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Summary In this paper, an optimal energy dissipation control algorithm is applied into a semi-active suspension-type tuned mass damper (SA-STMD) to suppress excessive vibration by means of variable pendulum length. The SA-STMD mechanism consists of a mass block, a suspension rope, and a movable fulcrum that can be a short tube driven by a linear motor to vertically move along the suspension rope. As the fulcrum goes up, the pendulum length is extended, resulting in a smaller stiffness of the SA-STMD, and vice versa. Accordingly, the restoring force in the SA-STMD can be adjusted by varying the fulcrum positions. In the case where the energy dissipation ability by the original STMDs is insufficient, the movable fulcrum in the SA-STMD system can compensate the STMDs for stiffness according to the proposed optimal energy dissipation control algorithm to provide controllable restoring forces. The controllable restoring forces are designed to act as viscous dampers that can make up for the lack of energy dissipation capacity. The numerical results from the time domain and frequency domain analyses show that the proposed approach utilizing the optimal energy dissipation control algorithm to adjust the pendulum length can induce controllable restoring forces with a butterfly-shaped hysteresis loop, supplying a sufficient energy dissipation capacity to reduce responses to the unexpectedly large external vibration. Another potential benefit is cost reduction because of use of a less number of conventional viscous dampers in the STMD system. Copyright © 2016 John Wiley & Sons, Ltd.

An isolation system is not very effective when an inappropriate level of damping is used. This paper proposes a theoretical method which can be used to determine the optimal frictional coefficient of an isolation system. Only a one-dimensional isolation system and ground motion are considered. The frictional coefficient is optimized by minimizing the sum of squares of structural absolute accelerations, with the optimization results being validated graphically. Sensitivity studies were used to verify the feasibility of the optimal frictional coefficient, coupled with a practical example in Taipei under the conditions of the Hualien and El Centro earthquakes. Consequently, the feasibility and reliability of the proposed optimal design were verified.

The present study aims at proposing an innovative phase control methodology for semi-active tuned mass dampers (SA-TMDs) that intend to minimize the off-tuned problems associated with passive tuned mass dampers (P-TMDs). The phase control algorithm is first developed, the essential of which is to apply the variable friction force to slow down the mass block at specific moments when the phase lag of the SA-TMD with respect to the structure is different from 90°, resulting in the SA-TMD back to the desired phase lag, i.e., −90° phase deviation, so that the SA-TMD has the maximum power flow to reduce the structural vibration. The feasibility of the application of the phase control in SA-TMDs is verified by performing numerical analyses of a simplified Taipei 101 structure model with a SA-TMD subjected to sinusoidal loads and design level wind loads. The numerical simulation results show that the SA-TMD implemented with phase control can enable the mass block to vibrate in a manner with a phase lag close to the −90° when the structure model is under sinusoidal excitations with frequencies different from the structural fundamental mode. The SA-TMD with phase control not only exhibits better performance than the optimal P-TMD in terms of suppressing the structural vibration, but also enhances its robustness, particularly when the SA-TMD is off-tuned to the structure.

SUMMARY Tuned mass dampers with viscous damping and isolation systems with friction pendulums have been proposed and widely applied over the past several decades. By combining these two ideas, a friction pendulum tuned mass damper (FPTMD) is proposed in this study. Because the restoring and friction forces are provided by the spherical surface of the FPTMD, springs and dampers are not needed. Moreover, suspension is not necessary and the installation space is greatly reduced. The optimal design of the FPTMD with varying friction coefficients for wind-excited high-rise structures is investigated. The optimization procedures are demonstrated by the FPTMD implemented on Taipei 101 under white-noise wind force, and the optimization results are validated by three-dimensional graphs. From the results of the sensitivity study, the effectiveness of the FPTMD with two different patterns of friction coefficients is sensitive to the tuning frequency ratio but not very sensitive to the friction parameters. Moreover, an FPTMD with a friction coefficient that linearly varies with displacement is even less sensitive to the friction parameters and the amplitude of excitation. The feasibility of the FPTMD with two different patterns of friction coefficient is illustrated by Taipei 101 subjected to the design wind force with a return period of 50 years. Following design optimization and numerical verification, the effect of vibration reduction for Taipei 101 is demonstrated. Copyright © 2012 John Wiley & Sons, Ltd.

