• Earthquakes and Structures
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• v.5 no.1
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• pp.83-109
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• 2013

A simple damper optimization method is proposed to find optimal damper allocation for shear buildings under both target added damping ratio and interstorey drift ratio (IDR). The damping coefficients of added dampers are considered as design variables. The cost, which is defined as the sum of damping coefficient of added dampers, is minimized under a target added damping ratio and the upper and the lower constraint of the design variables. In the first stage of proposed algorithm, Simulated Annealing, Nelder Mead and Differential Evolution numerical algorithms are used to solve the proposed optimization problem. The candidate optimal design obtained in the first stage is tested in terms of the IDRs using linear time history analyses for a design earthquake in the second stage. If all IDRs are below the allowable level, iteration of the algorithm is stopped; otherwise, the iteration continues increasing the target damping ratio. By this way, a structural response IDR is also taken into consideration using a snap-back test. In this study, the effects of the selection of upper limit for added dampers, the storey mass distribution and the storey stiffness distribution are all investigated in terms of damper distributions, cost function, added damping ratio and IDRs for 6-storey shear building models. The results of the proposed method are compared with two existing methods in the literature. Optimal designs are also compared with uniform designs according to both IDRs and added damping ratios. The numerical results show that the proposed damper optimization method is easy to apply and is efficient to find optimal damper distribution for a target damping ratio and allowable IDR value.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.3
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• pp.349-359
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• 2016

In order to analytically evaluate buffeting responses, the analysis of wind characteristics such as turbulence intensity, turbulence length, gust, roughness coefficient, etc must be a priority. Static aerodynamic force coefficients, flutter coefficients, structural damping ratios, aerodynamic damping ratios and natural frequencies affect the analytical responses. The bridge interested in this paper has being been used for 32 years. As the time passes, current terrain conditions around the bridge are different markedly from the conditions it was built 32 years ago. Also, wind environments were considerably varied by the climate change. For this reason, it is necessary to evaluate the turbulence intensity, length, spectrum and roughness coefficient of the bridge site from full-scale measurements using the structural health monitoring system. The evaluation results indicate that wind characteristics of bridge site is analogous to that of open terrain although the bridge is located on the coastal area. To calculate buffeting responses, the analysis variables such as damping ratios, static aerodynamic force coefficients and natural frequency were evaluated from measured data. The analysis was performed with regard to 4 cases. The evaluated variables from measured data are applied to the first and second analysis cases. And the other analysis cases were performed based on Design Guidelines for Steel Cable Supported Bridges. The calculated responses of each analysis cases are compared with the buffeting response measured at less than 25m/s wind speed. It is verified that the responses by the numerical analysis applying the estimated variables based on full-scale measurements are well agreed with the measured actual buffeting responses under wind speed 25m/s. Also, the extreme wind speed corresponding to a recurrence interval 200 years is derived from Gumbel distribution. The derived wind speed for return period of 200 years is 45m/s. Therefore the buffeting responses at wind speed 45m/s is determined by the analysis applying the estimated variables.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.1-10
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• 2022

In this study, to evaluate the possibility of using a steel spring as a displacement-dependent damping device, tensile loading and cyclic loading tests were performed. The main experimental variables were the type of steel (SAE9254 and SS275), the spring constant (700 N/mm, 1,000 N/mm, and 1,400 N/mm), and the presence or absence of heat treatment for SAE9254. As a result of the tensile test, the ratios of the measured spring constant to the design spring constant of the steel springs made with SAE9254 ranged from 1.08 to 1.13, while the ratios of the design spring constant and the measured spring constant of the steel springs made with SS275 ranged from 0.86 to 0.97. After yielding, the slope values of the load-displacement curve of the SAE9254 with/without heat treatment were about 240~251 N/mm and 92 N/mm, respectively, but the slope values of the load-displacement response of SS275 were almost zero. According to the uniaxial cyclic loading test results, all specimens were satisfied with three conditions for a displacement-dependent damping device in KDS 41 17 00 (2019): the maximum force and minimum force at zero displacement, the maximum force and minimum force at the maximum displacement, and the energy dissipation capacity. In addition, the equivalent damping ratios of steel springs made with SAE9254(non-heat treatment) and SS275 were approximately 2.8 times and 1.9 times greater, respectively, than that of steel springs made with SAE9254.

