Search for: linear-response
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    Seismic performance evaluation and design of steel structures equipped with dual-pipe dampers

    , Article Journal of Constructional Steel Research ; Volume 122 , 2016 , Pages 25-39 ; 0143974X (ISSN) Mahjoubi, S ; Maleki, S ; Sharif University of Technology
    Elsevier Ltd 
    Dual-pipe damper (DPD) is a metallic yielding device for passive control of structures, introduced recently by the authors. The objective of the current study is to provide guidelines for implementing DPDs in actual steel buildings, evaluate and compare their performance against other metallic dampers. In this study, a representative load-displacement model for DPDs is proposed for the first time, and assessed based on previous experimental cyclic tests. Guidelines for the design of DPD devices are also presented. Three steel moment resisting frames of 5, 10 and 20 stories are designed and then equipped with DPDs of various properties. The responses of the frames to seven earthquake... 

    Effects of foundation uplift on the dynamic response of steel frames

    , Article Structures Congress 2017: Buildings and Special Structures - Selected Papers from the Structures Congress 2017, 6 April 2017 through 8 April 2017 ; 2017 , Pages 459-472 ; 9780784480410 (ISBN) Salehi, M ; Jafarieh, A. H ; Ghannad, M. A ; Sharif University of Technology
    This paper examines the effects of foundation uplift on the dynamic response of steel frames supported by shallow foundations. In order to achieve this goal, the dynamic responses of a number of two-dimensional concentrically braced steel frames with fixed base, flexible base preventing uplift, and flexible base allowing uplift, are compared. The steel frames are modeled by considering material nonlinearities and P-Delta effects, while the soil-foundation system is modeled through the Winkler foundation approach. The dynamic analyses are conducted using 15 far-fault ground-motions with various intensities and different response parameters are monitored. According to the achieved responses,... 

    The structural performance of monolithic intersecting walls in a tall reinforced concrete building

    , Article Structural Design of Tall and Special Buildings ; Volume 17, Issue 1 , 2008 , Pages 1-23 ; 15417794 (ISSN) Moghaddam, H ; Samadi, M ; Sharif University of Technology
    Results of the seismic performance assessment of a new structural system that has been used in a 54-story reinforced concrete building are presented. The structure, which is still under construction, and has a 'Y-shape' form, utilizes a special structural system that does not include any beams or columns. Instead, walls and slabs are used for carrying both gravitational and lateral loads. The general distinctions of the system are discussed. The structural efficiency of the system is compared with other conventional systems in some existing tall buildings. The seismic responses and dynamic behavior of the structure that were achieved by conducting various analyses are presented. The effects... 

    Structural damage estimation using seismic and spectral parameters

    , Article 10th International Conference on Civil, Structural and Environmental Engineering Computing, Civil-Comp 2005, Rome, 30 August 2005 through 2 September 2005 ; 2005 ; 1905088000 (ISBN); 9781905088003 (ISBN) Bakhshi, A ; Tavallali, H ; Karimi, K ; Sharif University of Technology
    Estimation of damage to structures after severe earthquakes is important for loss estimation and is an essential step for rescue program. Using seismic or spectral parameters could be a quick method for this purpose. In this article damage estimation for some world's destructive earthquakes has been carried out. For this purpose some earthquake seismic parameters, response spectra and damage indices have been calculated and compared. Damage indices are calculated for three types of intermediate sway concrete frame buildings, i.e. low-rise, mid-rise and high-rise, designed according to Iranian Seismic Code and ACI 318-95. Finally the trend between earthquake seismic parameters, response... 

    Nonlinear dynamic analysis of an axially loaded rotating Timoshenko beam with extensional condition included subjected to general type of force moving along the beam length

    , Article JVC/Journal of Vibration and Control ; Volume 19, Issue 16 , 2013 , Pages 2448-2458 ; 10775463 (ISSN) Mamandi, A ; Kargarnovin, M. H ; Sharif University of Technology
    In this paper the non-planar nonlinear dynamic responses of an axially loaded rotating Timoshenko beam subjected to a three-directional force traveling with a constant velocity is studied. On deriving the nonlinear coupled partial differential equations (PDEs) of motion the stretching effect of the beam's neutral axis due to the pinned-pinned ends' condition in conjunction with the von Karman strain-displacement relation are considered. The beam's nonlinear governing coupled PDEs of motion for the bending rotations of warped cross-section, longitudinal and lateral displacements are derived using Hamilton's principle. To obtain the dynamic responses of the beam, derived PDEs of motion are... 

