• 한국지반공학회논문집
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• 제24권9호
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• pp.23-32
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• 2008

본 논문에서는 계단식 형태로 시공되는 블록식 보강토 옹벽의 전체 안정성이 고려된 설계에 관한 내용을 다루었다. 다양한 계원과 이격거리로 설계된 네 가지 설계사례에 대해 현재 통용되고 있는 FHWA 및 NCMA 설계기준에 근거하여 내 외적 안정해석을 수행하고 그 결과를 토대로 두 설계기준의 차이점을 검토하였다. 아울러 대상옹벽에 대해 한계평형해석에 근거한 사면안정해석과 연속체역학 기반의 강도감소기법 해석을 수행하여 계단식 옹벽의 설계를 지배하는 파괴 메카니즘을 고찰하였다. 그 결과 내 외적 안정성 공히 FHWA에서 채택하고 있는 설계기준이 NCMA 보다 보수적인 결과(낮은 안전율)를 주는 것으로 나타났다. 또한 계단식 옹벽의 보강재의 소요 포설 길이는 전반적으로 전체 안정성에 좌우되는 것으로 검토되었으며 상부 옹벽의 보강재의 길이는 현 설계기준 보다 현저히 증가시켜야 하는 것으로 검토되었다.

• Journal of Advanced Marine Engineering and Technology
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• 제21권5호
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• pp.512-521
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• 1997

This paper deals with an evaluation of the residual stress due to shot peening induced in a car¬burized gear tooth and its application to the fatigue crack propagation problem. The residual stress is estimated based on the assumption that the main cause of residual stress is the volume difference between the case and core due to martensitic transformation in cooling, and the influ¬ence of both the reduction of retained austenite and the strain in the surface layer induced by shot peening are considered. The reliability of the method is examined by comparison with stresses measured by the X-ray diffraction method. The stresses intensity factors are computed by the influence function method and the reduction of the factor due to the residual stress is demonstrat¬ed and discussed based on the fracture mechanics.

• Earthquakes and Structures
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• 제13권4호
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• pp.337-351
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• 2017

In the present study a capacity spectrum method based on constant ductility inelastic spectra to estimate the seismic performance of structures equipped with elastic viscous dampers is presented. As the definition of the structures' effective damping, due to the damping system, is necessary, an alternative method to specify the effective damping ratio ${\xi}eff$ is presented. Moreover, damping reduction factors (B) are introduced to generate high damping elastic demand spectra. Given the elastic spectra for damping ratio ${\xi}eff$, the performance point of the structure can be obtained by relationships that relate the strength demand reduction factor (R) with the ductility demand factor (${\mu}$). As such expressions that link the above quantities, known as R - ${\mu}$ - Τ relationships, for different damping levels are presented. Moreover, corrective factors (Bv) for the pseudo-velocity spectra calculation are reported for different levels of damping and ductility in order to calculate with accuracy the values of the viscous dampers velocities. Finally, to evaluate the results of the proposed method, the whole process is applied to a four-storey reinforced concrete frame structure and to a six-storey steel structure, both equipped with elastic viscous dampers.

• Journal of the Korean Wood Science and Technology
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• 제24권3호
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• pp.65-71
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• 1996

In the design of wood structures, the consideration of the dynamic load effect has been increased. Generally, damping ratio is presented as the method of considering dynamic load effect. So, the relationship between joint type and damping ratio was investigated. It has been known that the joint extremely damp the dynamic load in wood structures. Static test was performed to determine the effects of nail size and friction area on joint strength and stiffness. Joint strength and stiffness were increased with nail size. However, the static properties of joint was not affected by friction area. Cyclic test was performed to determine the effects of nail size, friction area and load magnitude on damping ratio, Damping ratio was affected by all factors. Increasing the width of the bottom plate was suggested as the most adequate method to increase the damping ratio without the reduction of the static properties of the structures.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2003년도 추계학술대회 논문집(III)
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• pp.446-454
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• 2003

This paper derived a theoretical method to estimate structural characteristics of carbody members when material substitution designs were performed, and verified the theoretical method with finite element analyses. For important factors in rolling stock design, such as bending stiffness, natural frequency, bending strength and buckling strength, some performance indices to estimate structural behaviors were developed in order to derive an equivalent design in spite of material substitutions. The developed method was used to reduce the weights of carbody components, as example problems, by substituting the aluminium alloy for the structural steel. The analysis results of the examples show that the proposed technique gives a reasonable initial guess in the case of a material substitution design.

• 대한기계학회논문집A
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• 제27권5호
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• pp.724-733
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• 2003

Fatigue design rules for welds in the ASME Boiler and Pressure Vessels Code are based on the use of Fatigue Strength Reduction Factors(FSRF) against a code specified fatigue design curve generated from smooth base metal specimens without the presence of welds. Similarly, stress intensification factors that are used in the ASME B3l.1 Piping Code are based on component S-N curves with a reference fatigue strength based on straight pipe girth welds. But the determination of either the FSRF or stress intensification factor requires extensive fatigue testing to take into account the stress concentration effects associated with various types of component geometry, weld configuration and loading conditions. As the fatigue behavior of welded joints is being better understood, it has been generally accepted that the difference in fatigue lives from one type of weld to another is dominated by the difference in stress concentration. However, general finite element procedures are currently not available for effective determination of such stress concentration effects. In this paper, a mesh-insensitive structural stress method is used to re-evaluate the S-N test data, and then more effective method is proposed for pressure vessel and piping fatigue design.

