Modeling of chloride diffusion in concrete considering wedge-shaped single crack and steady-state condition

양근혁,천주현,권성준 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.2

Crack on concrete surface allows more rapid penetration of chlorides. Crack width and depth are dominant parameters for chloride behavior, however their effects on chloride penetration are difficult to quantify. In the present work, the previous anisotropic (1-D) model on chloride diffusion in concrete with single crack is improved considering crack shape and roughness. In the previous model, parallel-piped shape was adopted for crack shape in steady-state condition. The previous model with single crack is improved considering wedge shape of crack profile and roughness. For verifying the proposed model, concrete samples for nuclear power plant are prepared and various crack widths are induced 0.0 to 1.2 mm. The chloride diffusion coefficients in steady-state condition are evaluated and compared with simulation results. The proposed model which can handle crack shape and roughness factor is evaluated to decrease chloride diffusion and can provide more reasonable results due to reduced area of crack profile. The roughness effect on diffusion is evaluated to be 10-20% of reduction in chloride diffusion.

Crosstie 훅크 형상에 따른 R. C. 기둥의 휨 거동에 관한 연구 ( A Study on the Effectiveness of Hook Type of Crossties in the Flexural Behavior of Confined Concrete Columns )

양근혁,이영호,곽노현,정헌수 대한건축학회 1999 大韓建築學會論文集 : 構造系 Vol.15 No.9

개구부가 설치된 철근콘크리트 깊은 보의 전단거동에 대한 개구부 보강근 배근방법의 영향

양근혁,은희창,정헌수,김광두,김자영 대한건축학회 2004 大韓建築學會論文集 : 構造系 Vol.20 No.3

The objective of this study was to evaluate the shear capacity of opening reinforcement in reinforced concrete deep beams with rectangular openings. Main variables were shear span-to-overall depth ratio(a/h), and the configuration of opening reinforcement. The size of opening was 0.5a×0.3h and the location of centerlines of openings and shear spans were the same for all specimens. Opening reinforcement identically consisted of three 10 mm diameter deformed bar of 4,000kgf/cm2 yield strength. The vertical reinforcement was U-typed stirrups in top and bottom of opening. The horizontal and 45 degree diagonal reinforcements were arranged in both sides of the beams and anchored according to KCI code method. In the following, the performance of opening reinforcement was described according to the variety of configuration of reinforcement and a/h. Based on previous and this experiments, an equation estimating the shear capacity of opening reinforcement was suggested through considering the average tie-action and the equilibrium of energy of opening reinforcement along the fracture surface in deep beams with openings.

ALC 블록성능의 기포콘크리트 배합설계 연구

양근혁 한국건축시공학회 2015 한국건축시공학회지 Vol.15 No.1

The objective of this study is to develop a high-performance foamed concrete made with a new mixtureproportioning as an alternative of autoclaved lightweight concrete (ALC) block. For the early-strength gain of thefoamed concrete under an atmospheric curing condition, the binders and chemical agents were specially contrived asfollows: 3% anhydrous gypsum was added to ordinary portland cement (OPC) in which 3CaO·SiO2 content wascontrolled to be above 60%; and the content of polyethylene glycol alkylether in a polycarboxylate-basedwater-reducing agent was modified to be 28%. Using these binders and chemical agents, 11 mixes were prepared withthe parameters of W/B ratio (30% to 20% in a interval of 2.5%) and unit binder content (400kg/m3 to 650kg/m3 in ainterval of 50kg/m3). The quality and availability of the mixed foamed concrete were examined according to theminimum requirements specified in the KS for ALC block and existed conventional foamed concrete. The measuredproperties satisfied the minimum requirement of KS for ALC block and proved that the developed high-performancefoamed concrete had considerable potential for practical application. 본 연구의 목적은 ALC 블록대체를 위한 고성능 기포콘크리트 배합설계를 개발하는 것이다. 대기양생 하에서 기포콘크리트의 고강도 발현(특히 초기재령에서)을 위하여결합재 및 혼화제를 사전연구에서 다음과 같이 설계하였다. 규산3칼슘이 60% 이상인 보통포틀랜드시멘트에 무수석고 3%를 첨가하였으며, 폴리카르본산계 감수제에서 폴리알킬에테르 성분을 28%로 조절하였다. 이들 재료를 사용하여 물-결합재비와 단위결합재양을 변수로 기포콘크리7트 11배합을 실험하였다. 배합된 기포콘크리트의 품질 및실용성은 KS 규격의 ALC 블록의 요구조건 및 기존의 일반기포콘크리트와 비교하였다. 실험결과 본 연구의 고성능기포콘크리트는 ALC 블록의 요구조건을 만족하면서 높은실용가능성을 보였다.

