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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.

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.

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.

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.

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.

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.

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.

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.

Summary A particle tuned mass damper (PTMD), which is a creative integration of a traditional tuned mass damper and an efficient particle damper in the vibration control area, is proposed. This paper presents a comprehensive study that involves experimental, analytical, and computational approaches. The vibration control effects of a PTMD that is attached to a five-story steel frame under seismic input are investigated by a series of shaking table tests. The influence of some parameters (auxiliary mass ratio, gap clearance, mass ratio of particles to the total auxiliary mass, frequency characteristics, and amplitude level of the input) is explored, and the performance of the PTMD with/without buffered material is compared. The experimental results show that the PTMD can achieve significant damping effects under seismic excitations, and the bandwidth of the suppression frequency is expanded, showing the device's robustness and control efficiency. In addition, an approximately analytical solution that is based on the concept of an equivalent single-particle damper is presented, and the method to determine the corresponding system parameters is introduced. A comparative study between experimental and numerical results is conducted to verify the feasibility and accuracy of this analytical model. Copyright © 2016 John Wiley & Sons, Ltd.

Structural damping ratio which quantifies the energy dissipation of civil structures under external excitations plays a critical role in the seismic design and assessment of civil structures. In existing building design provisions and guidelines, however, the structural damping ratio is only suggested either as a single fixed value or as an optional value for the general structure type adopted. For example, damping ratio 5% is commonly recommended for all reinforced concrete (RC) structures in practical seismic design, which may not be sufficient to represent the realistic damping features of different RC structures under ground motions with different amplitudes. This research explored deeper understandings on the structural damping features of different RC structures under actual ground motion excitations. A series of seismic response records of RC structures were collected from the “Center for Engineering Strong Motion Data” (CESMD) database. These records were then categorized into three typical lateral resisting systems: moment-resisting frame systems, shear wall systems, and moment-resisting frame plus shear wall systems. The equivalent structural damping ratios for different systems of RC structures were then estimated based on the categorized response records with different amplitudes. Finally, an empirical statistical relationship was established, offering a refined basis for civil engineers to reasonably choose the equivalent damping ratios during the design and post-earthquake assessment of the RC structures.

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.

Based on the modern image recognition technology, this study used the fractal theory to examine the surface cracks of concrete and the fractal dimension was used as an index to identify the bearing capability of concrete components. Through processing and simulating the experimental data obtained by other researchers, the relationship of crack fractal dimension D and the loading-ratio ξ of the concrete component was calculated. The D-ξ relationship of concrete beams is D = 0.1684 ξ + 1.0307. Based on this relationship, a fast evaluation method based on the fractal dimension of the crack surface to judge the bearing capacity of concrete components was proposed in this study, and its accuracy was verified by the analysis of experimental results.

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.

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.

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.

Adjacent base-isolated buildings with corridor bridges have a large seismic displacement demand in their isolation layer, and therefore are prone to collision. Moreover, seismic wave incidence angles may have a great impact on their seismic collision response, especially for near-fault ground motions that may exhibit strong directionality dependence. This paper studies the impact of seismic wave incidence angle and near-fault pulse effect on seismic collision potential of adjacent buildings connected by corridor bridges, retrofitted with base isolation. Two adjacent-building systems are established in OpenSees to facilitate analyses. One is a base-isolated (BI) building system adopted as the baseline model, each building of which consists of lead-rubber bearings (LRB) and ordinary-rubber bearings (LNR). The other one is a base-isolation-with-damper (BID) system, where two additional groups of viscous dampers were added to the isolation layers of BI system. The first group of dampers is used to connect the buildings in order to reduce their out-of-phase motion. The second group of dampers is placed at the base of individual buildings to dissipate seismic energy. The effectiveness of using the dampers of the BID results against the BI baselines was compared. A collision potential index D was proposed to quantify the collision potential of the adjacent base-isolated buildings. The research shows that, the seismic wave incidence angle has a great influence on the building collision potential, which does not necessarily be greatest in the maximum pulse direction. Using dampers may not be useful for reducing building deformation demands, but can effectively coordinate the asynchronous movement of adjacent buildings, reducing the potential of seismic collision. Finally, the Pseudo-Spectral Acceleration (PSA) based on the isolation periods of the buildings was shown to correlate well with the index D, which can be used as the pair of seismic Intensity Measure (IM) and Engineering Demand Parameter (EDP) to describe the collision potential between adjacent base-isolated buildings with corridor bridges.

