• Advances in concrete construction
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• 제10권6호
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• pp.547-557
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• 2020

This paper presents one of the demonstration projects undertaken during the FP7 EU-funded Anagennisi project (Innovative reuse of all tyre components in concrete-2014-2017) on a full-scale (30 m×40 m, thickness: 0.2 m) Steel Fibre Reinforced Concrete (SFRC) slab-on-grade using a blend of manufactured steel fibres (MSF) and Recycled Tyre Steel Fibres (RTSF). The aim of the project was to assess the use of RTSF in everyday construction practice. The Anagennisi partners, Dulex Ltd in collaboration with Gradmont-Gradacac Ltd and University of Zagreb, designed, cast and monitored the long-term shrinkage deformations of the indoor slab-on-grade slab at Gradmont's precast concrete factory in Gradacac, Bosnia and Herzegovina. A hybrid RTSF mix (20 kg/㎥ of MSF+10 kg/㎥ of RTSF) was used to comply with the design criteria which included a maximum load capacity of 20 kN/㎡. The slab was monitored for one year using surveying equipment and visual inspection of cracks. During the monitoring period, the slab exhibited reasonable deformations (a maximum displacement of 3.3 mm for both, horizontal and vertical displacements) whilst after five years in use, the owners did not report any issues and were satisfied with the construction methodology and materials used. This work confirms that RSTF is a viable and sustainable solution for slab-on-grade applications.

• Steel and Composite Structures
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• 제38권2호
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• pp.121-139
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• 2021

Ultra-high strength concrete (UHSC) encased steel columns are receiving growing interest in high-rise buildings owing to their economic and architectural advantages. However, UHSC encased steel columns are not covered by the modern fire safety design code. A total of 14 fire tests are conducted on UHSC (120 MPa) encased steel columns under constant axial loads and exposed to ISO-834 standard fire. The effect of load ratio, slenderness, stirrup spacing, cross-section size and concrete cover to core steel on the fire resistance and failure mode of the specimens are investigated. The applicability of the tabulated method in EC4 (EN 1994-1-2-2005) and regression formula in Chinese code (DBJ/T 15-81-2011) to fire resistance of UHSC encased steel columns are checked. Generally, the test results reveal that the vertical displacement-heating time curves can be divided into two phases, i.e. thermal expansion and shortening to failure. It is found that the fire resistance of column specimens increases with the increase of the cross-section size and concrete cover to core steel, but decreases with the increase of the load ratio and slenderness. The EC4 method overestimates the fire resistance up to 186% (220 min), while the Chinese code underestimates it down to 49%. The Chinese code has a better agreement than EC4 with the test results since the former considers the effect of the load ratio, slenderness, cross section size directly in its empirical formula. To estimate the fire resistance precisely can improve the economy of structural fire design of ultra-high strength concrete encased steel columns.

• 한국지반신소재학회논문집
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• 제21권3호
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• pp.11-19
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• 2022

최근 도시화 및 경제 성장에 따라 기피시설로 인식되는 소각장, 매립지와 같은 지상 환경 기초 시설의 지하화에 대한 요구가 증대하고 있다. 대규모 지하 복합플랜트 건설을 위해서는 다양한 지반 조건 및 하중 조건에 따른 안정성 검토가 필요하다. 본 논문에서는 유한요소해석(FEM)을 활용하여 지하 대공간 상부하중과 수평토압을 고려한 지하연속벽체 건설 공정에 따른 수평, 연직 변위 및 응력 발생 경향을 분석하였다. 다양한 조건의 해석 결과를 바탕으로 지하 복합플랜트 상세설계 및 시공단계에서 고려해야 할 요소들을 검토하고, 지하 대공간 건설을 위한 설계인자(중간벽체 설치 유무, 사전 보강 영역 등)에 관한 시사점을 도출하였다.

