• Magazine of the Korea Concrete Institute
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• v.8 no.2
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• pp.119-127
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• 1996

Objection of this study is to present the three-dimensional material nonlinear analysis of reinforced concrete. A concrete is idealized with three-dimensional 16-node solid element including triaxial nonlinear stress-strain behavior, cracking, crushing and strain softening: a steel with three-dimensional 3 node truss element including elastic-plastic behavior with strain hardening. The cracked shear retention factor is introduced to estimate the effective shear modulus con sidering aggregate interlock after c:racking and a modified newton method is used to obtain a nu merical solution. Numerical results in a gauss point is displayed graphically. Numerical examples of Krahl's reinforced concrete beam and Hedgreds shell are selected to compare with the experimental and numerical results.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.100-106
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• 2006

NiTi alloy known as its shape memory effect also has superelastic characteristic, which makes it possible to be elastic under large deformation. Since the tensile strength of the alloy is very high and density is low compared to carbon steel, it can be applied to lightweight structural design. In order to design structures with shape memory alloy, finite element analysis is used and a constitutive algorithm based on Aurrichio's model is added to LS-DYNA as a user subroutine. Explicit time integration and shell element formulation are used to simulate thin-walled structures. The algorithm uses Drucker-Prager type loading condition to calculate martensite volume fraction during the transformation. The implemented algorithm is verified in uni-axial loading condition and martensite phase transformation can be detected well with the algorithm. In this study, as a energy absorbing structure, thin-walled tube is modeled with finite elements and the deformation behavior is studied. Simulation results has shown that the martensite transformation was generated in loading condition. After plastic deformation reached, the load decreases linearly without reverse martensite transformation.

• Structural Engineering and Mechanics
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• v.41 no.6
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• pp.805-822
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• 2012

Offshore pipelines have to withstand combined actions of tension and bending during deepwater installation, which can possibly lead to elliptical buckle and even catastrophic failure of whole pipeline. A 2D theoretical model initially proposed by Kyriakides and his co-workers which carried out buckling response analysis of elastic-plastic tubes under various load combinations, is further applied to investigate buckling behavior of offshore pipelines under combined tension and bending. In association with practical pipe-laying circumstances, two different types of loadings, i.e., bent over a rigid surface in the presence of tension, and bent freely in the presence of tension, are taken into account in present study. In order to verify the accuracy of the theoretical model, numerical simulations are implemented using a 3D finite element model within the framework of ABAQUS. Excellent agreement between the results validates the effectiveness of this theoretical method. Then, this theoretical model is used to study the effects of some important factors such as load type, loading path, geometric parameters and material properties etc. on buckling behavior of the pipes. Based upon parametric studies, a few significant conclusions are drawn, which offer a theoretical reference for design and installation monitoring of deepwater pipelines.

• Geomechanics and Engineering
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• v.29 no.1
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• pp.41-51
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• 2022

Tunneling in rocks having the time-dependent behavior, causes some difficulties like tunnel convergence and, as a result, pressure on concrete lining; and so instability on this structure. In this paper the time-dependent behaviour of squeezing phenomenon in a large cross section tunnel was investigated as a case study: Alborz tunnel. Then, time-dependent behaviour of Alborz tunnel was evaluated using FLAC2D based on the finite difference numerical method. A Burger-creep viscoelastic model was used in numerical analysis. Using numerical analysis, the long-time effect of squeezing on lining stability was simulated.This study is done for primary lining (for 2 years) and permanent lining (for 100 years), under squeezing situations. The response of lining is discussed base on Thrust Force-Bending Moment and Thrust Force-Shear Force diagrams analysing. The results determined the importance of consideration of time-dependent behaviour of tunnel that structural forces in concrete lining will grow in consider with time pass and after 70 years can cause instability in creepy rock masses section of tunnel. To show the importance of time-dependent behavior consideration of rocks, elastic and Mohr-Coulomb models are evaluated at the end.

• Magazine of the Korea Concrete Institute
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• v.2 no.2
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• pp.81-92
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• 1990

Concrete, a mixed material, has heterogeniety, anisotrophy and nonlinearity. Therefore, in its 'racture analysis, it is more reasonable to evaluate its fracture toughness by applying the concept of 'racture mechanics rather than the strength concept. Up to the present the concepts of fracture mechanics which were applied to concrete have been divided into two main classes. The one is the concept of linear elastic fracture mechanics and the other is the concept of elastic-plastic fracture mechanics. But it has been pointed out that there are many problems and irrationalities in applying the concept of linear elastic fracture mechanics to concrete. In this study, the J -integral method and the COD method mainly used in the analysis of nonlinear fracture mechanics, were introduced and the three point bending test was carried out for investigating the effects of the variation of the maximum aggregate size and notch depth on the fracture behavior and the crack growth of concrete, and the relationships of fracture energy and crack opening displacement. According to the results of this study the more the maximum aggregate size and the notch depth increased, the more the nonlinearity of load-deflection behavior was remarkable. The increase of the coarse aggregate size created the more ductility of concrete. Thus concrete showed the more stable fracture. As for the path of the crack growth, the more the coarse aggregate size increased, the more it was irregulary deviated from the straight line but it was not almost affected by the variation of the notch depth. Also, the fracture energy increased according as the coarse aggregate size increased and the notch depth decreased.

