Protection of seismic structures using semi‐active friction TMD

Although the design and applications of linear tuned mass damper (TMD) systems are well developed, nonlinear TMD systems are still in the developing stage. Energy dissipation via friction mechanisms is an effective means for mitigating the vibration of seismic structures. A friction‐type TMD, i.e. a nonlinear TMD, has the advantages of energy dissipation via a friction mechanism without requiring additional damping devices. However, a passive‐friction TMD (PF‐TMD) has such disadvantages as a fixed and pre‐determined slip load and may lose its tuning and energy dissipation abilities when it is in the stick state. A novel semi‐active‐friction TMD (SAF‐TMD) is used to overcome these disadvantages. The proposed SAF‐TMD has the following features. (1) The frictional force of the SAF‐TMD can be regulated in accordance with system responses. (2) The frictional force can be amplified via a braking mechanism. (3) A large TMD stroke can be utilized to enhance control performance. A non‐sticking friction control law, which can keep the SAF‐TMD activated throughout an earthquake with an arbitrary intensity, was applied. The performance of the PF‐TMD and SAF‐TMD systems in protecting seismic structures was investigated numerically. The results demonstrate that the SAF‐TMD performs better than the PF‐TMD and can prevent a residual stroke that may occur in a PF‐TMD system. Copyright © 2009 John Wiley & Sons, Ltd.     

Predictive control of seismic structures with semi‐active friction dampers

In this paper a predictive control method especially suitable for the control of semi‐active friction dampers is proposed. By keeping the adjustable slip force of a semi‐active friction damper slightly lower than the critical friction force, the method allows the damper to remain in its slip state throughout an earthquake of arbitrary intensity, so the energy dissipation capacity of the damper can be improved. The proposed method is formulated in a discrete‐time domain and cast in the form of direct output feedback for easy control implementation. The control algorithm is able to produce a continuous and smooth slip force for a friction damper and thus avoid exerting the high‐frequency structural response that usually exists in structures with conventional friction dampers. Using a numerical study, the control performance of a multiple degrees of freedom (DOF) structural system equipped with passive friction dampers and semi‐active dampers controlled by the proposed method are compared. The numerical case shows that by merely using a single semi‐active friction damper and a few sensors, the proposed method is able to achieve better acceleration reduction than the case using multiple passive dampers. Copyright © 2004 John Wiley & Sons, Ltd.     

Dynamic response and optimal design of structures with large mass ratio TMD

This paper investigates the dynamic behavior and the seismic effectiveness of a non‐conventional Tuned Mass Damper (TMD) with large mass ratio. Compared with conventional TMD, the device mass is increased up to be comparable with the mass of the structure to be protected, aiming at a better control performance. In order to avoid the introduction of an excessive additional weight, masses already present on the structure are converted into tuned masses, retaining structural or architectural functions beyond the mere control function. A reduced order model is introduced for design purposes and the optimal design of a large mass ratio TMD for seismic applications is then formulated. The design method is specifically developed to implement High‐Damping Rubber Bearings (HDRB) to connect the device mass to the main structure, taking advantage of combining stiffness and noticeable damping characteristics. Ground acceleration is modeled as a Gaussian random process with white noise power spectral density. A numerical searching technique is used to obtain the optimal design parameter, the frequency ratio alpha, which minimizes the root‐mean‐square displacement response of the main structure. The study finally comprises shaking table tests on a 1:5 scale model under a wide selection of accelerograms, both artificial and natural, to assess the seismic effectiveness of the proposed large mass ratio TMD. Copyright © 2011 John Wiley & Sons, Ltd.     

常摩擦TMD地震控制效果的理论和实验研究

在TMD中采用摩擦阻尼代替传统的粘滞阻尼,可有效降低TMD的造价,从而促进其推广应用。但摩擦元件是非线性的,给摩擦TMD分析和设计造成了一定的困难。为了研究常摩擦TMD地震控制的特点和规律,文中采用时程分析法进行了简谐激励和地震激励下摩擦TMD对单自由度结构响应控制的理论分析;在理论分析结果的指导下,进行了单自由度主结构和摩擦TMD系统在简谐激励和地震激励下的振动台试验。理论分析和试验结果表明:除了频率比和质量比的影响,摩擦TMD的控制效果和摩擦力大小、激励幅值有关,只要参数设置合适,其控制效果是令人满意的;在设计摩擦TMD时要针对激励大小、目标控制效率进行具体分析。     

