deformation. The properly designed highway bridges with SMA isolators are subjected to limited damage under frequent and design basis earthquakes.

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.