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An ultra-high voltage (UHV) composite bypass switch (BPS) faces increasing seismic challenges when UHV projects extend to high seismic intensity areas. The UHV composite BPS still generates excessive stress at the bottom section although hollow composite insulators with high flexural strength are adopted. Since the standard retrofitting strategy by using stiffer supports cannot reduce stress responses, wire rope isolation is introduced. The optimal design of isolation considers both stress and displacement responses since the slenderness and composite material of insulators contribute to significant displacement. The results show that properly designed isolation can significantly reduce stress without excessive displacement responses. A larger radius configuration helps to improve the applicability of small stiffness isolators under high winds. When the isolation still cannot satisfy the requirement, smaller stiffness isolators with a larger radius, or isolators with increased loops and smaller radius, can be introduced to gain better energy dissipation capacity and effectiveness in response mitigation. Accordingly, a three-step design procedure is proposed to increase the damping force but fix the rotational stiffness of isolation. Hence, the application of wire rope isolation can be extended to UHV composite BPS with a low natural frequency, but conductors with enough redundancy should be used.

The distributed long-gauge fiber Bragg grating sensing technology has been studied and developed in recent years for structural health monitoring of civil engineering structures. Also, the corresponding damage identification method is one of the research hotspots and still needs to be enhanced. In this article, a novel damage detection method based on the distributed long-gauge fiber Bragg grating sensing technique is proposed to detect and localize damages. The method is based on the advanced complete ensemble empirical mode decomposition adaptive noise algorithm. Measured macrostrain responses from the long-gauge fiber Bragg grating sensors are decomposed into intrinsic mode functions, and the quasi-static macrostrains are extrapolated and extracted. A damage indicator is therefore proposed and built based on the quasi-static macrostrain time history. The effectiveness of the proposed damage detection approach was validated by numerical simulations of a cantilever beam. The robustness of the method was further verified by considering the noise pollution contained within the measured macrostrain. Experiments with a practical cantilever steel beam with different damage scenarios were also conducted and studied. Results proved that the proposed method could not only detect but also locate the damages accurately, and therefore has the promising potential for structural damage detection in civil engineering.

This paper evaluates the influence of supporting frames on the seismic performance of an ultra-high voltage (UHV) gas insulated switchgear (GIS) bushing. Shaking table tests were carried out on a full-size UHV-GIS bushing mounted on two identical supporting frames except for their braces and joints. Finite element analyses were carried out on the joints' stiffness of the two frames, and seismic analyses on the bushing-supporting frame systems were conducted. Afterwards, parametric analyses on the joints' rotational and axial stiffness in the frames were carried out. The results indicated that the dynamic properties of the supporting frames affect the seismic performance of the bushing. After retrofitting, the amplification effects of the frame were reduced, and the seismic performance of the system improved. Moreover, the frame mainly amplified the acceleration response spectra near the fundamental frequency of the frame itself. The supplemented braces made greater contributions to reduce the seismic responses of the GIS bushiung, and increasing the joints' stiffness could reduce the severity of seismic responses on a bushing.

Since the seismic performance of the bypass switch (BPS) cannot satisfy the stress safety factor requirement, an isolated combination of wire ropes with linear viscous dampers was employed. The assembled base isolation was designed using modal parameters, and the effectiveness of the isolation was validated numerically using finite element (FE) analysis and experimentally by the shaking table test. The numerical study shows that wire rope isolation can reduce the stress of a BPS considerably. Furthermore, the implementation of supplementary viscous dampers can further reduce the stress and, more importantly, displacement response, which is significant for UHV equipment. The middle section of BPS generates obvious high frequency vibration during test, although the root section still experiences the maximum stress response. Besides, testing verified the reliability of the FE model and confirmed that the stress safety factor requirement was satisfied. Therefore, the isolation comprised of wire ropes and a viscous damper is proposed to improve the seismic performance of the slender 800 kV composite BPS.

A model of interconnected electrical equipment was established to study how flexible conductors affect the seismic responses of electrical equipment. The model was validated by conducting shaking table tests on an interconnected 220-kV full-size disconnecting switch-breaker system. The system was connected by flexible conductors of varying slackness. Afterwards, the model was adopted to carry out parametric analyses of the interconnected equipment. The tests and analyses showed that the critical sag-to-span ratio of a flexible conductor is related to equipment frequency and peak ground acceleration. Specifically, when the sag-to-span ratio of the conductor was less than the critical ratio, the horizontal terminal force increased rapidly. Even if the conductor was not straightened in the earthquakes considered, its vibration amplified the seismic responses of the interconnected equipment. Both the frequency ratio of the interconnected equipment and the frequency of the softer equipment influenced the interconnected effects of the electrical equipment. Furthermore, the displacement of the lower-frequency equipment made a larger contribution to the observed coupling effects.

