• Journal of Korean Association for Spatial Structures
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• v.1 no.1 s.1
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• pp.109-115
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• 2001

Composite materials also known as fiber reinforced plastics have been developed and used in many engineering applications due to their outstanding mechanical properties. Laminated plates as structural components that are made of in composite material are widely used. Therefore, nonlinear response of laminated composite plates modeled with finite elements and excited by stochastic loading is studied. The classical laminated plate theory is used to account for the variation of strains through the thickness for modeling laminated thin plates. Approximate nonlinear random vibration analysis is performed using the method of equivalent linearization to account for material non-linearity.

• Structural Engineering and Mechanics
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• v.41 no.4
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• pp.441-458
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• 2012

The shear strength is an important factor in the design of prestressed concrete beams. Therefore, researchers have utilized various methods to determine the shear strength of these elements for the design purposes. To evaluate some of the proposed theoretical methods, numerous models of post-tensioned beams with or without vertical prestressing are selected and analyzed using the finite element method and assuming nonlinear behavior for the materials. In this regard the validity of modeling is evaluated based on some tests results. In the second part of the study two beam specimens are built and tested and their load-deformation curve and cracking pattern are studied. The analytical results consist of compressive strut slope and mid span load deflection are compared with some experimental results, and the results of some codes' formulas. Finally comparing the results of nonlinear analysis with the experimental values, a new formula is proposed for determining strut slopes in prestressed concrete beams.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.04a
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• pp.85-92
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• 1998

Most of tall apartment buildings constructed in our county are wall-type R/C structures composed of hear walls and slabs. It is necessary to evaluate of hysteretic properties of shear walls in wall-type R/C structures which resist lateral loads as well as axial loads. In this study, first to evaluate the wall's hysteretic behavior nonlinear analyses with IDARC 4.0 are performed for eight specimens subjected to horizontal load reversals. As a result of nonlinear analyses of specimens we can obtain three parameters which determined the hysteretic parameters such as stiffness degrading, strength deterioration and inching behavior respectively. With this three parameters, strength and deformation capacity of 5, 10, 20-story shear wall of apartment building is estimated from the results of push-over analysis.

• Steel and Composite Structures
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• v.7 no.5
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• pp.355-376
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• 2007

The purpose of this study is to predict and investigate the time-dependent creep behavior of composite materials. For this, firstly the evaluation method for the modulus of elasticity of whole fiber and matrix is presented from the limited information on fiber volume fraction using the singular value decomposition method. Then, the effects of fiber volume fraction on modulus of elasticity of GFRP are verified. Also, as a creep model, the nonlinear curve fitting method based on the Marquardt algorithm is proposed. Using the existing Findley's power creep model and the proposed creep model, the effect of fiber volume fraction on the nonlinear creep behavior of composite materials is verified. Then, for the time-dependent analysis of a composite material subjected to uniaxial tension and simple shear loadings, a user-provided subroutine UMAT is developed to run within ABAQUS. Finally, the creep behavior of center loaded beam structure is investigated using the Hermitian beam elements with shear deformation effect and with time-dependent elastic and shear moduli.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1990.04a
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• pp.59-64
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• 1990

The cable structures undergo large deformation because of its highly flexibility. Therefore, we must take account of its geometric nonlinearity before analysis and find the equiribrated shape of cable structures. To solve these problems, a numerical procedures included nonlinear near theory which is applicable to general cable net, flexible transmission lines and suspended cable roofs, are presented in this paper. Now, this procedures are devided two parts : the one is to obtain the equibrated shape and stress of the cable structures applied uniform load by flexibility iteration method, the other is to analysis the equibrated structures subjected to nodal external forces by nonlinear finite element mothed. Its accuracy and efficiency are found to be comparable to some of other method and, in some aspect, it is mere applicable to cable structures.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1990.04a
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• pp.18-23
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• 1990

The paper is concerned with the elasto-plastic and geometrically nonlinear analysis of shell structures using an improved degenerated shell element. In the formulation of the improved degenerated shell element, an enhanced interpolation of transverse shear strains in the natural coordinate system is used to overcome the shear locking problems; the reduced integration technique in in-plane strains is applied to avoid membrane locking behavior; selective addition the nonconforming displacement modes improve the element performances. This element is free of serious locking problems and undesirable compatible or commutable spurious kinematic deformation modes and passes the patch tests. An incremental total Lagrangian formulation is presented which allows the calculation of arbitrarily large displacements and rotations. The resulting nonlinear equations are solved by the Newton-Raphson solution scheme. The versatility and accuracy of this improved degenerated shell element are demonstrated by solving several numerical examples.

