• Earthquakes and Structures
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• 제9권4호
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• pp.767-788
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• 2015

A steel shear wall with double-tapered links and in-plane reference was developed for assisting the assessment of the structural condition of a building after an earthquake while maintaining the original role of the wall as a passive damper device. The double-tapered link subjected to in-plane shear deformation is designed to deform torsionally after the onset of local buckling and works as an indicator of the maximum shear deformation sustained by the shear wall during an earthquake. This paper first examines the effectiveness of double-tapered links in the assessment of the structural condition under various types of loading. A design procedure using a baseline incremental two-cycle loading protocol is verified numerically and experimentally. Meanwhile, in-plane reference links are introduced to double-tapered links and greatly enhance objectivity in the inspection of notable torsional deformation with the naked eye. Finally, a double-layer system, which consists of a layer with double-tapered links and a layer with rectangular links made of low-yield-point steel, is tested to demonstrate the feasibility of realizing both structural condition assessment and enhanced energy dissipation.

• Smart Structures and Systems
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• 제15권4호
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• pp.963-995
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• 2015

The effectiveness of the various control algorithms for semi-active structural control systems proposed in the literature is highly questionable when dealing with earthquake actions, which never reach a steady state. From this perspective, the paper summarizes the results of an experimental activity aimed to compare the effectiveness of four different semi-active control algorithms on a structural mock up representative of a class of structural systems particularly prone to seismic actions. The controlled structure is a near full scale 2-story steel frame, equipped with two semi-active bracing systems including two magnetorheological dampers designed and manufactured in Europe. A set of earthquake records has been applied at the base of the structure, by utilizing a shaking table facility. Experimental results are compared in terms of displacements, absolute accelerations and energy dissipation capability. A further analysis on the percentage incidence of undesired and/or unpredictable operations corresponding to each algorithm gives an insight on some factors affecting the reliability and, in turn, the real effectiveness of semi-active structural control systems.

• Smart Structures and Systems
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• 제4권5호
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• pp.685-696
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• 2008

This paper deals with the numerical model of a bracing-friction damper system and its deployment using the optimal slip load distribution for the seismic retrofitting of a damaged building. The Slotted Bolted Connection (SBC) type friction damper system was tested to investigate its energy dissipation characteristic. Test results coincided with the numerical ones using the conventional model of a bracing-friction damper system. The placement of this device was numerically explored to apply it to the assumed damaged-building and to evaluate its efficiency. It was found by distributing the slip load that minimizes the given performance indicies based on structural response. Numerical results for the damaged building retrofitted with this slip load distribution showed that the seismic design of the bracing-friction damper system under consideration is effective for the structural response reduction.

• Earthquakes and Structures
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• 제12권5호
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• pp.479-487
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• 2017

Frictional dampers are used in structural engineering as means of passive control. Meanwhile, frictional damper shave a disadvantage compared to viscous rivals since the slippage force must be exceeded to activate the device, and cannot be ideal full range of possible events. The concept of semi-active control is utilized to overcome this shortcoming. In this paper, a new semi-active frictional damper called Smart Adjustable Frictional (SAF) damper is introduced. SAF damper consists of hydraulic, electronic units and sensors which are all linked with an active control discipline. SAF acts as a smart damper which can adapt its slippage threshold during a dynamic excitation by measuring and controlling the structural response. The novelty of this damper is, while it controls the response of the structure in real time with acceptable time delay. The paper also reports on the results of a series of experiments which have been performed on SAF dampers to obtain their prescribed hysteretic behavior for various control algorithms. The results show that SAF can produce the desired slippage load of various algorithms in real time. Numerical models incorporating control simulations are also made to obtain the hysteretic response of the system which agrees closely with test results.

• JSTS:Journal of Semiconductor Technology and Science
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• 제4권1호
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• pp.52-62
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• 2004

In this paper we look at the effect of Fringe-Enhanced-Barrier-lowering (FEBL) for high-K dielectric MOSFETs and the dependence of FEBL on various technological parameters (spacer dielectrics, overlap length, dielectric stack, S/D junction depth and dielectric thickness). We show that FEBL needs to be contained in order to maintain the performance advantage with scaled high-K dielectric MOSFETs. The degradation in high-K dielectric MOSFETs is also identified as due to the additional coupling between the drain-to-source that occurs through the gate insulator, when the gate dielectric constant is significantly higher than the silicon dielectric constant. The technology parameters required to minimize the coupling through the high-K dielectric are identified. It is also shown that gate dielectric stack with a low-K material as bottom layer (very thin $SiO_2$ or oxy-nitride) will be helpful in minimizing FEBL. The circuit performance issues with high-K MOS transistors are also analyzed in this paper. An optimum range of values for the dielectric constant has been identified from the delay and the energy dissipation point of view. The dependence of the optimum K for different technology generations has been discussed. Circuit models for the parasitic capacitances in high-K transistors, by incorporating the fringing effects, have been presented.

