Earthquake-induced Vibrations Research Articles

Compliant liquid dampers-inerter for mitigating wind-, wave-, and earthquake-induced vibrations of monopile offshore wind turbines

This work explores the possibility of installing compliant liquid dampers-inerter (CLDI) on monopile offshore wind turbines (OWTs) for controlling combined vibrations from wind, wave, and earthquakes. For numerical demonstration, the 5-MW NREL monopile OWT is taken up. Seven different wind speeds and a set of 20 earthquakes are considered. Hence, the means of structural response quantities are chosen. The peak and root mean square (RMS) values of displacement and acceleration responses of tower-top are monitored. A genetic algorithm-based multi-objective optimization is performed, and the optimum CLDI parameters are estimated for different ranges of inertance ratio and inerter topology. The optimization comprises four cases: firstly, minimizing the mean of peak responses and second, minimizing the mean of RMS responses in fore-aft (FA) as well as in side-side (SS) directions. Hence, each case has four objective functions, covering two loading scenarios, wind & wave, and earthquake. With the obtained optimum parameters, considering all these cases, the control effectiveness of CLDI is further investigated in time and frequency domains. The time domain results reveal that the CLDI controls the SS vibrations effectively, whereas, in FA direction, the efficiency is marginally less. Additionally, the frequency domain plots indicate the multi-mode control capability of CLDI.

A novel three-dimensional isolation bearing for buildings subject to metro- and earthquake-induced vibrations: Laboratory test and application

The implementation of three-dimensional (3D) isolation technology effectively enhances the structural seismic resilience and mitigates the impact of vibrations induced by metro trains. However, the challenge remains to increase the vertical loading capacity of 3D isolation bearings while reducing their vertical stiffness and guaranteeing excellent stability. The 3D isolation bearing (3DIB) consisting of an improved laminated natural rubber bearing (LNR-400-imp) and spring bearings (SBs) built vertically in series were proposed in this study. Its design principle and working mechanism were introduced, and prototype specimens were designed and manufactured. The 3D mechanical performance of the 3DIB was investigated through horizontal and vertical tests. Furthermore, the earthquake and metro vibration isolation performances of the building installed with the 3DIB were analyzed using a case study. The results demonstrated that the 3DIB exhibited horizontal energy dissipation effect, and had stable vertical performance, higher vertical loading capacity, and lower vertical stiffness attributing to the improved LNR-400-imp and SBs. Specifically, the vertical stiffness of the 3DIB was about 1/14 of that of the traditional LNR-400-tra. The case study demonstrated that the 3DIB had remarkable earthquake and metro vibration isolation effects, behaving huge potentials in enhancing the seismic resilience of structures and mitigating the impact of metro vibrations. This study offers valuable insight and practical guidance for future research on 3DIB in the field of vibration isolation, contributing to the advancement of 3D isolation technology.

Control of seismic induced response of wind turbines using KDamper

Earthquake-induced vibrations of wind turbines may compromise structural serviceability and safety. Most previous studies adopted passive control devices to mitigate the seismic responses of wind turbines. However, their control effectiveness is heavily dependent on the mass ratio between control devices and wind turbines, and they were typically housed at the tower top or within the nacelle. The restricted space within the hollow tower and the nacelle imposes considerable challenges for the implementation of such devices, rendering the application of large-scale control devices unfeasible for structural vibration control of wind turbines. To this end, this paper integrates a negative stiffness element within a conventional tuned mass damper (TMD), termed KDamper, to mitigate vibrations of wind turbine towers under seismic loads. Specifically, the widely used NREL 5 MW wind turbine is selected as a prototype structure and its tower is modelled as a multiple-degree-of-freedom system. Then KDamper is incorporated into the developed model and its parameters are optimized based on the H2 criterion. Subsequently, the control effectiveness of KDamper is investigated and compared with TMD in the frequency domain, and the control performances in terms of the effectiveness and robustness of KDamper are further examined under a series of earthquake records. Results show that KDamper has superior control effectiveness and robustness than TMD, indicating it has considerable potential for application in improving wind turbine performances against earthquake hazards.

