• Computers and Concrete
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• 제26권3호
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• pp.293-307
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• 2020

The aim of this paper is to develop design-oriented models for the prediction of the ultimate strength and ultimate axial strain for concrete confined with glass fiber-reinforced polymer (GFRP) wraps. Twenty of most used and recent design-oriented models developed to predict the strength and strain of GFRP-confined concrete in circular sections are selected and evaluated basing on a database of 163 test results of concrete cylinders confined with GFRP wraps subjected to uniaxial compression. The evaluation of these models is performed using three statistical indices namely the coefficient of the determination (R²), the root mean square error (RMSE), and the average absolute error (AAE). Based on this study, new strength and strain models for GFRP-wrapped concrete are developed using regression analysis. The obtained results show that the proposed models exhibit better performance and provide accurate predictions over the existing models.

• 한국항해항만학회지
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• 제33권1호
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• pp.27-33
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• 2009

압축하중 및 횡하중의 조합하중을 받는 연속 보강판넬의 좌굴강도 및 최종강도의 평가는 선체구조 안정성을 재고하는데 아주 중요한 요소이다. 예를들면, 선박의 공창 상태에서 선체외판은 수압하중에 의해서 파생되는 횡방향 면내 압축하중과 선체외판에 작용하는 횡하중은 대표적인 하중 성분이다. 지금까지의 대부분의 연구 결과들은 실험테스트 및 이론석인 접근 그리고 수치계산 방법에 의해서 수행되었으며, 단일 판 또는 보강판의 조합하중에 대한 많은 업적들이 있다. 그러나, 이들 중 대부분의 연구는 종방향 면내 압축하중과 횡하중에 의한 연구결과가 대부분이며, 횡방항 면내 압축하중과 횡하중에 대한 결과들은 상대적으로 많지가 않다. 게다가 이전의 연구들은 주고 네변 단순지지된 판부재를 고려하였으나, 실제의 구조를 고려해보면, 횡방향 프레임과 종방향 거더들이 교차되어 있는 보강 판넬 구조이다. 본 연구는, 3척의 실적선에서 얻은 이중저 판넬 모델을 적용하고, 횡하중의 크기를 변수로 한 탄소성대변형 유한요소해석을 수행하였다. 이러한 여러 가지 수치 해석을 통하여, 횡하중의 크기 변화에 대한 영향과 횡방향 압축하중이 작용하는 붕괴 매커니즘에 대해서 고찰하였다.

• Steel and Composite Structures
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• 제18권5호
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• pp.1259-1277
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• 2015

The present study is focused on the behavior and design of perforated steel storage rack columns under axial compression. These columns may exhibit different types of behavior and levels of strength owing to their peculiar features including their complex cross-section forms and perforations along the member. In the present codes of practice, the design of these columns is carried out using analytical formulas which are supported by experimental tests described in the relevant code document. Recently proposed analytical approaches are used to estimate the load carrying capacity of axially compressed steel storage rack columns. Experimental and numerical studies were carried out to verify the proposed approaches. The experimental study includes compression tests done on members of different lengths, but of the same cross-section. A comparison between the analytical and the experimental results is presented to identify the accuracy of the recently proposed analytical approaches. The proposed approach includes modifications in the Direct Strength Method to include the effects of perforations (the so-called reduced thickness approach). CUFSM and CUTWP software programs are used to calculate the elastic buckling parameters of the studied members. Results from experimental and analytical studies compared very well. This indicates the validity of the recently proposed approaches for predicting the ultimate strength of steel storage rack columns.

• Steel and Composite Structures
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• 제47권3호
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• pp.405-421
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• 2023

An experimental study on six axially-loaded composite short columns with different thicknesses of steel tube and that of the concrete plate was carried out. Compared to the mechanical behavior of component specimens under axially compressed, the failure modes, compression deformation, and strain process were obtained. The two main parameters that have a significant enhancement to cross-sectional strength were also analyzed. The failure of an axially loaded UHPC-CFST short column is due to the crushing of the UHPC plate, while the CFST member does reach its maximum resistance. A reduction coefficient K'c, related to the confinement coefficient, is introduced to account for the contribution of CFST members to the ultimate load-carrying capacity of the UHPC-CFST composite short columns. Based on the regression analysis of the relationship between the confinement index ξ and the value of fcc/fc, a unified formula for estimating the axial compressive strength of CFST short columns was proposed, combined with the experimental results in this research, and an equation for reliably predicting the strength of UHPC-CFST composite short columns under axial compression were also proposed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.891-896
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• 2001

The determination of compressive zone at the critical section of concrete walls under in-plane flexure is important in both assessing the ductility and designing the seismic retrofit. Recognizing this, the once-predominated code approach to determine the compressive zone was advanced by considering concrete rectangular stress block parameters varying with the extreme fiber strain in compression. It is shown that the major factors influencing the magnitude of compressive zone are axial load ratio, concrete strength, longitudinal steel ratio, yield strength and the level of strain at extreme compression fiber of wall sections. The present paper closes with the discussion for the research agenda requiring further study to investigate the behavior of reinforced concrete walls.

