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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.

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.

© 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

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.

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.

This study developed a new cable-less seismograph system, which can transmit seismic data in real-time and automatically perform high-precision differential self-positioning. Combining the ZigBee technology with the high-precision differential positioning module, this new seismograph system utilized the wireless personal area network (WPAN) and real-time kinematic (RTK) technologies to improve its on-site performances and to make the field quality control (QC) and self-positioning possible. With the advantages of low-cost, good scalability, and good compatibility, the proposed new cable-less seismograph system can improve the field working efficiency and data processing capability. It has potential applications in noise seismology and mobile seismic monitoring.

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...

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.

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.

Accurate knowledge of wind turbine tower vibration damping is essential for the estimation of fatigue life. However, the responses in the fore-aft and side-side directions are coupled through the wind-rotor interaction under operational conditions. This causes energy transfers and complicates aerodynamic damping identification using conventional damping ratios. Employing a reduced two-degree of freedom wind turbine model developed in this paper, this coupling can be accurately expressed by an unconventional aerodynamic damping matrix. Simulated time series obtained from this model were successfully verified against the outputs from the wind turbine simulation tool FAST. Based on the reduced system obtained, a matrix-based identification method is proposed to identify the aerodynamic damping for numerically simulated wind turbine tower responses. Applying harmonic excitations to the tower allowed the frequency response functions of the wind turbine system to be obtained and the aerodynamic damping matrix to be extracted. Results from this identification were compared to traditional operational modal analysis methods including standard and modified stochastic subspace identification. The damping in the fore-aft direction was successfully identified by all methods, but results showed that the identified damping matrix performs better in capturing the aerodynamic damping and coupling for the side-side responses.

Tower-like structures have been extensively applied in a variety of infrastructures and facilities such as wind turbines, TV towers, and chimneys. These structures, acting as important loading bearing components, are inevitable to operate in harsh environment, which may result in harmful vibrations. Being different from the existing techniques on vibration reduction, a novel energy dissipating system is proposed in this study by employing cables in order to transfer the bending deformation of the tower into the rigid motions of the cable extremities. The energy is then dissipated by the connected damper placed on the ground. In the present work, the effect of the cable-based energy dissipating system (CEDS) is firstly studied by means of an analytical model, indicating that the damping of the whole system can be greatly increased at an optimal damping coefficient of the damper. Based on the finite element (FE) formulation, a customized damping element, which allows to simulate the behavior of the CEDS along the tower, is next derived and included into the self-developed toolbox of finite element analysis (TFEA). Lastly, a wind turbine tower modeled in TFEA is taken for a case study. From the time-domain analysis, it has been verified that the response of the wind turbine can effectively be reduced when equipped with the proposed energy dissipating system, confirming the potential of its application for broader cases in the field of tower-like structures.

Large earthquakes cause damage to buildings. The peak nonlinear inelastic responses of a building for given seismic ground motions are often used as a proxy for the damage measure. However, the peak responses are rarely recorded or observed for an earthquake event. The residual drift or the permanent deformation of the building after the seismic event can be measured and may be used to infer the degree of sustained damage of the building. Although the use of the residual drift to infer the seismic performance of buildings under earthquakes was explored in the literature, its validation by using full-scale experimental data is unavailable. In this study, test results of a full-scale four-story Reinforced Concrete (RC) building were used as the basis to assess the adequacy of using the residual drift to estimate the damage sustained by the building subjected to ground motions. The seismic performance assessment of this tested building was performed with the peak roof drift calculated from the residual deformation. Analysis results indicated that the approach could be used to infer probabilistically the peak drift of the building based on its residual drift. The degree of uncertainty in this inference is large and should be considered as an integral part of this estimation. Additional issues of using the residual drift as a measure of seismic performance of the building were discussed.

The strong drive to harness wind energy has recently led to rapid growth of wind farm construction. Wind turbine towers with increased sizes and flexibility experience large vibrations. Structural health monitoring of wind turbines is proposed in the wind energy industry to ensure their proper performance and save maintenance costs. This study proposes a system identification method for vibration-based structural assessment of wind turbine towers. This method developed based on the stochastic subspace identification method can identify modal parameters of structures in operating conditions with harmonic components in excitations. It benefits wind turbine tower structural health assessment because classical operational modal analysis methods can fail as periodic rotation excitation from a turbine introduces harmonic disturbance to tower structure response data. The effectiveness, accuracy and robustness of the proposed method were numerically investigated and verified through a lumped-mass system model. The method was then applied to an in-service utility-scale wind turbine tower. The field testing campaign and modal parameter identification as well as structural assessment results were presented. Copyright © 2017 John Wiley & Sons, Ltd.

