• Title/Summary/Keyword: geometric non-linear stiffness

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Seismic response of current RC buildings in Kathmandu Valley

  • Chaulagain, Hemchandra;Rodrigues, Hugo;Spacone, Enrico;Varum, Humberto
    • Structural Engineering and Mechanics
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    • v.53 no.4
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    • pp.791-818
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    • 2015
  • RC buildings constitute the prevailing type of construction in earthquake-prone region like Kathmandu Valley. Most of these building constructions were based on conventional methods. In this context, the present paper studied the seismic behaviour of existing RC buildings in Kathmandu Valley. For this, four representative building structures with different design and construction, namely a building: (a) representing the non-engineered construction (RC1 and RC2) and (b) engineered construction (RC3 and RC4) has been selected for analysis. The dynamic properties of the case study building models are analyzed and the corresponding interaction with seismic action is studied by means of non-linear analyses. The structural response measures such as capacity curve, inter-storey drift and the effect of geometric non-linearities are evaluated for the two orthogonal directions. The effect of plan and vertical irregularity on the performance of the structures was studied by comparing the results of two engineered buildings. This was achieved through non-linear dynamic analysis with a synthetic earthquake subjected to X, Y and $45^{\circ}$ loading directions. The nature of the capacity curve represents the strong impact of the P-delta effect, leading to a reduction of the global lateral stiffness and reducing the strength of the structure. The non-engineered structures experience inter-storey drift demands higher than the engineered building models. Moreover, these buildings have very low lateral resistant, lesser the stiffness and limited ductility. Finally, a seismic safety assessment is performed based on the proposed drift limits. Result indicates that most of the existing buildings in Nepal exhibit inadequate seismic performance.

Static Non-linear Finite Element Analysis of Spatial Cable Networks (3차원 케이블망의 초기평형상태 결정 및 정적 비선형 유한요소해석)

  • 김문영;김남일;안상섭
    • Computational Structural Engineering
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    • v.11 no.1
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    • pp.179-190
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    • 1998
  • A geometrically nonlinear finite element formulation of spatial cable networks is presented using two cable elements. Firstly, derivation procedures of tangent stiffness and mass matrices for the space truss element and the elastic catenary cable element are summarized. The load incremental method based on Newton-Raphson iteration method and the dynamic relaxation method are presented in order to determine the initial static state of cable nets subjected to self-weights and support motions. Furthermore, static non-linear analysis of cable structures under additional live loads are performed based on the initial configuration. Challenging example problems are presented and discussed in order to demonstrate the feasibility of the present finite element method and investigate static nonlinear behaviors of cable nets.

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A geometrically nonlinear thick plate bending element based on mixed formulation and discrete collocation constraints

  • Abdalla, J.A.;Ibrahim, A.K.
    • Structural Engineering and Mechanics
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    • v.26 no.6
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    • pp.725-739
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    • 2007
  • In recent years there are many plate bending elements that emerged for solving both thin and thick plates. The main features of these elements are that they are based on mix formulation interpolation with discrete collocation constraints. These elements passed the patch test for mix formulation and performed well for linear analysis of thin and thick plates. In this paper a member of this family of elements, namely, the Discrete Reissner-Mindlin (DRM) is further extended and developed to analyze both thin and thick plates with geometric nonlinearity. The Von K$\acute{a}$rm$\acute{a}$n's large displacement plate theory based on Lagrangian coordinate system is used. The Hu-Washizu variational principle is employed to formulate the stiffness matrix of the geometrically Nonlinear Discrete Reissner-Mindlin (NDRM). An iterative-incremental procedure is implemented to solve the nonlinear equations. The element is then tested for plates with simply supported and clamped edges under uniformly distributed transverse loads. The results obtained using the geometrically NDRM element is then compared with the results of available analytical solutions. It has been observed that the NDRM results agreed well with the analytical solutions results. Therefore, it is concluded that the NDRM element is both reliable and efficient in analyzing thin and thick plates with geometric non-linearity.

