Search

This paper proposes using spatially distributed TMD-type counterweights for the multiple-mode vibration control of irregular bridges subjected to wind loads. In particular, the governing equations of the bridge with TMD-type counterweights that are spatially distributed at any transverse and/or longitudinal positions of the bridge girder are established. Four objective functions are formulated and compared, and an optimum design method is developed to obtain the optimal design parameters of the TMD-type counterweights for each objective. Subsequently, an irregular cable-stayed bridge equipped with counterweight blocks is chosen as the prototype to demonstrate the control effectiveness of TMD-type counterweights. The results show that the proposed method is feasible for the multiple-mode vibration control of irregular bridges, and TMD-type counterweights show good control efficiency and robustness performance, providing an attractive alternative to traditional counterweights in the vibration control, especially multiple-mode vibration control, of irregular bridges.

Electricity transmission system is well recognized as a lifeline system in the modern society, and its failures in past major earthquakes have aroused the concern about its seismic vulnerability. In the present study, fragility curves are developed to assess the vulnerability of a typical transmission tower subjected to near-field ground motions. A probabilistic seismic demand model (PSDM) is constructed for the transmission tower in terms of the maximum inter-segment drift ratio (ISDR) and the spectral acceleration (Sa) at the fundamental period of the structure. Pushover analysis is performed to define the capacity limit states for the transmission tower, which are serviceability, damage control and collapse prevention in this research. The data for the PSDM are acquired by using incremental dynamic analyses (IDAs) of a suite of seismic records. Additionally, the influence of the seismic incident angles and the coupling effect between the transmission tower and lines on the structural fragility are further investigated. The results quantify the seismic vulnerability of the transmission tower and demonstrate the influence of the seismic incident angles and the dynamic coupling effect between the transmission tower and lines.

The undesirable motions resulting from wave loading can lead to the long-term fatigue damage or even catastrophic sinking of offshore semi-submersible platforms (SSP). It is therefore by all means necessary to suppress the excessive vibrations of SSP. Many methods have been proposed to mitigate the heave motion of offshore platforms, such as using a fixed heave plate (FHP) to increase the draft and damping of the system, or adopting a tuned heave plate (THP) to form a tuned mass damper (TMD) system. In this paper, a novel inerter-based control system, namely a tuned heave plate inerter (THPI), is proposed for control of SSP heave vibrations. In this system, an inerter device, which can transform the linear motion into the high-speed rotational motion and thus significantly amplifies the physical mass of the system, is added to the THP to further improve the performance of conventional THP. Analytical studies are performed to investigate the effectiveness of the proposed method. The mean square heave motions of SSP without control device and with FHP, THP and THPI are stochastically formulated, and the optimal design parameters for THP and THPI are derived. Parametric studies are conducted to investigate the influences of the size and original depth of heave plate on the optimal performances of FHP, THP and THPI. Finally, a novel waterwheel inerter is developed to realize the suggested device. The analytical results show that THPI is more effective to mitigate the heave motion of SSP compared to the conventional methods, and the novel waterwheel inerter is capable of generating a large apparent mass by using a small waterwheel.

The collapse problem of transmission tower upon strong winds was well noted in past few years. This article analyses the wind-induced collapse problem of a long-span transmission tower–line system. The member buckling effect was particularly considered. In doing so, a three-dimensional finite element model of the long-span transmission tower–line system was established in ABAQUS based on a practical project. The transmission tower and line were simulated by the frame and truss elements, respectively. The nonlinear behavior of a compressive member was simulated using the Marshall model, and the nonconvergence of numerical calculation was set to be the collapse criterion. The critical wind speed, damage position, and collapse probability were obtained from a collapse analysis of the long-span transmission tower–line system under different wind attack angles. The collapse mechanism of the long-span transmission tower–line system under a wind attack angle of 45° was investigated, and an incremental dynamic analysis was performed to evaluate the collapse-resistant capacity of the transmission tower. The study reveals that the interaction between bending moment and shear deformation is critical to the collapse of transmission tower.

