• Structural Engineering and Mechanics
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• v.67 no.1
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• pp.53-67
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• 2018

The changes of parameters of pressure and velocity of propagation of elastic pressure and shear waves in uniformly deformed solid compressible media are studied within the nonclassically linearized approach (NLA) of nonlinear elastodynamics to create a new theoretical basis of the geomechanical interpretation of various groups of geophysical observational and experimental data. The cases of small and large deformations are considered while their describing by various elastic potentials, i.e., problems considering the physical and geometric nonlinearity. Convenient analytical formulae are obtained to calculate the indicated parameters in the deformed isotropic media within the nonclassical linear and nonlinear solution in the NLA. Specific numerical experiments are conducted in case of overall compression of various materials. It is shown that the method (generally accepted in the studies of mechanics of standard constructional materials) of additional linearization (relative to the pressure parameter) in the basic correlations of the NLA introduces substantial quantitative and qualitative errors into the results at significant preliminary deformations. The influences of the physical and geometric nonlinearity on the studied characteristics of the medium are large in various materials and differ qualitatively. The contribution of nonlinear components to the values of the considered parameters prevails over linear components at large deformations. When certain critical values of compression deformations in the medium are achieved, elastic waves with actual velocity cannot propagate in it. The values of the critical deformations for pressure and shear waves differ within different elastic potentials and variants of the theory of initial deformations.

• Journal of Korean Society of Steel Construction
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• v.12 no.4 s.47
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• pp.375-385
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• 2000

The required connection ductility has been evaluated, considering geometric, material and connection nonlinearity, for 6-story unbraced and 20-story braced steel structures subjected to ultimate lateral load. For material nonlinearity, section moment-curvature relationship and member stiffness matrix have been derived utilizing fiber model and linear flexibility distribution model. In 6-story structure with semi-rigid connections for rigid connection, the required connection ductility is less than that for rigid connection. In 20-story structure, the required connection ductility for semi-rigid connection is almost the same as that for shear connection and the required ductility for rigid connection is larger than that for semi-rigid or shear connection.

• Structural Engineering and Mechanics
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• v.36 no.1
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• pp.57-78
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• 2010

A novel flexibility-based 1D element that captures the material nonlinearity and second order P-$\Delta$ effects within a reinforced concrete frame member is developed. The formulation is developed for 2D planar frames in the modified fiber element framework but can readily be extended to 3D cases. The nonlinear behavior of concrete including cracking and crushing is taken into account through a modified hypo-elastic model. A parabolic and a constant shear stress distribution are used at section level to couple the normal and tangential tractions at material level. The lack of objectivity due to softening of concrete is addressed and objectivity of the response at the material level is attained by using a technique derived from the crack band approach. Finally the efficiency and accuracy of the formulation is compared with experimental results and is demonstrated by some numerical examples.

• Steel and Composite Structures
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• v.7 no.1
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• pp.35-52
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• 2007

The cold formed light-gauge profiled steel sheeting can offer considerable shear resistance acting in the steel building frame. This paper conducted the full-scale test on the shear behavior of stressed skin diaphragm using profiled sheeting connected by the self-tapping screws. A three-dimensional finite element model that simulates the stressed skin diaphragm was developed. The sheet was modeled using thin element model while the supporting members were simulated using beam elements. Fasteners were represented in the numerical model as equivalent springs. A joint test program was conducted to characterize the properties of these springs and results were reported in this study. Finite element model of the full-scale test was analyzed by use of the ANSYS package, considering nonlinearity caused by the large deflection and slip of fasteners. The experimental data was compared with the results acquired by the EUR formulas and finite element analysis.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.4 s.97
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• pp.395-403
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• 2005