Inerter location effect on the generalized tuned mass damper inerter control

This paper investigates the inerter location effect on the generalized tuned mass damper inerter (TMDI) control, in which the end of the inerter is located at any position of the primary structure. A good understanding of the inerter location effect can help us achieve an optimal generalized TMDI control. Two mass ratios weighting the mass amplification effect and negative stiffness effect are defined to understand the inerter location effect. Based on the two mass ratios, the relationship between the TMD and generalized TMDI is established, the analytical solution of the optimal tuning frequency is derived, and a high-accuracy prediction equation judging whether the generalized TMDI performs better than the TMD is proposed. Finally, numerical analyses on a 76-story high building equipped with TMD and generalized TMDI are performed. The results show that the the generalized TMDI in fact is a large mass ratio TMD with a frequency-dependent stiffness, the generalized TMDI with larger inertance and smaller physical mass has more inerter location choices, and the damping ratio of the primary structure has no influence on the critical inerter location. The generalized TMDI considering the inerter location effect has better control effect than the TMD in suppressing both the wind-induced vibration and earthquake-induced vibration. The mean reduction ratios of peak floor accelerations for the TMD and TMDI controls are 60.53% and 54.5% under the wind-induced force excitation, and those of maximum floor drift ratios for the TMD and TMDI controls are 94.32%, 87.56% under the earthquake excitation.

Seismic performance assessment and benefit-cost analysis of mid-rise reinforced concrete base-isolated building using double-curvature friction pendulum bearings

Base isolation technology is highly advocated by the research community worldwide for efficient mitigation of earthquake-induced vibrations and alleviating seismic risks posed to civil engineering structures. However, the construction cost of implementing this advanced technique to real-life buildings compared to the conventional ones remains a debatable topic, and a research problem to examine. Therefore, the present study focuses on assessing the short- and long-term cost-benefits of base-isolated buildings vis-é-vis fixed-base buildings over their service life. Notably, the benefit-cost analysis methodology prescribed in FEMA-356 is utilized to quantify the economic consequences of natural calamities on the base-isolated building. Various aspects, such as structural responses, damage vulnerability, collapse probability, and occupancy rate are thoroughly analyzed. A real-life mid-rise reinforced concrete building in the Indian subcontinent, having double-curvature friction pendulum bearings (FPBs) at stilt level is deliberated in this study. A series of quasi-static and nonlinear time-history analyses are carried out based on the recently drafted Indian seismic code for base isolation to comprehend the improved performance of the FPB-isolated building. Additionally, two fixed-base buildings are designed with an aim to make their performance almost at par with the base-isolated building, and then to assess the cost implications of attaining such comparable performance. The outcomes of this study, particularly the structural performance enhancement and cost benefits, will assist both decision makers and structural designers to have a persuasive opinion on the better adaptability of the base isolation technology for improved seismic resistance and financial outlooks associated thereof.

Vulnerability analysis of earthquake-driven blast load on a reinforced concrete structure

It is common practice in earthquake-prone areas to design structures with earthquake loading in mind. The severity of the damage to a structure depends on the earthquake's magnitude and the type of structure. Sometimes, a high-intensity earthquake can trigger explosive materials to explode inside structures. This combination of loading scenarios could lead to an overall increase in damage to the structures. So, it is essential to study the vulnerability analysis of the structures subjected to multi-hazard loading scenarios. This study mainly discusses the combined effect of the earthquake followed by the blast loading on the reinforced concrete structure. The results show that damage to the structure increases under combined earthquake and blast loading. Furthermore, the earthquake-induced vibrations in the structure intensify after the blast load. A parametric study of the structure is also performed, taking into account the possible load combinations of earthquake and blast loading. Moreover, this study discusses a numerical solution to the aforementioned problem, which strengthens fundamental knowledge and provides structural engineers with a deeper insight regarding the multi-hazard loading scenario considered in this study.