Extreme winds may expose overhead transmission lines to loads that may result in the collapse of transmission towers leading to severe economic losses. This paper develops a modelling framework to assess the fragility of transmission towers under extreme winds such as tropical storms. To this end, the wind loading on a transmission tower is represented by a combination of three wind load components (i.e., the transverse and longitudinal tower loads as well as the wire load) expressed in terms of three key wind load-related input parameters (wind speed, wind angle of attack and horizontal span of the transmission line). The wind load-carrying capacity of towers is accordingly defined by a three-dimensional convex-curve surface with the three wind load components as the principle axes. A kriging surrogate model is established for the tower capacity surface as a function of uncertain structural parameters, based on the results from the nonlinear static analysis of the tower and Latin-hypercube sampling. Accordingly, the limit state function would suggest tower failure if the wind load effect exceeds the tower capacity defined by the surface. In this framework, the tower fragility is established by the Monte Carlo simulation. If the wind intensity, wind direction and line configuration are known, the wind load components can be evaluated. Utilizing the surrogate model, the capacity surfaces of sample towers are also obtained in terms of the simulated uncertain structural parameters simulated. Comparison between the estimated wind load components and the simulated sample surfaces yields the fragility curve. The proposed framework is demonstrated by a numerical example, as well as an application to a typhoon scenario analysis in which the failure probability of a real-world long-distance transmission line is assessed.

To evaluate the terminal force and configuration of bundled flexible conductors used in high voltage substations, this study developed a parametric method for modelling the large planar deflection of the flexible conductors. The flexible conductors were assumed to be planar beams. Based on the chained-beam constraint model (CBCM), the equations of the constraint effects of spacers and the geometric constraint of the bundled conductors were added to the model. Additionally, the CBCM was modified to capture the loading of a concentrated force on the intermediate part of the conductors. The model was validated by static tests and finite element analyses. Some case studies on the terminal force and configuration of the bundled flexible conductors based on this model were carried out. The terminal force and configuration of the bundled conductors calculated with and without bending stiffness were compared, showing that the constraint effects of the spacers increased the stiffness of the bundled conductors. Ignoring the bending stiffness and the constraint effects of the spacers will lead to analytical errors in the terminal force and configurations of the bundled flexible conductors used in high voltage substations.

To evaluate and improve the seismic performance of a ±800 kV ultra-high voltage (UHV) wall bushing-valve hall system, a finite element model of the system was established. Sixteen different earthquake ground motions were adopted in the analysis, and the critical seismic responses of the system were obtained. Moreover, a vibration theoretical model of the UHV wall bushing-valve hall system was established, and an investigation was conducted on the influence of different vibration components on the wall bushing seismic responses. The results indicate that the valve hall has an amplification effect on the seismic responses of the wall bushing and the vibration of the gable wall has a remarkable influence on the responses of the wall bushing. Two retrofitting measures were carried out on the valve hall to reduce the seismic responses of the wall bushing. It is concluded that increasing the stiffness of the gable wall could improve the seismic performance of the UHV wall bushing-valve hall system.

Inerter-based vibration control systems have been developed rapidly in recent years. However, previous studies mainly focus on the development of new devices and parameter optimization strategies, while ignoring the improvements in the utilization efficiency of the inerter system that the bracing system and novel installation methods may bring. In this paper, a cross-layer installed cable-bracing inerter system (CICBIS) is proposed to improve the utilization efficiency of the inerter system, which can cross more layers and is suitable for shear-type multi-degree-of-freedom (MDOF) structures. A demand-based cable-bracing inerter system (CBIS) design method is developed. The mass enhancement and utilization efficiency improvement of the inerter system caused by the cross-layer installation are quantified through calculating the effective inerter-mass ratio of the CBIS-equipped MDOF structure. A 10-story benchmark structure is used to verify the control performance of the CICBIS and the design method. The analysis results show that the proposed design method can exert the cable-bracing system&rsquo, s adjustability and the damping enhancement of the inerter system. The CICBIS can reduce the total apparent mass and damping coefficient requirements of the inerter systems without increasing the control force. It means that the proposed design method is effective, and the CICBIS has a high efficiency.

Wind turbine tower vibration parameters are critical for design and maintenance of wind farms. In this paper, measurement campaigns of two in-service 65-m tall wind turbine towers are inves...