• 한국건설순환자원학회논문집
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• 제10권3호
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• pp.219-226
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• 2022

본 실험적 연구에서는 수개의 코일과 릴레이 스위치를 활용하여 전자기력 위치를 지속적으로 교란하는 방법이 파괴에너지에 미치는 영향을 분석하였다. 마이크로 강섬유와 일반 후크 강섬유로 보강된 일반몰탈, 모래의 50 %와 100 %를 스틸슬래그로 치환한 스틸슬래그 몰탈을 제작하고, 전자기에 노출하였다. 전자기력이 유도방식은 기존의 방식인 한 개의 코일을 사용하고 릴레이 스위치 없이 일정한 전자기력을 유도하는 기존의 방법과 이를 상과 하로 두 개로, 상중하 세 개로 분할하고 릴레이 스위치를 두어 지속적으로 변화시키는 방법으로 하였다. 실험결과로부터 획득한 하중-수직변위곡선으로부터 파괴에너지를 계산하고 이를 상호 비교하였다. 실험결과, 동일한 전력량을 사용하더라도 코일을 분리하고 릴레이 스위치를 활용하여 전자기력을 교란하는 방식이 파괴에너지를 증가시키는데 효과적인 것으로 확인되었다.

• Wind and Structures
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• 제34권2호
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• pp.173-183
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• 2022

The galloping of iced conductors has long been a severe threat to the safety of overhead transmission lines. Compared with normal transmission lines, the ultra-high-voltage (UHV) transmission lines are more prone to galloping, and the damage caused is more severe. To control the galloping of UHV lines, it is necessary to conduct a comprehensive analysis of galloping characteristics. In this paper, a large-span 1000-kV UHV transmission line in China is taken as a practical example where an 8-bundled conductor with D-shaped icing is adopted. Galerkin method is employed for the time history calculation. For the wind attack angle range of 0°~180°, the galloping amplitudes in vertical, horizontal, and torsional directions are calculated. Furthermore, the vibration frequencies and galloping shapes are analyzed for the most severe conditions. The results show that the wind at 0°~10° attack angles can induce large torsional displacement, and this range of attack angles is also most likely to occur in reality. The galloping with largest amplitudes in all three directions occurs at the attack angle of 170° where the incoming flow is at the non-iced side, due to the strong aerodynamic instability. In addition, with wind speed increasing, galloping modes with higher frequencies appear and make the galloping shape more complex, indicating strong nonlinear behavior. Based on the galloping amplitudes of three directions, the full range of wind attack angles are divided into five galloping regions of different severity levels. The results obtained can promote the understanding of galloping and provide a reference for the anti-galloping design of UHV transmission lines.

• Earthquakes and Structures
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• 제21권5호
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• pp.531-549
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• 2021

Analytical models were developed and seismic behaviors were analyzed for a three-story stone pagoda at the Cheollyongsa temple site, which was damaged by the Gyeongju earthquake of 2016. Both finite and discrete element modeling were used and the analysis results were compared to the actual earthquake damage. Vulnerable parts of stone pagoda structure were identified and their seismic behaviors via sliding, rocking, and risk analyses were verified. In finite and discrete element analyses, the 3F main body stone was displaced uniaxially by 60 and 80 mm, respectively, similar to the actual displacement of 90 mm resulting from the earthquake. Considering various input conditions such as uniaxial excitation and soil-structure interaction, as well as seismic components and the distance from the epicenter, both models yielded reasonable and applicable results. The Gyeongju earthquake exhibited extreme short-period characteristics; thus, short-period structures such as stone pagodas were seriously damaged. In addition, we found that sliding occurred in the upper parts because the vertical load was low, but rocking predominated in the lower parts because most structural members were slender. The third-floor main body and roof stones were particularly vulnerable because some damage occurred when the sliding and rocking limits were exceeded. Risk analysis revealed that the probability of collapse was minimal at 0.1 g, but exceeded 80% at above 0.3 g. The collapse risks at an earthquake peak ground acceleration of 0.154 g at the immediate occupancy, life safety, and collapse prevention levels were 90%, 52%, and 6% respectively. When the actual damage was compared with the risk analysis, the stone pagoda retained earthquake-resistant performance at the life safety level.

• 한국지반공학회논문집
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• 제23권8호
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• pp.87-95
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• 2007

본 연구에서는 대심도 풍화대에 시공되는 2차로 도로터널을 기준으로 터널의 굴착방법과 지반보강그라우팅에 의한 지반변위 및 지반응력의 분석을 통하여 최적의 시공방안을 찾고자 하였다. 터널 직경은 약 12m를 적용하였으며, 상부 강관다단그라우팅 및 측벽 보강그라우팅을 적용하였다. 검토된 굴착방법은 링컷 굴착방법과 중벽분할 굴착방법이다. 터널 천단의 소성율과 연직응력비를 분석한 결과, 풍화대지반에 굴착되는 터널에서 토피고(H)가 터널직경(D)의 4배 이상일 경우(H>4D) 대심도 터널로 판단할 수 있었다. 해석결과 중벽분할 굴착방법이 링컷 굴착방법에 비하여 대심도 풍화대 NATM터널에서 안정성이 높은 굴착방법으로 판단할 수 있었다. 또한, 측벽 보강그라우팅 실시로 터널 내공변위 및 침하 발생을 억제할 수 있었다.

