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The seismic performance of a ring–beam connection system to integrate concrete-filled steel tubular columns and reinforced concrete (RC) frames was studied. Physical experiments on two specimens were conducted under monotonic and cyclic loading. The results showed the connection system had a displacement ductility ratio of 4.68 and an energy dissipation coefficient over 2.0. A finite-element model was established and the numerical and experimental results were compared in terms of skeleton curves and stiffness degradation trends. Parametric studies were then performed to evaluate the effects of the axial compressive force ratio, concrete strength and reinforcement ratio of the ring–beam joint (RBJ) and the reinforcement ratio of the frame beam on the seismic performance of the proposed RBJ connection system. The results showed that an increase in the axial compression ratio or strength of the concrete material improved the initial stiffness and strength of the connection system. The effects of the RBJ reinforcement ratio and the frame beam reinforcement ratio on seismic performance were negligible.

With more wind turbines being constructed in cyclone-prone regions, tower failure cases are increasingly reported in recent years. To simulate the genuine tower performance under extreme events, nonlinear dynamic analyses on a highly refined finite element model were adopted in recent research. However, existing research based on such practice has certain deficiencies in terms of computational cost reduction, aero-structure interaction characterization and failure mode classification. This article proposed a numerically efficient framework in the failure mode identification and evaluation of a wind turbine tower under cyclones (hurricanes/typhoons) to cope with the forenamed deficiencies. The aero-structure interaction, geometric and material nonlinearity of a turbine structure are realized and validated before involved into that framework, in which three different failure modes can be classified and analyzed with high numerical efficiency. At last, the effects of external environmental and internal structural parameters, e.g., wind velocity, turbine scale, parking status, section slenderness and material model are considered for both onshore and offshore wind turbines (OWTs), so as to reflect the wide applicability of this proposed framework and provide instructive reference for wind turbine design under extreme conditions like cyclones.

Telecom structures such as high guyed masts are tall and flexible, so that not only the main structure but also the components (i.e., guy cable and antenna) suffer from vibrations induced by wind or earthquakes. The installation of contact inertial accelerometers for high guyed mast cables or antenna can be logistically challenging and the original vibration state may be influenced by these sensors. With convenient implementation and acceptable accuracy, computer vision technologies have been applied for vibration tests both in labs and field. In this paper, videos taken with smartphone cameras are processed to extract guy cable and antenna vibration information for telecom structures and, as a result, providing an efficient cost-effective method for vibration investigation of this type of structure. The video processing method can also be used in similar cases for other structures.

Industrial facilities play a significant role in economic growth now and for the foreseeable future. However, past earthquake reconnaissance surveys have revealed that the seismic vulnerability of these facilities has resulted in huge economic losses mainly due to operational failures. As per ASCE 7, industrial facilities could be classified as building-like and nonbuilding-like types. In this paper, the fragility of building-like industrial facilities is focused. First, relevant design code requirements and provisions were summarized for further discussion on possible improvements. This is followed by a review of the latest techniques, challenges, and knowledge gaps related to the fragility development of building-like industrial facilities. The review indicates gaps in fragility development specific to seismic loss quantification. The need for updated design guidelines, component interdependencies, robust seismic modeling, and analysis techniques for improved decision-making are hence recommended.

The continuous cost reduction of wind turbines has consolidated the competitiveness of wind energy. With the increasing installation of wind turbines in seismic-prone regions, it is likely that earthquakes will strike farms in operation. A practical approach to predict the dynamic behavior of a wind turbine under simultaneous seismic and operational wind loads is investigated in this work. The combined action can be determined by analyzing the wind and the seismic-induced responses separately. However, an accurate definition of the aerodynamic damping is required for this purpose and there are few experimental studies on the additional damping source. A 1/100-scaled wind turbine model was designed and the aerodynamic damping of the model was identified. Subsequently, the ground motion was applied in the model by means of a shake table and the combined wind/earthquake response that was measured experimentally was compared with the response predicted by several combination rules. A numerical study using the FAST analysis package for wind turbines was also conducted to complement the experiments with fully-coupled simulations that include aeroelastic effects. This work provides a necessary experimental reference for structural engineers to use adequate aerodynamic damping and load combination methods for the seismic analysis of wind turbines in operation.