The dynamic characteristics of delaminated smart composite laminates are studied using animproved layerwise laminate theory. The theory is capable of capturing interlaminar shear stresses that are critical to delamination. The presence of discrete delamination is modeled through the use of Heaviside unit step functions. Stress free boundary conditions are enforced at all free surfaces. Continuity in displacement field and transverse shear stresses are enforced at each ply level. In modeling piezoelectric composite plates, a coupled piezoelectric-mechanical formulation is used in the development of the constitutive equations. Numerical analysis is conducted to investigate the effect of nonlinearity in the transient vibration of bimodular behavior caused by the contact impact of delaminated interfaces. Composite plates with delamination, subject to external loads and voltage history from surface bonded sensors, are investigated and the results are compared with corresponding experimental results and plates without delamination.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.217-222
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• 2015

In this paper, a study was conducted for the optimization through shear web of shape the Edison program in wind power blade. We measured the displacement and stress distribution through two optimization methods to select the model with the smallest displacement and stress values. Before running the analysis, We try to find the inflection point through the shear web of the model and then analyze by introducing the geometric nonlinearity. The first optimization variables are introduced by the pitch angle and three web shapes. Third model such a honeycomb structure is good way to get an advantage for bending test. According to a method of previous optimization, third model is chosen and then the thickness of the web and blade as a variable is introduced, it is extracted as a result of displacement and the maximum stress per mass.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.97-103
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• 2008

Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.469-475
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• 2004

The transient analysis of delaminated smart composite laminates is studied using an improved layerwise laminate theory. The theory is capable of capturing interlaminar shear stresses that are critical to delamination. The presence of discrete delamination is modeled through the use of Heaviside unit step functions. Stress free boundary conditions are enforced at all fee surfaces. Continuity in displacement field and transverse shear stresses are enforced at each ply level. In modeling piezoelectric composite plates, a coupled piezoelectric-mechanical formulation is used in the development of the constitutive equations. Numerical analysis is conducted to investigate the effect of nonlinearity in the transient vibration of bimodular behavior caused by the contact impact of delaminated interfaces. Composite plates with delamination, subject to external loads and voltage history from surface bonded sensors, are investigated and the results are compared with corresponding experimental results and plates without delamination.

• Structural Engineering and Mechanics
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• v.66 no.5
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• pp.557-568
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• 2018

An investigation is made in the present work on the post-buckling and geometrically nonlinear behaviors of moderately thick perfect and imperfect rectangular plates made-up of functionally graded materials. Spectral collocation approach based on Legendre basis functions is developed to analyze the functionally graded plates while they are subjected to end-shortening strain. The material properties in this study are varied through the thickness according to the simple power law distribution. The fundamental equations for moderately thick rectangular plates are derived using first order shear deformation plate theory and taking into account both geometric nonlinearity and initial geometric imperfections. In the current study, the domain of interest is discretized with Legendre-Gauss-Lobatto nodes. The equilibrium equations will be obtained by discretizing the Von-Karman's equilibrium equations and also boundary conditions with finite Legendre basis functions that are substituted into the displacement fields. Due to effect of geometric nonlinearity, the final set of equilibrium equations is nonlinear and therefore the quadratic extrapolation technique is used to solve them. Since the number of equations in this approach will always be more than the number of unknown coefficients, the least squares technique will be used. Finally, the effects of boundary conditions, initial geometric imperfection and material properties are investigated and discussed to demonstrate the validity and capability of proposed method.

• Journal of Korean Association for Spatial Structures
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• v.18 no.4
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• pp.31-39
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• 2018

This paper analyse the mechanical characteristics of geometrical and material nonlinearity behavior of cylindrical shell roofs subjected to a concentrated load. The shell elements were modeled using 'NISA2016' software as 3D general shell element and 3D composite shell element. The 3D shell element includes deformation due to bending, membrane, membrane-bending coupling and shear perpendicular to the grain effects is suited for modeling moderately thick or thin general shells and laminated composite shells. And The 3D composite shell element consists of a number of layers of perfectly bonded anisotropic and orthotropic materials. The purpose of this research is to analysis the load-deflection curves considering the combined geometric and material nonlinearity of cylindrical shells. In a shallowed cylindrical shell, snap-through curve can be found.