A variable-stiffness isolation system, whose isolation stiffness can be altered instantaneously in response to the seismic load, is able to provide better seismic protection for vibration-sensitive equipment or facilities than a conventional isolation system with a fixed stiffness. To determine its time-variant isolation stiffness, this system usually requires an effective on-line control law. In this study, a control strategy called the least input energy control (LIEC) is proposed for a general variable-stiffness isolation system. With the feedback of the ground velocity, at each time step the LIEC is able to determine the optimal isolation stiffness that minimizes the input seismic energy transmitted onto the isolated object. In order to evaluate its control performance, the LIEC was physically implemented on a leverage-type variable-stiffness isolation system, and tested in a seismic simulation test. The experimental response of the LIEC was then compared to the uncontrolled response, as well as the simulated responses of two semi-active control laws derived from the widely used LQR control and modal control. A comparison of the results demonstrates that, among all the control cases considered, the LIEC transmits the least seismic input energy to the isolated system, and thus has the best isolation performance. In addition, the test data also show that the LIEC requires the least control force and control energy. This indicates that the LIEC is also a very efficient control method for variable-stiffness isolation systems.

Recently, the benefit of nonlinear isolation systems under resonance or near-fault earthquake has been investigated. In this paper, an eccentric rolling isolation system (ERIS) with additional friction damping is proposed. The isolation object is eccentrically pinned on a set of circular isolators so that the restoring force is nonlinear. To investigate the advantage of the ERIS, a corresponding isolation system with linear restoring force is also considered for comparison. The friction parameters of the two systems with linear and nonlinear restoring force are designed under the far-field El Centro earthquake. The performances of the two isolation systems are inspected under excitations other than the design one. In free vibration, the response of the ERIS decays faster than the corresponding linear system. In resonance sinusoidal excitation, the responses are divergent for the linear system but convergent for the ERIS. The linear system is ineffective but the ERIS is effective due to the nonlinearity under the near-fault Chi-Chi earthquake with various peak ground accelerations.

SUMMARY Optimal design for tuned mass dampers (TMDs) with linear or nonlinear viscous damping is formulated in order for design practitioners to directly compute the optimal parameters of a TMD in a damped structure subjected to wind excitations. The optimal TMD tuning frequency ratio and damping coefficient for a viscous TMD system installed in a damped structure under 10 white noise excitations are determined by using the time-domain optimization procedure, which minimizes the structural response. By applying a sequence of curve-fitting schemes to the obtained optimal values, design formulas for optimal TMDs are then derived. These are expressed as a function of the mass ratio and damping power-law exponent of the TMD as well as the damping ratio of the structure. The feasibility of the proposed optimal design formulas is verified in terms of formulary accuracy and of comparisons with existing formulas from previous research works. In addition, one numerical example of the Taipei 101 building with a nonlinear TMD, which is redesigned according to the proposed optimal formulas, is illustrated in effort to describe the use of the formulas in the TMD design procedure and to investigate the effectiveness of the optimal TMD. The results indicate that the proposed optimal design formulas provide a convenient and effective approach for designing a viscous TMD installed in a wind-excited damped structure. Copyright © 2011 John Wiley & Sons, Ltd.

The algorithm of modified predictive control (MPC) is derived with the partial-state concept of direct output feedback (DOF) to reduce the number of sensors for real implementation. The feasibility of using modified predictive control with direct output feedback (MPCwDOF) is verified through numerical and experimental study. According to the MPCwDOF algorithm, the online control forces are simply generated from the actual output measurements that are multiplied by a prescribed constant output feedback gain matrix. An off-line numerical method is introduced to find the feedback gain systematically and efficiently. Numerical examples of two control systems with respect to single-controller and multiple-controller systems are illustrated for validating the feasibility of using the MPCwDOF algorithm and the application of the decentralized control strategy to the MPCwDOF algorithm. An experiment of a large-scale 5-story structural model with an MPCwDOF-controlled active mass damper on the roof is also performed. Results indicate that the controlled structures achieve good performance under environmental excitations. Simple online calculations and a small number of sensors make the proposed control algorithm more favorable to real implementation. Copyright © 2010 John Wiley & Sons, Ltd.

