• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.5
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• pp.74-84
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• 1996

Dynamic loading of structures often causes excursions of stresses well into the inelastic range and the influence of geometric changes on the dynamic response is also significant in many cases. Therefore, both material and geometric nonlinearity effects should be considered in case that a dynamic load acts on the structure. For developing a program to analyze the dynamic response of an axisymmetric shell in this study, the material nonlinearity effect on the dynamic response was formulated by the elasto-viscoplastic model highly corresponding to the real behavior of the material. Also, the geometrically nonlinear behavior is taken into account using a total Lagrangian coordinate system, and the equilibrium equation of motion was numerically solved by a central difference scheme. A complete finite element program has been developed and the results obtained by it are compared with those in the references 1 and 2. The results are in good agreement with each other. As a case study of its application, the developed program was applied to a dynamic response analysis of a nuclear reinforced concrete containment structure. The results obtained from the' numerical examples are summarized as follows : 1. The dynamic magnification factor of the displacement and the stress were unrelated with the concrete strength. 2. As shown by the results that the displacement dynamic magnification factor were form 1.7 to 2.3 and the stress dynamic magnification factor from 1.8 to 2.5, the dynamic magnification factor of stress were larger than that of displacement. 3. The dynamic magnification factor of stress on the exterior surface was larger than that on the interior surface of the structure.

• Structural Engineering and Mechanics
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• v.5 no.5
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• pp.507-521
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• 1997

The ultimate behavior of a reinforced concrete hyperbolic paraboloid saddle shell under uniformly distributed vertical load is investigated using an inelastic, large displacement finite-element program originally developed at North Carolina State University. Unlike with the author's previous study which shows that the saddle shell possesses a tremendous capacity to redistribute the stresses, introducing tension stiffening in the model the cracks developed are no longer through cracks and formed as primarily bending cracks. Even though with small tension stiffening effect, the behavior of the shell is changed markedly from the one without tension stiffening effect. The load-deflection curves are straight and the slope of the curves is quite steep and remains unchanged with varying the tension stiffening parameters. The failure of the shell took place quite suddenly in a cantilever mode initiated by a formation of yield lines in a direction parallel to the support-to-support diagonal. The higher the tension stiffening parameters the higher is the ultimate load. The present study shows that the ultimate behavior of the shell primarily depends on the concrete tensile characteristics, such as tensile strength (before cracking) and the effective tension stiffening (after cracking). As the concrete characteristics would vary over the life of the shell, a degree of uncertainty is involved in deciding a specified ultimate strength of the saddle shell studied. By the present study, however, the overload factors based on ACI 318-95 are larger than unity for all the cases studied except that the tension stiffening parameter is weak by 3 with and without the large displacement effect, which shows that the Lin-Scordelis saddle shell studied here is at least safe.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.1
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• pp.399-405
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• 2012

This paper investigates the characteristics of buckling loads for steel arches with new type cross section which is consisted of T-section and pipe-section. A general purpose finite-element program ABAQUS was used to evaluate the inelastic buckling strengths of the arches which included the influence of the geometric and material nonlinearity. According to the comparisons between earlier studies and results from finite-element analyses, new design equations should be developed for the new arches. New buckling factors were developed to consider influence of rise-to-span ratio and boundary conditions. It is found that the presented factors are sufficiently accurate to predict the inplane buckling loads of new type section steel arches subjected to uniformly distributed loading. The proposed equations can be used to investigate new type steel arches subjected to unsymmetrical loading and composited arches.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.3
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• pp.275-280
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• 2011

In the present study, a unified viscoplastic-damage model has been applied in order to describe the mechanical characteristics of fresh water ice such as nonlinear material behavior and volume fraction. The strain softening phenomenon of fresh water ice under quasi-static compressive loading has been evaluated based on unified viscoplastic model. The material degradation such as growth of slip/fraction has quite close relation with material inside damage. The volume fraction phenomenon of fresh water ice has been identified based on volume fraction (nucleation and growth of damage) model. The viscoplastic-damage model has been transformed to the fully implicit formulation and the discretized formulation has been implemented to ABAQUS user defined subroutine (User MATerial: UMAT) for the benefit of application of commercial finite element program. The proposed computational analysis method has been compared to uni-axial compression test of fresh water ice in order to validate the compatibilities, clarities and usefulness.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.4
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• pp.345-351
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• 2003

Due to increasing legal and market demands for safety in the automotive design process, the design of integrated seat is important more and mote because it should satisfy the conflict between stronger and lower weight for safety and environmental demands. In this study for crash simulations, the numerical simulations have been carried out using the explicit finite element program LS-Dyna according to the FMVSS 210 standard for safety test of seat. Since crash simulations are very time-consuming and a series of simulations that does not lead to a better result is very costly, the optimization method must be both efficient and reliable. As a result of that, statistical approaches such as design of experiments and response surface model have been successfully implemented to reduce time-consuming LS-Dyna simulations and optimize the safety and environmental demands together with nonlinear optimization algorithm. Design of experiments is used lot exploring the design space of maximum displacement and total weight and for building response surface models in order to minimize the maximum displacement and total weight of integrated seat.