Purpose This paper aims to develop a comprehensive uncertainty quantification method using evidence theory for Park–Ang damage index-based performance design in which epistemic uncertainties are considered. Various sources of uncertainty emanating from the database of the cyclic test results of RC members provided by the Pacific Earthquake Engineering Research Center are taken into account. Design/methodology/approach In this paper, an uncertainty quantification methodology based on evidence theory is presented for the whole process of performance-based seismic design (PBSD), while considering uncertainty in the Park–Ang damage model. To alleviate the burden of high computational cost in propagating uncertainty, the differential evolution interval optimization strategy is used for efficiently finding the propagated belief structure throughout the whole design process. Findings The investigation results of this paper demonstrate that the uncertainty rooted in Park–Ang damage model have a significant influence on PBSD design and evaluation. It might be worth noting that the epistemic uncertainty present in the Park–Ang damage model needs to be considered to avoid underestimating the true uncertainty. Originality/value This paper presents an evidence theory-based uncertainty quantification framework for the whole process of PBSD.

Evidence theory, with its powerful features for uncertainty analysis, provides an alternative to probability theory for representing epistemic uncertainty, which is an uncertainty in a system caused by the impreciseness of data or knowledge that can be conveniently addressed. However, this theory is time-consuming for most applications because of its discrete property. This article describes an adaptive sub-interval perturbation-based computational strategy for representing epistemic uncertainty in structural dynamic analysis with evidence theory. The possibility of adopting evidence theory as a general tool for uncertainty quantification in structural transient response under stochastic excitation is investigated using an algorithm that can alleviate computational difficulties. Simulation results indicate that the effectiveness of the presented strategy can be used to propagate uncertainty representations based on evidence theory in structural dynamics.

A wind tunnel test on the aero-elastic model of UHV transmission tower line system was carried out for researching tower line system's dynamic behavior under different wind speeds. The effect of wires' vibration on tower was particularly addressed in the paper. For comparison, the single tower model and tower line system model were involved. Both alongwind and crosswind responses of tower were investigated. The wire's dynamic strain was traced synchronously for exploring the coupling vibration effect of tower line system. Comparing the responses of the single tower model and the tower line model, it is found that 70–90% displacement and strain are induced by wires. This action is more prominent in the alongwind direction. However, the peak response values of the tower line model are smaller than those of the single tower model. Test results in frequency domain indicate that the dynamic behavior of the tower becomes more susceptible to wind speed when it connects with wires. As to the tower line system, the response power spectra of the tower and the conductors show the tendency of moving to lower and higher frequency region respectively with the crests weakened and vibration energy dispersed when wind speed increases.

Uncertainties originate from physical variability, data uncertainty, and modeling errors in the fatigue crack growth prediction analysis. This study presents an evidential uncertainty quantification (UQ) approach for determining uncertainties involved in revealing the material constants of the metal fatigue crack growth model with imprecise uncertainty information (i.e., epistemic uncertainty). The parameters in fatigue crack growth model are obtained by fitting the available sparse experimental data, and then the uncertainties in these parameters are considered. To alleviate the computational difficulties in the UQ analysis based on evidence theory, an interval optimization method based on differential evolution is used in finding the propagated belief structure. The overall procedure is demonstrated using the results of several replicated experiments on aluminum alloy CCT specimens.

With the rapid development of subway systems, the negative environmental impacts of vibration induced by subways has gradually become a research hotspot. For the purpose of developing predictive models of vibration and designing effective vibration mitigation systems, continuous field dynamic measurements were conducted simultaneously in a subway tunnel, ground, and building in eastern China, the most prosperous region in China. The characteristics of vibration transmission and attenuation induced by subway were analyzed by statistical analysis of large amounts of measurement data. The results showed that most prominent and visible attenuation of vibration is from the track to the ballast bed in the tunnel, where the ground-borne vibration would quickly decrease exponentially with distance. The results also showed that the measured attenuation value of indoor vibration was approximate 0.76 dB on average between each floor. Moreover, the decay ratio of the vibration increased with the increase in the frequency range. Based on these findings, construction gauge of 20&ndash, 25 m outside of the tunnel is recommended. In addition, reducing the vibration source excitation intensity is the most effective vibration isolation method, especially by track structural transformation.