• Tunnel and Underground Space
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• v.32 no.5
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• pp.312-326
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• 2022

The generalized Hoek-Brown (GHB) criterion, which is recognized as one of the standard failure conditions for rock mass, is specialized for rock engineering applications and covers a wide range of rock mass conditions. Accordingly, many research efforts have been devoted to the incorporation of this criterion into the stability analysis of rock structures. In this study, the slip-line analysis method, which is a kind of elastoplastic analysis method, is combined with the GHB failure criterion to derive analytical equations that can easily calculate the plastic radius and stress distribution in the vicinity of the circular tunnel. In the process of derivation of related formulas, it is assumed that the behavior of rock mass after failure is perfectly plastic and the in-situ stress condition is hydrostatic. In the formulation, it is revealed that the plastic radius can be calculated analytically using the two respective tangential friction angles corresponding to the stress conditions at tunnel wall and elastic-plastic boundary. It is also shown that the plastic radius and stress distribution calculated using the derived analytical equations coincide with the results of Lee & Pietruszczak's numerical method published in 2008. In the latter part of this paper, the influence of the quality of the rock mass on the size of the plastic zone, the stress distribution, and the change of the tangential friction angle was investigated using the derived analytical equations.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.141-152
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• 2002

Although a number of constitutive models have been proposed to define the behavior of geotechnical materials including elastic, plastic, and dynamic response, flew numerical models have been developed for the cyclic shear behavior of rock joints or interfaces. Such realistic constitutive models play an important role in analyzing and predicting the response of joints under dynamic loads. The purpose of this research is to verify the constitutive model modified for rough granite joints based on Disturbed State Concept(DSC) model, which has been successfully verified with respect to other materials such as dry sand-steel interface and wet sand-concrete interface. Furthermore, DSC model is compared and verified with respect to cyclic shear tests and numerical analysis results based on Plesha model. Based on the results of this research, it can be stated that DSC model is capable of characterizing the cyclic shear behavior of rough granite joints under dynamic loads.

• Earthquakes and Structures
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• v.18 no.5
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• pp.527-542
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• 2020

In traditional eccentrically braced steel frames, damages and plastic deformations are limited to the links and the main structure members are required tremendous sizes to ensure elasticity with no damage based on the force-based seismic design method, this limits the practical application of the structure. The high strength steel frames with eccentric braces refer to Q345 (the nominal yield strength is 345 MPa) steel used for links, and Q460 steel utilized for columns and beams in the eccentrically brace steel frames, the application of high strength steels not only brings out better economy and higher strength, but also wider application prospects in seismic fortification zone. Here, the structures with four type eccentric braces are chosen, including K-type, Y-type, D-type and V-type. These four types EBFs have various performances, such as stiffness, bearing capacity, ductility and failure mode. To evaluate the seismic behavior of the high strength steel frames with variable eccentric braces within the similar performance objectives, four types EBFs with 4-storey, 8-storey, 12-storey and 16-storey were designed by performance-based seismic design method. The nonlinear static behavior by pushover analysis and dynamic performance by time history analysis in the SAP2000 software was applied. A total of 11 ground motion records are adopted in the time history analysis. Ground motions representing three seismic hazards: first, elastic behavior in low earthquake hazard level for immediate occupancy, second, inelastic behavior of links in moderate earthquake hazard level for rapid repair, and third, inelastic behavior of the whole structure in very high earthquake hazard level for collapse prevention. The analyses results indicated that all structures have similar failure mode and seismic performance.

• Composites Research
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• v.36 no.5
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• pp.369-376
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• 2023

This study focuses on investigating the influence of epoxy polymer crosslinking density, a crucial aspect in composite material matrices, on the yield surface using molecular dynamics simulations. Our approach involved generating epoxy models with diverse crosslinking densities and subjecting them to both uniaxial and multiaxial deformation simulations, accounting for the elasto-plastic deformation behaviors. Through this, we obtained key mechanical parameters including elastic modulus, yield point, and strain hardening coefficient, all correlated with crosslinking conversion ratios. A particularly noteworthy finding is the rapid expansion of the yield surface in the biaxial compression region with increasing crosslinking ratios, compared to the uniaxial tensile region. This unique behavior led to observable yield surface variations, indicating a significant pressure-dependent relationship of the yield surface considering plastic strain and crosslinking conversion ratio. These results contribute to a deeper understanding of the complex interplay between crosslinking density and plastic mechanical response, especially in the aspect of multiaxial deformation behaviors.

• Proceedings of KOSOMES biannual meeting
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• 2005.05a
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• pp.147-154
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• 2005

The ship plating is generally subjected to combined in-plane load and lateral pressure loads. In-plane loads include axial load and edge shear, which are mainly induced by overall hull girder bending and torsion of the vessel. Lateral pressure is due to water pressure and cargo. These load components are not always applied simultaneously, but more than one can normally exist and interact Hence, for more rational and safe design of ship structures, it is of crucial importance to better understand the interaction relationship of the buckling and ultimate strength for ship plating under combined loads. Actual ship plates are subjected to relatively small water pressure except for the impact load due to slamming and panting etc. The present paper describes an accurate and fast procedure for analyzing the elastic-plastic large deflection behavior up to the ultimate limit state of ship plates under combined loads. In this paper, the ultimate strength characteristics of plates under axial compressive loads and lateral pressure loads are investigated through ANSYS elastic-plastic large deflection finite element analysis with varying lateral pressure load level.