• Title, Summary, Keyword: Moment-Rotation Functions

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A measuring system for determination of a cantilever beam support moment

  • Loktionov, Askold P.
    • Smart Structures and Systems
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    • v.19 no.4
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    • pp.431-439
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    • 2017
  • This investigation is aimed to develop a model of experimental-computation determination of a support moment of a cantilever beam loaded with concentrated force at its end including the optimal choice of coordinates of deflection data points and parameters of transformation of deflection data in case of insufficient accuracy of the assignment of initial parameters (support settlement, angle of rotation of the bearing section) and cantilever beam length. The influence of distribution and characteristics of sensors on the cantilever beam on the accuracy of determining the support moment which improves in the course of transition from the uniform distribution of sensors to optimal non-uniform distribution is shown. On the basis of the theory of inverse problems the method of transformation reduction at numerical differentiation of deflection functions has been studied. For engineering evaluation formulae of uncertainty estimate to determine a support moment of a cantilever beam at predetermined uncertainty of measurements using sensors have been obtained.

Prediction of Member Plastic Rotation Demands for Earthquake Design of Moment Frames (모멘트골조의 내진설계를 위한 부재 소성변형 요구량 예측)

  • Eom, Tae-Sung;Park, Hong-Gun
    • Journal of the Earthquake Engineering Society of Korea
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    • v.13 no.5
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    • pp.51-60
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    • 2009
  • To secure the structural safety of structures and members against earthquakes, the plastic deformation capacity demand of members should be accurately predicted. In the present study, a method for the evaluation of the plastic deformations of members for moment frames was developed. To facilitate the practical use of the proposed method in equivalent seismic design, the plastic deformations of members were evaluated based on the results of elastic analysis, without using nonlinear analysis. The plastic deformation demands of members were formulated as functions of story drift demand, redistributed moment and member stiffness. Story drift demand and moment redistribution were directly determined from elastic analysis. The proposed method was applied to an 8 story-2 bay moment frame, and the predicted plastic deformations were verified using nonlinear analysis. The results showed that the proposed method could be used to accurately predict the member plastic rotations with simple calculations. The proposed method can be applied both to the earthquake design of new structures and to the performance evaluation of existing structures.

A Numerical Study on the Semi-Rigid Behavior of Steel Tubular Column to H Beam Connection with Exterior Square-Plate Diaphragms (직각판형 외다이아프램 각형강관기둥-H형강보 접합부의 방강접거동에 관한 해석적연구)

  • Chae, Yong-Soo;Choi, Sung-Mo;Kim, Dong-Kyu
    • Journal of Korean Society of Steel Construction
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    • v.13 no.3
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    • pp.289-299
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    • 2001
  • The purpose of this study was to analyze the characteristics of semi-igid behavior of the steel tubular column to H-beam connection reinforced with exterior square-plate diaphragms and to check the main parameters that affect this behavior. Steel tube connections without interior diaphragm and/or complicated exterior diaphragm show the considerable flexibility due to out of-plane deformation of tube flange. For the exact analysis well-reflected the effect of this flexibility on the overall frame performance. it need to find out the moment-rotation curve function that well trace the result of experiment in the whole region and the function should be simply transformed into an adequate form for the nonlinear analysis program. After collecting several test data same to the connection type considered. we carried out FEM analysis using ANSYS for the assumed beam-to-column connection developed from the simple tension test and the results are compared with experimental values. Based on the parametric study. we proposed the moment-relation curve function and performed the multiple-regression analysis procedure for three parameters consisting of this function with the main geometric parameter of this connection type.

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Blast Fragility and Sensitivity Analyses of Steel Moment Frames with Plan Irregularities