    Modeling of self-controlling hyperthermia based on nickel alloy ferrofluids: Proposition of new nanoparticles

    , Article Journal of Magnetism and Magnetic Materials ; Volume 335 , 2013 , Pages 59-63 ; 03048853 (ISSN) Delavari H. H ; Madaah Hosseini, H. R ; Wolff, M ; Sharif University of Technology
    In order to provide sufficient heat without overheating healthy tissue in magnetic fluid hyperthermia (MFH), a careful design of the magnetic properties of nanoparticles is essential. We perform a systematic calculation of magnetic properties of Ni-alloy nanoparticles. Stoner-Wohlfarth model based theories (SWMBTs) are considered and the linear response theory (LRT) is used to extract the hysteresis loop of nickel alloy nanoparticles in alternating magnetic fields. It is demonstrated that in the safe range of magnetic field intensity and frequency the LRT cannot be used for the calculation of the area in the hysteresis for magnetic fields relevant for hyperthermia. The best composition and... 

    Seismic performance assessment of steel frames equipped with a novel passive damper using a new damper performance index

    , Article Structural Control and Health Monitoring ; Volume 22, Issue 4 , 2015 , Pages 774-797 ; 15452255 (ISSN) Mahjoubi, S ; Maleki, S ; Sharif University of Technology
    John Wiley and Sons Ltd  2015
    Seismic response of steel moment-resisting frames equipped with a novel passive damper called infilled-pipe damper (IPD) is investigated in this study. The IPD is a very economical and easily assembled structural control device with high energy absorption, invented recently by the authors. A simplified trilinear load-displacement model for IPD devices is suggested to be used in this study and further investigations. Next, criteria for IPD elements size selection are proposed for passive control of structures against earthquake loads. Steel frame structures of 5, 10, and 20 stories are designed without any IPD devices. Then, the frames are equipped with IPDs of different stiffness. The frames... 

    Displacement-based design considering soil-structure interaction effects

    , Article 8th US National Conference on Earthquake Engineering 2006, San Francisco, CA, 18 April 2006 through 22 April 2006 ; Volume 4 , 2006 , Pages 1928-1937 ; 9781615670444 (ISBN) Jafarieh, A. H ; Ghannad, M. A ; Sharif University of Technology
    Recently, the traditional strength-based design (SBD) philosophy is being replaced by more relevant displacement-based design (DBD) approach. As a main step, DBD method requires a simplified procedure to estimate the inelastic displacement demands of the structure. This step is usually done by either replacing the non-linear system by an equivalent linear system or employing the well-known concepts of inelastic design spectra. The application of different DBD procedures and their deficiencies, thus, have been the subject of numerous researches during the recent years. However, the effect of soil is usually ignored. On the other hand, it is well-known that soil affects the structural behavior... 

    Evaluation the nonlinear response function of a HPGe detector for 59 keV to 10.7 MeV gamma-rays using a Monte Carlo simulation and comparison with experimental data

    , Article Journal of Instrumentation ; Volume 16, Issue 7 , 2021 ; 17480221 (ISSN) Saheli, F ; Riazi, Z ; Jokar, A ; Shahabinejad, H ; Vosoughi, N ; Ghasemi, S. A ; Sharif University of Technology
    IOP Publishing Ltd  2021
    Modeling of High Purity Germanium (HPGe) detector on a wide energy range is important in gamma-ray spectroscopy. The precisely modeled detector can be used for proton-induced prompt gamma-ray spectroscopy. In this work, we used both the gamma-rays of calibration sources and prompt gamma-rays emitted in proton capture reactions to model a coaxial p-type HPGe detector using Geant4 Monte Carlo simulation for the gamma-ray energy range of 59–10764 keV. The calibration sources were 137Cs, 241Am, 60Co, 152Eu, and 133Ba, while the prompt gamma-rays were due to the gamma-ray cascades following the 27Al(p,γ)28Si reaction capture at the resonant energies of 992, 1317 and 2483 keV, as well as the... 

    Nonlinear responses of unbalanced flexible rotating shaft passing through critical speeds

    , Article Meccanica ; 2021 ; 00256455 (ISSN) Amirzadegan, S ; Rokn Abadi, M ; Firouz Abadi, R.D ; Mehralian, F ; Sharif University of Technology
    Springer Science and Business Media B.V  2021
    This work studies the nonlinear oscillations of an elastic rotating shaft with acceleration to pass through the critical speeds. A mathematical model incorporating the Von-Karman higher-order deformations in bending is developed and analyzed to investigate the nonlinear dynamics of rotors. A flexible shaft on flexible bearings with springs and dampers is considered as rotor system for the present work. The shaft is modeled as a beam with a circular cross-section and the Euler Bernoulli beam theory is applied. The kinetic and strain energies of the rotor system are derived and Lagrange method is then applied to obtain the coupled nonlinear differential equations of motion for 6° of freedom.... 