• 한국터널지하공간학회 논문집
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• 제13권2호
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• pp.115-131
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• 2011

최근 들어 방재 및 환경훼손 측면을 고려하여 병설터널의 시공 사례가 증가하고 있다. 병설터널의 굴착 시 필라(Pillar)부에 응력이 집중되어 터널의 안정성이 저하된다. 필라부의 거동에 대한 기존 연구들은 주로 수치해석과 실내 모형 실험을 통한 병설터널의 거동평가 및 지표침하 경향 분석 등에 국한되어 있어서, 필라부의 정량적 안정성 평가에는 한계가 있다. 따라서 본 연구에서는 병설터널의 필라폭이 터널의 안정성에 미치는 영향을 정량적으로 살펴보았다. 이를 위해 토피고가 다른 두 단면에 대해 전단강도 감소법을 이용한 수치해석적 방법으로 구한 터널 전체 안전율, Matsuda 등이 제안한 식을 이용하여 구한 필라부 국부안전율, 및 필라부의 강도/응력비를 산정하고 결과를 분석하였다. 합리적인 병설터널의 필라부 설계를 위해, 평균 강도/응력비, Matsuda 제안식에 의한 안전율, 수치해석적으로 구한 전체 안전율이 독립적으로 사용되기보다는 유기적으로 사용되어야 할 것으로 판단되었다.

• 한국지반환경공학회 논문집
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• 제8권4호
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• pp.57-65
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• 2007

토목구조물의 안정성에 영향을 미치는 인자 중 지진에 의한 피해를 들 수가 있다. 최근의 지진 피해 사례를 분석하여 보면 모래와 같은 조립토뿐만 아니라 점성토, 실트 등과 같은 세립토에서도 크고 작은 피해 사례가 보고되고 있다. 이에 본 연구에서는 지진에 의한 기초지반의 강도저하를 평가하는 방법을 조사하기 위하여, 반복단순전단시험기를 이용하여 비배수상태에서 조립토 및 세립토에 반복하중을 작용시켜 지반의 강도저하특성을 조사하고 조립토의 경우에는 여유간극비, 세립토의 경우에는 소성지수를 이용하여 간단한 평가방법을 제안하였다. 분석결과에 따르면 액상화강도를 비교 분석하여 보면 조립토에서는 여유간극비의 증가에 따라 감소하고, 세립토의 경우에는 소성지수가 증가함에 따라 커지는 것을 알았다. 특히, 화강풍화토는 Collapse현상이 발생하여 다른 흙보다 현저한 강도 감소 경향이 나타났다. 간이강도저하 평가방법을 통해서 조립토와 세립토 거의 대부분이 양대수곡선상에서 -0.15 ~ -0.2의 범위내의 비슷한 기울기 내에서 분포하였지만, 화강풍화토와 같은 흙은 강도저하 경향이 -0.3으로 다른 흙보다 크게 나타남을 알 수 있었다. 본 강도저하 평가방법은 추가 연구가 필요하지만, 실무에서 간단하게 적용 가능할 것으로 보인다.

• 한국재료학회지
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• 제22권2호
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• pp.71-77
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• 2012

When a new bonding agent using coal ash is utilized as a substitute for cement, it has the advantages of offering a reduction in the generation of carbon dioxide and securing the initial mechanical strength such that the agent has attracted strong interest from recycling and eco-friendly construction industries. This study aims to establish the production conditions of new hardening materials using clean bottom ash and an alkali activation process to evaluate the characteristics of newly manufactured hardening materials. The alkali activator for the compression process uses a NaOH solution. This study concentrated on strength development according to the concentration of the NaOH solution, the curing temperature, and the curing time. The highest compressive strength of a compressed body appeared at 61.24MPa after curing at $60^{\circ}C$ for 28 days. This result indicates that a higher curing temperature is required to obtain a higher strength body. Also, the degree of geopolymerization was examined using a scanning electron microscope, revealing a micro-structure consisting of a glass-like matrix and crystalized grains. The microstructures generated from the activation reaction of sodium hydroxide were widely distributed in terms of the factors that exercise an effect on the compressive strength of the geopolymer hardening bodies. The Si/Al ratio of the geopolymer having the maximum strength was about 2.41.

• Steel and Composite Structures
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• 제33권6호
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• pp.849-864
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• 2019

One way to achieve sustainable construction is to reduce concrete consumption by use of more sustainable and higher strength concrete. Modern building codes do not cover the use of ultra-high strength concrete (UHSC) in the design of composite structures. Against such background, this paper investigates experimentally the mechanical properties of steel fibre-reinforced UHSC and then the structural behaviors of UHSC encased steel (CES) members under both concentric and eccentric compressions as well as pure bending. The effects of steel-fibre dosage and spacing of stirrups were studied, and the applicability of Eurocode 4 design approach was checked. The test results revealed that the strength of steel stirrups could not be fully utilized to provide confinement to the UHSC. The bond strength between UHSC and steel section was improved by adding the steel fibres into the UHSC. Reducing the spacing of stirrups or increasing the dosage of steel fibres was beneficial to prevent premature spalling of the concrete cover thus mobilize the steel section strength to achieve higher compressive capacity. Closer spacing of stirrups and adding 0.5% steel fibres in UHSC enhanced the post-peak ductility of CES columns. It is concluded that the code-specified reduction factors applied to the concrete strength and moment resistance can account for the loss of load capacity due to the premature spalling of concrete cover and partial yielding of the encased steel section.