•An inerter-based damper is employed for vibration mitigation and energy harvesting.•A new nonlinear mechanical model is proposed and validated for an EIMD.•A model is proposed to predict the ...energy-harvesting performance of an EIMD.
Recently, a novel inerter-based damper termed electromagnetic inertial mass damper (EIMD) that is capable of generating a large inertance and providing a controllable electromagnetic (EM) damping has been used as an energy dissipation device for seismic response control. Structural vibration energy induced by external loading is converted into electricity via the EIMD, for being dissipated and harvested. In this paper, the EIMD is proposed for simultaneous vibration mitigation and energy harvesting for the first time. A new mechanical model is proposed to predict the nonlinear behavior of the EIMD, and a linearized model is subsequently deduced based on the equal energy dissipation rule. In addition, an energy-harvesting model is presented to predict the output power and energy harvesting efficiency of the EIMD. To maximize the efficiency of the EIMD, this paper derives the corresponding optimal load resistance that can serve as the design criteria for an energy harvesting circuit (EHC). The proposed models are validated by the dynamic test of a prototype EIMD using harmonic excitation.
•An active learning method combining Kriging and Subset Simulation (AK–SS) is proposed.•AK–SS takes advantages of Subset Simulation and the Kriging metamodel.•The proposed method is applied to ...several benchmark functions and a tunnel lining structure.•AK–SS is shown to be more efficient than the other methods in the literature.•AK–SS can deal with small probability problems with time-consuming function evaluations.
With complex performance functions and time-demanding computation of structural responses, the estimation of small failure probabilities is a challenging problem in engineering. Although Subset Simulation (SS) is a powerful tool for small probabilities, the computation amount is still large for time-consuming numerical procedures. Metamodelling is an important approach to increase the computational efficiency for engineering problems, however, a larger set of sample points is required for higher accuracy. This is a time-consuming task when the performance function needs to be numerically evaluated. To address this issue, AK–SS: an active learning method combining Kriging model and SS is proposed in this paper. The efficiency of this new method relies upon the advantages of SS in evaluating small failure probabilities and the Kriging model with active learning and updating characteristic for approximating the true performance function. The proposed method is applied to several benchmark functions in the literature, and to the reliability analysis of a shield tunnel, which requires finite element analysis. The results demonstrated that as compared to the other approaches in literature, AK–SS can provide accurate solutions more efficiently, making it a promising approach for structural reliability analyses involving small failure probabilities, high-dimensional performance functions, and time-consuming simulation codes in practical engineering.
•A full-scale experiment on using an EIMD for cable vibration mitigation is presented.•EIMD provides a super-high cable damping ratio, which triples that of viscous dampers.•Mechanism of EIMD on ...cable vibration mitigation is investigated in terms of energy dissipation.•Multi-mode control performance of EIMD is validated.
Previous numerical study has shown tremendous improvements in increasing the modal damping of bridge stay cables using inerter-based dampers. This article presents an experimental and numerical study on the vibration mitigation of a 135 m long full-scale cable using a novel inerter-based damper termed electromagnetic inertial mass damper (EIMD). The effect of the inerance and damping coefficient of the EIMD on the dynamic characteristics of the cable-EIMD system were systematically investigated using total 133 sets of free vibration data. A numerical model of the cable-EIMD system was established using finite difference method for implementing complex eigenvalue analysis. The relation between the first modal damping ratio and the EIMD parameters was observed in the experiment, which matches well with the prediction by the complex eigenvalue analysis. When installed at 2.5% of cable length away from the anchorage, the EIMD has achieved the maximum first modal damping ratio up to 3.66%, which is 192.8% larger than the theoretical upper limit (1.25%) of a viscous damper (VD). We also observed that the inerter element of the EIMD amplified the damper vibration amplitude and caused approximate π/2 phase lag of damper response. Such unique mechanism remarkably increases the energy dissipation of the EIMD. The inerter element significantly reduces the optimal damping coefficient required for cable vibration mitigation compared to that of the VD. The vibration mitigation performance of the EIMD for higher modes is also validated via harmonic vibration test using sine sweep excitations. The EIMD is capable of achieving superior vibration mitigation performance for bridge stay cables if both the inertance and damping coefficient were set as their optimal values.
