• International Journal of Korean Welding Society
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• 제3권1호
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• pp.8-16
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• 2003

A major concern in Gas Metal Arc (GMA) welding process is the determination of welding process variables such as wire diameter, gas flow rate, welding speed, arc current and welding voltage and their effects on the desired weld bead dimensions and shape. To successfully accomplish this objective, 81 welded samples from mild steel AS 1204 flats adopting the bead-on-plate technique were employed in the experiment. The experimental results were used to develop a mathematical model to predict the magnitude of bead geometry as follows; weld bead width, weld bead height, weld bead penetration depth, weld penetration shape factor, weld reinforcement shape factor, weld bead total area, weld bead penetration area, weld bead reinforcement area, weld bead dilution, length of weld bead penetration boundary and length of weld bead reinforcement boundary, and to establish the relationships between weld process parameters and bead geomery. Multiple regression analysis was employed for investigating and modeling the GMA process and significance test techniques were applied for the interpretation of the experimental data.

• 생물환경조절학회지
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• 제18권3호
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• pp.192-199
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• 2009

파프리카를 재배하는 농가에서는 생산성 증대를 위하여 비닐하우스 측고를 관행 3.0m에서 4.5m까지 높이고 있으나 이에 대한 구조안전성 검토 없이 시공이 이루어지고 있는 실정이다. 이 연구에서는 측고가 4.5m로 상승된 1-2W형 비닐하우스를 대상으로 풍속 $40m{\cdot}s^{-1}$, 적설심 40cm의 설계하중에 대하여 구조안전성 분석을 수행하고 적절한 구조보강방법을 제시하였다. 3차원 프레임해석을 이용하여 구조해석을 수행한 결과, 측면 방풍벽의 보강이 반드시 필요한 상태였으며 파프리카 작물하중으로 인하여 매우 취약해지는 중방의 보강이 요구되었다. 측면 보강 방법으로써는 외측 기둥과 방풍벽을 보강이음을 이용하며 서로 연결해주고, 외측 기둥 간격에 따라 방풍벽 부재를 보강하는 방법이 가장 효과가 큰 것으로 분석되었다. 중방의 경우 비닐하우스 폭의 $1/17{\sim}1/20$의 높이로 2중 중방구조를 만들고 그 사이를 사재로 연결하여 트러스 형태로 보강하는 방법이 가장 큰 효과를 보였다.

• 한국터널공학회:학술대회논문집
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• 한국터널공학회 2005년도 학술발표회 논문집
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• pp.233-247
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• 2005

Most tunnel lining material which has been used in the domestic is a concrete. But many problems as the construction period, the cost, and the crack occurrence for the design, construction, and management were happened in the concrete lining. For this reason, many research institutes like the Korea Highway Corporation recognize the necessity of an alternate material development and grow on the interest for that. So in this study, the seismic behaviour characteristics for the application of the Corrugated Steel Plate Lining in cut-and-cover tunnel are evaluated as several conditions for the backfill height, the cutting slope, and the relative density of backfill soil are changed. The compressive stress which is calculated in the Corrugated Steel Plate Lining by the seismic load is decreased as the backfill height increases and the cut slope grows gentle. Also, the moment shows the tendency of decrease according to the increase of the backfill height. But in the case of the relative density of the backfill soil is small, the moment increases according to the increase of the backfill height and affects the dynamic behaviour characteristic. So it is considered that the relative density of the backfill soil is also the important point. As the result in analyzing the seismic response characteristics of the reinforcement spacing of the Corrugated Steel Plate, the variation in the compressive force is hardly happened, but the moment and the shear force increase on the reinforcement spacing being narrow.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1686-1704
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• 2021