Adaptive fuzzy variable fractional-order sliding mode vibration control of uncertain building structures

A novel robust adaptive fuzzy variable fractional-order sliding mode control (FVFOSMC) strategy is proposed to suppress earthquake-induced vibrations on uncertain building structures. Firstly, a new variable fractional-order sliding mode controller (VFOSMC) is established by embedding the concepts of variable fractional-order (VFO) calculus into a sliding mode controller. Then, the FVFOSMC is designed by using VFO fuzzy logic with online adaptive approximation to avoid chattering or inaccurate switching. The global stability of the closed-loop system is proved based on VFO Lyapunov stability theory. Three examples illustrate the performance of the proposed FVFOSMC. The results confirm the robustness and superior performance of the new method in the presence of uncertain structure parameters and external unknown earthquake excitation.

Real time vibration measurement and inverse analysis for dynamic properties of an axisymmetric masonry structure

ABSTRACT Historic buildings are public symbols, standing as sacred reminders. Many of them have been recognized as World Heritage Sites. In this study, real time vibration measurement of an important axisymmetric masonry pagoda was performed. With the measured vibration data, inverse analysis was proposed to backward determine its damping and natural period. The proposed algorithm utilizes Duhamel’s time integration method for solving the equation of motion and the Gauss-Newton algorithm to minimize the sum-of-squares error between the calculated and real-time measured accelerations of the structure. Four distant earthquake-induced vibrations were recorded and used for the analysis. The results show that the dynamic parameters determined by the proposed method agree with those obtained from the previous study adopting finite element analysis. The obtained dynamic properties of the two perpendicular directions are slightly different, indicating the non-homogenous body of the axisymmetric structure or there would be a particular damage zone. From the results, an onsite damage investigation can be specifically identified. In summary, continuous structural health monitoring and time-dependent deterioration of historic buildings are possible with real time measurement and the proposed analytical algorithm.

Fuzzy Fractional-Order PD Vibration Control of Uncertain Building Structures

A new control strategy is proposed to suppress earthquake-induced vibrations on uncertain building structures. The control strategy embeds fuzzy logic in a fractional-order (FO) proportional derivative (FOPD) controller. A new improved FO particle swarm optimization (IFOPSO) algorithm is derived to adjust the initial parameters of the FOPD controller. An original fuzzy logic-FOPD (FFOPD) controller is then designed by combining the advantages of the fuzzy logic and FOPD control, to deal with large displacements on structures under earthquake excitation. Simulation experiments are carried out on uncertain building structures subjected to the effects of different kinds of seismic signals, illustrating the validity and feasibility of the proposed method.

Multi active tuned mass dampers for earthquake-induced vibration response control of high rise building

Multi active tuned mass dampers for earthquake-induced vibration response control of high rise building

Seismic performance of modular steel buildings (MSBs) equipped with resilient slip friction joints (RSFJs)

Modular construction is becoming a prevalent technique combining off-site construction and on-site assembly to provide fast, reliable and high-quality permanent buildings. The modular method is a good alternative to traditional on-site construction when the layout consists of repetitive units such as hotels and multifamily dwellings, and when the construction schedule is tight. The dynamic performance of Modular Steel Buildings (MSBs) has not yet been fully studied, and a limited number of investigations on the nonlinear dynamic behavior of MSBs showed that they are susceptible to damage during strong ground motions. This paper considers the use of a self-centering energy dissipation device, called Resilient Slip Friction Joint (RSFJ), in MSBs to avoid seismic damage, enable immediate occupancy, and reduce the repair costs after a severe earthquake event. Two different configurations of RSFJs (namely tension-compression and tension-only configurations) were introduced to Seismic Force Resisting Systems (SFRSs) of 6- and 12-story MSBs. This study presents a step-by-step design procedure by following the capacity design for RSFJs in accordance to National Building Code of Canada (NBCC). The dynamic performances of both configurations were evaluated by performing bi-directional Nonlinear Time History Analysis (NLTHA). In addition to global response of MSBs, component level maximum demands of RSFJs were assessed to shed a light on the overall performance of MSBs under three different hazard levels. It was shown that low- and mid-rise MSBs can efficiently be equipped with RSFJ to mitigate earthquake-induced vibrations and minimize the damage to the structural members.