  • Kumar, Anil;Matsagar, Vasant
    • International journal of steel structures
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    • v.18 no.5
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    • pp.1684-1698
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    • 2018
  • Fragility functions are determined for braced steel moment frames (SMFs) with plans such as square-, T-, L-, U-, trapezoidal-, and semicircular-shaped, subjected to blast. The frames are designed for gravity and seismic loads, but not necessarily for the blast loads. The blast load is computed for a wide range of scenarios involving different parameters, viz. charge weight, standoff distance, and blast location relative to plan of the structure followed by nonlinear dynamic analysis of the frames. The members failing in rotation lead to partial collapse due to plastic mechanism formation. The probabilities of partial collapse of the SMFs, with and without bracing system, due to the blast loading are computed to plot fragility curves. The charge weight and standoff distance are taken as Gaussian random input variables. The extent of propagation of the uncertainties in the input parameters onto the response quantities and fragility of the SMFs is assessed by computing Sobol sensitivity indices. The probabilistic analysis is conducted using Monte Carlo simulations. The frames have least failure probability for blasts occurring in front of their corners or convex face. Further, the unbraced frames are observed to have higher fragility as compared to counterpart braced frames for far-off detonations.

Spatial Free Vibration and Stability Analysis of Thin-Walled Arches with Variable Curvature (곡률이 변하는 박벽 아치의 3차원 자유진동 및 좌굴해석)

  • 서광진;민병철;김문영
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.169-176
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    • 1999
  • An improved formulation for spatial stability md free vibration of thin-walled curved beams with variable curvature and non-symmetric cross sections are presented based on the displacement field considering the second order terms of finite semitangential rotations. By introducing Vlasov's assumptions, the total potential energy is derived from the principle of linearized virtual work for a continuum. In this formulation, all displacement parameters and the warping function are defined at the centroid axis so that the coupled terms of bending and torsion are added to the elastic strain energy. Also, the potential energy due to initial stress resultants is consistently derived corresponding to the semitangential rotation and moment. The cubic Hermitian polynomials are utilized as shape functions for development of the curved thin-walled beam element having eight degrees of freedom. In order to illustrate the accuracy and practical usefulness of this study, . numerical solutions for free vibration of arches are presented and compared with resells of other researchers and solutions analyzed by the ABAQUS's shell element.

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Frequency analysis of beams with multiple dampers via exact generalized functions

  • Failla, Giuseppe
    • Coupled systems mechanics
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    • v.5 no.2
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    • pp.157-190
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    • 2016
  • This paper deals with frequency analysis of Euler-Bernoulli beams carrying an arbitrary number of Kelvin-Voigt viscoelastic dampers, subjected to harmonic loads. Multiple external/internal dampers occurring at the same position along the beam axis, modeling external damping devices and internal damping due to damage or imperfect connections, are considered. The challenge is to handle simultaneous discontinuities of the response, in particular bending-moment/rotation discontinuities at the location of external/internal rotational dampers, shear-force/deflection discontinuities at the location of external/internal translational dampers. Following a generalized function approach, the paper will show that exact closed-form expressions of the frequency response under point/polynomial loads can readily be derived, for any number of dampers. Also, the exact dynamic stiffness matrix and load vector of the beam will be built in a closed analytical form, to be used in a standard assemblage procedure for exact frequency response analysis of frames.

Static impedance functions for monopiles supporting offshore wind turbines in nonhomogeneous soils-emphasis on soil/monopile interface characteristics

  • Abed, Younes;Bouzid, Djillali Amar;Bhattacharya, Subhamoy;Aissa, Mohammed H.
    • Earthquakes and Structures
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    • v.10 no.5
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    • pp.1143-1179
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    • 2016
  • Offshore wind turbines are considered as a fundamental part to develop substantial, alternative energy sources. In this highly flexible structures, monopiles are usually used as support foundations. Since the monopiles are large diameter (3.5 to 7 m) deep foundations, they result in extremely stiff short monopiles where the slenderness (length to diameter) may range between 5 and 10. Consequently, their elastic deformation patterns under lateral loading differ from those of small diameter monopiles usually employed for supporting structures in offshore oil and gas industry. For this reason, design recommendations (API and DNV) are not appropriate for designing foundations for offshore wind turbine structures as they have been established on the basis of full-scale load tests on long, slender and flexible piles. Furthermore, as these facilities are very sensitive to rotations and dynamic changes in the soil-pile system, the accurate prediction of monopile head displacement and rotation constitutes a design criterion of paramount importance. In this paper, the Fourier Series Aided Finite Element Method (FSAFEM) is employed for the determination of static impedance functions of monopiles for OWT subjected to horizontal force and/or to an overturning moment, where a non-homogeneous soil profile has been considered. On the basis of an extensive parametric study, and in order to address the problem of head stiffness of short monopiles, approximate analytical formulae are obtained for lateral stiffness $K_L$, rotational stiffness $K_R$ and cross coupling stiffness $K_{LR}$ for both rough and smooth interfaces. Theses expressions which depend only on the values of the monopile slenderness $L/D_p$ rather than the relative soil/monopile rigidity $E_p/E_s$ usually found in the offshore platforms designing codes (DNV code for example) have been incorporated in the expressions of the OWT natural frequency of four wind farm sites. Excellent agreement has been found between the computed and the measured natural frequencies.