The uncertainty in parameter estimation arises from structural systems&rsquo, input and output measured errors and from structural model errors. An experimental verification of the shuffled complex evolution metropolis algorithm (SCEM-UA) for identifying the optimal parameters of structural systems and estimating their uncertainty is presented. First, the estimation framework is theoretically developed. The SCEM-UA algorithm is employed to search through feasible parameters&rsquo, space and to infer the posterior distribution of the parameters automatically. The resulting posterior parameter distribution then provides the most likely estimation of parameter sets that produces the best model performance. The algorithm is subsequently validated through both numerical simulation and shaking table experiment for estimating the parameters of structural systems considering the uncertainty of available information. Finally, the proposed algorithm is extended to identify the uncertain physical parameters of a nonlinear structural system with a particle mass tuned damper (PTMD). The results demonstrate that the proposed algorithm can effectively estimate parameters with uncertainty for nonlinear structural systems, and it has a stronger anti-noise capability. Notably, the SCEM-UA method not only shows better global optimization capability compared with other heuristic optimization methods, but it also has the ability to simultaneously estimate the uncertainties associated with the posterior distributions of the structural parameters within a single optimization run.

The industrial chimney is one of the important components used in industrial processes. The tuned mass damper was introduced in previous studies to improve its reliability for resisting earthquakes. However, a large additional mass is generally required for applying a tuned mass damper in a chimney, which may be inappropriate owing to the additional moment action. In this study, the tuned mass inerter system (TMIS) is adopted as an ungrounded lightweight passive control device for the seismic response mitigation of high-rise chimneys. The ungrounded TMIS consists of a tuned mass element and a parallel-connected tuning spring and inerter subsystem. Considering that the influence of high modes on the responses of a high-rise chimney may not be neglected, distributed TMISs (d-TMISs) are proposed for installation on the chimney for multimode control of seismic response. A strategy to optimize d-TMISs for multimode control of high-rise chimneys is developed. A typical numerical chimney model is established to illustrate the proposed optimal design method. Time history analysis and comparative studies are conducted to verify the optimal multimode control design and the lightweight effect of d-TMISs compared to the traditional tuned mass dampers. The results show that by applying the proposed optimization in d-TMISs, the performance objectives can be achieved and the chimney’s responses involving the high-order modes can be reduced as anticipated. The required weight of d-TMISs is less than that for tuned mass dampers under an identical performance objective. It is observed that the proposed optimal multimode control method is effective and that d-TMISs can achieve the lightweight effect.

A robust multi-objective optimization method for truss optimum design is presented. In the robust design, materials and loads are assumed to be affected by epistemic uncertainties (imprecise or lack of knowledge). Uncertainty quantification using evidence theory in optimum design subject to epistemic uncertainty is undertaken. In addition to a functional objective, an evidence-based plausibility measure of failure of constraint satisfaction is minimized to formulate the robust design into a multi-objective optimization problem. In order to alleviate the computational difficulties in the evidence theory-based uncertainty quantification analysis, a combined strategy of differential evolution-based interval optimization method and parallel computing technique is proposed. A population-based multi-objective differential evolution optimization algorithm is designed for searching robust Pareto front. Two truss structures with shape and sizing optimum design problems are presented to demonstrate the effectiveness and applicability of the proposed method.

In this paper, the full rehabilitation process of a damaged passively controlled building is reported. A hybrid retrofit plan that uses tin-rubber bearings to replace the damaged oil dampers is pro...

The damping estimation of an eight-story steel building equipped with oil dampers is examined, carried out by adopting a proposed framework, which consists of an enhanced strain-energy method and an improved direct method for model updating. The building is located at Tohoku Institute of Technology and is equipped with a structural monitoring system that measures its seismic response, including floor acceleration and displacement and force of oil dampers. The enhanced strain-energy method is first developed and employed to assess the supplemental damping and stiffness provided by oil dampers, herein quantified in the form of equivalent damping ratios and natural frequencies. Then, modal characteristics extracted from the earthquake measurements are modified accordingly and utilized for the building model updating, in which mass and stiffness matrices are corrected by the improved direct method. The updated model accurately reproduces the target modal data, especially measured mode participation factors, and is further used for the building response predictions. Through prediction validations, the precision of the modified modal parameters is verified. Finally, a large earthquake event is chosen to demonstrate the effectiveness of the proposed framework for the damping estimation of the investigated building.