This study addresses the numerical simulation of the shield building of an AP1000 nuclear power plant (NPP) subjected to a large commercial aircraft impact. First, a simplified finite element model (F.E. model) of the large commercial Boeing 737 MAX 8 aircraft is established. The F.E. model of the AP1000 shield building is constructed, which is a reasonably simplified reinforced concrete structure. The effectiveness of both F.E. models is verified by the classical Riera method and the impact test of a 1/7.5 scaled GE-J79 engine model. Then, based on the verified F.E. models, the entire impact process of the aircraft on the shield building is simulated by the missile-target interaction method (coupled method) and by the ANSYS/LS-DYNA software, which is at different initial impact velocities and impact heights. Finally, the laws and characteristics of the aircraft impact force, residual velocity, kinetic energy, concrete damage, axial reinforcement stress, and perforated size are analyzed in detail. The results show that all of them increase with the addition to the initial impact velocity. The first four are not very sensitive to the impact height. The engine impact mainly contributes to the peak impact force, and the peak impact force is six times higher than that in the first stage. With increasing initial impact velocity, the maximum aircraft impact force rises linearly. The range of the tension and pressure of the reinforcement axial stress changes with the impact height. The perforated size increases with increasing impact height. The radial perforation area is almost insensitive to the initial impact velocity and impact height. The research of this study can provide help for engineers in designing AP1000 shield buildings.

• Earthquakes and Structures
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• 제7권4호
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• pp.463-484
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• 2014

Solid piers with a rounded rectangular cross-section are widely used in railway bridges for high-speed trains in China. Compared to highway bridge piers, these railway bridge piers have a larger crosssection and less steel reinforcement. Existing material models cannot accurately predict the seismic behavior of this kind of railway bridge piers. This is because only a few parameters, such as axial load, longitudinal and transverse reinforcement, are taken into account. To enable a better understanding of the seismic behavior of this type of bridge pier, a simultaneous influence of the various parameters, i.e. ratio of height to thickness, axial load to concrete compressive strength ratio and longitudinal to transverse reinforcements, on the failure characteristics, hysteresis, skeleton curves, and displacement ductility were investigated. In total, nine model piers were tested under cyclic loading. The hysteretic response obtained from the experiments is compared with that obtained from numerical studies using existing material models. The experimental data shows that the hysteresis curves have significantly pinched characteristics that are associated with small longitudinal reinforcement ratios. The displacement ductility reduces with an increase in ratio of axial load to concrete compressive strength and longitudinal reinforcement ratio. The experimental results are largely in agreement with the numerical results obtained using Chang-Mander concrete model.

• Earthquakes and Structures
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• 제17권5호
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• pp.435-445
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• 2019

The collapses of curved bridges are mainly caused by the damaged columns, subjected to the combined loadings of axial load, shear force, flexural moment and torsional moment, under earthquakes. However, these combined loadings have not been fully investigated. This paper firstly investigated the mechanical characteristics of the bending-torsion coupling effects, based on the seismic response spectrum analysis of 24 curved bridge models. And then 9 reinforced concrete (RC) and circular column specimens were tested, by changing the bending-tortion ratio (M/T), axial compression ratio, longitudinal reinforcement ratio and spiral reinforcement ratio, respectively. The results show that the bending-torsion coupling effects of piers are more significant, along with the decrease of girder curvature and the increase of pier height. The M/T ratio ranges from 6 to 15 for common cases, and influences the crack distribution, plastic zone and hysteretic curve of piers. And these seismic characteristics are also influenced by the compression ratio, longitudinal reinforcement ratio and spiral reinforcement ratios of piers.

• 해양환경안전학회지
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• 제24권4호
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• pp.438-444
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• 2018

최근 국내에서는 지구온난화로 인한 해수면 상승과 이에 따른 태풍 및 해일의 증가로 인해 22개항을 선정하여 방파제 보강 및 방호시설 설치 등의 공사를 시행중에 있다. 또한, 지속적인 선박대형화로 인해 대형선 접안을 위한 수심 준설, 접안부두 확장 등의 항만 공사를 수행하고 있으나, 접안선박의 안전한 계류와 밀접한 영향이 있는 마루높이의 상향 및 보강 등의 뚜렷한 공사 계획은 없는 실정이다. 본 연구는 국내 외 마루높이 설계기준을 분석하고, 환경 및 선박 요소로 나누어 마루높이 평가지표 및 평가방법을 개발하였다. 특히, 선박 평가지표의 경우 각 요소별로 국내 외 규정에 의거하여 4단계로 설정하고, 각 단계별로 평가값을 부여하여 평가값의 곱으로 마루높이 안전도를 평가하였다. 10만톤급 크루즈선의 계류안전성 시뮬레이션 결과, 적정 최저 마루높이 기준은 약최고고조위에서 3 m 상향된 값인 $H_3$으로 도출되었다. 본 연구 결과는 선박 특성을 반영한 부두 마루높이 기준을 제안하기 위한 기초 자료로 활용될 수 있을 것으로 기대된다.