Stability and Post-Buckling Analyses of Thin-Walled Space Frames Using Finite Element Method (박벽 공간뼈대구조의 안정성 및 후좌굴 유한요소해석)

  • 김문영;안성원
    • Computational Structural Engineering
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    • v.10 no.4
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    • pp.205-216
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    • 1997
  • In order to trace the lateral post-buckling behaviors of thin-wafled space frames, a geometrically nonlinear finite element formulation is presented by applying incremental equilibrium equations based on the updated Lagrangian formulation and introducing Vlasov's assumption. The improved displacement field for symmetric thin-walled cross sections is introduced based on inclusion of second order terms of finite rotations, and the potential energy corresponding to the semitangential rotations and moments is consistently derived. For finite element analysis, tangent stiffness matrices of the thinwalled space frame element with 7 degrees of freedom including the restrained warping for each node are derived by using the Hermition polynomials as shape functions. A co-rotational formulation in order to evaluate the unbalanced loads is presented by separating the rigid body rotations and pure deformations from incremental displacements and evaluating the updated direction cosines of the frame element due to rigid body rotations and incremental member forces from pure deformations. Finite element solutions for the spatial buckling and post-buckling analysis of thin-walled space frames are presented and compared with available solutions and other researcher's results.

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Lateral-Torsional Post-Buckling Analyses of Thin-Walled Space Frames with Non-symmetric Sections (비대칭단면을 갖는 박벽 공간뼈대구조의 횡-비틂 후좌굴 유한요소해석)

  • Park, Hyo Gi;Kim, Sung Bo;Kim, Moon Young;Chang, Sung Pil
    • Journal of Korean Society of Steel Construction
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    • v.11 no.2
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    • pp.153-165
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    • 1999
  • In order to trace the lateral-torsional post-bucking behaviors of thin-walled space frames with non-symmetric cross sections, a geometrically non-linear finite element formulation is presented by applying incremental equilibrium equations based on the updated Lagrangian formulation and introducing Vlasov's assumption. The improved displacement field for non-symmetric thin-walled cross sections is introduced based on inclusion of second order terms of finite rotations, and the potential energy corresponding to the semitangential rotations and moments is consistently derived. For finite element analysis, tangent stiffness matrices of thin-walled space frame element are derived by using the Hermition polynomials as shape functions. A co-rotational formulation in order to evaluate the unbalanced loads is presented by separating the rigid body rotations and pure deformations from incremental displacements and evaluating the updated direction cosines and incremental member forces.

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Out-of-plane Buckling Analysis of Doubly Symmetric Thin-walled Circular Arch (이축 대칭단면을 갖는 박벽 원형아치의 면외좌굴해석)

  • Kim, Moon Young;Min, Byoung Cheol;Kim, Sung Bo
    • Journal of Korean Society of Steel Construction
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    • v.10 no.3
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    • pp.509-523
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    • 1998
  • A consistent finite element formulation and analytic solutions are presented for stability of thin-walled circular arch. The total potential energy is derived by applying the principle of linearized virtual work and including second order terms of finite semitangential rotations. As a result, the energy functional corresponding to the semitangential moment is newly derived. Analytic solutions for the out-of-plane buckling of symmetric thin-walled curved beam subjected to pure bending or uniform compression with simply supported boundary conditions are obtained. For finite element analysis, the cubic Hermitian polynomials are utilized as shape functions and $16{\times}16$ stiffness matrix for curved beam elements and $14{\times}14$ stiffness matrix for straight beam elements are evaluated, respectively. In order to illustrate the accuracy of this study, analytical and numerical results for lateral buckling problems of circular arch are presented and compared with available analytical solutions.

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