During an earthquake, buildings are simultaneously excited by multiple (horizontal and vertical) ground motion components. In the design process, the combinatorial effects of multicomponent...

Vibration serviceability of footbridges is important in terms of fitness for purpose. Human-induced dynamic loading is the primary excitation of footbridges and has been researched with traditional sensors, such as inertial sensors and force plates. Along with the development of computer hardware and algorithms, e.g., machine learning, especially deep learning, computer vision technology improves rapidly and has potential application to the problem. High precision pedestrian detection can be realized with various computer vision methods, corresponding to different situations or demands. In this paper, two widely recognized computer vision approaches are used for detecting body center of mass and ankle movement, to explore the potential of these methods on human-induced vibration research. Consumer-grade cameras are used without artificial markers, to take videos for further processing and wearable inertial sensors were used to validate and evaluate the computer vision measurements.

In condition monitoring of structures, acceleration time histories are usually recorded due to ease of instrumentation. In cases where the information about a displacement time history is required, the acceleration data needs to be integrated to obtain the velocity and then the velocity needs to be integrated to obtain the displacements. However, the numerical integration of the acceleration data usually introduces an unrealistic drift component to the velocity as well as displacement. This paper presents an eigenfunction method to derive velocity and displacement time histories from a given acceleration time history. The paper analyzes displacements in two case studies using the numerical integration as well as the proposed eigenfunction method. It is concluded that the eigenfunction method is a viable approach to derive the displacement information from the acceleration data.

This paper studies the structural responses and failure modes of a 1.5-MW horizontal-axis wind turbine under strong ground motions and wind loading. Ground motions were selected and scaled to match the two design response spectra given by the seismic code, and wind loads were generated considering tropical cyclone scenarios. Nonlinear dynamic time-history analyses were conducted and structural performances under wind loads as well as short- and long-period ground motions compared. The results show that under strong wind loads the collapse of the wind turbine tower is driven by the formation of a plastic hinge at the lower section of the tower. This area is also critical when the tower is subject to most ground motions. However, some short-period earthquakes trigger the collapse of the middle and upper parts of the tower due to the increased contribution of high-order vibration modes. Although long-period ground motions tend to result in greater structural responses, short-period earthquakes may cause brittle failure modes in which the full plastic hinge develops quickly in regions of the tower with only a moderate energy dissipation capacity. Based on these results, recommendations for future turbine designs are proposed.

The seismic performance of electric power system is of paramount importance to maintain functionality of the served urban communities after earthquakes. Passive control techniques are widely accepted as effective measures to improve the seismic resilience of structural buildings. In this study, an actual thermal power plant building characterized by mass and vertical irregularities was studied. For a comparison purpose, two different design schemes in which one adopted the conventional steel braced frame scheme and the other retrofit one endowed with heavy equipment isolation and metallic dampers were considered. Shaking table tests were conducted to investigate the seismic performance of the two cases. The test models were designed and constructed based on the similitude law with a length scale factor of 1/10. Extensive test scenarios were performed with three ground motion pairs taken as inputs. The seismic responses between the conventional model and the retrofit model are compared in terms of tier drift, floor acceleration, base shear and damage observations. The experimental results indicated the effectiveness of employed passive control strategies in mitigating tier drift and base shear responses. The detrimental effects induced by heavy coal bunkers were addressed by using isolation technique. The results validated the metallic dampers have limited control effect in floor acceleration response and the effect is dependent on the seismic input. Discussions were made at the end regarding the scaling effect on the test results and cost-benefit of using passive control devices for the thermal power plant building.

