• Wind and Structures
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• 제19권3호
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• pp.339-352
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• 2014

This paper discusses the appropriate duration for basic gust wind speeds in wind loading codes and standards, and in wind engineering generally. Although various proposed definitions are discussed, the 'moving average' gust duration has been widely accepted internationally. The commonly-specified gust duration of 3-seconds, however, is shown to have a significant effect on the high-frequency end of the spectrum of turbulence, and may not be ideally suited for wind engineering purposes. The effective gust durations measured by commonly-used anemometer types are discussed; these are typically considerably shorter than the 'standard' duration of 3 seconds. Using stationary random process theory, the paper gives expected peak factors, $g_u$, as a function of the non-dimensional parameter ($T/{\tau}$), where T is the sample, or reference, time, and ${\tau}$ is the gust duration, and a non-dimensional mean wind speed, $\bar{U}.T/L_u$, where $\bar{U}$ is a mean wind speed, and $L_u$ is the integral length scale of turbulence. The commonly-used Durst relationship, relating gusts of various durations, is shown to correspond to a particular value of turbulence intensity $I_u$, of 16.5%, and is therefore applicable to particular terrain and height situations, and hence should not be applied universally. The effective frontal areas associated with peak gusts of various durations are discussed; this indicates that a gust of 3 seconds has an equivalent frontal area equal to that of a tall building. Finally a generalized gust response factor format, accounting for fluctuating and resonant along-wind loading of structures, applicable to any code is presented.

• Steel and Composite Structures
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• 제21권3호
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• pp.629-659
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• 2016

In cold-formed stainless steel lipped channel-sections, web openings are becoming increasingly popular. Such openings, however, result in the sections becoming more susceptible to web crippling, especially under concentrated loads applied near the web opening. This paper presents the results of a finite element parametric study into the effect of circular web openings on the web crippling strength of cold-formed stainless steel lipped channel-sections for the interior-one-flange (IOF) loading condition. This involves a bearing load applied to the top flange of a length of member, away from the end supports. The cases of web openings located centred beneath the bearing load (i.e. beneath the bearing plate delivering the load) and offset to the bearing plate, are considered. Three grades of stainless steel are considered: duplex EN1.4462, austenitic EN1.4404 and ferretic EN1.4003. In total, 2218 finite element models were analyzed. From the results of the parametric study, strength reduction factors for load bearing capacity are determined, where these reduction factors are applied to the bearing capacity calculated for a web without openings, to take account the influence of the web openings. The strength reduction factors are first compared to equations recently proposed for cold-formed carbon steel lipped channel-sections. It is shown that for the case of the duplex grade, the strength reduction factor equations for cold-formed carbon steel are conservative but only by 2%. However, for the cases of the austentic and ferritic grades, the cold-formed carbon steel equations are around 9% conservative. New strength reduction factor equations are proposed for all three stainless steel grades.

• Steel and Composite Structures
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• 제17권5호
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• pp.601-621
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• 2014

Repairing and strengthening structural members by bonding composite materials have received a considerable attention in recent years. The major problem when using bonded FRP or steel plates to strengthen existing structures is the high interfacial stresses that may be built up near the plate ends which lead to premature failure of the structure. As a result, many researchers have developed several analytical methods to predict the interface performance of bonded repairs under various types of loading. In this paper, a numerical solution using finite - difference method (FDM) is used to calculate the interfacial stress distribution in beams strengthened with FRP plate having a tapered ends under thermal loading. Different thinning profiles are investigated since the later can significantly reduce the stress concentration. In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both beam and bonded plate. The shear correction factor for I-section beams is also included in the solution. Numerical results from the present analysis are presented to demonstrate the advantages of use the tapers in design of strengthened beams.

