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۱HYDRO–PNEUMATIC SEMI–ACTIVE RESETTABLE DEVICE BY USING MR–FLUID (MR–HSRD) FOR VIBRATION SUPPRESSION
نویسنده(ها): ، ،
اطلاعات انتشار: ششمین کنفرانس بین المللی زلزله شناسی و مهندسی زلزله، سال
تعداد صفحات: ۹
In this article, a novel hydro–pneumatic semi–active resettable device is proposed and studied for vibration suppression applications. The novel device consists of a cylinder–piston system with a control valve as well as a MR–valve mounted on a bypass pipe connecting two sides of thecylinder. The cylinder has two chambers; each chamber contains two parts, pressured gas and MR–fluid. The device behaves effectively as a spring with an adjustable unstressed length. The MR–HSRD is set by changing the stiffness and the damping of the device independently. Moreover, the hysteresis behaviour can be changed by using different control logics for control valve. The stiffness is changed by altering the gas pressure and damping can be adjusted by altering the electrical current. When the device is excited by external load, at the instants when energy in the device is maximized, this energy is dissipated as heat in the MR–fluid by opening a control valve for a short time interval and letting the MR–fluid to flow through the MR–valve. This dissipates the main part of input energy, which is stored in the pressurized gas. In this paper, the experimental results of the MR–HSRD under cyclic loading are presented and the ability of the MR–HSRD for vibration suppression is studied.<\div>

۲EFFECTS OF DIFFERENT MODELING ASSUMPTIONS ON MAIN–SHOCK DAMAGED FRAGILITY CURVES OF STEEL STRUCTURES
نویسنده(ها): ، ، ،
اطلاعات انتشار: دومین کنگره بین المللی سازه ، معماری و توسعه شهری، سال
تعداد صفحات: ۸
Evaluation of seismic performance of main–shock damaged structures, affected by aftershocks, leads to more accurate and reliable seismic loss estimation. Seismic fragility curves, as a measure of seismic performance, are estimated by nonlinear time history analysis of structural models against earthquake acceleration records. The modeling assumptions will affect the results of seismic performance measures. In this paper the effects of modeling assumptions on seismic fragility curves are investigated. Lumped plasticity of steel beams by deteriorating rotational springs as beam to column connections and distributed plasticity of steel beams by fiber elements are considered as modelling assumptions. Seismic fragility curves for two models, affected by main shocks and aftershocks are developed and compared for structural damage states defined by HAZUS. Aftershock fragility curves are achieved based on back–to–back dynamic analysis of two models.<\div>

۳Linear seismic response of arch dams to non–uniform excitations considering load combination effects
نویسنده(ها): ،
اطلاعات انتشار: اولین همایش ملی مهندسی سازه ایران، سال
تعداد صفحات: ۱۳
In the present paper, the effect of non–uniform excitation due to spatially varying earthquake ground motions(SVEGM) on linear responses of concrete arch dams is investigated. An iterative scheme is utilized to generate seismicground motion time–histories at several locations along foundation boundaries that are compatible with prescribedtarget response spectra and are correlated according to a given coherence function including the wave propagationeffect. A double curvature arch dam is selected as case study in which the reservoir is modeled as a compressiblemedium and the foundation is assumed to be massless. Various load combinations are considered based on thecorresponding reservoir water levels and thermal loads. It is observed that using SVEGM leads to higher values in bothtensile stresses and percentage of overstressed parts within the dam body in comparison with uniform excitation andtherefore to be more realistic in calculating the dam response, this phenomenon should be incorporated in seismicanalyses especially in high seismicity regions.<\div>

۴Modelling of crack propagation in layered structures using extended finite element method
نویسنده(ها): ، ،
اطلاعات انتشار: سومین کنفرانس بین المللی پژوهشهای کاربردی در مهندسی عمران، معماری و مدیریت شهری، سال
تعداد صفحات: ۹
Crack propagation in structuresis animportant issue which isengineers and designersshould consider. Modelingcrack propagation in structures and study the behavior ofthis phenomenoncangive a better insight to engineers and designers forselecting the construction’smaterials. Extended finite element method (XFEM) was used successfullyin the past few years for simulating crack initiation and propagation insophisticatedand complexgeometries in elastic fracture mechanics. In this paper,crack propagation in three–point bending beam includinginitial crackwasmodeled based onABAQUSsoftware.The following consequenceswere attained through the study of simulation data. First,theeffectsof young’s modulus and fracture energy on force–displacementcurve atthree–pointbending beam wereinvestigated.It was observed that,by increasing the value of young’s modulus and fracture energy,three–point bendingbeam was showed more loadcarryingagainst initiation. Second,in multi–layer beam, the effect ofyoung’s modulusonforce–displacementcurvewas investigated.In case I (the thin upper layer is harder than the substrate)the value of young’s modulus in substrate was kept constant and the amount of young’s modulus in thin layer was risenin each steprather than the substrate,the peak in force–displacementcurve wasascendedand three–point bendingbeamresistedbetter against crack initiation. Next,similar conditions was consideredin caseII (the thin upper layer is softer than the ubstrate), by decreasingthevalue of young’ modulusin top layer, peak in force–displacementcurve was declined and crack initiation was happened in lower loadingin eachstep.Finally,sensitivity analysisfor thickness of top layerwas conductedand the impactof this parameter was studied.<\div>
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