Effect of higher order terms of Maclaurin expansion in nonlinear analysis of the Bernoulli beam by single finite element

  • Zahrai, Seyed Mehdi;Mortezagholi, Mohamad Hosein;Mirsalehi, Maryam
    • Structural Engineering and Mechanics
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    • v.58 no.6
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    • pp.949-966
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    • 2016
  • The second order analysis taking place due to non-linear behavior of the structures under the mechanical and geometric factors through implementing exact and approximate methods is an indispensible issue in the analysis of such structures. Among the exact methods is the slope-deflection method that due to its simplicity and efficiency of its relationships has always been in consideration. By solving the differential equations of the modified slope-deflection method in which the effect of axial compressive force is considered, the stiffness matrix including trigonometric entries would be obtained. The complexity of computations with trigonometric functions causes replacement with their Maclaurin expansion. In most cases only the first two terms of this expansion are used but to obtain more accurate results, more elements are needed. In this paper, the effect of utilizing higher order terms of Maclaurin expansion on reducing the number of required elements and attaining more rapid convergence with less error is investigated for the Bernoulli beam with various boundary conditions. The results indicate that when using only one element along the beam length, utilizing higher order terms in Maclaurin expansion would reduce the relative error in determining the critical buckling load and kinematic parameters in the second order analysis.

A study on the optimal control of Long Stroke Fast Tool Servo Systems (장거리 구동용 FTS 의 최적 제어에 관한 연구)

  • 이상호;이찬홍;김갑순
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2004.10a
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    • pp.818-821
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    • 2004
  • With a rapid development in the area of micro and ultra precision technology, the micro surface machining of small size parts are explosively increased. Especially, to improve efficiency of various beams in lens and reflector, non-rotational symmetric form and several mm level heights changeable surface can be machined at a time. These geometric complex 3D surface cannot be machined by general short stroke FTS. The long stroke FTS if firmly needed to move directly several mm and have nm level positioning accuracy for the complex surface form. The long stroke FTS used linear motors to drive moving unit long and fine, aero static bearings to decrease friction and moving errors in guide way, optical linear scale with nm level resolution to measure position of FTS. Furthermore, to increase the performance of acceleration of FTS, the light material, such as AL is used for the structure and the high stiffness box type structure is selected. In this paper, the genetic algorithm approach is described to determine a set of design parameters for auto tuning. The authors have attempted to model the design problem with the objective of minimizing the error, such as variable pattern change. This method can give the better alternative than existing other method.

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Experimental investigation of the large amplitude vibrations of a thin-walled column under self-weight

  • Goncalves, Paulo B.;Jurjo, Daniel Leonardo B.R.;Magluta, Carlos;Roitman, Ney
    • Structural Engineering and Mechanics
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    • v.46 no.6
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    • pp.869-886
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    • 2013
  • This work presents an experimental methodology specially developed for the nonlinear large-amplitude free vibration analysis of a clamped-free thin-walled metal column under self-weight. The main contribution of this paper is related to the developed experimental methodology which is based on a remote sensing technique using a computer vision system that integrates, on-line, the digital image acquisition and its treatment through special image processing routines. The main importance of this methodology is that it performs large deflections measurements without making contact with the structure and thus, not introducing undesirable changes in its behavior, for instance, appreciable changes in mass and stiffness properties. This structure presents, in most cases, highly non-linear responses, which cannot be reproduced by conventional finite-element softwares due, mainly, to the simultaneous influence of geometric and inertial non-linearities. To capture the non-linearities associated with large amplitude vibration and be able to describe the buckling process, the structure is discretized as a sequence of jointed coupled elastic pendulums. The obtained numerical results are favorably compared with the experimental ones, in the pre- and post-buckling regimes.

