• 한국해양공학회지
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• 제4권2호
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• pp.15-21
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• 1990

This study focuses the mechanical deformation response predicted by the plasticity model for polycrystalline ice. To describe various deformation characteristics, ice is idealized as a perfectly plastic material using an asymptotic exponential failure criterion. This criterion is suite for describing materials which exhibit brittle deformation at low hydrostatic pressure and ductile deformation at high hydrostatic pressure. The results are compared to those of continuum damage mechanics model. Plasticity model shows good agreement with damage model and experimental results for high confining pressures even at high strain-rates which is usually considered as a brittle condition under uniaxial compression.

• 한국해양공학회지
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• 제4권2호
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• pp.165-165
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• 1990

This study focuses the mechanical deformation response predicted by the plasticity model for polycrystalline ice. To describe various deformation characteristics, ice is idealized as a perfectly plastic material using an asymptotic exponential failure criterion. This criterion is suite for describing materials which exhibit brittle deformation at low hydrostatic pressure and ductile deformation at high hydrostatic pressure. The results are compared to those of continuum damage mechanics model. Plasticity model shows good agreement with damage model and experimental results for high confining pressures even at high strain-rates which is usually considered as a brittle condition under uniaxial compression.

• 한국방재학회 논문집
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• 제10권2호
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• pp.15-21
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• 2010

교량의 내하력을 평가할 때 수행되는 구조해석은 재하시험을 통한 구조물의 실제거동과 유사한 거동특성을 구현하여야 되나 지점의 거동특성, 구조해석시 모델링 방법, 재하시험의 오류, 단면손상에 따른 강도 및 강성변화 등으로 인해 그렇지 못하는 경우가 있다. 특히, 교량받침이 손상하였거나 설치되지 않아 받침의 기능수행이 미비한 교량에서 이를 고려하지 않고 일률적으로 모델링을 하는 경우에는 이러한 문제가 더욱 심화될 수 있다. 본 연구에서는 단일보의 내민구간을 구속시켜 얻어진 실측처짐($\delta$실측)과 비구속상태에서의 계산처짐($\Delta$계산)과의 차이값인 $\Delta{\delta}$으로부터 얻어진 지점모멘트를 구조해석모델에 작용시켜 실제거동과 유사한 해석결과를 얻었다. 이에 따라 실제 공용중인 교량을 대상으로 지점의 구속조건을 고려하여 내하력을 평가한 결과 기존 방법에 의한 내하력에 비해 15~19% 적게 평가되었다.

• 지질공학
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• 제25권1호
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• pp.93-102
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• 2015

지반은 동결이 발생함에 따라 물리적 특성이 변화하며, 동결현상에 따른 기초구조물의 안정성 평가는 설계시 중요한 고려사항 중 하나이다. 본 연구에서는 동결 및 전단과정 중 연직응력 변화에 따른 동결토의 전단강도 및 강성을 평가하고자 하였다. 동결토의 강도평가를 위하여 직접전단실험을 수행하였으며, 직접전단실험 중 강성평가를 위한 전단파 측정을 동시에 수행하였다. 실험수행을 위하여, 동결용 직접전단상자를 제작하였으며, 상·하부 전단상자의 벽면에는 전단파 트랜스듀서인 벤더 엘리먼트를 각각 설치하였다. 시료는 주문진사 및 실트, 그리고 증류수를 이용하여 포화도 10%로 혼합하였으며, 상대밀도가 모든 조건에서 동일하게 유지되도록 조성하였다. 조성된 시료는 -5℃까지 동결을 진행시킨 후, 온도를 유지한 상태로 직접전단실험을 수행하였다. 동결 및 전단과정 중 시료에는 다양한 크기의 연직응력이 가해졌으며, 전단과정 중 수평변위에 따른 전단응력 및 수직변위, 그리고 전단파를 측정하였다. 실험결과, 모든 구속조건의 경우에서 동결 혹은 전단과정의 연직응력이 증가함에 따라 전단강도는 증가하였으며, 전단과정의 연직응력만 증가한 경우보다 동결과정의 연직응력도 함께 증가한 경우 전단강도가 더 크게 증가하는 것으로 나타났다. 또한, 전단파 속도의 변화는 측정위치에 따라 다른 경향을 보였으며, 전단면을 통과하여 측정한 경우 전단파 속도는 전단변형이 진행됨에 따라 감소하는 것으로 나타났다. 본 연구는 동결 및 전단과정 시 구속조건의 효과를 평가한 연구로써, 포화도가 낮은 상태의 동결토의 강도 및 강성에 대한 기초자료로 활용될 수 있을 것으로 예상된다.

• 한국재난정보학회 논문집
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• 제3권2호
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• pp.147-169
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• 2007

This study investigates the reinforcing effects of the Multi-bar Spring nails with respect to the conventional Soil-nails in artificial slopes. Based on wide experience related to design and construction, soil nails have been widely applied to reinforce slope in the world. Multi-bar spring nails are one of the improved soil nailing methods. These method maximizes bending, shearing, pull-out resistance for those multi-nails, not unit nail, that are inserted in the borehole using special spacer at regular intervals. In addition, because cutting plane is confined effect resulting from a pressured plate at the end of the nails with compression spring equipment, slope stability is secured using MS-nailing method. Analyzing bending, pull-out, shearing condition of MS-nail, it was examined throughly elastic region, load transfer capacity, reinforcing effect on cutting plate of MS-nails. In addition, Pilot and laboratory tests, numerical analysis were carried out to verify the superiority of MS-nailing method. In case, MS nailing method is applied to reinforce artificial slope, it was analyzed that bending, pull-out, shearing resistance was increased more than existing nailing method was applied. In this study, it was shown that surface failure was more or less prevented using MS-nailing method, confining effect on cutting plane using spring stuck to flexible equipment.