• Structural Engineering and Mechanics
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• 제66권2호
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• pp.161-172
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• 2018

The passive control of structures using a pendulum tuned mass damper has been extensively studied in the technical literature. As the frequency of the pendulum depends only on its length and the acceleration of gravity, to tune the frequency of the pendulum with that of the structure, the pendulum length is the only design variable. However, in many cases, the required length and the space necessary for its installation are not compatible with the design. In these cases, one can replace the classical pendulum by a virtual pendulum which consists of a mass moving over a curved surface, allowing thus for a greater flexibility in the absorber design, since the length of the pendulum becomes irrelevant and the shape of the curved surface can be optimized. A mathematical model for a building with a pendular tuned mass damper and a detailed parametric analysis is conducted to study the influence of this device on the nonlinear oscillations and stability of the main system under harmonic and seismic base excitation. In addition to the circular profiles, different curved surfaces with softening and hardening characteristics are analyzed. Also, the influence of impact on energy dissipation is considered. A detailed parametric analysis is presented showing that the proposed damper can not only reduce sharply the displacements, and consequently the internal forces in the main structure, but also the accelerations, increasing user comfort. A review of the relevant aspects is also presented.

• Smart Structures and Systems
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• 제4권6호
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• pp.809-828
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• 2008

Real-time hybrid testing is an attractive method to evaluate the response of structures under earthquake loads. The method is a variation of the pseudodynamic testing technique in which the experiment is executed in real time, thus allowing investigation of structural systems with time-dependent components. Real-time hybrid testing is challenging because it requires performance of all calculations, application of displacements, and acquisition of measured forces, within a very small increment of time. Furthermore, unless appropriate compensation for time delays and actuator time lag is implemented, stability problems are likely to occur during the experiment. This paper presents an approach for real-time hybrid testing in which time delay/lag compensation is implemented using model-based response prediction. The efficacy of the proposed strategy is verified by conducting substructure real-time hybrid testing of a steel frame under earthquake loads. For the initial set of experiments, a specimen with linear-elastic behavior is used. Experimental results agree well with the analytical solution and show that the proposed approach and testing system are capable of achieving a time-scale expansion factor of one (i.e., real time). Additionally, the proposed method allows accurate testing of structures with larger frequencies than when using conventional time delay compensation methods, thus extending the capabilities of the real-time hybrid testing technique. The method is then used to test a structure with a rate-dependent energy dissipation device, a magnetorheological damper. Results show good agreement with the predicted responses, demonstrating the effectiveness of the method to test rate-dependent components.

• 한국지진공학회논문집
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• 제26권4호
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• pp.165-172
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• 2022

This study is conducted to verify the seismic reinforcement effects of internally inserted buckling-restrained braces supported laterally by buckling-restrained rings for the seismic reinforcement of existing reinforced concrete buildings with non-seismic details. First, to evaluate the performance of KDS, the hysteretic characteristics of buckling-restrained braces are verified, and it is discovered that they satisfy the conformance criteria of the displacement-dependent damping device. Three full-scale, two-story reinforced concrete framework specimens are prepared to verify the seismic reinforcement effects, and the proposed buckling-restrained braces are bolstered with single diagonal and V-shaped braces to be compared with non-reinforced specimens. By performing a comparison with non-reinforced specimens that present intensive shear cracks at the bottom of first-floor columns, it is revealed that the maximum load and energy dissipation of specimens reinforced with the proposed buckling restrained braces, in which the structural damage extends evenly throughout the system, are approximately 4 and 6.2 times higher, respectively, which proves the effectiveness of the proposed seismic reinforcement method.

• Steel and Composite Structures
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• 제44권2호
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• pp.283-294
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• 2022

In this study, a new seismic retrofit scheme of building structures is developed by combining a steel moment frame and steel slit plates to be installed inside of an existing reinforced concrete frame. This device has the energy dissipation capability of slit dampers with slight loss of stiffness compared to the conventional steel frame reinforcement method. In order to investigate the seismic performance of the retrofit system, it was installed inside of a reinforced concrete frame and tested under cyclic loading. Finite element analysis was carried out for validation of the test results, and it was observed that the analysis and the test results match well. An analytical model was developed to apply the retrofit system to a commercial software to be used for seismic retrofit design of an example structure. The effectiveness of the retrofit scheme was investigated through nonlinear time-history response analysis (NLTHA). The cyclic loading test showed that the steel frame with slit dampers provides significant increase in strength and ductility to the bare structure. According to the analysis results of a case study building, the proposed system turned out to be effective in decreasing the seismic response of the model structure below the given target limit state.

• Structural Engineering and Mechanics
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• 제81권6호
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• pp.677-689
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• 2022

Generally, the goal of seismic retrofit design of an existing structure using energy dissipation devices is to determine the optimum design parameters of a retrofit device to satisfy a specified limit state with minimum cost. However, the presence of multiple parameters to be optimized and the computational complexity of performing non-linear analysis make it difficult to find the optimal design parameters in the realistic 3D structure. In this study, genetic algorithm-based optimal seismic retrofit methods for determining the required number, yield strength, and location of steel slit dampers are proposed to retrofit an asymmetric soft first-story structure. These methods use a multi-objective and single-objective evolutionary algorithms, each of which varies in computational complexity and incorporates nonlinear time-history analysis to determine seismic performance. Pareto-optimal solutions of the multi-objective optimization are found using a non-dominated sorting genetic algorithm (NSGA-II). It is demonstrated that the developed multi-objective optimization methods can determine the optimum number, yield strength, and location of dampers that satisfy the given limit state of a three-dimensional asymmetric soft first-story structure. It is also shown that the single-objective distribution method based on minimizing plan-wise stiffness eccentricity turns out to produce similar number of dampers in optimum locations without time consuming nonlinear dynamic analysis.