•Optimum design formulas for TID are derived for seismic response control.•Seismic control performance of the optimally designed TID is demonstrated.•TID outperforms the conventional TMD for seismic ...response control.•TID can prolong the fundamental period of a structure-TID system.•TID greatly reduces acceleration response of short-to-moderate period structures.
Tuned inerter damper (TID) is a promising passive vibration control device in earthquake engineering because it achieves a large inertance-to-mass ratio without requiring a large space and thus can effectively decrease the cost. This paper presents a theoretical and numerical study of a structure-TID system subjected to earthquake ground motions. Using the fixed-point theory, we derived simple design formulas for the TID when it attached to a single-degree-of-freedom system subjected to ground acceleration excitations. Analytical and numerical results demonstrate that the optimally designed TID using the proposed parameters is capable of suppressing the displacement response of structures with natural period ranging from 0.3 s to 5 s, and the performance positively relates to the inertance-to-mass ratio used. Particularly, a TID with a large inertance-to-mass ratio can significantly prolong the fundamental period of a structure-TID system, which is similar to a seismic isolation system. The optimally designed TID can effectively mitigate the absolute acceleration response of short-to-moderate period structures, but is far less likely to be effective for long-period structures. It is suggested that a value of less than one is used for the inertance-to-mass ratio of long-period structures if one intended to mitigate both displacement and absolute acceleration responses. In addition, numerical results illustrate that an optimal inertance-to-mass ratio exists when a single TID is applied to a multi-degree-of-freedom building structure. The results also indicate that the emerging TID outperforms the conventional tuned mass damper for seismic response control because the former device introduce no additional seismic energy to the system and is more robust due to large inertance-to-mass ratio used.
Piezoelectric lead zirconate titanate (PZT) is being gradually applied into practice as a new intelligent material for structural health monitoring. In order to study the damage detection properties ...of PZT on concrete slabs, simply supported reinforced concrete slabs with piezoelectric patches attached to their surfaces were chosen as the research objects and the Electromechanical Impedance method (EMI) was adopted for research. Five kinds of damage condition were designed to test the impedance values at different frequency bands. Consistent rules are found by calculation and analysis. Both the root mean square deviation (RMSD) and the correlation coefficient deviation (CCD) damage indices are capable of detecting the structural damage. The newly proposed damage index Ry/Rx can also predict the changes well. The numerical and experimental studies verify that the Electromechanical Impedance method can accurately predict changes in the amount of damage in reinforced concrete slabs. The damage index changes regularly with the distance of damages to the sensor. This relationship can be used to determine the damage location. The newly proposed damage index Ry/Rx is accurate in determining the damage location.
In engineering measurements, metal foil strain gauges suffer from a limited range and low sensitivity, necessitating the development of flexible sensors to fill the gap. This paper presents a ...flexible, high-performance piezoresistive sensor using a composite consisting of graphene nanoplatelets (GNPs) and polydimethylsiloxane (PDMS). The proposed sensor demonstrated a significantly wider range (97%) and higher gauge factor (GF) (6.3), effectively addressing the shortcomings of traditional strain gauges. The microstructure of the GNPs/PDMS composite was observed using a scanning electron microscope, and the distribution of the conductive network was analyzed. The mechanical behavior of the sensor encapsulation was analyzed, leading to the determination of the mechanisms influencing encapsulation. Experiments based on a standard equal-strength beam were conducted to investigate the influence of the base and coating dimensions of the sensor. The results indicated that reducing the base thickness and increasing the coating length both contributed to the enhancement of the sensor's performance. These findings provide valuable guidance for future development and design of flexible sensors.
In the electromechanical impedance (EMI) method, the PZT patch performs the functions of both sensor and exciter. Due to the high frequency actuation and non-model based characteristics, the EMI ...method can be utilized to detect incipient structural damage. In recent years EMI techniques have been widely applied to monitor the health status of concrete and steel materials, however, studies on application to timber are limited. This paper will explore the feasibility of using the EMI technique for damage detection in timber specimens. In addition, the conventional damage index, namely root mean square deviation (RMSD) is employed to evaluate the level of damage. On that basis, a new damage index, Mahalanobis distance based on RMSD, is proposed to evaluate the damage severity of timber specimens. Experimental studies are implemented to detect notch and hole damage in the timber specimens. Experimental results verify the availability and robustness of the proposed damage index and its superiority over the RMSD indexes.