Electricity transmission towers are vital in minimizing the risk of disruption of power supply after earthquakes. However, no guidelines currently exist for seismic performance evaluations of electricity transmission towers. Considering electricity transmission towers should have the same desirable performance as electric substations, this research team assessed seismic performance of transmission towers using the Institute of Electrical and Electronics Engineers (IEEE) recommended document for seismic design of substations (IEEE 693). A representative existing system was identified as the prototype. A computer model was developed for Response History Analyses (RHA) of the prototype. Three suites of ground motions matching the IEEE 693 required response spectrum were considered, consisting of one suite of three pre-approved empirical and random records and another two suites of records selected based on different criteria. It was found that the prototype designed according to the equivalent static force method meets the qualification requirements of IEEE 693. Additionally, it was found that a filtered version of the pre-approved empirical record to accommodate the limitations of some shake tables do not always provide results consistent with the un-filtered record. Moreover, analysis results reveal that different historic records selected matching the same target spectrum cause different responses in the prototype, suggesting the need to consider variation of ground motions. Further, it was found that the artificial ground motions may not always be adequate for analyses of transmission towers depending on what criterion is used in record selection. Last, it was found that failure of the prototype is highly non-ductile and seismic performance of the prototype is very sensitive to the amplitude of the input ground motions.

Semi-submersible platforms (SSPs) may subject to excessive wave-induced vibrations, which should be effectively suppressed. In the past decades, some vibration control methods have been proposed and developed, such as the fixed heave plate (FHP) and tuned heave plate (THP). Recently, the authors proposed using inerter-based control device, i.e. rotational inertia dampers (RIDs), to control the vibrations of SSPs, and the control effectiveness has been demonstrated through analytical studies. To further investigate the feasibility and effectiveness of the proposed method, wave flume tests are conducted and reported in the present study. In particular, a 1:70 scaled SSP model was manufactured, and the vibration characteristics of the platform were determined firstly through free vibration tests. After that, the bare and RID equipped SSPs were tested under the regular and irregular waves. For comparison, the SSP equipped with the commonly used FHP was also tested. The experimental results demonstrate that both the RID and FHP systems are effective in reducing the heave motion of SSP. However, compared to the FHP, the RID system showed a much better control performance with a very small physical mass. The wave flume tests demonstrated the superior vibration control performances of RID on SSP.

Structural vibration control has received considerable research attentions in the past few decades, with special emphasis on developing effective, affordable and applicable control systems to protect the structures against natural or man-made hazards. In 2002, a two-terminal mechanical element, dubbed inerter, was proposed based on the force-current analogy, offering many potentials for upgrading conventional structural vibration control systems. Over the past two decades especially in the recent five years, extensive research efforts have been made for the development of inerter-based vibration control systems. This paper aims to provide a state-of-the-art review on the research and development of inerter-based passive vibration control systems and their applications. It begins with the concept and physical realizations of inerter. The mechanical models of inerter are then presented. Subsequently, this paper reviews the applications of inerter in civil engineering and discusses its benefits comparing to conventional vibration control systems. Finally, some discussions are made on the unresolved problems and the possible topics for future studies.

Research on progressive collapse has a practical significance for long-span transmission tower-line system. Considering material damage effect, the Tian–Ma–Qu model is used to capture the nonlinear...

An inerter is a two-terminal mechanical device with the property of generating a resisting force that is proportional to the relative acceleration across its terminals. Due to its distinct mass amplification and negative stiffness effects, inerter has been applied to enhance the performance of conventional control systems, e.g. tuned mass damper (TMD) and vibration isolation system (VIS). Very recently, a novel inerter-based damper dubbed rotational inertia damper (RID) that is capable of generating a significant damping force was proposed by the authors to control the vibrations of offshore platforms, and its control effectiveness was examined through analytical studies. In the present study, a RID prototype was manufactured and tested under harmonic excitations for an in-depth understanding and demonstration of its mechanical behaviors. A precise mechanical model considering inerter nonlinearities is proposed to predict the behaviors of the RID, and the corresponding parameters are identified by using a nonlinear least squares method based on the experimental results. The theoretical results predicted by the proposed mechanical model are then compared with the experimental results, good agreements are achieved. The results demonstrate that the developed RID has a good capacity for energy dissipation, and the proposed mechanical model is accurate in predicting the behaviors of the RID.

