• 제목, 요약, 키워드: Number of Excitations

검색결과 78건 처리시간 0.038초

A new damage index for reinforced concrete structures

  • Cao, Vui V.;Ronagh, Hamid R.;Ashraf, Mahmud;Baji, Hassan
    • Earthquakes and Structures
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    • v.6 no.6
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    • pp.581-609
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    • 2014
  • Reinforced concrete (RC) structures are likely to experience damage when subjected to earthquakes. Damage index (DI) has been recognised as an advanced tool of quantitatively expressing the extent of damage in such structures. Last 30 years have seen many concepts for DI proposed in order to calibrate the observed levels of damage. The current research briefly reviews all available concepts and investigates their relative merits and limitations with a view to proposing a new concept based on residual deformation. Currently available DIs are classified into two broad categories - non-cumulative DI and cumulative DI. Non-cumulative DIs do not include the effects of cyclic loading, whilst the cumulative concepts produce more rational indication of the level of damage in case of earthquake excitations. Ideally, a DI should vary within a scale of 0 to 1 with 0 representing the state of elastic response, and 1 referring to the state of total collapse. Some of the available DIs do not satisfy these criteria. A new DI based on energy is proposed herein and its performances, both for static and for cyclic loadings, are compared with those obtained using the most widely accepted DI in literature. The proposed DI demonstrates a rational way to predict the extent of damage for a number of case studies. More research is encouraged to address some identified issues.

Flutter and Buffeting Control of Long-span Suspension Bridge by Passive Flaps: Experiment and Numerical Simulation

  • Phan, Duc-Huynh;Nguyen, Ngoc-Trung
    • International Journal of Aeronautical and Space Sciences
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    • v.14 no.1
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    • pp.46-57
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    • 2013
  • Flutter stability and buffeting response have been the topics of most concern in the design state of long-span suspension bridges. Among approaches towards the aerodynamic stability, the aerodynamic-based control method which uses control surfaces to generate forces counteracting the unstable excitations has shown to be promising. This study focused on the mechanically controlled system using flaps; two flaps were attached on both sides of a bridge deck and were driven by the motions of the bridge deck. When the flaps moved, the overall cross section of the bridge deck containing these flaps was continuously changing. As a consequence, the aerodynamic forces also changed. The efficiency of the control was studied through the numerical simulation and experimental investigations. The values of quasi-steady forces, together with the experimental aerodynamic force coefficients, were proposed in the simulation. The results showed that the passive flap control can, with appropriate motion of the flaps, solve the aerodynamic instability. The efficiency of the flap control on the full span of a simple suspension bridge was also carried out. The mode-by-mode technique was applied for the investigation. The results revealed that the efficiency of the flap control relates to the mode number, the installed location of the flap, and the flap length.

Application of simple adaptive control to an MR damper-based control system for seismically excited nonlinear buildings

  • Javanbakht, Majd;Amini, Fereidoun
    • Smart Structures and Systems
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    • v.18 no.6
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    • pp.1251-1267
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    • 2016
  • In this paper, Simple Adaptive Control (SAC) is used to enhance the seismic response of nonlinear tall buildings based on acceleration feedback. Semi-active MR dampers are employed as control actuator due to their reliability and well-known dynamic models. Acceleration feedback is used because of availability, cost-efficiency and reliable measurements of acceleration sensors. However, using acceleration feedback in the control loop causes the structure not to apparently meet some requirements of the SAC algorithm. In addition to defining an appropriate SAC reference model and using inherently stable MR dampers, a modification in the original structure of the SAC is proposed in order to improve its adaptability to the situation in which the plant does not satisfy the algorithm's stability requirements. To investigate the performance of the developed control system, a numerical study is conducted on the benchmark 20-story nonlinear building and the responses of the SAC-controlled structure are compared to an $H_2/LQG$ clipped-optimal controller under the effect of different seismic excitations. As indicated by the results, SAC controller effectively reduces the story drifts and hence the seismically-induced damage throughout the structural members despite its simplicity, independence of structural parameters and while using fewer number of dampers in contrast with the $H_2/LQG$ clipped-optimal controller.