Improved external device for a mass‐carrying sliding system for shaking table testing

Shaking tables are suitable facilities to assess and validate the behavior of structures and nonstructural components under actual seismic actions. Because of the size and weight limitations of the tables, some approaches, like testing reduced‐scale models or testing only the main structural components, are deemed necessary. In these cases, to comply with modeling requirements, large amount of extra‐mass should be added to the specimen. Therefore, to avoid the risk of lateral instability of models, to maintain the weight of test specimens within table payload, while maintaining the amount of mass needed, an external device for transmitting the inertia forces to the models using an improved sliding system is proposed. Although friction devices for similar purposes have been developed using sliding bearings (Teflon pads or rollers), the measured coefficient of dynamic friction and the energy dissipated by friction have been very high. In order to drastically diminish the damping added to the specimen response when a friction device is used, the improved device employs a linear motion guide system (LMGS) with very low friction. Shaking table tests to collapse of reinforced concrete walls were used to evaluate the effectiveness of the proposed device. Measured dynamic friction coefficients, spectral accelerations and hysteresis loops show that friction developed in the LMGS did not add any significant amount of damping into the specimen response. Thus, the proposed device is a reliable and suitable mass‐carrying sliding system (MCSS) for dynamic testing using medium‐size shaking tables. Copyright © 2010 John Wiley & Sons, Ltd.     

Inelastic buildings with tuned mass dampers under moderate ground motions from distant earthquakes

The effectiveness of tuned mass dampers (TMD) in vibration control of buildings was investigated under moderate ground shaking caused by long‐distance earthquakes with frequency contents resembling the 1985 Mexico City (SCT) or the 1995 Bangkok ground motion. The elastic–perfectly plastic material behaviour was assumed for the main structure, with linear TMDs employed by virtue of their simplicity and robustness. The accumulated hysteretic energy dissipation affected by TMD was examined, and the ratio of the hysteretic energy absorption in the structure with TMD to that without it is proposed to be used, in conjunction with the peak displacement ratio, as a supplementary TMD performance index since it gives an indication of the accumulated damage induced in the inelastic structures. For the ground motions considered, TMD would be effective in reducing the hysteretic energy absorption demand in the critical storeys for buildings in the 1.8–2.8 s range. The consequence is reduction in damage of the buildings which would otherwise suffer heavy damage in the absence of TMD, resulting in economical restorability in the damage control limit state. This is of practical significance in view of the current trend toward performance‐based design. Copyright © 2001 John Wiley & Sons, Ltd.     

Slide roof system for dynamic response reduction

A slide roof system (SRS) is proposed to reduce the dynamic response of buildings to earthquake excitations. A SRS consists of a roof structure, springs and friction materials, providing mass, stiffness and damping, respectively. The method of optimization of stiffness and friction coefficient for the SRS is introduced. A numerical analysis of an eight‐story frame structure subjected to ground motions and shaking table tests of a five‐story frame was carried out to study the effectiveness of the SRS. The results show that the SRS can reduce the maximum dynamic response as much as 60–70% in the first resonate band and 35–50% in the second resonate band. Copyright © 2007 John Wiley & Sons, Ltd.     

Linear dynamic modeling of a uni‐axial servo‐hydraulic shaking table system

This paper focuses on the development of a linear analytical model (even though servo‐hydraulic actuation systems are inherently non‐linear, especially for large amplitude simulations — near the performance capacity of the system — linearized models proved experimentally to be quite effective overall in capturing the salient features of shaking table dynamics) of a uni‐axial, servo‐hydraulic, stroke controlled shaking table system by using jointly structural dynamics and linear control theory. This model incorporates the proportional, integral, derivative, feed‐forward, and differential pressure gains of the control system. Furthermore, it accounts for the following physical characteristics of the system: time delay in the servovalve response, compressibility of the actuator fluid, oil leakage through the actuator seals and the dynamic properties of both the actuator reaction mass and test structure or payload. The proposed model, in the form of the total shaking table transfer function (i.e. between commanded and actual table motions), is developed to account for the specific characteristics of the Rice University shaking table. An in‐depth sensitivity study is then performed to determine the effects of the table control parameters, payload characteristics, and servovalve time delay upon the total shaking table transfer function. The sensitivity results reveal: (a) a potential strong dynamic interaction between the oil column in the actuator and the payload, and (b) the very important effect of the servovalve time delay upon the total shaking table transfer function. Copyright © 2000 John Wiley & Sons, Ltd.     