• 한국결정성장학회지
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• 제32권1호
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• pp.33-39
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• 2022

3D 프린터 관련 특허가 만료되고 주요 기술이 공개되면서 3D 프린터 가격이 하락하면서 원하는 제품을 쉽게 찾을 수 있는 환경이 조성되고 있다. 특히 가장 저렴한 FDM(Fused Deposition Modeling) 3D 프린터가 다양한 분야에서 사용되고 있다. FDM 방식은 형상을 출력할 때 특정 조건이상에서는 지지대(Support)를 붙여야만 형상의 무너짐 없이 제작이 가능하다. 지지대를 달지 않고 형상을 출력할 때 특정 각도에서 발생하는 불규칙한 표면은 제품에 있어서는 불량이지만 예술과 공예적 측면에서는 또 다른 재미를 느낄 수 있는 요소로 활용될 수 있다고 사료된다. 본 논문에서는 이러한 불규칙한 표면을 얻기 위해 출력에 영향을 줄 수 있는 요인들을 제어하고 출력 각도만 변위요소로 실험하였다. 실험 결과 수직에서 62°~70°의 각도로 프린팅 시 필라멘트가 흘러내리지 않고 불규칙한 표면을 얻을 수 있었다. 또한 인위적으로 불규칙한 표면을 공예적인 제품에 적용해 보았다.

• 대한치과교정학회지
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• 제52권2호
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• pp.131-141
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• 2022

Objective: The purpose of this study was to compare the differences in dentoskeletal and soft tissue changes following conventional tooth-borne rapid maxillary expansion (RME) between adolescents and adults. Methods: Dentoskeletal and soft tissue variables of 17 adolescents and 17 adults were analyzed on posteroanterior and lateral cephalograms and frontal photographs at pretreatment (T1) and after conventional RME using tooth-borne expanders (T2). Changes in variables within each group between T1 and T2 were analyzed using Wilcoxon signed-rank test. Mann-Whitney U test was used to determine the differences in the pretreatment age, expansion and post-expansion durations, and dentoskeletal and soft tissue changes after RME between the groups. Spearman's correlation between pretreatment age and transverse dentoskeletal changes in the adolescent group was calculated. Results: Despite similar amounts of expansion at the crown level in both groups, the adult group underwent less skeletal expansion with less intermolar root expansion after RME than the adolescent group. The skeletal vertical dimension increased significantly in both groups without significant intergroup difference. The anteroposterior position of the maxilla was maintained in both groups, while a greater backward displacement of the mandible was evident in the adult group than that in the adolescent group after RME. The soft tissue alar width increased in both groups without a significant intergroup difference. In the adolescent group, pretreatment age was not significantly correlated with transverse dentoskeletal changes. Conclusions: Conventional RME may induce similar soft tissue changes but different dentoskeletal changes between adolescents and adults.

• 한국지반공학회논문집
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• 제39권11호
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• pp.33-40
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• 2023

본 연구에서는 산화마그네슘계 내화물(Magnesium oxide-based refractory)을 함유한 팽창성 지반에서의 말뚝기초 거동을 분석하였다. 고정단 말뚝이 설치된 모형토조에 용융마그네시아(Fused magnesia, FM)를 활용하여 지반의 융기를 유도하였으며, FM함유량(FM_c = 30%, 50%, 70%)을 변화하여 시간에 따른 깊이별 융기량과 말뚝의 축력을 분석하였다. FM_c가 증가할수록 더 큰 융기량이 측정되었으며, 시료의 표면으로 갈수록 융기량이 누적되어 깊이에 따라 융기량이 감소하였다. 그러나 깊이별 융기율의 차이와 그에 따른 팽창압의 차이로 인하여 FM_c = 30%와 50%일때 말뚝에 뚜렷한 압축력과 인장력이 발현되었으며, FM_c = 70%일 때에는 말뚝 전체에 인장력만이 발현되었다. 이런한 결과는 산화마그네슘계 내화물이 포함된 혼합토 내의 말뚝거동을 분석하는데 중요한 자료로 활용할 수 있을 것으로 판단된다.