• Structural Engineering and Mechanics
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• 제44권6호
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• pp.775-799
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• 2012

This work approaches the structural performance of masonry arches that have a small ratio between number of vossoirs and span length. The aim of this research is to compare and validate three different methods of analysis (funicular limit analysis F.L.A., kinematic limit analysis K.L.A. and plane stress Finite Element Analysis F.E.A.) with an experimental campaign. 18 failure tests with arches of different shapes and boundary conditions have been performed. The basic failure mechanism was the formation of enough hinges in the geometry. Nevertheless, in few cases, sliding between vossoirs also played a relevant influence. Moreover, few arches didn't reach the collapse. The FLA and KLA didn't find a solution close to the experimental values for some of the tests. The low number of vossoirs and joints become a drawback for an agreement between kinematic mechanism, equilibrium of forces and geometry constraints. FLA finds a lower bound whereas KLA finds an upper bound of the ultimate load of the arch. FEA is the most reliable and robust method and it can reproduce most of the mechanism and ultimate loads. However, special care is required in the definition of boundary conditions for FEA analysis. Scientific justification of the more suitability of numerical methods in front of classic methods at calculating arches with a few vossoirs is the main original contribution of the paper.

• 대한기계학회논문집
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• 제15권2호
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• pp.404-412
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• 1991

In the design of high speed machinery, designers must consider the problem of possible structural failure due to excessive dynamically varying stresses, which are induced by the varying external loads and internal inertia forces, in the links of the mechanism. A study of the dynamically induced stresses would indicate what values of the minimum permissible fatigue strength should be for safe mechanism operation. This paper investigates the nature of the stress fluctuation in high speed mechanism on the basis of the effects of both the loads and the friction. The latter is apt to be neglected in the usual analysis in spite of the fact that it is always generated in the operating machinery. The analysis is performed on the coupler of the slider-crank mechanism for illustrative purposes and the results are expressed in a non-dimensional form for design applications.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2006년도 추계 학술논문 발표대회 논문집
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• pp.99-102
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• 2006

This paper reviews the relevant literatures and investigates spalling mechanism of high strength concrete, in order to clearly inform spalling problem in fire. Firstly, we studies literatures on spalling occurrence and resistance methods. Secondly chemical change of concrete components in elevated temperature was presented. Finally, mechanism of the spalling occurrence and spalling resistance were carried out with fiber content. In addition, our research team introduced spalling mechanism, being different from other points of view, which has been generally accepted. To secure this mechanism theory, we investigate spalling properties of certain specimens fabricated by roller spindle and made with mortar or concrete condition.

• 콘크리트학회논문집
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• 제15권2호
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• pp.297-304
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• 2003

본 연구에서는 철근콘크리트 기둥과 철골보로 구성된 혼합 골조구조의 접합부에 대한 구조적 특성을 평가하였다. 주요변수로는 본 연구에서 제안한 자주식(子株式) 횡보강근 상세와 기존의 RCS 공법에서 사용되고 있는 ㄱ-4조각 조합형 및 용접형 등의 횡보강근 상세를 대상으로 하였다. 실험체는 총 5개의 내부접합부를 대상으로 2/3 축소로 제작하여 접합부의 전단 및 내진성능을 평가하였다. 실험의 결과, 모든 실험체에서 최대내력 이후 강도 및 강성의 큰 저하없이 실험이 종료되었다. 따라서, 자주식(子株式) 횡보강근을 사용한 RCS 접합부의 구조성능은 4조각 조합형 및 용접형 등의 기존 공법과 동등 이상의 구조적 성능을 확보하는 것으로 나타나 외부 판넬의 전단기여도는 압축스트러트에 의해 평가하는 것이 보다 적절할 것으로 판단된다.

• 한국환경과학회지
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• 제14권8호
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• pp.723-737
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• 2005

The effects of pH (5, 7 and 9) and ionic strength of different salts on the flocculation characteristics of humic acid by inorganic (alum, polyaluminum chloride (PAC) with degree of neutralization, r=(OH/Al) of 1.7) and organic (cationic polyelectrolyte) coagulants, have been examined using a simple continuous optical technique, coupled with measurements of zeta potential. The results are compared mainly by the mechanisms of its destabilization and subsequent removal. The destabilization and subsequent removal of humic acid by PAC and cationic polyelectrolyte occur by a simple charge neutralization, regardless of pH of the solution. However, the mechanism of those by alum is greatly dependent on pH and coagulant dosage, i.e., both mechanisms of charge neutralization at lower dosages and sweep flocculation at higher dosages at pH 5, by sweep flocculation mechanism at pH 7, and little flocculation because of electrostatic repulsion between negatively charged humic acid and aluminum species at pH 9. The ionic strength also affects those greatly, mainly based on the charge of salts, and so is more evident for the salts of highly charged cationic species, such as $CaCl_2$ and $MgCI_2.$ However, it is found that the salts have no effect on those at the optimum dosage for alum acting by the mechanism of sweep flocculation at pH 7, regardless of their charge.