크기효과를 고려한 철근콘크리트 깊은 보의 전단내력 예측 ( The Prediction on the Shear Strength of Reinforced Concrete Deep Beams Included Size Effect )

양근혁,은희창,정헌수 대한건축학회 2001 大韓建築學會論文集 : 構造系 Vol.17 No.12

황토결합재를 사용한 무시멘트 모르터의 배합특성에 따른 압축강도 및 건조수축 거동

양근혁,황혜주,송진규,김선영 대한건축학회 2006 大韓建築學會論文集 : 構造系 Vol.22 No.6

The objective of this study which is a part of fundamental investigations for positive application of eco-friendly concrete to healthy housing is to develop the mixing design of cementless mortar with hwangto binder (HB). Elements influencing on the compressive strength and the shrinkage of mortar, such as water-HB ratio, fine aggregate-HB ratio, and the maximum size and particle distribution of the fine aggregate, were selected as main variables. Also, the models to predict the initial flow and the compressive strength at age 28 days of cementless mortar with hwangto binder were proposed by non-linear multiple regressive analysis based on test results. Test results showed that the compressive strength of cementless mortar with hwangto binder relative to that of the corresponding cement mortar had 86~115%. The shrinkage strain of cementless mortar with hwangto binder was higher than that of the corresponding cement mortar by average of 20%. High possibility on the application of cementless mortar using hwangto binder as building material was ensured from this study.

IEEE 802.l1e 무선랜에서 MSI를 이용한 개선된 스케줄링 및 수락제어 알고리즘

양근혁,옥치영,이채우,Yang, Geun-Hyuk,Ok, Chi-Young,Lee, Chae-Woo 대한전자공학회 2007 電子工學會論文誌-TC (Telecommunications) Vol.44 No.10

무선랜에서 QoS를 지원하기 위해 제안된 IEEE 802.l1e의 HCCA (HCF Controlled Channel Access)는 폴링에 의한 채널 제어 방식이다. 즉 HCCA는 중앙 제어 방식이기 때문에 자원을 분배하기 위한 스케줄링 알고리즘이 필요하며 IEEE 802.11e 표준에는 Reference 스케줄러가 제시되어 있다. Reference 스케줄러븐 폴링 리스트에 있는 모든 스테이션들을 동일한 주기로 폴링하기 때문에 잦은 폴링으로 인해 오버헤드 면에서 비효율적이며, TXOP (Transmission Opportunity)의 활용률 면에서도 낮다. 본 논문에서는 이러한 단점을 극복하고자 스테이션들의 MSI (Maximum Service Interval)에 따라 폴링 주기를 단계별로 나누어서 스케줄링하기 위한 트래픽 스케줄링 및 수락 제어 (admission control) 알고리즘을 제안한다. 제안하는 알고리즘에서는 스테이션들이 자시의 MSI와 가능한 비슷한 주기로 폴링되기 때문에 Reference 스케줄러에 비해 폴링 오버헤드가 감소하게 되며, TXOP 활용률도 증가하게 된다. 시뮬레이션을 통한 Reference 스케줄러와의 성능 비교는 제안된 알고리즘이 전체적인 전송률 면에서 더 높은 성능을 보이고 더 많은 수의 스테이션이 서비스가 가능함을 보여준다. IEEE 802.lie is being proposed to improve QoS by IEEE 802.11 working group. HCCA (HCF Controlled Channel Access) a centralized polling based mechanism of IEEE 802.11e, needs a scheduling algorithm that decides on how the available radio resources are allocated to the polled STAs. In IEEE 802.l1e standard Reference Scheduler is presented. Reference Scheduler Polls all STAs in a polling list by the same interval that causes ineffectively frequent polling. It increases not only the overhead but it decreases the TXOP (Transmission Opportunity) utilization. In this paper, we propose the scheduling and admission control algorithm that poll stations depending on the MSI (Maximum Service Interval)o( stations to solve these shortcomings. In our proposed algorithm a station is polled by an interval close to its MSI, so polling overhead decrease and TXOP utilization increases than Reference Scheduler. Simulation results show that our algorithm outperforms Reference Scheduler. Our algorithm maintains higher aggregate throughput and services mere stations than Reference Scheduler.