• Geomechanics and Engineering
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• 제27권6호
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• pp.583-594
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• 2021

The gas permeability behavior of unsaturated bentonite-based materials is of major importance for ensuring effective sealing of high-level radwaste repositories. This study investigated this by taking a sample of Granular Bentonite Material (GBM) at the end of the Engineered Barrier Emplacement (EB) experiment in the Opalinus Clay, placing it under different humidity conditions until it achieved equilibration, and testing the change in the gas permeability under loading and unloading. Environmental humidity is shown to have a significant effect on the water content, saturation, porosity and dry density of GBM and to affect its gas permeability. Higher sensitivity to confining pressure is exhibited by samples equilibrated at higher relative humidity (RH). It should be noted that for the sample at RH=98%, when the confining pressure is raised from 1 MPa to 6 MPa, gas permeability can be reduced from 10^-16 m² to 10^-19 m², which is close to the requirements of gas tightness. Due to higher water content and easier compressibility, samples equilibrated under higher RH show greater irreversibility during the loading and unloading process. The effective gas permeability of highly saturated samples can be increased by 2-3 orders of magnitude after 105℃ drying. In addition, cracks possibly occurred during the dehydration and drying process will become the main channel for gas migration, which will greatly affect the sealing performance of GBM.

• 대한토목학회논문집
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• 제29권2A호
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• pp.109-118
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• 2009

이 연구에서는 CFT부재를 거더로 사용하는 신형식 강합성 교량 시스템 개발을 최종목표로 하고, CFT부재의 휨거동 특성을 규명하기 위한 부재실험을 수행하였다. 실험체는 충전재 강도 및 합성조건 변화 등 설계에 영향을 미치는 주요 매개변수를 고려하여 제작하였고, 휨재하 실험의 결과분석을 통해 CFT부재가 갖는 내력성능을 효율적으로 설계에 반영하기 위한 방안을 고찰하였다. 충전강관은 중공강관에 비해 휨강도 및 연성이 크게 증가함을 확인할 수 있었으며, 콘크리트의 취성적 재료 특성이 강관의 구속효과로 보완되는 결과를 확인하였다. 내부 전단연결재를 둠으로써 충전재와 강관 사이의 미끄러짐을 억제하여 완전합성단면으로 거동하였고, ㄱ형 전단연결재의 보강재 효과가 휨내력 증가에 다소 기여하고 있음을 알 수 있었다.

• 한국지반환경공학회 논문집
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• 제4권3호
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• pp.19-26
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• 2003

최근 연약지반상의 말뚝기초설계에 있어서 경시효과는 말뚝의 지지력 특성을 나타내는 중요한 요소 중의 하나로 인식되고 있다. 본 논문에서는 이러한 지지력 증가효과를 연구하기 위해 두 곳의 현장에서 13개의 말뚝에 대해, 항타시 EOID(초기 동재하시험)을 실시한 후 일정한 시간이 경과한 다음 재항타시험을 수행하였다. 느슨한 실트지반에 H말뚝, 강관말뚝, PHC말뚝을 항타에 의해 설치하고 9일 후 재항타 한 결과 H말뚝, 강관말뚝의 경우 지지력이 증가된 반면, PHC말뚝은 지지력의 증가가 거의 없는 것으로 나타났다. 7일 후 재항타시험을 수행한 결과 단단한 실트지반의 경우 H말뚝과 강관말뚝은 지지력이 1.17배 증가하였다. 그러나 PHC말뚝의 경우 6일 후 수행한 제 1차 재항타시험에서는 지지력이 감소하였다가, 13일 후 수행한 3차 재항타시험에서는 지지력이 1.38배 정도 증가하는 것으로 나타났다.