Reinforced concrete chimneys with steel liners are widely used in waste gas discharge of industrial facilities, and guaranteeing their safety performance in harsh environments is important for industries and society. This paper proposes a novel method for the reduction of along-wind vibration in chimneys with liners by tuning the movement of the suspended liners to the response of the outer cylinder, and the conventional rigid supporting platform is replaced by a combination of radial horizontal tuning systems and vertical suspension systems. This ‘tuned liners’ method is applied to a simplified beam-like model that is able to capture the liners/chimney interaction and is validated against a more detailed finite-element shell model. A design method is proposed to obtain parameters of the tuning system that lead to significant reductions of along-wind vibrations whilst satisfying the relative response requirement. A comprehensive study of the structural vibration under stochastic wind actions is performed to demonstrate the effectiveness of the proposed system. The characteristics of the relative vibration of the outer cylinder and the liners are studied. Comparison with conventional TMD solution is conducted to further explore the advantage of the tuned-liners system under stochastic wind actions. The results indicate that the top displacement and acceleration of the outer cylinder are effectively reduced by 62% and 70% with the tuned liners, respectively. A similar performance using a conventional TMD would require an auxiliary vibrating mass that is approximately 300 tons, which is avoided with the proposed tuned liners. Results show that the proposed technique could be effective in the along-wind control of chimneys in multiple directions, even with some unintentional eccentricities.

A bi-normalized Newmark–Hall response spectrum is presented for seismic design and assessment of structures. The period axis is normalized with respect to a characteristic period relating only to peak ground-motion parameters. The amplification factors are determined through a statistical analysis by normalizing spectral pseudo-acceleration, spectral pseudo-velocity, and spectral displacement, relative to peak ground acceleration, peak ground velocity, and peak ground displacement, respectively, in the low-, intermediate-, and high-period ranges, which do not need to be prescribed prior to normalization. A total of 671 three-component accelerograms are selected from the New Zealand Strong Motion Database for the statistical analysis. The relationship between peak ground-motion parameters is studied, enabling the construction of a design spectrum from either a given design scenario earthquake, or a code-specified peak ground acceleration value.

This paper implemented an optimal design of non-conventional multiple tuned mass damper (NC-MTMD) system for coal scuttles in power plant. The NC-MTMD was introduced using base isolation for the co...

Ground-motion amplification factors (GMAFs) are used to characterize amplification of a ground motion propagating from the bedrock to the ground surface. They are usually determined by ground response analysis, in which the soil parameter variabilities and input motion uncertainties contribute to their uncertainty. The construction of design response spectra requires mean GMAFs or GMAFs with different probability levels. Thus, it is significant to study the sensitivity of soil parameter variabilities and the number of random soil profiles for the estimation of GMAFs. This study investigates the minimum number of random soil profiles required to represent the extent of the epistemic uncertainty in the GMAFs obtained from ground response analysis. It shows that at least 20 and 60 random soil profiles are respectively required to estimate the mean and standard deviations of GMAFs with the maximum relative difference below 10%. In addition, potential reasons for a reduction in the mean GMAFs resulting from randomization of the soil column properties are discussed.

© 2018 Elsevier Ltd Vibration-based damage identification has been widely studied in the field of structural health monitoring (SHM) for several decades. It is well known, however, that low-order modal parameters, being among the most frequently used, are not sensitive to local damage. A suitable methodology is therefore needed to extract such damage features from the dynamic response of structures. In the present work, local bending behavior of cables is studied for damage identification. First, the dynamic response of a cable is decomposed into evanescent wave and propagating wave components. It is proven that the contribution of the evanescent wave is spatially concentrated, and is sensitive to local damage. A signal transform is proposed next, which allows the estimation of the wave components from the measured cable response. The reflection coefficient of the evanescent wave (REW), which can be calculated from the estimated wave coefficients, depends only on the characteristics of the local discontinuity, and proves to be a robust indicator for local damage. The feasibility of the proposed methodology is studied by means of a simulated experiment, considering a cable model with two locally damaged parts. The results show that the intensity of REW is significantly higher near the damage locations, allowing damage localization. From the estimated REW near the damage locations, the damage levels can be estimated, showing the potential of this methodology for damage assessment of cable structures. ispartof: JOURNAL OF SOUND AND VIBRATION vol:442 pages:527-551 status: published