Effects of Bohm Potentials and Fermi Temperatures on Nonplanar Solitary and Shock Excitations in a Strongly-Coupled Quantum Plasma

  • Dip, P.R.;Hossen, M.A.;Salahuddin, M.;Mamun, A.A.
    • Journal of the Korean Physical Society
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    • v.70 no.8
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    • pp.777-784
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    • 2017
  • An exhaustive theoretical investigation considering nonplanar geometry (cylindrical and spherical) in an unmagnetized, collisionless, strongly-coupled quantum electron-positron-ion (EPI) plasma (composed of viscous, positively-charged inertial heavy ion fluids, Fermi electrons and positrons) has been carried out on the nonlinear propagation of the ion-acoustic (IA) waves. The generalized quantum hydrodynamic model using the reductive perturbation method has been utilized to derive the Korteweg-de Vries (K-dV) and Burgers equations. The basic features (e.g., phase speed, amplitude, and width) of the IA solitary and shock waves are identified by analyzing the stationary solitary and shock wave solutions of the K-dV and Burgers equations, respectively. The basic characteristics of the IA nonlinear structures are found to be significantly modified by the ratio of the Fermi temperatures of positrons to electrons, the Fermi pressures of electrons and positrons, the plasma particle number densities, etc.. The results of this theoretical investigation may be useful in studying the IA waves propagating in both astrophysical and laboratory EPI plasmas (viz. white dwarfs, super-intense laser-dense matter experiments, etc.).

Comparison of the seismic performance of existing RC buildings designed to different codes

  • Zeris, Christos A.;Repapis, Constantinos C.
    • Earthquakes and Structures
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    • v.14 no.6
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    • pp.505-523
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    • 2018
  • Static pushover analyses of typical existing reinforced concrete frames, designed according to the previous generations of design codes in Greece, have established these structures' inelastic characteristics, namely overstrength, global ductility capacity and available behaviour factor q, under planar response. These were compared with the corresponding demands at the collapse limit state target performance point. The building stock considered accounted for the typical variability, among different generations of constructed buildings in Greece, in the form, the seismic design code in effect and the material characteristics. These static pushover analyses are extended, in the present study, in the time history domain. Consequently, the static analysis predictions are compared with Incremental Dynamic Analysis results herein, using a large number of spectrum compatible recorded base excitations of recent destructive earthquakes in Greece and abroad, following, for comparison, similar conventional limiting failure criteria as before. It is shown that the buildings constructed in the 70s exhibit the least desirable behaviour, followed by the buildings constructed in the 60s. As the seismic codes evolved, there is a notable improvement for buildings of the 80s, when the seismic code introduced end member confinement and the requirement for a joint capacity criterion. Finally, buildings of the 90s, designed to modern codes exhibit an exceptionally good performance, as expected by the compliance of this code to currently enforced seismic provisions worldwide.

Auxiliary domain method for solving multi-objective dynamic reliability problems for nonlinear structures

  • Katafygiotis, Lambros;Moan, Torgeir;Cheungt, Sai Hung
    • Structural Engineering and Mechanics
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    • v.25 no.3
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    • pp.347-363
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    • 2007
  • A novel methodology, referred to as Auxiliary Domain Method (ADM), allowing for a very efficient solution of nonlinear reliability problems is presented. The target nonlinear failure domain is first populated by samples generated with the help of a Markov Chain. Based on these samples an auxiliary failure domain (AFD), corresponding to an auxiliary reliability problem, is introduced. The criteria for selecting the AFD are discussed. The emphasis in this paper is on the selection of the auxiliary linear failure domain in the case where the original nonlinear reliability problem involves multiple objectives rather than a single objective. Each reliability objective is assumed to correspond to a particular response quantity not exceeding a corresponding threshold. Once the AFD has been specified the method proceeds with a modified subset simulation procedure where the first step involves the direct simulation of samples in the AFD, rather than standard Monte Carlo simulation as required in standard subset simulation. While the method is applicable to general nonlinear reliability problems herein the focus is on the calculation of the probability of failure of nonlinear dynamical systems subjected to Gaussian random excitations. The method is demonstrated through such a numerical example involving two reliability objectives and a very large number of random variables. It is found that ADM is very efficient and offers drastic improvements over standard subset simulation, especially when one deals with low probability failure events.