Development of a three-directional vibration isolator for buildings subject to metro- and earthquake-induced vibrations

In this paper, a new three-directional vibration isolator for buildings was developed to suppress vertical metro vibrations and horizontal seismic vibrations simultaneously. The isolator was a laminated rubber bearing (LRB) with vertical through-holes. The holes were filled with a mixture of sand and rubber particles. The pseudo-static testing results show that the compression stiffness of the new isolator is relatively smaller than that of the traditional LRB and that the stiffness can be easily adjusted. The vertical damping ratio reached 9%. These advantages are appropriate for suppressing vertical metro vibrations. Because of the frictional forces of the particle mixture, the horizontal damping ratio reached 24%, and the shear stiffness dependencies were similar to those of traditional LRBs. The ultimate shear strain reached 350%. Therefore, the isolator’s horizontal seismic isolation performance was similar to those of high-damping LRBs. By applying viscous damping forces to simulate frictional forces, a finite element (FE) model is proposed for the new isolator. The model can efficiently analyze the mechanical properties. To investigate the feasibility of the new isolator, field experiments were carried out using a full-scale masonry building adjacent to a metro line. The results show that the metro-induced vertical vibrations and vibration-induced noises were significantly suppressed after the installation of the new isolators. Finally, numerical analyses of the seismic isolation performance were carried out using a six-story building under rare earthquakes. The results show that no tensile stress occurred on the new isolators and both the compressive stress and shear strain were less than the bearing capacity. Therefore, the new isolator is feasible for buildings subject to metro- and earthquake-induced vibrations.

A backstepping control design for ATMD systems of building structure against earthquake excitations in the presence of parametric uncertainty

The design of a novel backstepping controller for using with active tuned mass damper (ATMD) system is investigated in this study. The main aim of this study is to design the controller for the ATMD system to reduce earthquake-induced vibrations in multistory buildings. Obtaining a generalizable control design for such systems is another important aim of this study. To reach this aim, the designed controller is based on the assumption that the system parameters are completely uncertain. The parametric uncertainty is coped with via adaptive compensation rules proposed in accordance with available system states. Effects of the control force on the displacement of the controller mass and the last floor of a multistory building are considered together. Owing to this approach, a control operation is provided in which zero convergence of the displacement of the mass of ATMD and all floors of the building can be guaranteed. Using Lyapunov-based arguments, theoretically, it has been proven that the designed controller can maintain its stability of the structure and controller mass while achieving this main control objective. The efficiency of the designed controller in terms of reaching the mentioned control objective is observed via numerical simulations. In these simulations, the designed controller is used in conjunction with an ATMD system placed on a multistory building model, and it has been shown that the controller designed in such structures can be used effectively for damping the earthquake-induced vibrations of these types of structures.

Exploring energy harvesting and vibration mitigation in tall buildings accounting for wind and seismic loads

With the changing climate and the limited supply of fossil fuels available for global energy use, much research has been done to develop innovative methods of producing clean and renewable energy. Out of the various energy sources, wind forces can cause tall buildings to undergo significant vibrations presenting a potential source of clean and renewable energy for buildings and the power grid. To mitigate wind-induced vibrations in tall buildings, viscous dampers have been widely utilized, which, unlike tuned-mass dampers, are also effective in mitigating earthquake-induced vibrations. Contrary to conventional designs, this research explores the use of energy harvesting transducers, in place of viscous dampers, as a means of not only mitigating vibrations under extreme loading conditions (e.g. earthquakes), but also harvesting energy from wind induced vibrations during service conditions and converting it to electricity. This research demonstrates the often conflicting requirements for supplemental damping related to energy harvesting (EH) from wind loads under service conditions vs. vibration mitigation (VM) under extreme events (e.g., earthquakes). Specifically, this research shows that large damping is usually required for VM, whereas small or moderate damping is often required to maximize EH. In doing so, this research develops, and validates using test data, a nonlinear model for an electromagnetic EH transducer, quantifies the EH potential of a selected tall building as a function of the supplemental damping and wind speed showing that EH power generation can reach kWs (as opposed to W), and assesses the seismic performance of the same building as a function of the supplemental damping for two seismic hazard levels. The findings of this research will support future studies pursuing the concept of energy harvesting in structural design.