This paper studies the effect of soil–structural interaction (SSI) on gravity‐based wind turbine towers equipped with tuned mass dampers (TMDs) subjected to earthquake loading. A small‐scale shaking table test of wind turbine towers with TMD was conducted, and the results showed that using TMD designed considering SSI resulted in larger vibration suppression. A simplified analytical numerical model was developed for SSI analysis considering TMD. The effect of soil site class and the earthquake intensity on the response reduction efficiency of the TMD was also discussed using the simplified model. It is concluded that the TMD efficiency depends not only on the soil stiffness but also on the characteristics of the applied ground motions, both of which are affected by the site classes and earthquake intensity levels. Moreover, the peak acceleration ratio (PAR), the root mean square acceleration ratio (RAR), the peak displacement ratio (PDR), and the root mean square displacement ratio (RDR) of the top of the wind turbine tower were obtained with and without TMD for different earthquake intensities and sites. These parameters can be used as references for the rational selection of TMD parameters considering SSI.

Traditional tuned mass dampers have been studied to reduce vibration responses of wind turbine towers. However, the large additional mass is usually required to be installed at the top of the tower, which may be not suitable for existing wind turbine tower. To provide a retrofit technology for in-service wind turbines, the use of a lightweight energy dissipation device, the tuned parallel inerter mass system (TPIMS), for seismic response mitigation of the wind turbine tower, was proposed in this study. The TPIMS consists of a tuned mass, a spring, and a parallel inerter subsystem, of which the spring is used for tuning the mass and the inerter subsystem is set for vibration energy absorbing and dissipation. A TPIMS-design optimization method was developed for wind turbine tower vibration depression with a target performance level. A typical wind turbine tower was modeled according to the Bernoulli-Euler beam theory and its seismic responses subject to stochastic seismic excitations were obtained. Parametric studies were conducted and the robustness of TPIMS for tower seismic vibration mitigation was proved. The results show that the tower top displacement, base shear, and moment can be reduced significantly with the help of TPIMS. Under a same design target, the required physical mass of TPIMS is much smaller than that of the tuned mass damper. Additionally, a lager apparent mass of TPIMS is more effective for reducing seismic responses of the wind turbine tower.

Industrial buildings often have irregularities due to operational and complex industrial process. In this paper, a thermal power plant with mass and vertical irregularities was designed with the 2010 ASCE and AISC design codes. Subsequently, a parametric study was undertaken on simplified braced frames to quantify the impact of mass and vertical irregularities, as well as their combined effect. Detailed numerical models were developed in Open System for Earthquake Engineering Simulation platform. With a high seismicity level in China, ground motions were selected and nonlinear time-history analyses were performed. Subsequently, probabilistic seismic demand models, seismic fragilities, and risks were developed for different performance levels. The results show that the vertical irregularity generated larger detrimental effect than mass irregularity, and need more attention in structural design. Collapse risk increased the most due to the combined effect of mass and vertical irregularities. Furthermore, under small earthquake intensities, the thermal power plant with the combined irregularities had higher risk in functional disruption.