大跨度斜拉桥钢塔施工阶段制振用TMD、TLD装置及其性能试验

本文以南京长江第三大桥为例,研制了用于钢塔施工阶段涡激振动响应制振的制振器TMD和TLD。对制振装置以及其所采用的一些关键技术进行了说明。通过振动台试验测试了制振器的动力特性。根据试验结果,对TMD的工作性能,即装置的频率特性、阻尼特性、起动时所需的外激励水平及装置的框架刚度等,进行了评价分析;对TLD实现了其阻尼方案的优化,并确定了其工作时的阻尼隔栅状态。确认了制作完成的制振器具有良好的工作性能。     

A study on using wide‐flange section web under out‐of‐plane flexure for passive energy dissipation

It is not common to purposely subject the web of wide‐flange or I‐sections to out‐of‐plane bending. However, yielding the web under this loading condition can be a stable source of energy dissipation as the transition at the corner from the web to the flanges is smooth and weld‐free; this prevents stress concentrations causing premature failure and eliminates uncertainties and imperfections associated with welding. Further, short segments of wide‐flange or I‐sections constitute a simple and inexpensive energy dissipating device as minimum manufacturing is required and leftovers not useful for other structural purposes can be re‐utilized. This paper proposes a new type of seismic damper in the form of braces based on yielding the web of short length segments of wide‐flange or I‐shaped steel sections under out‐of‐plane bending. The hysteretic behavior and ultimate energy dissipation capacity is investigated via component tests under cyclic loads. The experimental results indicate that the damping device has stable restoring force characteristics and a high energy dissipation capacity. Based on these results, a simple hysteretic model for predicting the load–displacement curve of the seismic damper is proposed, along with a procedure for predicting its ultimate energy dissipation capacity and anticipating its failure under arbitrarily applied cyclic loads. The procedure considers the influence of the loading path on the ultimate energy dissipation capacity. Finally, shaking table tests on half‐scale structures are conducted to further verify the feasibility and effectiveness of the new damper, and to assess the accuracy of the hysteretic model and the procedure for predicting its failure. Copyright © 2010 John Wiley & Sons, Ltd.     

电磁耗能TMD结构减震效率的振动台试验研究

通过钢框架TMD减震的振动台模型试验，测试电磁耗能TMD新装置的减震耗能性能。大量试验结果表明：利用电磁涡流耗能原理的TMD新装置具有良好的结构减震效率。     

考虑土与结构相互作用效应的结构减震控制大型振动台模型试验研究

本文设计并完成了考虑土与结构相互作用的结构减震控制大型振动台模型试验。通过对四种结构形式的对比试验，探讨了土与结构相互作用（ＳＳＩ）效应对结构地震反应的影响以及调谐质量阻尼器（ＴＭＤ）在刚性和柔性地基条件下对主体结构的减震效应。通过比较同一地震动作用下主体结构在刚性和柔性两种地基条件下的地震反应，可知：ＳＳＩ效应具有降低和提高结构减震控制效果的双重作用，其综合效果与输入地震动的频谱特性、加速度峰值大小有关。由于ＳＳＩ效应在结构地震反应中发挥着双重的作用，因而使得基于刚性地基假定下设计的ＴＭＤ减震控制系统在柔性地基条件下的控制效果不太理想，甚至会出现负面效应。本文还探讨了在柔性地基条件下影响结构减震控制效果的一些因素。     

Optimum design and experimental study of multiple tuned mass dampers with limited stroke