• 수산해양기술연구
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• 제51권4호
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• pp.512-519
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• 2015

A historical tragic disaster happened by capsizing the passenger ship Sewol at South Western Sea of Korea in 16, April 2014. The ship which left Incheon harbour to bound for Jeju port passed Maengol strait and reached to approach of Byung Pung island, and then capsized and sank with a sudden inclination to the portside in the mean time of starboard the helm. In this time, the ship which has very poor stability without sufficient ballast waters and with over loading cargo listed port side caused by the centrifugal force acting to the outside of turning. A lot of cargoes not fastened moved to the port side consequently, and the ship came to beam end to capsize and sank in the end. No crews including especially captain would offer their own duties in a such extremely urgent time, as a result, enormous number of victims broke out including a lot of student. In this report, author carried out some calculation on the factors which influenced on the stability of the ship, i.e. the ship's speed, the rudder angle, the weight of cargoes and distance of movement, the surface effect of liquid in the tank. We found out that the most causes of capsize were the poor stability with heavy cargoes and insufficient amount of ballast water against the rule, and the cargoes unfastened moved one side to add the inclination as well. Above all, the owner be blamable because of the illegally operating the ship without keeping the rule.

• 한국지반신소재학회논문집
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• 제8권2호
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• pp.11-20
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• 2009

본 연구는 국내의 초연약지반에 적용 가능한 표층보강재를 이용한 연약지반 표층처리공법을 정립시키기 위한 기초적 연구로서 표층처리공법 지지력 산정방법을 제안하는 것을 목적으로 하고 있다. 이를 위하여 직포, 지오그리드, 강봉(대나무 대채재료)을 이용한 보강재의 단부 구속조건을 완전구속, 부분구속(3종류)으로 한 21 종류의 실내모형실험을 수행하였다. 또한 실험결과를 이용해 보강재의 강성도가 지지력효과에 미치는 영향을 고려한 지지력 산정방법을 제안하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제24권2호
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• pp.111-118
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• 2020

이 논문에서는 섬유의 혼입량에 따른 휨부재의 장기거동에 대한 영향을 평가하기 위하여 후크형 강섬유로 보강된 고강도 콘크리트의 휨 크리프 거동에 대한 평가가 이루어졌다. 실험은 150 × 150 × 600mm 크기를 갖는 섬유 혼입량(0, 0.75 및 1.5%)을 변수로 하는 6개의 휨 시험체를 대상으로 하였다. 노치를 갖는 휨 시험체에 휨 크리프 하중을 도입하기 위하여 4점 가력 휨 시험장치가 활용되었다. 휨강도의 40%인 크리프 재하하중은 레버 장치를 활용하여 도입되었고 90일 동안 도입된 하중은 로드셀에 의해 제어되었다. 크리프 하중의 도입시, 시험체 중앙부에 설치된 노치의 균열개구변위(CMOD)가 측정되었다. 크리프 시험후 각 시험체 대한 휨시험을 실시하여 각 시험체의 잔여강도를 평가하였다. 이상과 같은 실험결과로부터 섬유 혼입량은 고강도 콘크리트의 휨 크리프 거동에 주요한 영향을 끼치고 휨강도의 40% 범위내의 지속하중은 섬유보강된 고강도 콘크리트의 잔여강도에 부정적인 영향을 끼치지 않았다.

• 한국지반환경공학회 논문집
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• 제2권3호
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• pp.71-80
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• 2001

쇄석말뚝-매트로 구성된 기초시스템은 지지력이 여러 인자에 의해 영향을 받게 되어 기초지반과 말뚝체의 상호작용을 정량적으로 평가하기에 어려움이 있다. 복합지반의 지지력은 말뚝-흙 경계면의 측방응력에 의해 발생되므로 쇄석말뚝의 거동을 규명하기 위해서는 경계면에서 발생하는 수평저항력에 영향을 미치는 인자들에 대한 평가가 필요하다. 또한, 말뚝간격과 근입비, 파괴각 등 기하학적 요인들도 영향을 미치는 것으로 알려져 있다. 따라서, 본 논문에서는 쇄석말뚝-매트로 구성된 기초시스템의 선단지지 단일말뚝과 군말뚝에 대한 실내모형실험을 통하여 쇄석말뚝의 한계깊이를 측정하고 파괴각에 영향을 미치는 인자들을 평가하였다. 또한, 실내실험결과를 이론식과 비교하였으며 유한요소해석을 통해 파괴거동을 평가하여 실내모형실험의 타당성을 검증하였다.