In the seismic design of structures, the combinatorial effects of multiple horizontal ground motion components are often determined using the 100/p% percentage rule (i.e. designs based on 100% in one direction and p% in the other). In this study, a reliability-based methodology is developed to explicitly link building collapse caused by percentage-rule-based-underestimation of the design force demands to the adopted p% value. The methodology is applied to three special concentrically braced frame (SCBF) buildings (4, 8, and 12 stories) with corner columns shared by orthogonal frames. Each building case is designed using the 100/30%, 100/65%, and 100/100% percentage rule. Response history analyses using bidirectional and unidirectional loading are performed on nonlinear structural models to obtain the “true” demands and percentage-rule-based demands, respectively. Models constructed with and without considering SCBF column failure are utilized within the overall reliability-based framework to isolate the effect of underestimated design force demands on collapse performance. A quantitative relationship between the adopted p% value and building structural collapse risk is established. The results show that there is a nonlinear relationship between an increase in p% and the benefits in terms of reduced collapse risk. Also, taller buildings are shown to benefit more from conservative (higher) p% values compared to shorter ones.

The global growth in wind energy suggests that wind farms will increasingly be deployed in seismically active regions, with large arrays of similarly designed structures potentially at risk of simultaneous failure under a major earthquake. Wind turbine support towers are often constructed as thin-walled metal shell structures, well known for their imperfection sensitivity, and are susceptible to sudden buckling failure under compressive axial loading. This study presents a comprehensive analysis of the seismic response of a 1.5-MW wind turbine steel support tower modelled as a near-cylindrical shell structure with realistic axisymmetric weld depression imperfections. A selection of 20 representative earthquake ground motion records, 10 ‘near-fault’ and 10 ‘far-field’, was applied and the aggregate seismic response explored using lateral drifts and total plastic energy dissipation during the earthquake as structural demand parameters. The tower was found to exhibit high stiffness, although global collapse may occur soon after the elastic limit is exceeded through the development of a highly unstable plastic hinge under seismic excitations. Realistic imperfections were found to have a significant effect on the intensities of ground accelerations at which damage initiates and on the failure location, but only a small effect on the vibration properties and the response prior to damage. Including vertical accelerations similarly had a limited effect on the elastic response, but potentially shifts the location of the plastic hinge to a more slender and, therefore, weaker part of the tower. The aggregate response was found to be significantly more damaging under near-fault earthquakes with pulse-like effects and large vertical accelerations than far-field earthquakes without these aspects.

According to the Global Wind Energy Council, the installation rate for wind turbines is accelerating around the world, leading to the introduction of new wind turbine farms in regions where wind is abundant. As a result, the number of wind turbine towers prone to severe wind loads is increasing, as is the rate of failure due to unexpectedly strong wind loading. Wind turbines are typically designed to resist the synoptic wind loads specified in current International Electrotechnical Commission (IEC) guidelines, but these standards do not account for High-Intensity Wind (HIW) events such as tornadoes or downbursts. Because of the localized nature of HIW events, identifying critical locations that result in peak forces acting on the tower and blades is a challenging task. For this reason, a built-in-house numerical model has been developed in this study for simulating a three-blade horizontal-axis wind turbine tower exposed to 3D tornado wind fields. An extensive study has been conducted with the goal of determining both the critical location of a tornado that will cause peak straining actions on the tower and blades, and the optimal pitch angle that will minimize the effects of that tornado. For the considered wind turbine, the minimum straining actions on the blades were found to occur when the pitch angles are 60°, while the minimum straining actions on the base of the tower takes place when the pitch angles are 15°. A comparison of the simulation results with the extreme wind load scenario, stated in the current IEC guidelines, revealed that the predicted straining actions on the blades arising from the conditions specified in the IEC recommendations are less than the straining actions due to the F2 tornado considered in the study.

Structural damping ratio, which quantifies the energy dissipation of civil engineering structures under dynamic excitations, plays a critical role in structural seismic design and assessment. However, structural damping ratio is usually identified as an empirical value in design or as an optional parameter for different structure types as suggested in existing building seismic design guidelines. In the present work, the structural damping features of a variety of reinforced concrete (RC) structures under real ground motion excitations are further investigated by processing their response records reported in the Center for Engineering Strong Motion Data (CESMD) database. From the storey-by-storey methodology developed in this study, the equivalent damping ratios of the structures are estimated, and the time-varying effect of damping ratio is further explored, confirming the correlation between the damping ratio and the amplitude of ground motion. Based on a statistical analysis, an empirical relationship between the equivalent damping ratio and the peak ground acceleration (PGA) has been developed and validated, providing civil engineers with a refined basis for reasonably selecting the equivalent damping ratios during either the design or the post-earthquake assessment of RC structures.

