• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3C
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• pp.105-113
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• 2009

Pressuremeter test estimates deformational properties of soil from the relationship between applied pressure and the displacement of cavity wall, and the results reflect the in-situ stress condition and the structure of soil particles. This study suggests the overall process of test and analysis for the evaluation of nonlinear degradation characteristics of shear moduli, based on the reloading curve of pressuremeter test. The method estimates the maximum shear modulus, taking into account the difference between the stress states around the probe in reloading and that of the in-situ state, and then combines the degradation characteristics of shear moduli taken from reloading curve. This procedure derives the shear moduli in overall strain range. Pressuremeter tests were carried out in various ground conditions using large calibration chamber, together with various reference tests. Shear moduli taken from pressuremeter tests were compared with bender element test and resonant column test results.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.4
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• pp.65-73
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• 2002

It has been recognized that the damage control must become a more explicit design consideration. In an effort to develop design methods based on performance it is clear that the evaluation of the nonlinear response is required. The methods available to the design engineer today are nonlinear time history analyses, monotonic static nonlinear analyses, or equivalent static analyses with simulated nonlinear influences. Some building codes propose the capacity spectrum method based on the nonlinear static analysis(pushover analysis) to determine the earthquake-induced demand given by the structure pushover curve. These procedures are conceptually simple but iterative and time consuming with some errors. This paper presents a nonlinear direct spectrum method(NDSM) to evaluate seismic performance of structures, without iterative computations, given by the structural initial elastic period and yield strength from the pushover analysis, especially for MDF(multi degree of freedom) systems. The purpose of this paper is to investigate the accuracy and confidence of this method from a point of view of various earthquakes and unloading stiffness degradation parameters. The conclusions of this study are as follows; 1) NDSM is considered as practical method because the peak deformations of nonlinear system of MDF by NDSM are almost equal to the results of nonlinear time history analysis(NTHA) for various ground motions. 2) When the results of NDSM are compared with those of NTHA. mean of errors is the smallest in case of post-yielding stiffness factor 0.1, static force by MAD(modal adaptive distribution) and unloading stiffness degradation factor 0.2~0.3.

• Journal of the Korean Geotechnical Society
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• v.38 no.3
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• pp.5-16
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• 2022

Ground in extremely cold and hot regions can sink by various environmental factors. Ground settlement can generate the negative skin friction to pile shaft, increase the base load of pile, and cut the stability of the pile. This study proposed a member responding ground deformation which can be inserted inside the pile. The member slightly compresses according to the ground settlement to reduce the negative skin friction. As the member materials, this study considered spring and spring-dashpot. To assess the ability of the member, the present research performed model tests for piles with or without the member within settled ground. In the model tests, the base load, total shaft resistance, and horizontal earth pressure were monitored and analyzed. Experimental results show that the pile with spring member can reduce the negative skin friction under small settlement conditions whereas it acts similar to the pile without the member under large settlement conditions as the spring was no longer compressed. However, the pile with the spring-dashpot member can reduce the negative skin friction continuously upon the ground settlement as the dashpot delays the load transfer to the spring and locates friction force on the unloading path.

• Polymer(Korea)
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• v.29 no.6
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• pp.536-542
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• 2005

The effect of lime-related parameters such as loading velocity, load application time, gauge reading time on Rockwell hardness measurement was investigated for PE, PP PVC, and PMMA. It was found that keeping the specific requirements in the same condition is very important to obtain reliable and repeatable darn in polymer hardness measurement. The optimum condition for hardness measurement was 4 sec for load application time,15 sec for test load application net time, and 15 sec for gauge reading time after unloading. Using thess conditions, round robin test was carried out for 6 laboratories and it was shown that the testing machine should be one in which time-related variables are controllable. Indirect verification of hardness tester using brass reference block was not enough to guarantee the test results for polymer.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.2
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• pp.257-268
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• 1994

An experimental study was carried out to elicit important factors causing cracks and rupture of steel members and their elements under imposed large repeated deformations, and of the quantitative relationships among the important physical factors leading to failure. Each of twenty-eight angles and nine thin-plates served as the specimen and was subjected to repeated axial load after undergoing inelastic buckling. Particular attention was paid to the effects of loading pattern, failure mode and cross-sectional shape on the very-low-cycle failure behavior under loading repetitions of the order of a few to twenty. The experimental results show that energy dissipation capacity depends heavily on the entire history of loading, the failure mode, the slenderness ratio and the width-to-thickness ratio. No simple quantitative relations were observed between the initiation of the visible cracks or rupture and the energy dissipation capacity. The maximum values of residual "net" strains are found to range from 25% to 40%, independent of the test parameters.