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.

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.

The wind energy industry has been growing rapidly during the past decades. Along with this growth, engineering problems have gradually emerged in the wind power industry, including those related to the structural reliability of turbine towers. This study proposes a rapid seismic analysis methodology for existing wind turbine tower structures. The method is demonstrated and validated using a case study on a 1.5 MW tubular steel wind turbine tower. Three finite element (FE) models are developed first. Field tests are conducted to obtain the turbine tower's vibrational characteristics. The tests include (1) remotely measuring the tower vibration frequencies using a long range laser Doppler Vibrometer and (2) monitoring the tower structural vibration by mounting accelerometers along the height of the tubular structure. In-situ measurements are used to validate and update the FE models of the wind turbine tower. With the updated FE model that represents the practical structural conditions, seismic analyses are performed to study the structural failure, which is defined by the steel yielding of the tubular tower. This research is anticipated to benefit the management of the increasing number of wind energy converters by providing an understanding of the seismic assessment of existing tubular steel wind turbine towers.

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.

Recognized as one of the most mature renewable energy technologies, wind energy has been developing rapidly in recent years. Many countries have shown interest in utilizing wind power, but they are concerned about the environmental impacts of the wind farms. The continuous growth of the wind energy industry in many parts of the world, especially in some developing countries and ecologically vulnerable regions, necessitates a comprehensive understanding of wind farm induced environmental impacts. The environmental issues caused by wind farms were reviewed in this paper by summarizing existing studies. Available mitigation measures to minimize these adverse environmental impacts were discussed in this document. The intention of this paper is to provide state-of-the-art knowledge about environmental issues associated with wind energy development as well as strategies to mitigate environmental impacts to wind energy planners and developers.

Structural health monitoring (SHM) of wind turbines has been applied in the wind energy industry to obtain their real-time vibration parameters and to ensure their optimum performance. For SHM, the accuracy of its results and the efficiency of its measurement methodology and data processing algorithm are the two major concerns. Selection of proper measurement parameters could improve such accuracy and efficiency. The Stochastic Subspace Identification (SSI) is a widely used data processing algorithm for SHM. This research discussed the accuracy and efficiency of SHM using SSI method to identify vibration parameters of on-line wind turbine towers. Proper measurement parameters, such as optimum measurement duration, are recommended.

Wind energy is one of the most mature renewable energy technologies and has been developing rapidly in recent years. Many countries have shown interest in utilizing wind energy, but its impact on the environmental is a concern. The primary environmental impacts include avian safety issues, biosystem disturbances, noise, visual pollutions, electromagnetic interferences, and local climate changes. This chapter provides a review and summary of the environmental impacts caused by the wind energy industry. Available mitigation technologies to minimize these adverse environmental impacts are also discussed. In addition to environmental impacts, structural safety is becoming an issue as many structural failures of wind turbines have been reported. A summary of studies related to these structural safety problems are included in this chapter; the focus here is on the structural performance of wind turbine towers under wind and seismic loads together with health monitoring and vibration control technologies. The intention of this chapter is to provide state-of-the-art knowledge about the aforementioned issues associated with wind energy development as well as strategies for wind energy planners and developers to mitigate the negative effects.