• 해양환경안전학회지
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• 제24권2호
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• pp.260-266
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• 2018

곡률을 갖고 있는 쉘 부재들은 선박 및 육상구조 내에서 캠버와 선수, 선미, 파이프 및 저장용 탱크에 주로 사용되고 있다. 이러한 곡률 쉘 부재들은 기본적으로 원통형 실린더 부재의 일부라고 간주할 수 있다. 일반적으로 곡률의 존재는 압축하중 작용 시 좌굴강도 및 최종강도를 증가시키는 것으로 알려져 있다. 본 논문에서는 이러한 영향을 확인하기 위하여 탄성대변형 시리즈해석을 수행하였으며, 매개변수의 영향을 분석하였다. 실린더의 최종강도 거동은 초기처짐과 해석모델링 방법에 큰 영향을 받는 것을 확인하였다.

• 한국주조공학회지
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• 제17권4호
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• pp.402-410
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• 1997

Developing a salt core for squeeze casting process, two different salt cores(pure salt core and mixed salt core) were fabricated and investigated. Pure salt core was composed of 100% NaCl and mixed salt core was made by mixtures of NaCl with MgO(1%), $Na_2B_4O_7$(2%), and talc(1%) as a binder or a strengthening agent. Salt cores were compacted to various theoretical density, heat treated, and then squeeze-cast with molten Al alloy(AC8A). The compression strength of salt cores were measured and the squeeze-cast products were examined for shape retention, infiltration of molten metal into the cores, and microstructures. The shape of salt core compacted at above 75% of the theoretical density was maintained stably. The higher theoretical density of salt cores gave higher compression strength, and the compression strength of mixed salt core was higher than that of pure salt core. Namely at 90% theoretical density, the compression strength of mixed salt core was $6.3 kg/mm^2$, compared to $4.6 kgmm^2$ for pure salt core. At a squeeze casting pressure of $1000 kg/cm^2$, molten Al alloy was infiltrated into pure salt core of under 85% of the theoretical density. At squeeze casting pressure of $1000 kg/cm^2$, only mixed salt core above 90% of the theoretical density were valid, but the shape of the core was altered in the case of pure salt core at 90% of theoretical density. A key factor for developing a salt core for squeeze casting process was estimated as the ultimate compressive strength of salt core.

• 대한조선학회논문집
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• 제32권3호
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• pp.83-97
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• 1995

본 논문의 목적은 종굽힘모멘트를 받는 선각거더의 최종강도를 계산하는 간이식을 도출하는 것이다. 먼저 기 제안된바 있는 계산식들을 조사 분석하였으며, 지금까지의 계산식 도출방법을 크게 해석적 방법, 경험적 방법 및 선형근사법의 3종류로 분류하였다. 선각거더는 종굽힘모멘트의 증가와 함께 압축플랜지의 붕괴와 인장플랜지의 항복에 의해 전체적으로 최종강도에 도달한다고 알려져 있다. 이때 선측부도 압축플랜지 부근에서는 붕괴하며, 인장플랜지 부근에서는 항복상태에 도달해 있는 경우가 많다. 그러나, 중립축부근에서는 여전히 탄성상태에 남아있는 것이 보통이다. 이같은 사실을 근거로 선각 횡단면에 걸쳐 적절한 응력분포를 가정하였으며, 이것으로부터 최종강도 계산식을 해석적인 방법으로 도출하였다. 본 계산식의 정도는 기존의 모형실험 및 수치해석결과와 비교하여 검증하였다.

• 한국방재학회 논문집
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• 제8권2호
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• pp.105-110
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• 2008

Flowable fill is generally a mixture of sand, fly ash, a small amount of cement and water. Sand is the major component of most flowable fill with waste materials. Various materials, including two waste foundry sands(WFS), an anti-corrosive waste foundry sand and natural soil, were used as a fine aggregate in this study. Natural sea sand was used for comparison. The flow behavior, hardening characteristics, and ultimate strength behavior of flowable fill were investigated. The unconfined compression test necessary to sustain walkability as the fresh flowable fill hardens was determined and the strength at 28-days appeared to correlate well with the water-to-cement ratio. The strength parameters, like cohesion and internal friction angle, were determined for the samples prepared by different curing times. The creep test for settlement potential was conducted. The data presented show that by-product foundry sand, an anti-corrosive WFS, and natural soil can be successfully used in controlled low strength materials(CLSM), and it provides similar or better properties to that of CLSM containing natural sea sand.

• Steel and Composite Structures
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• 제29권6호
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• pp.689-701
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• 2018

Corrosion of steel reinforcement is a principal cause of deterioration of RC columns. Making these corrosion-damaged columns conform to new safety regulations and functions is a tremendous technological challenge. This study presented an experimental investigation on steel-concrete jacketed corrosion-damaged RC columns. The influences of steel jacket thickness and concrete strength on the enhancement performance of the strengthened specimens were investigated. The results showed that the use of steel-concrete jacketing is efficient since the stub strengthened columns behaved in a more ductile manner. Moreover, the ultimate strength of the corrosion-damaged RC columns is increased by an average of 5.3 times, and the ductility is also significantly improved by the strengthening method. The bearing capacity of the strengthening columns increases with the steel tube thickness increasing, and the strengthening concrete strength has a positive impact on both bearing capacity, whereas a negative influence on the ductility. Subsequently, a numerical model was developed to predict the behavior of the retrofitted columns. The model takes into account corrosion-damage of steel rebar and confining enhancement supplied by the steel tube. Comparative results with the experimental results indicated that the developed numerical model is an effective simulation. Based on extensive verified numerical studies, a design equation was proposed and found to predict well the ultimate eccentric strength of the strengthened columns.