• Magazine of the Korea Concrete Institute
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• v.10 no.1
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• pp.179-188
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• 1998

캔틸레버 공법으로 시공되는 프리스트레스트 콘크리트 박스거더 교량의 구조적 거동은 단계적 시공에 따른 구조물의 순차적 변화 및 콘크리트의 재료적 특성에 의해 시간 의존적 거동을 나타낸다. 콘크리트의 시간의존적 특성, 즉 콘크리트의 크리프 및 건조수축 특성은 현장타설 세그멘탈 캔딜레버공법으로 가설되는 콘크리트 교량의 설계 및 시공에서 매우 중요한 역할을 한다. 본 연구에서는 콘크리트의 크리프 및 건조수축 특성이 교량의 시간의존적 거동, 특히 처짐 및 텐던응력예측에 미치는 영향을 연구하였다. 교량해석은 본 연구진에 의해 개발된 프리스트레스트 콘크리트 교량해석기법 및 프로그램을 이용하여 크리프의 ACI 모델, CEB-FIB모델, 그리고 국내 도로교 시방서 모델을 고려하여 해석하였다. 해석결과 최종크리프 값의 크기에 따라 장기처짐의 발생량이 차이가 큰 것으로 나타나고 있으며, 최종건조수축량과 상대습도도 영향을 주는 것으로 나타났다. 또한 ACI 모델과 CEB-FIB모델간에도 차이가 큰 것으로 나타나 실제교량의 크리프 특성 및 건조수축 특성의 정확한 예측이 교량의 정밀시공 및 거동예측에 매우 중요한 것으로 나타나고 있다.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.7
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• pp.19-26
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• 2018

This study tested 25 lightweight aggregate concrete (LWAC) mixtures using the expanded bottom ash and dredged soil granules to examine the compressive strength gain of such concrete with different ages. The test parameters investigated were water-to-cement ratios and the natural sand content for the replacement of lightweight fine aggregate. The compressive strength gain rate in the basic equation specified in fib model code was experimentally determined in each mixture and then empirically formulated as a function of the water-to-cement ratio and oven-dried density of concrete. When compared with 28-day compressive strength, the tested LWAC mixtures exhibited relatively low gain ratios (0.49~0.82) at an age of 3 days whereas the gain ratios (1.16~1.41) at 91 days were higher than that (1.05~1.15) of the conventional normal-weight concrete. Thus, the fib model equations tend to overestimate the early strength gain of LWAC but underestimate the long-term strength gain. The proposed equations are in good agreement with the measured compressive strength development of LWAC at different ages, indicating that the mean and standard deviation of the normalized root mean square errors determined in each mixture are 0.101 and 0.053, respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.265-268
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• 2008

Slab-column joints have been used in the constructions of many structures and buildings. However, as the prediction of the failure behavior and ultimate strength of the joints subjected to lateral loadings is very difficult, the current building and structural design codes do not explain the failure behavior of the joints clearly. In this study, the applicability of the 3-dimensional grid strut-tie model approach, suggested for analysis and design of 3-dimensional structural concrete with disturbed regions, to the ultimate analysis and design of the joints is examined by evaluating the failure strengths of 43 slab-column joints tested to failure. The validity of the 3-dimensional grid strut-tie model approach is also verified by comparing the strength evaluation results with those by ACI 318-05 and FIB 1999.

• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.343-350
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• 2014

A probabilistic construction stage analysis using the Monte Carlo Simulation was performed to address the effects of uncertainty regarding the material properties, environmental factors, and applied forces. In the previous research, creep and shrinkage were assumed to be completely independent random variables. However, because of the common influencing factors in the material models for the creep and shrinkage estimation, strong correlation between creep and shrinkage can be presumed. In this paper, an Monte Carlo Simulation using CEB-FIB creep and shrinkage equations were performed to actually evaluate the correlation coefficient between two phenomena, and then another Monte Carlo Simulation to evaluate the statistical properties of axial strain affected by partially correlated random variables including the material properties, environmental factors, and applied forces. The results of Monte Carlo Simulation were compared with measured strains of a column on a first story in a 58-story building. Comparison indicated that the variation due to the uncertainty related with the material properties were most severe. And measured strains was within the range of mean+standard deviation.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.517-517
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• 2013

세포막지질의 산화는 심각한 세포막의 기능저하를 유발하고 심하면 세포를 죽음에 이르게하여 생물학적으로 중요한 지표이다. 세포막지질의 산화는 간접적인 화학적 방법으로 측정하거나, 지질을 추출해내어 질량분석기나 핵자기공명분광기 같은 물리적 방법으로 분석한다. 우리는 이온유도 이차전자 방출계수(${\gamma}$) 변화를 측정하여 세포막지질의 산화를 지질추출 없이 측정할 수 있는지 조사해 보았다. 세포막분리가 쉬운 적혈구를 모델세포로 사용하였고, 다양한 라디칼을 발생시키는 대기압 공기 DBD플라즈마 장치를 이용하였다. 적혈구를 플라즈마에 노출하는 시간으로 산화의 정도에 차이를 만들어 측정값과 비교하였다. ${\gamma}$값은 Auger의 중화이론에 바탕을 둔 이온유도 이차전자 방출빔(${\gamma}$-FIB)장비를 이용하여 측정하였다. 측정결과 적혈구가 산화됨에 따라서 ${\gamma}$값이 증가함을 볼 수 있었고, 동시에 workfunction값이 변화함을 보았으며, 그 결과를 화학적 방법과 비교해 보았다.