• Geomechanics and Engineering
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• 제19권6호
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• pp.533-542
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• 2019

Geosynthetic reinforced soil method in coarse-grained soils has been widely used in last decades. Two effective factors on soil-geosynthetic interaction are confining stresses and loading rate in clay. In terms of methodology, one pull-out test with four different strain rates, namely 0.75, 1.25, 1.75 and 2.25 mm/min, and three different normal stresses equal to 20, 50, and 80 kg have been performed on specimens with dimensions of 30×30×17 cm in the saturated, consolidated condition. The obtained results have demonstrated that activation of geosynthetic strength at contact surface depends on the applied stress. In addition, the increase in normal stress would increase the shear strength at contact surface between clay and geogrid. Moreover, it is concluded that the strain rate increment would increase the shear strength.

• Computers and Concrete
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• 제19권4호
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• pp.339-346
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• 2017

The main objective of this paper was to illuminate the effect of marine environmental condition on durability of reinforced concrete (RC)-corroded columns strengthened with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) layers. Small-scale columns were prepared and corroded by an accelerated corrosion process. After strengthening, compressive strength tests were carried out on control and weathered specimens. In this research, a marine simulator was designed and constructed similar to the tidal zone of marine environment in south of Iran which was selected as a case study in this research. Mechanical properties of wrapped specimens were studied after placing them inside the simulator for 3000 hours. Marine environment decreased ultimate strength by 4.5% and 26.3% in CFRP and GFRP-wrapped columns, respectively. In some corroded-columns, strengthening was carried out after replacing damaged cover by self-compacted mortar. In this method, by confining with one layer of CFRP and GFRP, 4.2% and 22.4% reduction in ultimate strength was observed, respectively, after exposure. Furthermore, the elastic-brittle behavior has been verified in this retrofit method. Also results of tension tests revealed, the ultimate tensile strength was degraded by 2% and 28.8% in CFRP and GFRP sheets, respectively, after applying marine exposure.

• Earthquakes and Structures
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• 제11권5호
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• pp.887-904
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• 2016

An efficient, economical and practical strengthening method for hollow brick infill walls was proposed and investigated in the present study, experimentally and numerically. This method aims at increasing the overall lateral strength and stiffness of the structure by increasing the contribution of the infill walls and providing the non-bearing components of the structure with the capability of absorbing earthquake-induced energy to minimize structural damage during seismic excitations. A total of eleven full-scale infill walls strengthened with expanded mild steel plates were tested under diagonal monotonic loading to simulate the loading condition of the non-bearing walls during an earthquake. The contact surface between the plates and the wall was increased with the help of plaster. Thickness of the plates bonded to both faces of the wall and the spacing of the bolts were adopted as test parameters. The experiments indicated that the plates were able to carry a major portion of the tensile stresses induced by the diagonal loads and provided the walls walls with a considerable confining effect. The composite action attained by the plates and the wall until yielding of the bolts increased the load capacities, rigidities, ductilities and energy-absorption capacities of the walls, considerably.

• 한국지반공학회지:지반
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• 제10권2호
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• pp.5-24
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• 1994

실내다짐토와 현장다짐토의 회복탄성특성을 비교하기 위하여 5종류의 현장다짐점토와 3종류의 실내다짐점토에 대한 회복탄성계수실험 (Resilient Modulus Test)을 실시하였다. 실험 결과에 의하면 현장시료의 회복탄성계수는 동일한 함수비와 건조단위중량으로 다짐형성된 시료의 그것과 상당히 다른 것으로 나타났다. 회복탄성계수는 1% 변형률에서의 일축압축응력과 좋은 상관 관계를 가지는 것으로 확인되었으며 이들간의 상관관계는 회귀분석에 의하여 간단한 식과 도표로 제안되었다. 구해진 상관관계는 실내다짐토와 현장다짐 토에 대해 약간 다르나, 실제 노반에 존재할 것으로 예상되는 응력조건하에서는 크게 다르지 않다. 제안된 상관관계식 자체는 시공후 지반의 상태변화에 영향을 받지 않으므로 as-compacted나 in-service상태에 모두 적용 가능하다.

• Structural Engineering and Mechanics
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• 제83권3호
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• pp.387-400
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• 2022

The practice of using encased steel-concrete columns in medium to high-rise structures has expanded dramatically in recent years. The study evaluates existing methodologies and codal guidelines for estimating the ultimate load-carrying characteristics of concrete-encased short columns experimentally. The present condition of composite column design methods was analyzed using the Egyptian code ECP203-2007, the American Institute of Steel Construction's AISC-LRFD-2010, Eurocode EC-4, the American Concrete Institute's ACI-318-2014, and the British Standard BS-5400-5. According to the codes, the axial load carrying characteristics of both the encased steel and concrete sections was examined. The effect of load-carrying capacities in different forms of encased steel sections on encased steel-concrete columns was studied experimentally. The axial load carrying capacity of twelve concrete-encased columns and four conventional reinforced columns were examined. The conclusion is that the confinement was not taken into account when forecasting the strength and ductility of the encased concrete, resulting in considerable disparities between codal provisions and experimental results. The configuration of the steel section influenced the confining effect. Better confinement is achieved with the laced and battened section than with the infilled steel tube reinforced and conventionally reinforced section. The ECP203-2007 code reported the most conservative results of all the codes used.