    Two nanostructured polymers: Polyaniline nanofibers and new linear-dendritic matrix of poly(citric acid)-block-poly(ethylene glycol) copolymers for environmental monitoring in novel biosensors

    , Article International Journal of Polymeric Materials and Polymeric Biomaterials ; Volume 62, Issue 7 , Jul , 2013 , Pages 377-383 ; 00914037 (ISSN) Shamloo, A ; Vossoughi, M ; Alemzadeh, I ; Naeini, A. T ; Darvish, M ; Sharif University of Technology
    In this work two phenol biosensors, one based on polyaniline nanofibers (PNFs) and the other based on the newly created and introduced linear-dendritic matrix of poly(citric acid)-block-poly(ethylene glycol) copolymers (PCA-PEG-PCA), were chemically modified with horseradish peroxidase (HRP) enzyme. These phenol biosensors showed an oxidation peak at 0.55 V. The amperometric response for biosensors based on PNFs showed a linear response range from 2.5 × 10-6 to 2.5 × 10-5 mol/L, with a detection limit of 2.5 M phenol. Also, the amperometric response for a biosensor based on PCA-PEG-PCA showed a linear response range from 2.5 × 10-6 to 4 × 10-5 mol/L, with a detection limit of 1.5 M phenol  

    Human cardiac troponin i sensor based on silver nanoparticle doped microsphere resonator

    , Article Journal of Optics (United Kingdom) ; Volume 14, Issue 12 , 2012 ; 20408978 (ISSN) Saliminasab, M ; Bahrampour, A ; Zandi, M. H ; Sharif University of Technology
    Human cardiac troponin I (cTnI) is a specific biomarker for diagnosis of acute myocardial infarction (AMI). In this paper, a composite sensing system of an optical microsphere resonator and silver nanoparticles based on surface enhanced Raman scattering (SERS) and stimulated Raman scattering (SRS) techniques towards a point of care diagnostic system for AMI using the cTnI biomarker in HEPES buffered solution (HBS) is proposed. Pump and Raman signals enter the optical fiber coupling into the microsphere, and then SRS occurs in the microsphere. The presence of silver nanoparticles on the microsphere surface provides a tremendous enhancement of the resulting Raman signal through an... 

    Multiple-input describing function technique applied to design a single channel ON-OFF controller for a spinning flight vehicle

    , Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 226, Issue 6 , 2012 , Pages 631-645 ; 09544100 (ISSN) Nobahari, H ; Mohammadkarimi, H ; Sharif University of Technology
    In this study, the guidance and control problem of a single-channel spinning missile is investigated. The missile utilizes a single ON-OFF actuator to drive a pair of control surfaces (e.g. elevators) and consequently to perform all required lateral maneouvers. An approximated linear response of the so-called non-rotating frame to ON-OFF input, applied to the rotating frame, is derived using the multiple-input describing function technique. It is shown that there is a relationship between the response of the non-rotating frame and that of the equivalent non-rotating body. It is also shown that the two-channel flight controller, designed for the equivalent non-rotating body, can be reduced to... 

    A precise solution for prediction of fiber-reinforced concrete behavior under flexure

    , Article Journal of Zhejiang University: Science A ; Volume 12, Issue 7 , 2011 , Pages 495-502 ; 1673565X (ISSN) Ahmadi, R ; Ghoddousi, P ; Sharifi, M ; Bahreh, V. M ; Sharif University of Technology
    This paper presents a precise solution to predict the behavior of steel fiber reinforced concrete (SFRC) under the four point bending test (FPBT). All the force components at the beam section (before and after cracking) are formulated by applying these assumptions: a realistic stress-strain model is used for concrete behavior in compression, a linear response is considered for the uncracked tension region in a concrete constitutive model, and an exponential relationship is proposed as a stress-crack opening in the crack region which requires two parameters. Then the moment capacity of the critical cracked section is calculated by using these forces and satisfying equilibrium law at the... 

    Nonlinear vibration of a three-dimensional moving gantry crane subjected to a travelling trolley hoisting a swinging object

    , Article Transactions of the Canadian Society for Mechanical Engineering ; Volume 34, Issue 3-4 , 2010 , Pages 333-350 ; 03158977 (ISSN) Younesian, D ; Ghafoori, E ; Sadeghpour, M ; Sharif University of Technology
    Nonlinear vibration of a three-dimensional moving gantry crane carrying a trolley hoisting a swinging object is studied in this paper.A finite element method is used to solve nonlinear coupled governing equations of the structure. A combinational technique (Newmark-Runge-Kutta) is employed for direct integration procedure. To develop a comprehensive parametric study and sensitivity analysis of the coupled nonlinear system, sequence of numerical simulations are carried out. Parametric study is directed to find out how different parameters like speed and acceleration of the trolley and gantry crane as well as the mass of the moving trolley and swinging object may affect the linear and... 

