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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.

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

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

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...

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.

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.

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.

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.

When constructed on tall building rooftops, the vertical axis wind turbine (VAWT) has the potential of power generation in highly urbanized areas. In this paper, the ambient dynamic responses of a rooftop VAWT were investigated. The dynamic analysis was based on ambient measurements of the structural vibration of the VAWT (including the supporting structure), which resides on the top of a 24-story building. To help process the ambient vibration data, an automated algorithm based on stochastic subspace identification (SSI) with a fast clustering procedure was developed. The algorithm was applied to the vibration data for mode identification, and the results indicate interesting modal responses that may be affected by the building vibration, which have significant implications for the condition monitoring strategy for the VAWT. The environmental effects on the ambient vibration data were also investigated. It was found that the blade rotation speed contributes the most to the vibration responses.

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.

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...

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.

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.