• Wind and Structures
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• v.25 no.1
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• pp.1-24
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• 2017

This paper presents a 1:25 multi-freedom aero-elastic model for a high lighting pole at the Zhoushan stadium. To validate the similarity characteristics of the model, a free vibration test was performed before the formal test. Beat phenomenon was found and eliminated by synthesis of vibration in the X and Y directions, and the damping ratio of the model was identified by the free decay method. The dynamic characteristics of the model were examined and compared with the real structure; the similarity results were favorable. From the test results, the major along-wind dynamic response was the first vibration component. The along-wind wind vibration coefficient was calculated by the China code and Eurocode. When the peak factor equaled 3.5, the coefficient calculated by the China code was close to the experimental result while Eurocode had a slight overestimation of the coefficient. The wind vibration coefficient during typhoon flow was analyzed, and a magnification factor was suggested in typhoon-prone areas. By analyzing the power spectrum of the dynamic cross-wind base shear force, it was found that a second-order vortex-excited resonance existed. The cross-wind response in the test was smaller than Eurocode estimation. The aerodynamic damping ratio was calculated by random decrement technique and the results showed that aerodynamic damping ratios were mostly positive at the design wind speed, which means that the wind-induced galloping phenomenon is predicted not to occur at design wind speeds.

• Geotechnical Engineering
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• v.11 no.1
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• pp.101-112
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• 1995

Deformational characteristics of soils, often expressed in terms of shear modulus and material damping ratios, are important parameters in the design of soil-structure systems subjected to cyclic and dynamic loadings. In this paper, deformational characteristics of dry sand at small to intermediate strains were investigated using resonant column/torsional shear(RC 175) apparatus. Both resonant column(dynamic) and torsional shear (cyclic) tests were performed in a sequential series on the same specimen. With the modification of motion monitoring system, the elastic zone, where the stress strain relationship is independent of loading cycles and strain amplitude, was veri tied and hysteretic damping was found even in this zone. At strains above cyclic threshold, shear modulus increases and damping ratio decreases with increasing number of loading cycles. Moduli and damping ratios of dry sand are independent of loading frequency and values obtained from pseudostatic torsional shear tests are Identical with the values from the dynamic resonant column test, provided the effect of number of loading cycles is considered in the conlparison. Therefore, deformational characteristics determined by RC/TS tests may be applied in both dynamic and static analyses of soil-structure systems.

• The Korean Journal of Pesticide Science
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• v.9 no.1
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• pp.35-40
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• 2005

Damping-off of summer spinach caused by Rhizoctonia solani AG-4 has become a very important disease. For the control of summer spinach damping-off, antifungal activity of thirteen fungicides (pencycuron, trifloxystrobin, pyraclostrobin, azoxystrobin, kresoxim-methyl, validamycin, fluazinam, Benlate-T, flutolanil, cyazofamid, hexaconazole, tebuconazole, prochloraz) were evaluated in vitro and in vivo. Pencycuron, pyraclostrobin, validamycin, fluazinam, Benlate-T, hexaconazole, tebuconazole, and flutolanil significantly suppressed the mycelial growth of the pathogenic fungus. However, trifloxystrobin, azoxystrobia kresoxim-methyl, cyazofamid, and prochloraz did not represent good inhibition on the growth of R. solani. When applied by soil drenching (2,000 mg/L), pencycuron, pyraclostrobin, validamycin, fluazinam, Benlate-T, and flutolanil provided spinach survival ratios of 97.8%, 84.4%, 93.3%, 95.6%, 91.1%, and 86.7%, respectively. Also when treated in seed at 2,000 ing/L, pencycuron and pyraclostrobin displayed survival ratios of more than 85.1%.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.308-318
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• 2000

This paper introduces the acceptance criteria for reinforced concrete moment frames based on structural testing of ACI in preparing and proposes criteria for acceptable limiting drift and energy dissipation ratios of reinforced concrete shear walls for structural testing. Limiting drift and energy dissipation ratios were examined for tests on shear walls having ductile type failures. Test data were analyzed and compared to results for a suggested acceptance criteria that involves a limiting drift that is a function of aspect ratio a limiting energy dissipation ratio that is a function of displacement ductility and damping.