This paper develops a two‐stage optimum design procedure for multiple tuned mass dampers (MTMD) to reduce structural dynamic responses with the limitation of MTMD's stroke. A new performance index, which is a linear combination of structural response ratio and MTMD stroke ratio by a weighting factor α, is proposed; α is in the range from 0 to 1.0. The larger the α, the more important the stroke. The case of α=1.0 indicates that MTMD is locked. The analytical results show that the MTMD's stroke can be significantly suppressed with little sacrifice of structural control effectiveness when an appropriate α is selected. To verify the design algorithm, a 360 kg‐MTMD composed of five TMD units arranged in parallel was fabricated. Shaking table tests of a large‐scale three‐story building with and without the MTMD under earthquake excitations were conducted at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan. The experimental results show that MTMD is not only effective in mitigating the building responses but also is successful in suppressing its stroke. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental study of the semi‐active control of building structures using the shaking table

A magnetorheological (MR) damper has been manufactured and tested and a non‐linear model is discussed. The parameters for the model are identified from an identification set of experimental data; these parameters are then used to reconstruct the force vs. displacement and the force vs. velocity hysteresis cycles of the MR damper for the hysteretic model. Then experiments are conducted on a three‐storey frame model using impact excitation, which identifies dynamic parameters of the model equipped with and without the MR damper. Natural frequencies, damping ratios and mode shapes, as well as structural properties, such as the mass, stiffness and damping matrices, are obtained. A semi‐active control method such as a variable structure controller is studied. Based on the ‘reaching law’ method, a feedback controller is presented. In order to evaluate the efficiency of the control system and the effect of earthquake ground motions, both numerical analysis and shaking table tests of the model, with and without the MR damper, have been carried out under three different ground motions: El Centro 1940, Taft 1952, and Ninghe 1976 (Tangshan Earthquake in Chinese). It is found from both the numerical analysis and the shaking table tests that the maximum accelerations and relative displacements for all floors are significantly reduced with the MR damper. A reasonable agreement between the results obtained from the numerical analysis and those from the shaking table tests is also observed. On the other hand, tests conducted at different earthquake excitations and various excitation levels demonstrate the ability of the MR damper to surpass the performance of a comparable passive system in a variety of situations. Copyright © 2003 John Wiley & Sons, Ltd.     

Optimal design of tuned mass dampers for a multi‐storey cross laminated timber building against seismic loads

In this paper, the effectiveness of different design solutions for tuned mass dampers (TMD) applied to high‐rise cross‐laminated (X‐Lam) timber buildings as a means to reduce the seismic accelerations was investigated. A seven‐storey full‐scale structure previously tested on shaking table was used as a reference. The optimal design parameters of the TMDs, i.e. damping and frequency ratios, were determined by using a genetic algorithm on a simplified model of the reference structure, composed by seven masses each representing one storey. The optimal solutions for the TMDs were then applied to a detailed finite element model of the seven‐storey building, where the timber panels were modelled with shell elements and the steel connectors with linear spring. By comparing the numerical results of the building with and without multiple TMDs, the improvement in seismic response was assessed. Dynamic time‐history analyses were carried out for a set of seven natural records, selected in accordance with Eurocode 8, on the simplified model, and for Kobe earthquake ground motion on the detailed model. Results in terms of acceleration reduction for different TMD configurations show that the behaviour of the seven‐storey timber building can be significantly improved, especially at the upper storeys. Copyright © 2016 John Wiley & Sons, Ltd.     

Apparent damping induced by spurious pitching in shaking‐table testing

A seismic shaking‐table test performed on a one‐storey steel frame with an 8 ton RC floor slab was reproduced on a similar specimen by means of the pseudo‐dynamic (PsD) method. A satisfactory agreement of the results could only be achieved after recalibration of the theoretical mass in the PsD equation and proper inclusion in the PsD test input of the horizontal and pitching accelerations measured on the table. In the shaking‐table test, the spurious pitching motion produced a significant increase in the apparent damping that could be estimated as a function of the pitching dynamic flexibility of the system. Dynamic and PsD snap‐back tests were also performed to provide an additional check of the reliability of the PsD method. The spurious pitching motion of the shaking table should always be measured during the tests and reported as a mean to increase the reliability and usefulness of the results. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental characterization,modeling and identification of the NEES‐UCSD shake table mechanical system

This paper proposes a simple conceptual mathematical model for the mechanical components of the NEES‐UCSD large high‐performance outdoor shaking table and focuses on the identification of the parameters of the model by using an extensive set of experimental data. An identification approach based on the measured hysteresis response is used to determine the fundamental model parameters including the effective horizontal mass, effective horizontal stiffness of the table, and the coefficients of the classical Coulomb friction and viscous damping elements representing the various dissipative forces in the system. The effectiveness of the proposed conceptual model is verified through a comparison of analytical predictions with experimental results for various tests conducted on the system. The resulting mathematical model will be used in future studies to model the mechanical components of the shake table in a comprehensive physics‐based model of the entire mechanical, hydraulic, and electronic system. Copyright © 2007 John Wiley & Sons, Ltd.     