    Seismic assessment of steel frames with the endurance time method

    , Article Journal of Constructional Steel Research ; Volume 66, Issue 6 , 2010 , Pages 780-792 ; 0143974X (ISSN) Riahi, H. T ; Estekanchi, H. E ; Sharif University of Technology
    In the endurance time (ET) method, structures are subjected to a specially designed intensifying ground acceleration function and their performance is judged based on their response at various excitation levels. A range of equivalent intensities can be covered in a single numerical or experimental simulation, thus significantly reducing the computational demand as compared to full nonlinear response-history analyses. The applied excitation intensity at various times has been correlated with those of the scaled ground motions. Response spectra of seven ground motions on stiff soil were used to produce intensifying acceleration functions that at each time window produce a response spectrum... 

    Nonlinear identification of electro-magnetic force model

    , Article Journal of Zhejiang University: Science A ; Volume 11, Issue 3 , 2010 , Pages 165-174 ; 1673565X (ISSN) Shabani, R ; Tariverdilo, S ; Salarieh, H ; Sharif University of Technology
    Conventional attractive magnetic force models (proportional to the coil current squared and inversely proportional to the gap squared) cannot simulate the nonlinear responses of magnetic bearings in the presence of electromagnetic losses, flux leakage or saturation of iron. In this paper, based on results from an experimental set-up designed to study magnetic force, a novel parametric model is presented in the form of a nonlinear polynomial with unknown coefficients. The parameters of the proposed model are identified using the weighted residual method. Validations of the model identified were performed by comparing the results in time and frequency domains. The results show a good... 

    Oscillatory response of charged droplets in hydrogels

    , Article Journal of Non-Newtonian Fluid Mechanics ; Volume 234 , 2016 , Pages 215-235 ; 03770257 (ISSN) Mohammadi, A ; Sharif University of Technology
    Elsevier  2016
    Characterization of droplet-hydrogel interfaces is of crucial importance to engineer droplet-hydrogel composites for a variety of applications. In order to develop electrokinetic diagnostic tools for probing droplet-hydrogel interfaces, the displacement of a charged droplet embedded in a polyelectrolyte hydrogel exposed to an oscillating electric field is determined theoretically. The polyelectrolyte hydrogel is modeled as an incompressible, charged, porous, and elastic solid saturated with a salted Newtonian fluid. The droplet is considered an incompressible Newtonian fluid with no charges within the droplet. The droplet-hydrogel interface is modeled as a surface with the thickness of zero... 

    Hysteretic response of confined masonry walls by Prandtl neural networks

    , Article 1st International Conference on Advances and Trends in Engineering Materials and their Applications, AES-ATEMA'2007, Montreal, QC, 6 August 2007 through 10 August 2007 ; 2007 , Pages 525-533 ; 19243642 (ISSN) ; 0978047907 (ISBN); 9780978047900 (ISBN) Joghataie, A ; Farrokh, M ; Mohebbi, M ; Sharif University of Technology
    In this paper a new method of modeling shear force-displacement relationship for confined masonry walls by neural networks has been presented. Although the mathematical models have been very useful in the simulations so far, however developing more accurate models is necessary. While developing precise mathematical models for highly hysteretic materials is itself challenging and practically cumbersome, the use of learning algorithms is an attractive alternative. The issue of material modeling by neural networks has been a challenging one itself, noticing available neural networks have some limitations in the learning of non-linearity. In this paper a new type neural network, called Prandtl... 

    Incorporation of Soil-Structure Interaction into seismic performance evaluation of buildings

    , Article 8th US National Conference on Earthquake Engineering 2006, San Francisco, CA, 18 April 2006 through 22 April 2006 ; Volume 15 , 2006 , Pages 9008-9017 ; 9781615670444 (ISBN) Bayat, M. R ; Ghannad, M. A ; Sharif University of Technology
    It has been known for many years that the type of soil under structures affects the structural performance during earthquakes. In fact, the soil affects the structural response in two ways, through the change in the free-field motion (usually known as the site effect) and due to Soil- Structure Interaction (SSI). The site effect has been included in the seismic codes from the most beginning. However, the SSI effect had not attracted much attention. The most significant intervention in this regard has been the 1978 inclusion of SSI in the tentative provisions of ATC3-06 in the United States, which is based on the results of studies on elastic response of soil structure systems. The effect of...