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

Carbon dioxide capture and geological storage (CCS) is a potential technology to reduce greenhouse gas emission. Suitable techniques are essential for site characterization as well as CO 2 injection and storage monitoring. A surface wave seismic method was explored in this study to investigate its feasibility for this purpose. Elastic wave responses of CO 2 flooded rock were first investigated numerically in two types of rocks, carbonate rock and sandstone. It is indicated that elastic wave velocities change more significantly as there is greater difference for bulk modulus between the injected CO 2 and the existing media in pore spaces. With the wave velocity and density variation ranges estimated from the rock sample study, the sensitivity of surface wave velocity was examined by perturbing parameters of the CO 2 storage layer in two layered reservoir models. It is found that the surface waves are more sensitive to the changes of shear wave velocity and thickness of CO 2 storage layer; but they are less sensitive to density and compressional wave velocity variations. The fundamental mode of Rayleigh waves is most sensitive to the physical parameter perturbation of the CO 2 storage layer for the carbonate case. However, high frequency modes were observed to be more active for shear wave velocity and thickness variation scenarios in the sandstone reservoir simulations. The simulations demonstrate that the monitoring feasibility increases as the CO 2 reservoir layer becomes thicker and the bury depth goes shallower. However, with the geological setting parameters found in existing CCS projects, it is concluded to be a challenge to detect abnormalities in a CO 2 storage reservoir by comparing the shift of shear wave velocity profiles that are derived from analysis of surface wave response data. It is, therefore, proposed to consider other microtremor attributes during the development of CO 2 monitoring techniques based on passive measurement of microseismicity, which is explored by some researchers.

A system identification method for estimating natural frequencies is proposed. This method developed based on the stochastic subspace identification method can identify modal parameters of structures in operating conditions with harmonic components in excitation. It benefits wind turbine tower structural health assessment because classical operational modal analysis methods can fail as periodic rotation excitation from a turbine introduces strong 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 bridges of the USA and China are inventoried, inspected and maintained by governmental agencies, promoting efficient national infrastructure and safety through the development of bridge management technology. This paper provides a brief comparison between the USA and China concerning the ability to implement foreign bridge management technology by analysing the regulatory practices in the bridge management process and the bridge management systems in each country. The goal is to investigate possible synergistic approaches to enhance bridge monitoring through comparing the two largest bridge inventories in the world.

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...

The U.S. transportation infrastructure has many wrought iron truss bridges that are more than a century old and still remain in use. Understanding the structural properties and identifying the health conditions of these historical bridges are essential to deciding the maintenance or rebuild plan of the bridges. This research involved an on-site full-scale system identification test case study on the historical Old Alton Bridge (a wrought iron truss bridge built in 1884 in Denton, Texas) using a wireless sensor network. The study results demonstrate a practical and convenient experimental system identification method for historical bridge structures. The method includes the basic steps of the in-situ experiment and in-house data analysis. Various excitation methods are studied for field testing, including ambient vibration by wind load, forced vibration by human jumping load, and forced vibration by human pulling load. Structural responses of the bridge under these different excitation approaches were analyzed and compared with numerical analysis results.

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.

To develop a defense strategy to protect power transmission lines against blast-induced ground motions, an understanding of the dynamic responses of these structures must be first established. This paper presents the results from ground motion monitoring at two blast sites in southern United States. These studies are being conducted as part of a research effort to establish strong ground motion characteristics necessary for developing blast limits for power transmission systems. Ground movements caused by the surface mining blast and quarry blasting were recorded using geophones and wireless triaxial sensing units. The process of establishing the ground motion response spectra via analyzing actual ground motion measurements, including noise filtration and signal processing, is then described. These ground motion response spectra are the necessary inputs for spectrum analysis of structural responses that can be used to establish ground vibration limits.

Due to the urbanization in China, some building construction sites are planned on areas above abandoned underground mines, which pose a concern for the stability of these sites and a critical need for the use of reliable site investigations. The array-based surface wave method has the potential for conducting large-scale field surveys at areas above underground mines. However, the dense deployment of conventional geophones requires heavy digital cables. On the other hand, the bulky and expensive standard stand-alone seismometers limit the number of stations for the array-based surface wave measurements. Therefore, this study developed a low-cost cableless geophone system for the array-based surface wave survey. A field case study using this novel cableless geophone system was conducted at an abandoned underground mine site in China to validate its functionality.