• Magazine of the Korea Concrete Institute
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• v.9 no.6
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• pp.147-156
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• 1997

지금까지 국내에서는 콘크리트의 크리프에 관한 실험적 연구가 많이 진행되지 못하여 해당 구조물의 설계기술 도입국의 규준에 따라 크리프를 예측해왔다. 그러나 예측된 크리프 모델이 국내 콘크리트 재료의 특성에 적합한지에 대한 실험적 검증은 제대로 이루어지지 않고 있는 실정이다. 본 연구에서는 국내에서 프리스트레스 콘크리트 구조물에 적용하는 실용 고강도 콘크리트의 크리프 값을 예측하기 위해 동일한 설계기준강도를 갖는 세 가지 배합에 대하여 재령별로 크리프 시험을 수행하고 이 실험결과를 ACI, CEB/FIB, KSCE, JSCE규준들의 크리프 예측식과 비교 분석하였다.시험결과와 이들규준들에 대한 비교분석에 의하면 CEB/FIB-90 크리프 예측식은 비교적 과대 평가되고 ACI 209-92와 JSCE-96의 경우는 과소 평가되었으나 콘크리트 표준시방서 KSCE -96 크리프 예측식은 비교적 시험결과에 근접하는 것으로 평가되었다. 그러나 구성재료의 양적 변동에 '따른 배합별 시험결과의 차이를 반영할 수 있는 점이 보완되어야 할 것으로 보며 향후 많은 실험결과를 바탕으로 국내에서 생산되는 콘크리트에 대하여 보다 정확히 크리프를 예측할 수 있는 연구가 필요하다.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.216-223
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• 2019

The objective of this study is to propose a reliable stress-strain model in compression for lightweight concrete using bottom ash aggregates and air foam(LWC-BF). The slopes of the ascending and descending branches in the fundamental equation form generalized by Yang et al. were determined from the regression analyses of different data sets(including the modulus of elasticity and strains at the peak stress and 50% peak stress at the post-peak performance) obtained from 9 LWC-BF mixtures. The proposed model exhibits a good agreement with test results, revealing that the initial slope decreases whereas the decreasing rate in the stress at the descending branch increases with the increase in foam content. The mean and standard deviation of the normalized root-square mean errors calculated from the comparisons of experimental and predicted stress-strain curves are 0.19 and 0.08, respectively, for the proposed model, which indicates significant lower values when compared with those(1.23 and 0.47, respectively) calculated using fib 2010 model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.45-54
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• 2006

To obtain realistic stress-strain relation in concrete, it is necessary to improve the constitutive model for creep and shrinkage of concrete. This study is made up with predicting model of creep using rheological approach and mathematical development which is solution for phenomenon of concrete creep. Long-term deformation components are combined based on traditional 4-parameters model. Creep deformation is obtained adequately using 4-parameters determined by considering aging effect and microprestress among gels. And coefficient of effective viscosity is able to represent both basic creep and total creep included drying creep. This study attempt to establish mathematical model considering effects of aging, hydration, and variations of pore humidity. It can predict both basic creep and total creep. Values of result between prediction and experiment have greater than correlation factor 99%. Additionally experimental results report bad consentaneity with highway design specification adopting FIB MC 90. Rather than those are similar to FIB MC 90 rev.99.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.379-386
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• 2020

The present study examined the effect of bottom ash aggregate contents on the compressive strength gain and mechanical properties(modulus of elasticity and rupture and splitting tensile strength) of concrete. Main test parameters were water-to-cement ratio and bottom ash aggregate contents for replacement of natural sand. Test results showed that the 28-days compressive strength of concrete and mechanical properties normalized by the compressive strength tended to decrease with the increase in bottom ash fine aggregate content. When compared with fib 2010 model equations, bottom ash aggregate concrete exhibited the following performances: lower rates of compressive strength gain at early ages but greater rates at long-term ages; slightly higher measurements for modulus of elasticity and rupture; and lower measurements for splitting tensile strength.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.1
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• pp.9-14
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• 2011

Due to the improvement of science technology, the future tank system will have the multi-function for more powerful firing. and the tank, mounted this multi-function, must be lighter to maintain the mobility. Therefore, new brecoil technology would be necessary to reduce the recoil force for lighter platform. The present study covers a FOOB(Fire-Out0-Of-Battery) system that can reduce the recoil force dramatically. The firing sequence of the FOOB system is radically different from that of a conventional system. The gun is latched in out-of-battery position prior to firing. As soon as firing is occurred, the gun is unlatched and accelerated. The forward momentum is imparted to the recoiling parts. This momentum is opposed by the ballistic force imparted by firing and the recoil force and recoil length will be reduced. In this study, the ADAMS simulation has been performed with the scale model of the FIB(Fire-In-Battery) system and the FOOB system. The ADAMS simulation results show that the FOOB system could reduce the operating time and recoil length and the recoil force.