Model-updating hybrid tests were conducted to reveal the seismic behaviour of a typical reinforced-concrete (RC) rigid-frame thin-walled tall pier bridge. The bottom of the left pier was isolated and experimentally tested in a laboratory as a physical substructure (PS) and the rest of the bridge was simulated as a numerical substructure (NS). The parameters of the concrete constitutive model were identified online based on the experimental data of the PS and refreshed to the NS to correct their values during the test. Then, test results of the PS, involving crack developments and the failure mode, were obtained and compared to other quasi-static tests. Moreover, the high-order effect was analysed based on the verified NS data. Finally, a method to predict the failure mode of bridges with thin-walled tall piers is presented in view of the phenomenon that such bridges are prone to shear-dominant brittle failure. In this method, new formulas of aspect ratio are proposed in both a broad and a narrow sense by considering the thin-walled effect and high-order modes. The newly proposed method was then used to predict the failure mode of the target bridge pier and the piers provided by other tests. The results show that the failure modes predicted by the proposed method are consistent with that observed from the tests.

Vibration-based force identification of cables has been studied for several decades. Most of this work relies on the natural frequencies of the cable for an estimation of the cable force. However, these natural frequencies are also affected by bending stiffness, sag effect and boundary conditions. In the present work, a two-step methodology is developed that allows taking into consideration these effects in the force identification. First, a segment of the cable is considered which is sufficiently short for the sag effect to be negligible. The axial force in this segment is estimated by fitting the measured response to the analytical solution for the transverse motion of the cable in the frequency domain. In this procedure, the bending stiffness is updated exploiting the fact that the estimated axial force should not depend on the frequency, while the boundary conditions do not need to be known. Next, an analytical solution of the static state of the entire cable is derived, taking into account the sag effect, bending stiffness and boundary conditions. The parameters of the entire cable model can then be updated, using the estimated value of the axis force at the location of the segment. Finally, the updated analytical model of the entire cable allows evaluating internal forces such as the cable force and bending moment, as required for estimating the stresses in the cable considering bending deformation. The feasibility of the proposed methodology is verified by means of numerical simulations considering measurement noise and an inaccurate initial guess of the bending stiffness, proving its potential for the health monitoring of cable structures.

Engineering structures usually exhibit time-varying behavior when subjected to strong excitation or due to material deterioration. This behavior is one of the key properties affecting the structural performance. Hence, reasonable description and timely tracking of time-varying characteristics of engineering structures are necessary for their safety assessment and life-cycle management. Due to its powerful ability of approximating functions in the time–frequency domain, wavelet multi-resolution approximation has been widely applied in the field of parameter estimation. Considering that the damage levels of beams and columns are usually different, identification of time-varying structural parameters of frame structure under seismic excitation using wavelet multi-resolution approximation is studied in this article. A time-varying dynamical model including both the translational and rotational degrees of freedom is established so as to estimate the stiffness coefficients of beams and columns separately. By decomposing each time-varying structural parameter using one wavelet multi-resolution approximation, the time-varying parametric identification problem is transformed into a time-invariant non-parametric one. In solving the high number of regressors in the non-parametric regression program, the modified orthogonal forward regression algorithm is proposed for significant term selection and parameter estimation. This work is demonstrated through numerical examples which consider both gradual variation and abrupt changes in the structural parameters.

The passive surface wave survey is a practical, non-invasive seismic exploration method that has increasingly been used in geotechnical engineering. However, in situ deployment of traditional wired geophones is labor intensive for a dense sensor array. Alternatively, stand-alone seismometers can be used, but they are bulky, heavy, and expensive because they are usually designed for long-term monitoring. To better facilitate field applications of the passive surface wave survey, a low-cost energy-efficient geophone system was developed in this study. The hardware design is presented in this paper. To validate the system’s functionality, both laboratory and field experiments were conducted. The unique feature of this newly-developed cableless geophone system allows for rapid field applications of the passive surface wave survey with dense array measurements.