한국표준원전 증기발생기의 관막음 집중 영역 근방에서의 유체유발진동 특성해석 (Characteristics of Flow-induced Vibration for KSNP Steam Generator Tube at Concentrated Tube Plugging Zone)

  • 유기완;조봉호;박치용;박수기
    • 한국소음진동공학회논문집
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    • v.13 no.6
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    • pp.452-459
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    • 2003
  • The characteristics of fluid-elastic instability and effects of turbulent excitations for the KSNP steam generator tubes were investigated numerically. The information for the thermal-hydraulic data of the steam generator has been obtained by using the ATHOS3-MOD1 code and the flow-induced vibration(FIV) analysis has been conducted by using the PIAT(program for Integrity assessment of SG tube) code. The KSNP steam generator has the concentrated plugging zone at the vicinity of the stay cylinder inside the SG. To investigate the cause of the concentrated tube plugging zone, the FIV analysis has been performed for various column and row number of the steam generator tubes. From the results of FIV analysis the stability ratio due to the fluid-elastic instability and vibrational amplitude due to the turbulent excitation in the concentrated plugged zone have a trend of larger values than those of the outer concentrated tube Plugging zone.

Theory of Radiative Transfer for 3.3-micron $CH_4$ emissions from the Auroral Regions of Jupiter

  • Kim, Sang Joon;Sohn, Mirim
    • 천문학회보
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    • v.39 no.1
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    • pp.66.1-66.1
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    • 2014
  • Radiative transfer programs to simulate the 3-micron auroral $CH_4$ emissions of Jupiter have been developed. The formalism of the radiative transfer calculations including the thermal, fluorescent, and auroral emissions of the $CH_4$ bands for an atmospheric layer having an optical depth of ${\tau}_v$ is given by: ${\mu}dI_v/d{\tau}_v=I_v-{\varpi}_v{^*}J_v(1-{\varpi}_v{^*})B_v-{\varpi}{^*}F_{ov}{e}{x}{p}(-{\tau}_v/{\mu}_o)4{\pi}-hv{\varpi}{^*}V/4{\pi}$ where ${\varpi}_v{^*}$ is the single scattering albedo of $CH_4$ consisting of Einstein A coefficient and collisional deexcitation rate. Other terms are usual radiative transfer parameters appearing in textbooks including the terms for scattered ${\varpi}_v{^*}J_v$, thermal $(1-{\varpi}_v{^*})B_v$, and attenuated solar radiations $F_{ov}$ at the certain atmospheric layer. For auroral excitations, we include V, which is the number of excited states per $cm^3$ persec by auroral particle bombardments. We apply this formalism to the high-resolution spectra of the auroral regions observed with GNIRS/Gemini North, and will present preliminary results for the 3 micron auroral processes of Jupiter.

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회전하는 복합재-VEM 박판보의 GHM 기법을 이용한 진동해석 (The Vibration Analysis of Composite-VEM Thin-Walled Rotating Beam Using GHM Methodology)

  • 박재용;나성수
    • 한국소음진동공학회:학술대회논문집
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    • pp.337-341
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    • 2004
  • This paper concerns the analytical modeling and dynamic analysis of advanced rotating blade structure implemented by a dual approach based on structural tailoring and viscoelastic materials technology. Whereas structural tailoring uses the directionality properties of advanced composite materials, the passive materials technology exploits the damping capabilities of viscoelastic material(VEM) embedded into the host structure. The structure is modeled as a composite thin-walled beam incorporating a number of nonclassical features such as transverse shear, warping restraint, anisotropy of constituent materials, and warping and rotary inertias. The VEM layer damping treatment is modeled by using the Golla-Mushes-McTavish(GHM) method, which is employed to account for the frequency-dependent characteristic o the VEM. The displayed numerical results provide a comprehensive picture of the synergistic implications of the application of both techniques, namely, the tailoring and damping technology on vibration response of thin-walled beam structure exposed to external time-dependent excitations.

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