• Earthquakes and Structures
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• v.26 no.6
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• pp.449-461
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• 2024

The vertical reinforcement connection between the precast reinforced concrete shear wall and the cast-in-place reinforced concrete member is vital to the performance of shear walls under seismic loading. This paper investigated the structural behavior of three precast reinforced concrete shear walls, with different levels of connection (i.e., full connection, partial connection, and no connection), subjected to quasi-static lateral loading. The specimens were subjected to a constant vertical load, resulting in an axial load ratio of 0.4. The crack pattern, failure modes, load-displacement relationships, ductility, and energy dissipation characteristics are presented and discussed. The resultant seismic performances of the three tested specimens were compared in terms of skeleton curve, load-bearing capacity, stiffness, ductility, energy dissipation capacity, and viscous damping. The seismic performance of the partially connected shear wall was found to be comparable to that of the fully connected shear wall, exhibiting 1.7% and 3.5% higher yield and peak load capacities, 9.2% higher deformability, and similar variation in stiffness, energy dissipation capacity and viscous damping at increasing load levels. In comparison, the seismic performance of the non-connected shear wall was inferior, exhibiting 12.8% and 16.4% lower loads at the yield and peak load stages, 3.6% lower deformability, and significantly lower energy dissipation capacity at lower displacement and lower viscous damping.

• The KSFM Journal of Fluid Machinery
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• v.5 no.3 s.16
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• pp.7-14
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• 2002

A new foil bearing, ViscoElastic Foil Bearing(VEFB) is suggested with the need for a high damping foil bearing. Sufficient damping capacity is a key technical hurdle to super-bending-critical operation as well as widespread use of foil bearings into turbomachinery. The super-bending-critical operation of the conventional bump foil bearing and the VEFB is examined, as well as the structural dynamic characteristics. The structural dynamic test results show that the equivalent viscous damping of the VEFB is much larger than that of the bump bearing, and that the structural dynamic stiffness of the VEFB is comparable or larger than that of the bump bearing. The results of super-bending-critical operation of the VEFB indicate that the enhanced structural damping of the viscoelastic foil dramatically reduces the vibration near the bending critical speed. With the help of increased damping resulting from the viscoelasticity, the suppression of the asynchronous orbit is possible beyond the bending critical speed.

• Earthquakes and Structures
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• v.16 no.4
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• pp.437-453
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• 2019

This study investigates a new optimal placement method for viscous dampers between structures in order to prevent pounding of adjacent structures with different dynamic characteristics under earthquake effects. A relative displacement spectrum is developed in two single degree of freedom system to reveal the critical period ratios for the most risky scenario of collision using El Centro earthquake record (NS). Three different types of viscous damper design, which are classical, stair and X-diagonal model, are considered to prevent pounding on two adjacent building models. The objective function is minimized under the upper and lower limits of the damping coefficient of the damper and a target modal damping ratio. A new algorithm including time history analyses and numerical optimization methods is proposed to find the optimal dampers placement. The proposed design method is tested on two 12-storey adjacent building models. The effects of the type of damper placement on structural models, the critical period ratios of adjacent structures, the permissible relative displacement limit, the mode behavior and the upper limit of damper are investigated in detail. The results of the analyzes show that the proposed method can be used as an effective means of finding the optimum amount and location of the dampers and eliminating the risk of pounding.

• Structural Engineering and Mechanics
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• v.76 no.5
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• pp.619-629
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• 2020

In current study, surface/interface effects for pull-in voltage and viscous fluid velocity effects on dimensionless natural frequency (DNF) of fluid-conveying piezoelectric nanosensor (FCPENS) subjected to direct electrostatic voltage DC with nonlinear excitation, harmonic force and also viscoelastic foundation (visco-pasternak medium and structural damping) are investigated using Gurtin-Murdoch surface/interface (GMSIT) theory. For this analysis, Hamilton's principles, the assumed mode method combined with Lagrange-Euler's are used for the governing equations and boundary conditions. The effects of surface/interface parameters of FCPENS such as Lame's constants (λI,S, μI,S), residual stress (τ0I,S), piezoelectric constants (e31psk,e32psk) and mass density (ρI,S) are considered for analysis of dimensionless natural frequency respect to viscous fluid velocity u̅f and pull-in voltage V̅DC.