• 한국구조물진단유지관리공학회 논문집
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• 제18권1호
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• pp.84-92
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• 2014

본 연구는 조강시멘트와 경화촉진제를 사용하여 조기강도 발현의 메커니즘을 분석하는 것이 목적이다. 연구결과 경화촉진제는 시멘트와의 수화반응시 $Ca(OH)_2$의 촉진시키는 것을 TG/DTA 실험을 통하여 검정하였다. 압축강도 측정결과 경화촉진제의 사용량이 증가 할수록 초기압축강도가 증가하는 것을 알 수 있었다. 또한 미소수화열 측정결과 경화촉진제는 시멘트의 성분중 $C_3S$의 수화반응을 촉진시키는 것으로 나타났다. XRD분석결과 재령별 수화생성물을 확인할 수 있었으며 경화촉진제의 사용량이 증가할수록 수화물들의 피크점이 높게 나타나는 것을 알 수 있었다. SEM찰영을 한 결과 촉진제의 첨가량에 따라 $Ca(OH)_2$의 생성과 재령에 따라 C-S-H의 형상을 관찰할 수 있었다. 따라서 본 연구에서 사용된 경화촉진제는 초기강도발현 시키는 것에 대해 효과적인 것을 확인 할 수 있었다.

• 한국구조물진단유지관리공학회 논문집
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• 제18권3호
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• pp.28-39
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• 2014

본 연구에서는 우선 화재에 노출된 고강도 콘크리트의 내화특성과 폭렬 메커니즘을 규명한 기존 국내외 연구자들의 연구문헌들을 심도 깊게 고찰하였다. 그 후 고온을 받은 고강도 콘크리트에 대한 국내외 연구자들의 주요 실험 변수를 분석하여 가장 최적의 변수를 설정하였으며 이를 토대로 하여 100MPa급 고강도 콘크리트의 내화 특성을 규명하기 위한 내화실험을 계획하였다. 또한 기존 연구의 실험결과를 분석한 결과 폭렬방지에 효과가 있는 것으로 알려져 있는 PP섬유와 친수성 재료로서 시멘트 입자와 부착성능이 우수하고 워커빌리티를 개선할 수 있는 NY섬유를 혼합한 신재료 HB섬유를 섬유혼입률 0.05%로 정해 배합설계에 반영하였다. 이러한 배합설계로 타설한 총 48개의 공시체를 28일 양생기간 후 온도변화 ($100^{\circ}C{\sim}700^{\circ}C$)에 따른 고강도 콘크리트의 역학적 특성을 분석하기 위해 화재를 받은 후 냉간상태에서의 내화실험을 수행하였으며 이를 통해 고강도 콘크리트의 내화 특성을 분석하였다.

• Computers and Concrete
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• 제33권2호
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• pp.217-240
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• 2024

The purpose of this study is to propose new hysteretic characteristics of medium- to low-rise RC structures controlled by both shear and flexure. Through previous study, the dual lateral force-resisting system composed of shear and flexural failure members has a new failure mechanism that cooperates to enhance the flexural capacity of the flexural failure member even after the failure of the shear member, and the existing theoretical equation significantly underestimates the ultimate strength. In this study, the residual lateral strength mechanism of the dual lateral force-resisting system was analyzed, and, as a result, an equation for estimating the residual flexural strength of each shear-failure member was proposed. The residual flexural strength of each shear-failure member was verified in comparison with the structural testing results obtained in previous study, and the proposed residual flexural strength equation for shear-failure members was tested for reliability using FEA, and its applicable range was also determined. In addition, restoring-force characteristics for evaluating the seismic performance of the dual lateral force-resisting system (nonlinear dynamic analysis), reflecting the proposed residual flexural strength equation, were proposed. Finally, the validity of the restoring-force characteristics of RC buildings equipped with the dual lateral force-resisting system proposed in the present study was verified by performing pseudo-dynamic testing and nonlinear dynamic analysis based on the proposed restoring-force characteristics. Based on this comparative analysis, the applicability of the proposed restoring-force characteristics was verified.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.429-432
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• 2006

The shrinkage mechanism of high strength concrete is different from that of normal concrete. The shrinkage of normal concrete is subjected to evaporate moisture in concrete, but most shrinkage in high strength concrete is caused by chemical reaction. To analyze shrinkage of concrete exactly, it is necessary to divide drying shrinkage with autogenous shrinkage in terms of degree of hydration, especially in concrete with low W/C ratio. The proposed method can provide a rational basis for prediction of shrinkage in high strength concrete structure.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.239-243
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• 2003

A reducing bearing angle theory for bond of ribbed reinforcing bars to concrete is proposed to simulate experimental observation. Analytical expressions to determine bond strength for splitting and pullout failure are derived, where the bearing angle is a key variable. As bearing angle is reduced, splitting strength decreases and shearing strength increases. The proposed reducing bearing angle theory is effective to simulate damage of the deformed bar-concrete interface and understand bond mechanism of ribbed reinforcing steel in concrete structures.