Tuned mass dampers (TMDs) are widely adopted to control the adverse vibrations of engineering structures. To further improve the effectiveness of TMD, inerter was introduced into TMD recently to form inerter-based TMD systems. Similar to TMD, inerter-based TMDs should be carefully designed (optimized) in order to get their best control performances. In the previous studies on using inerter-based devices for seismic induced vibration control, the external excitation was normally simplified as a white noise and the inherent structural damping was ignored. However, it is well known that seismic excitation cannot be simply assumed as a white noise and damping always exists in the structure. The parameters obtained by the previous optimization procedures thus do not necessarily result in the best performance of the device. In the present study, the equations of motion of a single-degree-of-freedom (SDOF) structure equipped with three types of inerter-based TMDs subjected to seismic excitation are firstly developed. Instead of using a white noise as input, the filtered Kanai-Tajimi spectrum, which is characterized by the site damping and frequency, is adopted to model seismic ground motion. Then the effects of site damping, site frequency and structural damping on the inerter-based TMDs are comprehensively investigated and formulas are proposed to estimate the optimal parameters. Lastly, the responses of a structure without control and controlled by an inerter-based TMD under simulated and recorded earthquake ground motions are analysed by using MATLAB/Simulink. Numerical results show that the optimal parameters of inerter-based TMDs are significantly dependent on the site frequency and structural damping, while the site damping has little influence. Moreover, the accuracy of the proposed formulas is validated, and the control effectiveness of the inerter-based TMD is confirmed.

This paper develops an inerter-based vibration isolation system (IVIS) for heave motion mitigation of semi-submersible platforms (SSPs) subjected to sea waves. An analytical model of a classical SSP equipped with IVIS is first established and validated by comparing the heave response amplitude operator (RAO) with the previous experimental and numerical results, and the corresponding equations of motion are derived. Optimization analyses are performed to search for the optimum inertance-to-mass ratio of IVIS by minimizing the heave motion standard deviation of the SSP. A case study is carried out to demonstrate the control performance of IVIS in the frequency and time domains. The results indicate that the proposed IVIS is more effective and has a wider effective frequency range compared to the conventional vibration isolation system (VIS). By introducing a parallel-connected inerter, the reduction ratio of the receiving body can be further improved by more than 23%. More importantly, the IVIS can achieve the best control performance under different wave conditions by adjusting the inertance in the system. The proposed IVIS is an attractive alternative to the conventional vibration isolation systems for offshore platforms.

Ultimate capacity evaluation is of vital importance for electricity transmission tower-line systems, which are well recognized as the lifeline engineering in modern society. Undoubtedly, full-scale tests are the most effective and straightforward method for an in-depth understanding of the structural ultimate capacity. In the present study, full-scale tests of a latticed steel tubular transmission tower are performed with emphasis on the failure mechanism of the tower under extreme wind load. Structural responses, ultimate capacity and failure mechanism of the transmission tower in the tests are presented and discussed, respectively. Numerical simulations are then carried out to reproduce the failure of the transmission tower in the tests. In the finite element (FE) model, a buckling and softening failure model is developed to capture the behaviors of the transmission tower. Finally, numerical results are investigated and compared with those obtained in the full-scale tests. Experimental and numerical results demonstrate that the latticed steel tubular transmission tower is designed with enough capacity to resist the designed loads, and the buckling failures of leg members are the dominant cause of the collapse of the transmission tower. Additionally, the developed buckling and softening failure model can accurately reproduce the displacements, ultimate capacity and failure mechanism of the transmission tower. This research can extend the current state of knowledge concerning full-scale tests of latticed transmission towers, and provide a more comprehensive understanding of the performance of latticed steel tubular transmission towers under extreme loads.

Semi-submersible platforms (SSPs) are widely applied for energy mining in the ocean. During its service life, SSP may be subjected to excessive heave and pitch motions induced by sea waves, which in turn may result in fatigue problems of structural components or even catastrophic capsizing of the platform. It is therefore important to mitigate the heave and pitch motions of SSP by all means. In the present study, a novel inerter-based control system, rotational inertia damper (RID), is proposed to simultaneously mitigate the heave and pitch motions of SSP in the shallow sea. The responses of SSP equipped with RID systems subjected to six typical wave conditions are calculated in the frequency and time domains respectively based on the developed analytical models and Simulink models. For comparison, the models and responses of SSP without and with traditional control devices, i.e. fixed heave plate (FHP) and tuned heave plate (THP), are also developed and calculated. The results reveal that the RID system can achieve almost the same or even better control effectiveness compared to the conventional systems with a much smaller additional mass to the SSP especially when the SSP is under harsher waves.