Many research studies were conducted on wind turbine towers subjected to either seismic loads or synoptic wind loading, such as: hurricanes, typhoons, and tropical cyclones. However, the behavior of wind turbines under localized high-intensity wind events (HIW), such as downbursts, is not well-understood. The localized nature of downbursts makes the prediction of critical loads on wind turbines quite challenging. In the current study, a numerical model is developed and validated to investigate the effect of downburst wind loading on wind turbines. This model incorporates a previously developed Computational Fluid Dynamics (CFD) model for the downburst wind field coupled with a newly developed wind turbine structural model. The numerical model is capable of predicting the effect of downbursts on wind turbines taking into consideration the different downburst parameters such as the jet velocity, the size of the downburst and its location relative to the wind turbine. The model also accounts for the change in the pitch angle of the blades, which is a parameter typically used to control the blades rotation and the power generation. An extensive parametric study is conducted using the developed numerical model to determine the peak moments at the tower base and the roots of the blades considering a large number of downburst configurations and different blade pitch angles. Downburst critical configurations for different pitch angles are obtained and the optimum pitch angle which minimizes the downburst effect on the wind turbine is recommended.

Damage assessment of concrete components is of vital importance for ensuring the safety of civil structures. The occurrence and development of cracks in reinforced concrete components are highly related to the damage condition. Based on the fractal characteristics of concrete cracks, a rapid damage assessment method of concrete components using the index of Fractal Dimension ( FD ) was proposed in this paper. Damages in structural concrete components were first categorized into four empirical levels according to the so-called loading-ratio. Through image processing of the crack developments from previous studies of concrete beam and column members at different loading stages, database of crack FD versus loading-ratio for concrete beams and columns were separately built. Linear regressions correlating the crack FDs and the loading-ratios were then constructed and validated for concrete beams and columns, respectively. The loading-ratio can be predicted by the linear regression using new crack FD of the concrete component for damage assessment. The proposed method was applied to a lab-tested specimen of a reinforced concrete shear wall - beam assembly. Results show that the proposed fast structural performance assessment method is reliable for identifying potential damage levels in concrete components.

Current numerical aerodynamic wind turbine blade models – models that calculate the aerodynamic loads on a blade based on the incoming wind – are generally computationally intensive. However, a surrogate aerodynamic blade model consisting of a neural network (NN) trained on high-accuracy data should be capable of achieving both high accuracy and fast computation times. In this study, six different NNs were trained using numerical data from aeroelastic blade simulations, then compared for the highest possible prediction accuracy while maintaining high speeds. The NNs include two time-independent multilayer perceptron (MLP) networks with a full and reduced set of input data. A time-dependent long short-term memory (LSTM) network was also trained, along with a similar Pseudo-time-dependent MLP. Finally, a time-dependent convolutional neural network (CNN) and a similar Multi-time-step MLP were trained and compared. Over 30 million data points of aeroelastic time history information of an operational 5MW wind turbine across 115 time histories and 23 different mean wind speeds were numerically generated for training the networks. The architecture, input and output data, and the optimization and training processes are provided in detail for each network, and the resulting accuracy and computation times are analyzed and compared. Ultimately, it was found that both the trained full-input MLP and the CNN were particularly accurate surrogate models, with average normalized root mean square errors of 1.11% and 0.66% respectively. While the CNN surpasses the full-input MLP in accuracy, the latter is simpler to train and faster to run, thus both are compelling options for future researchers. Such a surrogate model could be used to predict the aerodynamic loads on a wind turbine blade when computation speed is a priority, such as during design optimization or hybrid simulations.

Climate Change results in possible less frequent but more intensified storm events that include so called “super typhoons”. To ensure the resilience of the energy power delivery systems, this paper offers lessons learned from forensic investigations of the damaged power delivery systems from the Philippines after the 2013 Super Typhoon Haiyan. The objective is to investigate new strategies to design the power delivery systems, especially in the coastal regions, to defend against the intensified storm events brought on by climate change. A critical review of current power line system design approach, especially load design based on ASCE 7–10, is conducted. The review along with extreme loading calculations revealed limitations in current design philosophies. A design framework using a holistic approach that includes a strong backbone line system is suggested. The strong backbone line system is to be designed for extreme loading scenario with additional considerations including debris loading, wind-storm surge interactions and local geospatial condition with multiple wind directions. Preliminary design of a strong backbone system for McClellanville, South Carolina, power supply scenario is presented as a case study and is shown to be economically viable.