Noncontact operational modal analysis of light poles by vision-based motion-magnification method

Light and sign poles on elevated highway bridge are secondary structural elements that support functionality of a highway system. Over the time, they may suffer from fatigue damage due to traffic, wind, and earthquake-induced vibration in a direct or indirect manner. As a secondary structural component, vibrations of light and sign poles are influenced by the bridge vibration, the primary structure. Structural condition assessment of the light and sign poles are normally conducted by visual inspection and/or vibration measurement using contact or noncontact method. In this paper, a vision-based vibration measurement of the light poles on elevated highway bridges using motion magnification and dynamic mode decomposition methods is proposed. Using the method, vibrations of the light poles are captured by video camera and the phase-based motion magnification method is implemented to magnify micro-vibration of the structure. By employing discretized centroid searching method, spatial displacements of the light poles are extracted. Modal parameters of the structure are then identified from the displacement responses by dynamic mode decomposition method. The study includes laboratory experiments for verification, and the full-scale implementation on existing light poles on elevated highway bridges. The vision-based results are compared with the noncontact vibration measurement using Laser-Doppler vibrometers. Results of experiments and full-scale tests demonstrate the capability of the proposed method in extracting multi-mode vibration characteristics of the light poles accurately in a noncontact long-distance measurement.

Two-level friction damping and its application for passive multi-functional vibration control of high-rise buildings

In recent years, the use of structural elements and/or entire structures with low internal damping are favoured with the increasing trend for unconventional design of structures and infrastructures that combine high functionality and increased aesthetics. One example is the advancement of high-rise buildings, which are built taller, more slender and with more spectacular designs compared to the past. In many of these cases, supplementary damping is included in the structural design by installing distributed passive damping devices, among which the friction damper has become popular due to its relative low cost, high reliability and high efficiency. The conventional friction damper, however, can only mitigate vibrations optimally with respect to a single deformation shape at a single vibration amplitude, which is not enough in cases where additional damping is required to mitigate different magnitudes of the excitation. Thus, the paper scrutinises the performance of the passive two-level friction damper, recently proposed elsewhere, in comparison to the conventional one-level friction damper, and assesses its application for multi-functional vibration control of a high-rise building. Specifically, this paper scrutinises the application and performance of the two-level friction damper in two simulation-based frameworks and ultimately: (i) evaluates and demonstrates the vibration performance of a dynamic system when equipped with this damper type, and (ii) investigates the application of this damper type for mitigation of both wind- and earthquake-induced vibration of a high-rise building. It is found that the optimal performance of the two-level friction damper is covering a larger vibration amplitude range compared to the conventional friction damper, which enabled the two-level friction damper to, in contrast to the conventional friction damper, successfully mitigate both wind- and earthquake-induced vibration in the application example. Based on the findings, it is concluded that the two-level friction damper is able to overcome some of the limitation, application-wise, connected to the amplitude dependence of the one-level friction damper.

Seismic performance of optimal Multi-Tuned Liquid Column Damper-Inerter (MTLCDI) applied to adjacent high-rise buildings

Conventional vibration absorbers, e.g., a classical tuned mass damper, may be not efficient in simultaneously controlling the seismic response of adjacent high-rise buildings. In this paper, a novel passive vibration control system, denoted as Multi-Tuned Liquid Column Damper-Inerter (MTLCDI), is developed to control the seismic response of adjacent high-rise buildings. Two different configurations of this system, namely inter-story MTLCDI (IS-MTLCDI) and inter-building MTLCDI (IB-MTLCDI), are proposed, and related mathematical models are developed to investigate the seismic performance of MTLCDI. A case study project comprising two adjacent high-rise buildings equipped with the proposed system and subjected to ten earthquake records with various frequency characteristics is considered. Performance-based parametric optimization of the MTLCDI systems is performed through two distinct constrained multi-objective optimization problems via genetic algorithms, wherein peak absolute accelerations and inter-story drift ratios of the two adjacent buildings are selected as performance indexes. The mitigation effects of optimum IS-MTLCDI and IB-MTLCDI on earthquake-induced vibrations are scrutinized, with emphasis placed on the effects of natural frequency ratios between the two host structures. The results indicate that, when the two buildings have distinct natural frequencies, both IS-MTLCDI and IB-MTLCDI outperform inter-building single TLCDI as well as other vibration absorbers in terms of seismic vibration control of absolute acceleration and inter-story drift ratios. Under most natural frequency ratios, the IS-MTLCDI achieves a larger response reduction than IB-MTLCDI. Nevertheless, when the differences between natural frequencies of adjacent buildings are significant, applying an IB-MTLCDI may be preferable due to its satisfactory mitigation effects combined with ease of installation.