The linear isolator has fixed vibration frequency. When structures with these linear isolators are located near a fault, it may cause resonance and large displacement response. Hence, nonlinear isolation may avoid this situation. In this study, an eccentric nonlinear rolling isolator with a parameter, which is the eccentricity of the pin connection of the mass block (facility) to the circular isolator, is investigated. If the eccentricity is not equal to zero, the dynamic response is nonlinear rolling behavior. The equation of motion of the isolation system is derived. The frequency of the isolator increases with the eccentricity under the same initial angle. The influence of the eccentricity to the effect of isolation is scrutinized. Finally, the feasibility of the proposed isolation device is verified numerically. If the proposed isolator is designed properly, it is effective for far-field earthquake (El Centro earthquake). Even though the linearized frequency of the proposed isolator falls into the dominant frequency range of near-fault earthquake (Chi-Chi earthquake), resonance can be avoided due to nonlinearity. Copyright © 2008 John Wiley & Sons, Ltd.

Many experiments have been studied for bolted beam–column connections for past years to prevent the demerit of welding at the site. Wing plates welded at beam ends of bolted beam–column connections in CFT structures have been studied experimentally by authors to ensure that plastic hinges are away from the welding. This paper studies the effect of wing plates numerically by simulating H-beams in bolted beam–column connections as cantilever beams using ABAQUS. Through convergence and cyclic loading analyses, simulation agrees well with the experimental results. The brittle failure due to developed crack can be predicted once equivalent plastic strain exceeds the maximum plastic strain. From numerical results, the effect of wing plates is verified. Furthermore, suitable formulas for the width of wing plates are derived to prevent the brittle failure of beams. Consequently, it is suggested that the length and the width of wing plates in application should be designed by using the suggested design process proposed in this paper.

An optimal discrete-time direct output-feedback control algorithm is developed with the consideration of sampling period and appropriate time delay in its control force action. Optimal-delayed output-feedback gains are derived through a variation process and will be complementarily arranged with respect to the applied delay time by either altering their magnitude or phases to assure the efficacy and stability of the delayed direct digital control system. Parametric studies of single-degree-of-freedom (SDOF) systems with different feedback types demonstrate the relationships of the delayed gains and the modal properties corresponding to the sampling period used and the intentionally delay time added. The maximum allowable delay time defined at the onset of instability of controlled system can be the optimal delay time that reaches the optimal control performance if the delay time is considered in the delayed feedback gains. The inclusion of sampling period and delay time in the optimization process for discrete-time control illustrates the beneficial effect under the same delay time. Numerical simulation results of proposed direct digital control principles on a three-degree-of-freedom (3DOF) shaking table structure model show that the efficacy of the collocated control cases with optimal delay time to reduce the dynamic responses subjected to earthquake excitations is assured. Copyright © 2007 John Wiley & Sons, Ltd.

This research investigates the seismic performance of four steel beams to concrete filled steel tube (CFT) column connections with floor slabs, including two interior and two exterior joints. The objective of this research is to evaluate firstly the composite effect of the steel beam and floor slab commonly used in Taiwan in practice. Secondly, the seismic behavior of new connection details such as the taper flange or larger shear tab in the beam-end is investigated to prevent complete joint penetration welds (CJP) of the girder flanges from the unexpected brittle failure found in the latter after the Northridge earthquake. In addition to the experimental investigation, the development and validation of analytical models for the assessment of the force–deformation behavior of the joint components are also conducted. The slab effect on the shear transfer in the panel zone is investigated as well.

Concrete-filled steel tubes (CFT) have the advantage of high strength, high stiffness and being constructed quickly. However, because the behavior of the beam-to-column connection for CFT is complicated and its design has not been sufficiently verified, their use has been limited. In this paper, a new design of bolted beam-to-column connections for CFT is proposed. A mechanical model is established in order to derive theoretical equations for calculating the stiffness, the yielding shear strength and the ultimate shear strength of the panel zone. Also, a series of cyclic loading experiments have been conducted. The experimental results and theoretical results are very close, which demonstrates that the bolted connections have superior seismic resistance in stiffness, strength, ductility and energy dissipation mechanisms. From the laboratory studies, even though the story angular drift reaches 7% and the plastic angular displacement reaches 5%, the structure still stands. Those results indicate that the seismic resistance exceeds those specified in Taiwan and the US.

A nonlinear force-deformation model to simulate shear transfer behavior in the panel zone of CFT (Concrete-Filled Steel Tube) beam-column connections is proposed. In this model, influence of axial load on the shear transfer behavior is accounted for. To validate the proposed theory, five circular CFT beam-column connections were constructed and tested. Test results showed that all specimens failed by the welding fracture while entering nonlinear stage. It is found that the higher the axial load was applied, the better the ductility of connections was obtained. Comparison of analytical and experimental results shows that the proposed prediction for panel shear falls in a reasonable range for higher axial load tests, but tends to be conservative for lower axial load tests.