Carbon dioxide (CO2) capture and geological storage (CCS) is one of promising technologies for greenhouse gas effect mitigation. Many geotechnical challenges remain during carbon dioxide storage field practices, among which effectively detecting CO2 from deep underground is one of engineering problems. This paper reviews monitoring techniques currently used during CO2 injection and storage. A method developed based on measuring seismic microtremors is of main interest. This method was first successfully used to characterize a site in this paper. To explore its feasibility in CO2 storage monitoring, numerical simulations were conducted to investigate detectable changes in elastic wave signatures due to injection and geological storage of CO2. It is found that, although it is effective for shallow earth profile estimation, the surface wave velocity is not sensitive to the CO2 layer physical parameter variations, especially for a thin CO2 geological storage layer in a deep underground reservoir. Keywords: Microtremor, CO2 storage, Passive surface wave, Site characterization, Feasibility study

With the rapid development of the wind energy industry many wind farms have been constructed in regions prone to earthquakes and strong winds, which sometimes cause serious structural vibration problems for wind turbines. This paper details the development of a scissor-jack braced viscous damper system (VD-SJB) to suppress excessive vibration of the wind turbine tower. This system can be installed inside the tubular steel tower and is a suitable technology to enhance the structural performance of existing wind turbines. A detailed finite element wind turbine model was built and two damper systems with and without SJB were modelled and compared. Ground motions and strong lateral winds were applied as external loads to operational and parked turbines, respectively. Parameter optimization was performed by building a surrogate model using an artificial neural network and a multi-objective genetic algorithm. The resulting Pareto sets were discussed and the optimal system was evaluated to demonstrate the effectiveness of VD-SJB. Results show that both viscous dampers installed vertically and VD-SJB are able to reduce structural vibrations under seismic or wind conditions. However, VD-SJB is capable of magnifying the stroke of the damper and decrease the damping force, thus it is a more practical solution.

An explosion occurred at a fertilizer plant in the town of West, Texas, on Wednesday, April 17, 2013, devastating a populated neighborhood. A total of 15 people were killed, and approximately 160 people were injured. Approximately 150 buildings were damaged in the explosion. The damage to affected homes and businesses was estimated to exceed $100 million. The purpose of this study was to collect on-site technical data of the explosion and gain knowledge of blast loadings and structural responses from this unprecedented explosion. Specifically, this research documented the building damages caused by the West Fertilizer plant explosion and the affected buildings’ construction and materials and evaluated the technical information for the explosion, including the blast loadings, i.e., the air-blast incident overpressures and ground shocks, on different buildings with respect to the standoff distances. A total of two technical papers have been prepared. The Part I paper (this manuscript) focused on the...

Performing full-scale structural testing is an important methodology for researchers and engineers in the civil engineering industry. Full scale testing helps the researchers understand civil infrastructures’ loading scenarios, behaviors, and health conditions. It helps the engineers verify, polish, and simplify the structural design and analysis theories. To conduct a full-scale structural testing, sensors are used for data acquisitions. To help structural researchers and engineers get familiar with sensing technologies and select the most effective sensors, this study reviewed and categorized new sensing techniques for full-scale structural testing applications. The researchers of this study categorized sensors used for civil-infrastructure testing into traditional contact sensors and remote sensors based upon their application methodologies, and into cabled sensors and wireless sensors based upon their data communication strategies. The detailed descriptions of wireless sensors and remote sensing techniques and their on-site full-scale applications are presented.

To ensure power transmission safety, loss of structural integrity of critical transmission facilities due to extreme events, such as strong ground motions induced by blasting, should be avoided. This research intends to establish a vibration safety limit for electric power transmission poles close to blasting events through actual field monitoring and finite-element (FE) simulation of transmission structure dynamic behaviors. In this paper, structural responses of transmission poles during monitored blasting are used to illustrate the methodology for safety limit establishment. The blast response spectra generated based on peak particle velocities were used as a basis for spectrum analysis performed using validated FE models to obtain the structural displacements, reactions, and stress states. The actual recorded ground vibrations as well as modified acceleration time histories were used as input excitations during transient dynamic analysis. A quantitative blast limit was established by comparing structural responses with corresponding design requirements.