In bridge engineering, laser-based measurement techniques show promise in assisting field tests due to their noncontact features. A case study of using laser-based remote sensing to help collect data during in situ testing for a bridge finite-element (FE) model validation is reported in this paper. The skewed two-span bridge in this study was constructed with nine high performance steel girders in two phases. A three-dimensional (3D) FE model of the bridge superstructure was developed based on the information provided by the design files. Various field tests were performed to validate the model: (1) light detection and ranging (LiDAR) scanning, (2) static truck load tests, and (3) laser Doppler vibrometer testing. The LiDAR scanner collected geometrical information of the actual bridge. It was also used to measure girder deflections during load testing. The fundamental frequency of the bridge vibration was obtained by using a laser Doppler vibrometer (LDV). In situ dynamic and static measurements ...

Selected papers from the proceedings of the Geo-Hubei 2014 International Conference on Sustainable Civil Infrastructure, held in Yichang, Hubei, China, July 20-22, 2014. Sponsored by the China Three Gorges University, the Committee on Sustainability of ASCE, and the Geo-Institute of ASCE. Geotechnical Special Publication 245 contains 13 peer-reviewed papers covering innovative and sustainable use of geomaterials and geosystems. Topics include: reuse of geomaterials; in-situ testing methods for site characterization; design and quality control of earth structures; and dynamic behavior of soils and foundations. This GSP will be of interest to both researchers and practitioners in geotechnical engineering.

Recent advances in surface wave measurement capabilities allow for field collection of both human activity induced ground vibrations and background ambient noise caused microtremors. With designed sensor arrays, the passive surface wave survey provides a non-invasive seismic exploration method for subsurface profiling. In comparison to conventional geotechnical borehole tests, it is less expensive and it shows swiftness for site characterization over a large area. In this paper, the benefits of the surface wave survey method in earthquake geotechnical engineering for local site characterization were highlighted with case studies. A series of passive surface wave field measurements were performed by using sensor arrays. The collected data were processed to obtain the soil shear wave velocity profile and the fundamental site resonance frequency. Discussions were extended to compare the functionality of different accelerometers that were used as receivers in microtremor measurement. The accelerometer-based sensor array was found to be capable of collecting valid data for surface wave analysis.

The passive surface wave survey method provides a non-invasive seismic site exploration approach for civil engineers. It works through measuring either human activity induced ground vibrations or background ambient noise. It is superior to conventional geotechnical field testing approaches for site characterization over a large area. This paper reports surface wave survey case studies to demonstrate the application of this method to characterize local sites. Passive surface wave surveys were implemented in this research by collecting microtremors with designed sensor arrays. Measurements were processed to obtain the soil shear wave velocity profiles of the sites. Testing results were compared with borehole exploration data, which validated the passive surface wave survey measurements. Instrumentation, field testing design, and data analysis of this method were discussed. The paper envisages a great potential of the passive surface wave survey method in earthquake and geotechnical engineering applications in the urban environment.

Summary The tuned liquid damper (TLD) and particle damper (PD) have been used as effective passive vibration absorbers to suppress undesirable structural vibrations induced by dynamic loads such as earthquake and strong winds. In this paper, through an integrated use of the TLD and PD, a new damper system named the tuned liquid particle damper (TLPD) was developed. The dynamic characteristics of TLPD in terms of tuning conditions and transfer functions were investigated through a series of shaking table tests. Nonlinear behaviors of TLPD in the frequency domain were discussed, and a preliminary framework was applied in the design of a five-story steel frame building model using shaking table tests. Testing results confirmed the workability of the preliminary design framework as the primary structure is subjected to earthquake loadings. Performances of different TLPD-structure systems were summarized from these testing programs. One of observations is that the TLPD system worked as a modified TLD in this study. The testing programs provide proof-of-concept results for this proposed vibration absorber.

Bolted connections are widely employed in facility structures, such as light masts, transmission poles, and wind turbine towers. The complex connection behavior plays a significant role in the overall dynamic characteristics of a structure. A finite element (FE) modeling study of a bolt-connected square tubular steel beam is presented in this paper. Modal testing was performed in a controlled laboratory condition to validate the FE model, developed for the bolted beam. Two laser Doppler vibrometers were used simultaneously to measure structural vibration. A simplified joint model was proposed to further save computation time for structures with bolted connections. This study is an on-going effort to marshal knowledge associated with detecting damage on facility structures with bolted connections.