The collapse of a transmission tower under wind action is studied in this paper. A three-dimensional finite element model of the transmission tower is established based on a real project. The birth-to-death element technique is adopted in ABAQUS/Explicit. Kaimal fluctuating wind power spectrum and the harmony superposition method are used to simulate the fluctuating wind speed time history. The dynamic behavior and the collapse mechanism of the transmission tower under three different angles of attack α = 0o, 45o and 90o are carried out, respectively. The results show that the collapse of the transmission tower at 45o angle of attack occurs easily, but it is contrary at 90o angle of attack. The fracture position of the transmission tower under wind excitation is obtained, and the initial damage of the members happens simultaneously in the main and the secondary element. The results of the collapse analysis can provide reference to the design of the transmission tower and the reinforcement of this structure to prevent the collapse of the tower.

Collapses of power transmission towers had usually taken place in previous large earthquake. The collapse process of a power transmission tower under earthquake excitation is studied in this paper. Using international finite element software ABAQUS, the three-dimensional finite element model of the power transmission tower is created based on a practical engineering. Three typical seismic records are selected. The progress collapse processes of the power transmission tower under different seismic excitations are simulated using the nonlinear time history method. The collapse paths and failure positions of the power transmission tower are obtained under different seismic excitations. The results can provide reference for seismic design of power transmission tower which can prevent the collapse of the power transmission tower.

The North China Plain (NCP) has become one of the most polluted regions in China, with the rapidly increasing economic growth in the past decades. High concentrations of ambient O3 and aerosol have been observed at urban as well as rural sites in the NCP. Most of the in situ observations of air pollutants have been conducted near the ground so that current knowledge about the vertical distributions of tropospheric O3 and aerosol over the NCP region is still limited. In this study, vertical profiles of O3 and size-resolved aerosol concentrations below 2.5 km were measured in summer 2014 over a rural site in the NCP, using an unmanned aerial vehicle (UAV) equipped with miniature analyzers. In addition, vertical profiles of aerosol scattering property in the lower troposphere and vertical profiles of O3 below 1 km were also observed at the site using a lidar and tethered balloon, respectively. The depths of the mixed layer and residual layer were determined according to the vertical gradients of lidar particle extinction and aerosol number concentration. Average O3 and size-resolved aerosol number concentration in both the mixed and residual layer were obtained from the data observed in seven UAV flights. The results show that during most of the flights the O3 levels above the top of mixed layer were higher than those below. Such a positive gradient in the vertical distribution of O3 makes the residual layer an important source of O3 in the mixed layer, particularly during the morning when the top of mixed layer is rapidly elevated. In contrast to O3, aerosol number concentration was normally higher in the mixed layer than in the residual layer, particularly in the early morning. Aerosol particles were overwhelmingly distributed in the size range

Full-scale tests are conducted to investigate the load-bearing capacity and failure mechanism of power transmission towers subjected to various loading patterns (broken lines, wind and ice). Detailed finite element models of power transmission towers are established based on these experimental prototypes. To capture the member instability, the integral stability coefficients are obtained from different specifications and introduced into a user-defined material model. Subsequently, the failure analysis of power transmission towers is carried out using an explicit algorithm, and good agreement is found in comparison with experimental results. The results show that the proposed procedure is effective in simulating the power transmission tower failure process. The full-scale test and numerical simulation studies can provide a valuable database for the design of power transmission towers subjected to various loads.

The seismic control of power transmission tower-line coupled system subjected to multicomponent excitations is studied in this paper. The schematic of tuned mass damper is introduced, and equations of motion of a system with tuned mass damper under multi-component excitations are proposed. Three-dimensional finite tower-line system models are created based on practical engineering in studying the response of this system without and with control. The time domain analysis takes into account geometric nonlinearity due to finite deformation. The optimal design of the transmission tower-line system with tuned mass damper is obtained according to different mass ratio. The effects of wave travel, coherency loss, and different site conditions on the system without and with control are investigated, respectively.