Hybrid nonlinear control of a tall tower with a pendulum absorber

  • Orlando, Diego;Goncalves, Paulo B.
    • Structural Engineering and Mechanics
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    • v.46 no.2
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    • pp.153-177
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    • 2013
  • Pendulums can be used as passive vibration control devices in several structures and machines. In the present work, the nonlinear behavior of a pendulum-tower system is studied. The tower is modeled as a bar with variable cross-section with concentrated masses. First, the vibration modes and frequencies of the tower are obtained analytically. The primary structure and absorber together constitute a coupled system which is discretized as a two degrees of freedom nonlinear system, using the normalized eigenfunctions and the Rayleigh-Ritz method. The analysis shows the influence of the geometric nonlinearity of the pendulum absorber on the response of the tower. A parametric analysis also shows that, with an appropriate choice of the absorber parameters, a pendulum can decrease the vibration amplitudes of the tower in the main resonance region. The results also show that the pendulum nonlinearity cannot be neglected in this type of problem, leading to multiplicity of solutions, dynamic jumps and instability. In order to improve the effectiveness of the control during the transient response, a hybrid control system is suggested. The added control force is implemented as a non-linear variable stiffness device based on position and velocity feedback. The obtained results show that this strategy of nonlinear control is attractive, has a good potential and can be used to minimize the response of slender structures under various types of excitation.

Post-buckling and Elasto-plastic Analysis of Shell Structures using the Degenerated Shell Element (변형된 쉘요소를 이용한 판 및 쉘 구조의 후좌굴 및 탄.소성 유한요소해석)

  • 김문영;민병철
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1995.04a
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    • pp.17-27
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    • 1995
  • For the post-buckling and elasto-plastic analysis of shell structures, the total Lagrangian formulation is presented based upon the degenerated shell element. Geometrically correct formulation is developed by updating the direction of normal vectors in the iteration process and evaluating the total Green-Lagrange stain corresponding U total displacements. In the calculation of the stiffness matrix, the element formulation takes into account the effect of finite rotation increments by retaining second order rotation terms in the incremental displacement field. The selective or reduced integration scheme using the heterosis element is applied in order to overcome both shear locking phenomena and the zero energy mode. The load/displacement incremental scheme is adopted for geometric non-linear F .E. analysis. Based on such methodology, the computer program is developed and numerical examples to demonstrate the accuracy and the effectiveness of the proposed shell element are presented and compared with references's results.

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Free Vibrations of Ocean Cables under Currents (조류력을 받는 해양케이블의 자유진동해석)

  • 김문영;김남일;윤종윤
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.11 no.4
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    • pp.231-237
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    • 1999
  • A geometric non-linear finite element formulation of spatial ocean cable under currents is presented using multiple noded curved cable elements. Tangent stiffness and mass matrices for the isoparametric cable ele¬ment are derived and the initial equilibrium state of ocean cable subjected to self-weights, buoyancy, and current as well as support motions is determined using the load incremental method. Free vibration analysis of ocean cables is performed based on the initial equilibrium configuration. Numerical examples are presented and discussed in order to demonstrate the feasibility of the present finite element method and investigate dynamic characteristics of ocean cables.

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Soil-structure interaction and axial force effect in structural vibration

  • Gao, H.;Kwok, K.C.S.;Samali, B.
    • Structural Engineering and Mechanics
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    • v.5 no.1
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    • pp.1-19
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    • 1997
  • A numerical procedure for dynamic analysis of structures including lateral-torsional coupling, axial force effect and soil-structure interaction is presented in this study. A simple soil-structure system model has been designed for microcomputer applications capable of reflecting both kinematic and inertial soil-foundation interaction as well as the effect of this interaction on the superstructure response. A parametric study focusing on inertial soil-structure interaction is carried out through a simplified nine-degree of freedom building model with different foundation conditions. The inertial soil-structure interaction and axial force effects on a 20-storey building excited by an Australian earthquake is analysed through its top floor displacement time history and envelope values of structural maximum displacement and shear force.