Seismic vibration control of building structures with multiple tuned mass damper floors integrated

Floor isolation system (FIS) achieving very small floor accelerations has been used to ensure human comfortability or protect important equipments in buildings. Tuned mass damper (TMD) with large mass ratios has been demonstrated to be robust with respect to the changes in structural properties. This paper presents the concept of a TMD floor vibration control system, which takes advantages of both the FIS and TMD. Such a system is called ‘TMD floor system’ herein. The TMD floor system (TMDFS) in which building floors serve as TMDs can achieve large mass ratio without additional masses. Furthermore, multiple TMD floors installed in a building can control multimode vibrations. Then, an optimal design process, where the objective function is set as the maximum magnitude of the frequency response functions of inter‐storey drifts, is proposed to determine the TMD floor parameters. Additionally, the multimode approach is applied to determine the optimal locations of TMD floors if not all of the floors in a building can serve as TMDs. In addition to the numerical simulations, a scaled model shaking table experiment is also conducted. Both the numerical and experimental results show that the absolute accelerations of the TMD floors are smaller than those of the main structural storeys, which indicates the TMDFS maintains the merit of FIS while greatly reducing seismic responses of main structures. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel bidirectional pendulum tuned mass damper using variable homogeneous friction to achieve amplitude-independent control

Passive tuned mass dampers (TMDs) are widely used in controlling structural vibrations. Although their principle is well established, the search for improved arrangements is still under way. This effort has recently produced an innovative paradigm of bidirectional pendulum TMD (BTMD) that, moving along a specially designed three-dimensional (3D) surface, can simultaneously control two in-plane orthogonal structural modes. In existing versions of BTMDs, energy dissipation is provided either by ordinary horizontal viscous dampers or by an original arrangement of vertical friction dampers. In this paper, a new paradigm is proposed, in which energy dissipation comes from the tangential friction arising along the pendulum surface out of an optimal spatially variable friction coefficient pattern. Within this paradigm, if the friction coefficient is taken proportional to the modulus of the pendulum surface gradient, the dissipation model results nonlinear homogeneous in the small-displacement domain, and the performance of the absorber, herein called the homogeneous tangential friction BTMD (HT-BTMD), results independent from the excitation level. The present work introduces this concept, derives the analytical model of the HT-BTMD, establishes a method for its optimal design, and numerically verifies its seismic effectiveness in comparison with viscously damped devices. The validity and feasibility of the concept are demonstrated through experimental tests on a small-scale lab prototype, which also show the efficacy of a stepwise approximation of the homogeneous friction pattern. The new device proves a competing alternative to existing BTMDs, and homogeneous tangential friction proves a promising new paradigm to provide pendular systems with amplitude-independent structural damping.     

Optimal displacement feedback control law for active tuned mass damper

Optimal displacement feedback control law is derived for a vibration control of a single‐degree‐of‐freedom structure with an active tuned mass damper (ATMD). Analytical expressions of the linear quadratic regulator (LQR) feedback gains for the ATMD are derived by solving the Ricatti equation straightforwardly. Based on these solutions, it is found that if the stiffness of the tuned mass damper (TMD) is calibrated to satisfy a certain condition, the control law is simplified to be composed of the feedback gains only for the displacement of the structure and the velocity of the auxiliary mass stroke, which is referred to as ‘optimal displacement feedback control’. The mean‐square responses of the structure as well as the auxiliary mass against Gaussian white noise excitations are evaluated by solving the Lyapunov equation analytically based on the stochastic optimal control theory. Using these analytical solutions, the optimal damping parameter for the auxiliary mass is also derived. Finally, the optimal displacement feedback control law is presented. Copyright © 2001 John Wiley & Sons, Ltd.