• Steel and Composite Structures
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• 제38권1호
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• pp.17-31
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• 2021

Post-earthquake fire is a common disaster which causes serious safety issues to infrastructures. This study aims to investigate the residual loading capacities of circular concrete-filled steel tube (CFST) columns under post-earthquake fire experimentally and numerically. The experimental programme contains two loading steps - pre-damage cyclic loading at room temperature and transient state tests with constant compression loads. Three finite element models are developed and validated against the test results. Upon validation, a total of 48 numerical results were generated in the parametric study to investigate the effects of thickness and strengths of steel tube, axial compression ratio and damage degree on the fire resistance of circular CFST columns. Based on the analysis on experimental and numerical results, the loading mechanism of circular CFST columns is discussed. A design method is proposed for the prediction of fire resistance time under different seismic pre-damage and compression loads. The predictions by the new method is compared with the newly generated experimental and numerical results and is found to be accurate and consistent with the mean value close to the unity and a coefficient of variation around 1%.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.322-325
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• 2007

Dent resistance is an important characteristic to avoid damage on automotive outer panels. From a practical point of view, dents can be caused in a number of ways. Considering doors as an example, denting can occur from stone impacts or from the careless opening of an adjacently parked vehicle door. Denting can occur where the door surface is smooth and may not have sufficient curvature to resist dent. These exterior body parts are designed to improve dent resistance using a combination of work hardening and bake hardening. In brief, dent is affected by the shape of the parts and the material properties such as yield strength, strain and thickness. In this work, forming of door outer panel is investigated by Taguchi method. Main parameters are yield strength, thickness, blank size, blank holding force and so on. For the given value of design parameters, forming analysis of the thirty six cases are carried out according to L18 orthogonal array. After comparing the performance by simple conversion of simulation results into dent resistance, the final suggestion of the forming parameters is verified for the best improvement of dent resistance.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 추계 학술논문 발표대회
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• pp.148-149
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• 2016

In this paper, the increase in chloride resistance of footing concrete at coastal area was evaluated by replacement of Mineral Admixture. In KBC 2009, the footing concrete's minimum specific concrete strength at coastal area is determined to 35MPa. However, this is criteria only based on the strength aspect. Thus, it is not considered to increase the chloride resistance by replacement of Mineral Admixture. According to the test results of chloride ions penetration resistance, 35MPa class concrete with OPC 100% shown inaccessible state. Low-strength (24~30MPa class) concretes with Mineral Admixture, however, presented better performances. In addition, chloride diffusion coefficient tests showed identical appearance. Therefore, the current KBC's chloride resistance criteria based on only concrete strength has to review for the reason it can cause many problems (ex. cost increases by growing concrete strength and the environmental issues by a lot of cement use).

• 소성∙가공
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• 제16권4호
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• pp.254-259
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• 2007

Dent resistance is an important characteristic to avoid damage on automotive outer panels. From a practical point of view, dents can be caused in a number of ways. Considering doors as an example, denting can occur from stone impacts or from the careless opening of an adjacently parked vehicle door. Denting can occur where the door surface is smooth and may not have sufficient curvature to resist dent. These exterior body parts are designed to improve dent resistance using a combination of work hardening and bake hardening. In brief, dent is affected by the shape of the parts and the material properties such as yield strength, strain and thickness. In this work, forming of door outer panel is investigated by Taguchi method. Main parameters are yield strength, thickness, blank size, blank holding force and so on. For the given value of design parameters, forming analysis of the eighteen cases are carried out according to L18 orthogonal array. After comparing the performance by simple conversion of simulation results into dent resistance, the final suggestion of the forming parameters is verified for the optimal improvement of dent resistance.

• 수산해양기술연구
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• 제43권4호
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• pp.362-369
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• 2007

This paper was studied on the characteristics of acid resistance and thermal shock for epoxy coatings in the strong acidic environment. The exhaust gas system, such as a air preheater, desulfurization equipment, for industrial boiler is damaged by dew point corrosion. To protect the acid corrosion, the coating using nonmetal was applied. The electrochemical polarization test, acid resistance and thermal shock test for epoxy coatings were carried out. And the acid resistance and thermal shock characteristics, aspect, and electrochemical anti-corrosion characteristics for epoxy coatings in the strong acidic environment were considered. The main results are as followings: As the epoxy glass flake coating by acidic thermal shock was damaged to the crack, blistering and elution etc., the current density of epoxy glass flake coating is high. But the damage of epoxy metal complex coating by acidic thermal shock was not occurred. Therefore the characteristics of acid resistance and thermal shock for epoxy metal complex coating is better than those for epoxy glass flake coating.

• Structural Engineering and Mechanics
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• 제83권6호
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• pp.745-756
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• 2022

This study aims to determine the cause of the load resistance loss in storage racks that can be attributed to external forces such as earthquakes and to improve safety by developing reinforcement systems that can prevent load resistance loss. To this end, a static cyclic loading test was performed on pallet racks commonly used in logistics warehouses. The test results indicated that a pallet rack exposed to an external force loses more than 50% of its load resistance owing to the damage caused to column-beam joints. Three reinforcement systems were developed for preventing load resistance loss in storage racks exposed to an external force and for performing differentiated target functions: column reinforcement device, seismic damper, and viscoelastic damper. Shake table testing was performed to evaluate the earthquake response and verify the performance of these reinforcement systems. The results confirmed that, the maximum displacement, which causes the loss of load resistance and the permanent deformation of racks under external force, is reduced using the developed reinforcement devices. Thus, the appropriate selection of the developed reinforcement devices by users can help secure the safety of the storage racks.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.212-215
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• 2002

Interfacial evaluation and damage sensing of the carbon fiber/epoxy-amine terminated (AT)-polyetherimide (PEI) composites were performed using micromechanical test and electrical resistance measurement. As AT-PEI content increased, the fracture toughness of epoxy-AT-PEI matrix increased, and thus their interfacial shear strength (IFSS) was improved due to the improved toughness. After curing process, the changes in electrical resistance (ΔR) with increasing AT-PEI contents increased gradually because of the changes in thermal expansion coefficient (TEC) and thermal shrinkage of matrix. Matrix fracture toughness was correlated to the IFSS, residual stress and electrical resistance. The results obtained from the electrical resistance measurement during curing process, reversible stress/strain, and durability test were consistent with modified matrix toughness properties.