• Composites Research
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• v.14 no.6
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• pp.16-23
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• 2001

Analysis of mechanical behavior for a pultruded-wound hollow rod is presented. For this purpose, the pultruded-wound hollow rod is manufactured by the new winder attached to the conventional pultrusion system. And the conventional pultrusion process is newly altered to manufacture pultruded-wound specimens. A computer program, POST II, is modified to perform this study, In the nonlinear finite element formulation, the updated Lagrangian description method based on the second Piolar-Kirchhoff stress tensor and the Green strain tensor are used. For the finite element modeling of the composite hollow rod, the eight-node degenerated shell element is utilized. In order to estimate the failure, the maximum stress criterion is adopted to the averaged stress in the each layer of the finite elements. As numerical examples, the behavior of glass/up composite hollow rod is investigated from the initial loading to the final collapse. Present finite element results considering stiffness degradation and stress unload due to failure shows excellent agreement with experiments in the ultimate load, failure and deformations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.3
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• pp.21-30
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• 1986

A method for elasto-plastic analysis of grillages is proposed in this investigation. An effort to construct the stiffness matrix of the member with bending and torsional springs attached at both ends is made in this work to make each member of grillage behave elasto-plastically. A related computer program EPAG for elasto-plastic analysis of grillages is also developed. The characters of this program in comparison with existing methods are as fellows; grillage with arbitrary geometry can be analysed, collapse load is applied in one step instead of incremental procedure, unloading can be considered, and analysis results such as applied loads, member end forces and joint displacements are also obtained when individual plastic hinge is formed. For verification of performanse of the EPAG, illustrating examples are solved and compared with the results of specified literlatures.

• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.93-104
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• 2003

The Disturbed State Concept (DSC) model, with simplified unloading/reloading formulation, is implemented in a nonlinear dynamic finite element program fur porous media named DSC_DYN2D. In this research, the DSC constitutive model is utilized using the HiSS model for relative intact (RI) part and the critical state model for the fully adjusted (FA) part in the material. The general formulation for implementation is developed. The cyclic loading tests from the field load test data on a pile segment were numerically simulated using the finite element program DSC_DYN2D and compared with field measurements and those from the previous analysis with the HiSS model. The DSC predictions show improved agreement with the field behavior of the pile compared to those from the HiSS model. Overall, the computer procedure with the DSC model allows improved and realistic simulation of the complex dynamic soil-structure interaction problems.

• Journal of the Korean Geotechnical Society
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• v.35 no.5
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• pp.43-51
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• 2019

At present, the ground anchor method is commonly applied to securing the slope stability in Korea. The ground anchor is reported to decrease in tensile load due to aging and environmental influences with time such as corrosion, relaxation, creep and so on. In Korea, the lift-off test is performed for the periodic inspection or cases when the symptoms of deterioration on anchors and the residual tensile load of the anchors is checked. However, the current lift-off test standard (MOLIT, 2010) is not fully specified in details. In this study, the factors affecting the lift-off test were investigated based on the previous research and foreign standards and lift-off tests were performed with consideration for the loading and unloading cycle, load increment method, and tensioning tendon method. Based on the results, this paper proposes improved testing and evaluation procedures of the lift-off test considering the workability and time limits in the field.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.4
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• pp.435-444
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• 2001

Even todays, accurate and efficient algorithms for the large deformation analysis of elastoplastic frame structures lack due to the complexities of kinematics, material nonlinearities and numerical methods to cater for. The author suggests appropriate beam element based upon the incremental formulation from the 3D rod theory where Cauchy stress and engineering strain are variables to incorporate plasticity equations so that objectivity may be satisfied. A rectum mapping methods which can integrate and satisfy yield criteria efficiently is suggested and a continuation method which has global convergency and quadratic speed is developed as well. leading-unloading example problems are tested and the ideas are proved to be valuable.