Due to the increased service life, environmental corrosion, unreasonable construction, and other issues, local defects inevitably exist in civil structures, which affect the structural performance and can lead to structural failure. However, research on grout defect identification of precast reinforced concrete frame structures with rebars spliced by sleeves faces great challenges owing to the complexity of the problem. This study presents a multiple-variable spatiotemporal regression model algorithm to identify local defects based on structural vibration responses collected using a sensor network. First, numerical simulations were carried out on precast beam&ndash, column connection models by comparing the identification results based on a single-variable regression model, two-variable spatial regression model, and two-variable spatiotemporal regression model, furthermore, a multiple-variable spatiotemporal regression model was proposed and robustness analysis of the damage indicator was carried out. Then, to explore the validity of the proposed method, a nondestructive vibration experiment was considered on a half-scaled, two-floor, precast concrete frame structure with column rebars spliced by defective grout sleeves. The results show that local defects were successfully identified based on a multiple-variable spatiotemporal regression model.

Since physical parameters are much more sensitive than modal parameters, structural parameter identification with an extended Kalman filter (EKF) has received extensive attention in structural health monitoring for civil engineering structures. In this paper, EKF-based parameter identification technique is studied with numerical and experimental approaches. A four-degree-of-freedom (4-DOF) system is simulated and analyzed as an example. Different integration methods are examined and their influence to the final identification results of the structural stiffness and damping is also studied. Furthermore, the effect of different kinds of noise is studied as well. Identification results show that the convergence speed and estimation accuracy under Gaussian noises are better than those under non-Gaussian noises. Finally, experiments with a five-story steel frame are conducted to verify the damage identification capacity of the EKF. The results show that stiffness with different damage degrees can be identified effectively, which indicates that the EKF is capable of being applied for damage identification and health monitoring for civil engineering structures.

The small first passage probability of nonlinear dynamic structures under nonstationary seismic excitation implies a prohibitive computational demand because of the epistemic uncertainties rooted in structure system. In this work, a hybrid Kriging-high dimensional model representation (Kriging-HDMR) methodology for drastically simplifying this task is proposed. The epistemic uncertainties with well-defined bounds but no concrete distribution forms are addressed by interval model. Therefore, the first passage probability of the generic response process that the epistemic uncertainties involved, is represented by the conditional univariate extreme value distribution (EVD) of structural parameters with interval form. Then, a Kriging assisted HDMR together with third moment saddle point approximation (TMSA) is proposed to alleviate the computational burden and provides an accurate depiction of possible model outcome. The differential evolution (DE) interval optimization strategy is performed to accelerate the post process of searching the lower bound (LB) and upper bound (UB) of first passage probability with interval form. Finally, a nine-story shear frame with Bouc–Wen model is presented to demonstrate the accuracy and efficiency of proposed method.

This paper presents an experimental verification of the statistical time-series methods, which utilize adapted frequency response ratio (FRR), autoregressive (AR) model parameter and AR model residual as performance characteristics, for diagnosing the damage of wind turbine blades. Specifically, the statistical decision-making techniques are used to identify the status patterns from turbine vibration data. For experiments, a small-size, laboratory-used operating wind turbine structure is used. The performance of each method in diagnosing damages simulated by saw cut in three critical positions in the blade are assessed and compared. The experimental results show that these methods yielded a promising damage diagnosis capability in the condition monitoring of wind turbine.

Thin-walled section beams have Brazier effect to exhibit a nonlinear response to bending moments, which is a geometric nonlinearity problem and different from eigenvalue problem. This paper is aimed at investigating the Brazier effect in thin-walled angle-section beams subjected to pure bending about its weak axis. The derivation using energy method is presented to predict the maximum bending moment and section deformation. Both numerical analyses and experimental results were used to show the validity of the proposed formula. Numerical results show that the boundary condition can influence the results due to the end effect, and that the influence tends to be negligible when the length of angle beam goes up to 30 times as the length of beam side. When the collapse in experiments is governed by Brazier flattening, the moment vs. curvature curve deviates significantly from the linear beam theory, but coincides well with the proposed formula in consideration of the restraint due to limited span of experimental setup. It can be concluded that the proposed formula shows good agreement with numerical results and experimental results.

Structural parameters are the most important factors reflecting structural performance and conditions. As a result, their identification becomes the most essential aspect of the structural assessment and damage identification for the structural health monitoring. In this article, a structural parameter identification method based on Monte Carlo method and likelihood estimate is proposed. With which, parameters such as stiffness and damping are identified and studied. Identification effects subjected to three different conditions with no noise, with Gaussian noise, and with non-Gaussian noise are studied and compared. Considering the existence of damage, damage identification is also realized by the identification of the structural parameters. Both simulations and experiments are conducted to verify the proposed method. Results show that structural parameters, as well as the damages, can be well identified. Moreover, the proposed method is much robust to the noises. The proposed method may be prospective for the application of real structural health monitoring.