• Journal of the Korea Concrete Institute
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• v.28 no.4
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• pp.473-480
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• 2016

The purpose of this study is to provide analytical method to reasonably evaluate the complicated failure behaviors of shear friction of reinforced concrete shear wall specimens using grade 500 MPa high-strength bars. A total of 16 test specimens with a variety of variables such as aspect ratio, friction coefficient of interface in construction joint, reinforcement details, reinforcement ratio in each direction, material properties were selected and the analysis was performed by using a non-linear finite element analysis program (RCAHEST) applying the modified shear friction constitutive equation in interface based on the concrete design code (KCI, 2012) and CEB-FIP Model code 2010. The mean and coefficient of variation for maximum load from the experiment and analysis results was predicted 1.04 and 17% respectively and properly evaluated failure mode and overall behavior characteristic until failure occur. Based on the results, the analysis program that was applied modified shear friction constitutive equation is judged as having a relatively high reliability for the analysis results.

• Structural Engineering and Mechanics
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• v.42 no.2
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• pp.175-189
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• 2012

This paper presents an algorithm for structural reliability with the response surface method. For this aim, an approach with three stages is proposed named as improved response surface method. In the algorithm, firstly, a quadratic approximate function is formed and design point is determined with First Order Reliability Method. Secondly, a point close to the exact limit state function is searched using the design point. Lastly, vector projected method is used to generate the sample points and Second Order Reliability Method is performed to obtain reliability index and probability of failure. Five numerical examples are selected to illustrate the proposed algorithm. The limit state functions of three examples (cantilever beam, highly nonlinear limit state function and dynamic response of an oscillator) are defined explicitly and the others (frame and truss structures) are defined implicitly. ANSYS finite element program is utilized to obtain the response of the structures which are needed in the reliability analysis of implicit limit state functions. The results (reliability index, probability of failure and limit state function evaluations) obtained from the improved response surface are compared with those of Monte Carlo Simulation, First Order Reliability Method, Second Order Reliability Method and Classical Response Surface Method. According to the results, proposed algorithm gives better results for both reliability index and limit state function evaluations.

• Earthquakes and Structures
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• v.17 no.1
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• pp.75-89
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• 2019

The paper presents experimental and numerical studies carried out on low-rise RC frames, typically found in developing countries. Shake table tests were conducted on 1:3 reduced scaled two-story RC frames that included a code conforming SMRF model and another non-compliant model. The later was similar to the code conforming model, except, it was prepared in concrete having strength 33% lower than the design specified, which is commonly found in the region. The models were tested on shake table, through multiple excitations, using acceleration time history of 1994 Northridge earthquake, which was linearly scaled for multi-levels excitations in order to study the structures' damage mechanism and measure the structural response. A representative numerical model was prepared in finite element based program SeismoStruct, simulating the observed local damage mechanisms (bar-slip and joint shear hinging), for seismic analysis of RC frames having weaker beam-column joints. A suite of spectrum compatible acceleration records was obtained from PEER for incremental dynamic analysis of considered RC frames. The seismic performance of considered RC frames was quantified in terms of seismic response parameters (seismic response modification, overstrength and displacement amplification factors), for critical comparison.

• Journal of Korean Society of Steel Construction
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• v.24 no.4
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• pp.469-478
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• 2012

In this study, structural behavior of high tension bolted connections was analyzed in order to investigate effective utilizations. Also, the simplified numerical analysis method showing bolt behavior was proposed using the connector element in the ABAQUS, a nonlinear finite element program and verified by numerical analyses on the basis of the experiment of previous study. In an effort to analyze strength properties of plate girder which high tension bolts are applied to, the effects of each design parameter were compared and analyzed after moment-displacement relations were investigated according to design parameters (upper flange, lower flange, upper and lower flange, web) by action force standards.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.7
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• pp.44-50
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• 2002

Low-velocity impact on composite sandwich panel has been investigated. Contact force is computed from a proposed modified Hertzian contact law. The Hertzian contact law is constructed by adjusting numerical value of the exponent and reducing the through-the- thickness elastic constant of honeycomb core. The equivalent transverse elastic constant is calculated from the rule of mixture. Nonlinear equation to calculate the contact force is solved by the Newton-Raphson method and time integration is done by the Newmark-beta method. A finite element program for the low-velocity impact analysis is coded by implementing these techniques and an 18-node assumed strain solid element. Behaviors of composite sandwich panels subjected to low-velocity impact are analyzed for various cases with different geometry and lay-ups. It has been found that the present code with the proposed contact law can predict measured contact forces and contact times for most cases within reasonable error bounds.