A study of earthquake-induced vibration on laminated composite plates using finite element method

This study presents the dynamic response of an eight-noded composite plate under earthquake excitation. Koyna earthquake excitation frequency is considered for the present study. Central displacement and stresses at various positions are studied extensively. Variation in response under different boundary conditions and varying geometric conditions are presented. The ply angle in a lamina and the number of layers in a plate are also varied to observe their effect on displacement and stress. In almost all the cases, 45° lamination shows maximum displacement response, whereas 0°/90° lamination scheme always shows maximum normal stress values. On the other hand, inplane shear gives maximum response whenever a − 45° layer is present. The effect of plan dimension on displacement is also presented here. The displacement response is maximum when the plate becomes square for both cross- and angle-ply laminations. The displacement response with change in total thickness of the plate is presented in this article. The response increases drastically as the plate becomes thinner for angle and cross-ply laminations. The plate becomes unstable as the side to thickness ratio increases beyond 50. The variation of stresses for cross- and angle-ply laminated plates across their layers is reported here with different boundary conditions. A very important observation made through this comparison as a 45° clamped laminated plate should be designed under transverse shear stress, whereas the simply supported plate should be designed under inplane shear stress.

Smart structural control and analysis for earthquake excited building with evolutionary design

In recent years, with the maximization of control design and efficiency, and the improvement of economy and energy efficiency, building technology and control in the theory have attracted the attention of lots researchers. By trying various control theorems, many numerical methods have been investigated in the literature to achieve this target, but all these numerical methods are difficult to work out the problem correctly. This paper puts forward a potentially feasible evolutionary bat algorithm (EB) method for active control of earthquake-induced vibration in building structures. Based disturbance observer based control and S surface combined with the robust adaptive control scheme for solving optimization problems proposed, an important contribution in the control law is what the configuration control in the present study should not require known uncertainty limits and the disturbance is eliminated. A simulation case study was proposed to illustrate the possibility of implementing an apparent learning method in ANN to effectively control structural vibration under the influence of systematic motion under earthquake citations. The proposed learning numerical methods does not need to develop a mathematical model of structural dynamics or train another neural network to approximate the actual structural response to be performed.

Seismic Vibration Mitigation of Wind Turbine Tower Using Bi-Directional Tuned Mass Dampers

Wind turbines have been increasingly erected in earthquake regions to harvest abundant wind energy. However, the wind turbine tower is slender and lightly damping, which exhibits high susceptibility to earthquake-induced vibration. It is challenging to mitigate the seismic vibration of the tower. In this study, a bi-directional tuned mass damper (BTMD) is proposed to mitigate the seismic vibration of the wind turbine tower. Meanwhile, a lumped-mass finite element model (LFEM) and a coupled blade tower finite element model (CBFEM) are used to investigate the vibration mitigation performance of the BTMD. First, the BTMD and corresponding dynamic equilibrium equations are systemically introduced. Accordingly, the optimum stiffness and damping of the BTMD at different mass ratios are investigated. Then, the dynamic prosperities of the LFEM and CBFEM are compared. Subsequently, the seismic responses of the wind turbine with the BTMD are conducted using the LFEM and CBFEM. Meanwhile, the mitigation performances of the BTMD under uni- and bi-directional earthquakes are investigated. The displacement, acceleration, and bending moment of the wind turbine tower are analyzed in time domain and frequency domain. Note that the influential factors, including mass ratio and structural frequency, on the vibration mitigation performance of the BTMD are investigated. Results show that the proposed BTMD can significantly mitigate the peak values of the top displacement and bottom bending moment. However, the blade tower coupling effect and frequency variation of the tower would have influences on the mitigation efficiency of the BTMD. The results enable a better understanding of the seismic vibration mitigation of the wind turbine tower using tuned mass dampers.