• Structural Engineering and Mechanics
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• v.51 no.4
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• pp.601-625
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• 2014

Based on continuum mechanics and the principle of virtual displacements, incremental total Lagrangian formulation (T.L.) and incremental updated Lagrangian formulation (U.L.) were presented. Both T.L. and U.L. considered the large displacement stiffness matrix, which was modified to be symmetrical matrix. According to the incremental updated Lagrangian formulation, small strain, large displacement, finite rotation of three dimensional Timoshenko fiber beam element tangent stiffness matrix was developed. Considering large displacement and finite rotation, a new type of tangent stiffness matrix of the beam element was developed. According to the basic assumption of plane section, the displacement field of an arbitrary fiber was presented in terms of nodal displacement of centroid of cross-area. In addition, shear deformation effect was taken account. Furthermore, a nonlinear finite element method program has been developed and several examples were tested to demonstrate the accuracy and generality of the three dimensional beam element.

• Structural Engineering and Mechanics
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• v.47 no.1
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• pp.27-44
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• 2013

A finite element computational procedure for the accurate analysis of quasistatic thermorheological complex structures response is developed. The geometrical nonlinearity, arising from large displacements and rotations (but small strains), is accounted for by the total Lagrangian description of motion. The Schapery's nonlinear single-integral viscoelastic constitutive model is modified for a time-stress-temperature-dependent behavior. The nonlinear thermo-viscoelastic constitutive equations are incrementalized leading to a recursive relationship and thereby the resulting finite element equations necessitate data storage from the previous time step only, and not the entire deformation history. The Newton-Raphson iterative scheme is employed to obtain a converged solution for the non-linear finite element equations. The developed numerical model is verified with the previously published works and a good agreement with them is found. The applicability of the developed model is demonstrated by analyzing two examples with different thermal/mechanical loading histories.

• Wind and Structures
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• v.27 no.6
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• pp.369-380
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• 2018

In this research work, nonlinear thermal buckling behavior of functionally graded (FG) plates is explored based a new higher-order shear deformation theory (HSDT). The present model has just four unknowns, by using a new supposition of the displacement field which enforces undetermined integral variables. A shear correction factor is, thus, not necessary. A power law distribution is employed to express the disparity of volume fraction of material distributions. Three kinds of thermal loading, namely, uniform, linear, and nonlinear and temperature rises over z-axis direction are examined. The non-linear governing equations are resolved for plates subjected to simply supported boundary conditions at the edges. The results are approved with those existing in the literature. Impacts of various parameters such as aspect and thickness ratios, gradient index, type of thermal load rising, on the non-dimensional thermal buckling load are all examined.

• Steel and Composite Structures
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• v.33 no.2
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• pp.245-259
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• 2019

The present study aims to investigate the ultimate strength and geometric nonlinear behavior of composite plates containing initial imperfection subjected to combined end-shortening strain and lateral pressure loading by using a semi-analytical method. In this study, the first order shear deformation plate theory is considered with the assumption of large deflections. Regarding in-plane boundary conditions, two adjacent edges of the laminates are completely held while the two others can move straightly. The formulations are based on the concept of the principle of minimum potential energy and Newton-Raphson technique is employed to solve the nonlinear set of algebraic equations. In addition, Hashin failure criteria are selected to predict the failures. Further, two distinct models are assumed to reduce the mechanical properties of the failure location, complete ply degradation model, and ply region degradation model. Degrading the material properties is assumed to be instantaneous. Finally, laminates having a wide range of thicknesses and initial geometric imperfections with different intensities of pressure load are analyzed and discuss how the ultimate strength of the plates changes.