• Smart Structures and Systems
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• v.24 no.1
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• pp.15-26
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• 2019

Over the past decades, a great variety of dampers have been developed and applied to mechanical, aerospace, and civil structures to control structural vibrations. This study is focused on two emerging damper types, namely, eddy current dampers (ECDs) and electromagnetic damper (EMDs), both of which are regarded as promising alternatives to commonly-applied viscous fluid dampers (VFDs) because of their similar mechanical behavior. This study aims to enhance the damping densities of ECDs and EMDs, which are typically lower than those of VFDs, by proposing new designs with multiple improvement measures. The design configurations, mechanisms, and experimental results of the new ECDs and EMDs are presented in this paper. The further comparison based on the experimental results revealed that the damping densities of the proposed ECD and EMD designs are comparable to those of market-available VFDs. Considering ECDs and EMDs are solid-state dampers without fluid leakage problems, the results obtained in this study demonstrate a great prospect of replacing conventional VFDs with the improved ECDs and EMDs in future large-scale applications.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.135-142
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• 2020

In the case of a concrete structure, vibration problems occur under various conditions because of its low damping performance. To solve this problem, a study on the high damping performance of the polymer concrete with hybrid damper has recently been increased. Since water is not used in polymer concrete, the curing time is short. Also, the physical properties and dynamic properties of polymer concrete are quite excellent. So polymer concrete is widely expected to be used for structural materials. The hybrid damper is the structural system that consists of steel balls and viscous fluid inside the pipe which is embedded in polymer concrete. It can reduce the structural vibrations through the energy dissipation mechanism of viscous fluid and steel balls. In this study, the physical and dynamic properties of polymer concrete with hybrid damper were compared with ordinary concrete. As a result, the elasticity coefficient and the strength of the polymer concrete with hybrid damper were so much excellent. In particular, the tensile strength was 6.5 to 10 times higher than ordinary concrete. The frequency response function and damping ratio were also compared. As a result, the dynamic Stiffness of the polymer concrete was 25% greater than that of ordinary concrete. The damping ratio of the polymer concrete was approximately 3 times higher than that of ordinary concrete. Although the dynamic stiffness of the hybrid damper showed similar tendency, the damping ratio was 3.5 times higher than that of ordinary concrete. Therefore, the polymer concrete with hybrid damper was superior to ordinary concrete.

• International Journal of High-Rise Buildings
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• v.5 no.1
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• pp.63-70
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• 2016

The use of outriggers with dampers (the damped outrigger concept) has been shown to be a cost effective method of adding structural damping to a high rise building, and has been described in previous work by the author. This paper further develops the methods used to design such systems and highlights lessons learned in their application. This includes calculation methods, a review of subsequent research from others, and discussions regarding code-compliance.

• Structural Engineering and Mechanics
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• v.33 no.6
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• pp.709-724
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• 2009

In this paper a free-free uniform beam with damping effects subjected to follower and transversal forces at its end is considered as a model for a space structure. The effect of damping on the stability of the system is first investigated and the effects of the follower and transversal forces on the vibration of the beam are shown next. Proportional damping model is used in this work, hence, the effects of both internal (material) and external (viscous fluid) damping on the system are noted. In order to derive the frequency of the system, the Ritz method has been used. The mode shapes of the system must therefore be extracted. The Newmark method is utilized in the study of the system vibration. The results show that an increase in the follower and transversal forces leads to an increase of the vibrational motion of the beam which is not desirable.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.582-587
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• 2007

In this study, based on the results from the sinusoidal base excitation analyses of a single degree of freedom system with a tuned mass damper (TMD), it is verified that optimal friction force can improve the performance of a TMD like a linear viscous damper which has been usually used in general TMD. The magnitude of the optimal friction increases with increasing mass ratio of the TMD and decreases with increasing structural damping. Particularly, it is observed that the optimized friction force gives better control performance than the optimized viscous damping of the TMD. However, because the performance of the TMD considerably deteriorates when the friction force increases over the optimal value, it is required to keep the friction force from exceeding the optimal value.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.6 s.123
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• pp.553-559
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• 2007

In this study, based on the results from the sinusoidal base excitation analyses of a single degree of freedom system with a tuned mass damper (TMD), it is verified that optimal friction force can improve the performance of a TMD like a linear viscous damper which has been usually used in general TMD. The magnitude of the optimal friction increases with increasing mass ratio of the TMD and decreases with increasing structural damping. Particularly, it is observed that the optimized friction force gives better control performance than the optimized viscous damping of the TMD. However, because the performance of the TMD considerably deteriorates when the friction force increases over the optimal value, it is required to keep the friction force from exceeding the optimal value.