• Geomechanics and Engineering
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• v.29 no.2
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• pp.155-170
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• 2022

An accurate analysis of structures supported on soft soils and subjected to seismic loading requires the consideration of the soil-foundation-structure interaction. An important aspect of this interaction lies with the energy dissipation due to soil material damping. Unlike advanced constitutive models that can induce energy loss, the use of simple elastoplastic constitutive models requires additional damping. The frequency dependent Rayleigh damping is a formulation that is frequently used in dynamic analysis. The main concern of this formulation is the correct selection of the target damping ratio and the frequency range where the response is frequency independent. The objective of this study is to investigate the effects of the Rayleigh damping parameters in soil-pile-structure and soil-inclusion-platform-structure systems in the presence of soft soil under seismic loading. Three-dimensional analyses of both systems are carried out using the finite difference software Flac3D. Different values of target damping ratios and minimum frequencies are utilized. Several earthquakes are used to study the influence of different excitation frequencies in the systems. The soil response in terms of accelerations, displacements and strains is obtained. For the rigid elements, the results are presented in terms of bending moments and normal forces. The results show that when the frequency of the input motion is close to the minimum (central) frequency in the Rayleigh damping formulation, the overdamping amount is reduced, and the surface spectral acceleration of the analyzed pile and inclusion systems increases. Thus, the bending moments and normal forces throughout the piles and inclusions also increase.

• Smart Structures and Systems
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• v.20 no.4
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• pp.461-472
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• 2017

Explicit design formulae of liquid column vibration absorber (LCVA) for suppressing harmonic vibration of structures with small inherent structural damping are developed in this study. The developed design formulae are also applicable to the design of a tuned mass damper (TMD) and a tuned liquid column damper (TLCD) for damped structures under harmonic force excitation. The optimum parameters of LCVA for suppressing harmonic vibration of undamped structures are first derived. Numerical searching of the optimum parameters of tuned vibration absorber system for suppressing harmonic vibration of damped structure is conducted. Explicit formulae for these optimum parameters are then obtained by a series of curve fitting techniques. The analytical result shows that the control performance of TLCD for reducing harmonic vibration of undamped structure is always better than that of non-uniform LCVA for same mass and length ratios. As for the effects of structural damping on the optimum parameters, it is found that the optimum tuning ratio decreases and the optimum damping ratio increases as the structural damping is increased. Furthermore, the optimum head loss coefficient is inversely proportional to the amplitude of excitation force and increases as the structural damping is increased. Numerical verification of the developed explicit design expressions is also conducted and the developed expressions are demonstrated to be reasonably accurate for design purposes.

• Wind and Structures
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• v.7 no.2
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• pp.89-106
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• 2004

The response of tall buildings to gust buffeting is usually evaluated assuming that the structural damping is of a viscous nature. In addition, when dampers are incorporated in the design to mitigate the response, their effect is allowed for increasing the building modal damping ratios by a quantity corresponding to the additional energy dissipation arising from the presence of the devices. Even though straightforward, this procedure has some degree of inaccuracy due to the existence of a memory effect, associated with the damping mechanism, which is neglected by a viscous model. In this paper a more realistic viscoelastic model is used to evaluate the response to gust buffeting of tall buildings provided with energy dissipation devices. Both cases of viscous and hysteretic inherent damping are considered, while for the dampers a generic viscoelastic behaviour is assumed. The Laguerre Polynomial Approximation is used to write the equations of motion and find the frequency response functions. The procedure is applied to a 25-story building to quantify the memory effects, and the inaccuracy arising when the latter is neglected.