• 한국조경학회지
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• 제31권4호
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• pp.74-81
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• 2003

The need for insect and mite resistant turfgrass cultivars arose because of problems associated with pesticide use. Representative cultivars and genotypes of 18 warm-season turfgrass [Zoysia japonica Steud., Z. japonica${\times}$Z. metrella hybrids, Z. japonica${\times}$Z. tenuifotia hybrids, Z. matrella (L.) Merr., Cynodon dactylon (L.) Pers., C. dactylon${\times}$C. transvallensis hybrids, Paspalum notatum Flugge., P. vaginatum Swartz., Stenotaphrum secundatum (Walt.) Kuntze, Eremochloa ophiuroides (Munro.) and Buchloe dactyloides (Nutt.) Engelm.] and 20 cool-season turfgrasses [Poa pratensis L., Festuca arundinacea Schreb., F. rubra L., F. rubra var. commutata Gaud., F. ovina var. duriuscula L. Koch. Agrostis tenuis Sibth., A. palustris Huds., and Latium perenne L.] were evaluated for host resistance to feeding by the Spodoptera depravata (Butler) in the laboratory. Two experiments were set up in the laboratory using 8.5cm diameter${\times}$4.0cm deep plastic petri dishes as larvae feeding chambers. In experiment 1, one neonate larvae were place on the grass in each dish and the dishes were arranged with 5 replicates each within an environmental chamber maintained at $25^{\circ}C$ and 15h light: 9h dark Larval survival and larval weights at 7d and 14d, pupal weights, and days to pupation were compared among turfgrasses. In Experiment 2, 4cm sections of all grasses were oriented equidistant from each other in a pattern resembling the spokes of a wheel. Five one neonate larvae were introduced to the center of each dish. Dishes were immediately placed in an environmental chamber held at $25^{\circ}C$, 15h light: 9h dark Larvae were allowed to feed for 24h. Damage was rated from 0(no damage) to 9(completely consumed) were made for eachturfgrass. Resistance as antibiosis (high mortality, slowed growth, and least preference) was identified in Z. japonica${\times}$Z. tenuifolia hybirids ‘Emerald’, Z. japonica${\times}$Z. metrella hybirds ‘Miyako’ and Eremochloa ophiuroides (Munro.). Cool-season turfgrasses tested were susceptible to feeding by Spodoptera depravata (Butler).

• 콘크리트학회논문집
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• 제21권5호
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• pp.611-617
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• 2009

이 연구는 보통포틀랜드시멘트로 제조된 모르타르 및 페이스트 샘플의 황산염침식 저항성을 평가하기 위하여 수행되었다. 주요 실험변수는 사용된 황산염용액의 온도조건으로써, 각각 $4^{\circ}C$, $10^{\circ}C$ 및 $20^{\circ}C$로 유지된 5% 황산나트륨 용액에 침지한 모르타르의 침지재령별 팽창, 압축강도 및 휨강도를 측정 한 후, 황산염침식 저항성을 평가하였다. 뿐만 아니라, XRD, DSC 및 SEM/EDS와 같은 기기분석 기법을 이용하여 저온환경에 노출된 페이스트 샘플 중에 생성된 반응생성물 조사 및 미세구조 분석도 아울러 실시하였다. 실험 결과에 의하면, 황산염침식에 의한 모르타르의 성능 저하는 시험용액 온도에 매우 의존적으로 나타났으며, 특히, 저온환경에서는 쏘마싸이트의 생성으로 인한 성능 저하가 매우 극심하게 나타남을 확인할 수 있었다. 따라서, 저온의 황산염환경에 콘크리트구조물이 노출될 경우 세심한 주의가 요구된다.

• Steel and Composite Structures
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• 제46권6호
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• pp.773-791
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• 2023

Connections with damage concentrated to pre-selected components can enhance seismic resilience for moment resisting frames. These pre-selected components always yield early to dissipate energy, and their energy dissipation mechanisms vary from one to another, depending on their position in the connection, geometry configuration details, and mechanical characteristics. This paper presents behaviour insights on two types of beam-to-beam connections that the angles were designed as energy dissipation components, through the results of experimental study and finite element analysis. Firstly, an experimental programme was reviewed, and key responses concerning the working mechanism of the connections were presented, including strain distribution at the critical section, section force responses of essential components, and initial stiffness of test specimens. Subsequently, finite element models of three specimens were established to further interpret their behaviour and response that were not observable in the tests. The moment and shear force transfer paths of the composite connections were clarified through the test results and finite element analysis. It was observed that the bending moment is mainly resisted by axial forces from the components, and the dominant axial force is from the bottom angles; the shear force at the critical section is primarily taken by the slab and the components near the top flange. Lastly, based on the insights on the load transfer path of the composite connections, preliminary design recommendations are proposed. In particular, a resistance requirement, quantified by a moment capacity ratio, was placed on the connections. Design models and equations were also developed for predicting the yield moment resistance and the shear resistance of the connections. A flexible beam model was proposed to quantify the shear resistance of essential components.