• Structural Engineering and Mechanics
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• 제73권6호
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• pp.699-714
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• 2020

Force based design (FBD) approach is prevalent in most of the national seismic design codes world over. Direct displacement based design (DDBD) and energy based design (EBD) approaches are relatively new methods of seismic design which claims to be more rational and predictive than the FBD. These three design approaches are conceptually distinct and imparts different strength, stiffness and ductility property to structural members for same plan configuration. In present study behavioural assessment of frame of six storey RC building designed using FBD, DDBD and EBD approaches has been performed. Lateral storey forces distribution, reinforcement design and results of nonlinear performance using static and dynamic methods have been compared. For the three approaches, considerable difference in lateral storey forces distribution and reinforcement design has been observed. Nonlinear pushover analysis and time history analysis results show that in FBD frame plastic deformation is concentrated in the lower storey, in EBD frame large plastic deformation is concentrated in the middle storeys though the inelastic hinges are well distributed over the height and, in DDBD frame plastic deformation is approximately uniform over the height. Overall the six storey frame designed using DDBD approach seems to be more rational than the other two methods.

• 한국지진공학회논문집
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• 제11권4호
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• pp.1-11
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• 2007

This paper verifies the difference of the seismic behavior and seismic damage of the neighboring two reinforced concrete piers damaged by the 1995 Hyogoken Nanbu earthquake. The two piers were almost the same size, carrying slightly different dead load, and were provided with the same reinforcement arrangement except the amount of longitudinal reinforcement at the bottom portion of the piers. The pier with more reinforcement was completely collapsed due to this near field earthquake by shear failure at the longitudinal reinforcement cut-off while the other was only damaged at the bottom by flexure even though the longitudinal reinforcement cut-off was also existed at the mid height of the pier. According to the results of the pseudo dynamic test, the seismic damage was recognized to be greatly dependent on the ground motion characteristics even though the employed ground motions had the same peak acceleration. The severe damage was observed when the test employed the seismic wave that had strong influence to the longer period range compared to the initial natural period of the pier. On the other hand, based on the similar model experiment, the defect of gas-pressure welded splice of longitudinal reinforcement was revealed to save the piers against collapse due to the so-called fail-safe mechanism contrary to the intuitive opinion of some researchers. It was concluded that the primary cause of the collapse of the pier was the extremely strong intensity and peculiar characteristics of the earthquake motion according to both the site-specific and the structure-specific effects.

• 한국지반신소재학회논문집
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• 제18권1호
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• pp.55-65
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• 2019

본 연구에서는 최근 발생빈도가 증가하고 있는 지반함몰의 가장 큰 영향요소인 지중 공동에 대하여 콘크리트매트를 이용한 개착식 복구방법의 보강효과 분석을 위한 실험적 및 수치해석적 연구를 수행하였다. 먼저, 평판재하시험을 이용하여 지표로부터 10cm, 20cm, 30cm의 보강깊이에 대하여 콘크리트매트 보강에 따른 응력감소율을 평가한 결과, 약 60%의 응력감소 효과를 나타내었다. 또한 실내실험과 수치해석 결과를 이용하여 지반침하량과 응력감소율을 분석한 결과, 콘크리트매트 설치깊이가 지표로부터 10cm~20cm 깊이에서 보강효과가 우수한 것으로 확인되었다. 지반변형계수 측정을 위한 LFWD실험 결과, 콘크리트매트가 지표로부터 20cm의 깊이에 보강되었을 때의 변형계수가 가장 크게 나타났다. 따라서 지중 매설물 손상에 의한 지중공동이 포장체 하부까지 높이 방향으로 발달한 경우, 지표로부터 20cm 이내에 콘크리트 매트를 보강하는 것이 효과적인 것으로 분석되었다.