In the field of wireless strain monitoring, it is difficult for the traditional metal-made antenna sensor to conform well with steel structures and monitor large strain deformation. To solve this ...problem, this study proposes a flexible antenna strain sensor based on a ductile graphene film, which features a 6.7% elongation at break and flexibility due to the microscopic wrinkle structure and layered stacking structure of the graphene film. Because of the use of eccentric embedding in the feeding form, the sensor can be miniaturized and can simultaneously monitor strain in two directions. The sensing mechanism of the antenna is analyzed using a void model, and an antenna is designed based on operating frequencies of 3 GHz and 3.5 GHz. The embedding size is optimized using a Smith chart and impedance matching principle. Both the simulation and experimental results verify that the resonant frequency and strain magnitude are linearly inversely proportional. The experimental results show that the strain sensitivity is 1.752 kHz/με along the geometric length and 1.780 kHz/με along the width, with correlation coefficients of 0.99173 and 0.99295, respectively.
► The proposed technique can monitor and predict the earlier age strength of concrete, even the first day strength, which is difficult to implement by the surface-bonded PZT transducers. ► The ...indexes of MAPD and RMSD are introduced to further evaluate the correlation between the compressive strength of concrete and the electric admittances of PZT embedded into concrete. ► A waterproof process for PZT patches using asphalt lacquer material is briefly addressed in order to use PZT patches as embedded transducers into concrete.
Piezoelectric lead zirconate titanate (PZT) impedance transducer in the electro-mechanical impedance (EMI) technique has emerged as a potential sensing tool for structural health monitoring. In the EMI technique, PZT acts as both sensor and actuator simultaneously due to its direct and inverse piezoelectric effects. The PZT impedance transducer provides a new alternative for monitoring the compressive strength gain of concrete since the conventional nondestructive detection techniques have many limitations. This paper briefly presents a waterproof process for PZT patches using asphalt lacquer material in order to use PZT patches as embedded transducers into concrete, and also presents a new monitoring technique of concrete strength based on embedded PZT impedance transducers. In the technique, a PZT patch covered with asphalt lacquers are embedded into one of concrete cubes. By monitoring the PZT admittance (inversion of impedance) signals and measuring the compressive strength of concrete cubes in different ages, and by combining with the indexes of the root mean-square deviation (RMSD) and the mean absolute percentage deviation (MAPD), the correlations between concrete strength gain and RMSD as well as its correlation with MAPD are founded. The feasibility of the new EMI method based on embedded PZT transducers for monitoring the concrete strength development in early ages is verified.
•The effects of pier height and elastomeric bearing on the bridge response are studied.•RTHS is utilized to consider the rate-dependent behavior of elastomeric bearings.•Both hyper-viscoelastic and ...bilinear models of elastomeric bearings are implemented.•The effects on the component- and system- level of the bridge are investigated.
Elastomeric bearings are widely utilized in highway bridges and attracting a great deal of attention, although their mechanical behavior has been clearly recognized, the coupled effects of critical bridge structural components and complex mechanical behavior of elastomeric bearings are yet to be well characterized. In this study, experimental investigation and seismic fragility analysis were conducted to evaluate the seismic performance of isolated highway bridges, with a special emphasis on considering the coupled effects of pier height and rate-dependent behavior of elastomeric bearings on the bridge response. To this end, real-time hybrid simulation (RTHS) tests featured by a velocity loading control were performed on a typical highway bridge. Two pier heights and two common types of elastomeric bearings including low damping rubber bearing and high damping rubber bearing were paired and tested. The effects of pier height and elastomeric bearings were illustrated by comparing and analyzing a wide range of response quantities of the bridge. The test results indicated that pier height and rate-dependent behavior of elastomeric bearings could remarkably influence the seismic response of the bridge in both individual and combined ways. Subsequently, a hyper-viscoelastic model of elastomeric bearings was proposed to capture their mechanical behavior, then, both the proposed and conventional bilinear models were implemented in the numerical simulation to evaluate the seismic fragility of the bridge. Fragility curves for two bridge components including piers and elastomeric bearings as well as for the bridge system were developed and discussed. The study reveals crucial effects of pier height and mechanical behavior of elastomeric bearings on both the component and system fragility curves of the bridge, it is found that an optimal combination of pier height and elastomeric bearings should be considered to improve the seismic performance of isolated highway bridges.
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