상계치 이론을 이용한 개구부를 갖는 철근콘크리트 단순·연속 깊은 보 내력의 수치해석 모델

양근혁,은희창,정헌수,Yang, Keun-Hyeok,Eun, Hee-Chang,Chung, Heon-Soo 한국콘크리트학회 2006 콘크리트학회논문집 Vol.18 No.4

상계치 이론을 이용하여 개구부를 갖는 단순 연속 깊은 보의 최대내력을 평가하기 위한 모델들이 제시되었다. 콘크리트는 인장강도를 무시한 수정 Coulomb 파괴기준을 따르는 완전 소성체로 가정하였으며, 철근은 기존 상계치 이론과는 달리 완전 탄 소성 재료로 고려하여 콘크리트의 한계 주 압축변형률을 사용하여 응력을 산정하였다. 파괴기구들은 실험 결과에 근거하여 포물선형의 항복선에 의해 분리되는 강체들로 이상화 하였다. 콘크리트의 유효압축 강도는 Vecchio & Collins의 모델에 의해 계산되었다. 본 연구에서 제시된 모델은 단순 연속 깊은 보의 실험 결과와 잘 일치하였으며, 특히 개구부 보강철근의 하중부담에 대한 과대평가를 감소시켰다. Models to predict the ultimate strength of simply supported or continuous deep beams with web openings are proposed. The derived equations are based on upper-bound theorem. The concrete is assumed as a perfectly plastic material obeying the modified Coulomb failure criteria with zero tension cutoff. Reinforcing bar is considered as elastic-perfectly plastic material and its stress is calculated from the limiting principal compressive strain of concrete. The governing failure mechanisms based on test results are idealized as rigid moving blocks separated by a hyperbolic yield line. The effective compressive strength of concrete is calculated from the formula proposed by Vecchio and Collins. Comparisons with existing test results are performed, and they show good agreement.

알카리활성 기포콘크리트의 품질특성 및 환경영향 평가

양근혁,유성원,이현호,김상철,Yang, Keun-Hyeok,Yoo, Sung-Won,Lee, Hyun-Ho,Kim, Sang-Chel 한국건설순환자원학회 2013 한국건설순환자원학회 논문집 Vol.1 No.2

본 연구에서는 공동주택의 난방시스템을 위한 단열재로서 지속가능한 알카리활성 기포콘크리트 배합설계를 제시하기 위한 5배합을 실험하였다. 알카리활성 결합재를 위해 73.5%의 고로슬래그와 15%의 고로슬래그가 5%의 수산화칼슘과 6.5%의 규산나트륨에 의해 활성화되었다. 주요 실험변수인 단위 결합재양은 $325kg/m^3$에서 $425kg/m^3$까지 $25kg/m^3$ 단위로 증가하였다. 실험결과 AA 기포콘크리트는 단위 결합재양이 $375kg/m^3$일 때 KS F 4039에서 제시하는 최소 강도조건 및 경제성을 만족시켰다. 또한 보통포틀랜드시멘트 기포콘크리트 대비 알카리활성 기포콘크리트의 환경영향 저감율은 광화학산화물의 경우 99%, 지구온난화의 경우 87~89%, 자원고갈의 경우 78~82%, 그리고 산성화와 인간독성의 경우 70~75% 수준으로서 매우 높았다. The present study tested 5 concrete mixes to develop reliable mixing proportions for the sustainable alkali-activated(AA) foamed concrete as a thermal insulation material for the floor heating system of buildings. The AA binder used was composed of 73.5% ground granulated blast-furnace slag, 15% fly ash, 5% calcium hydroxide, and 6.5% sodium silicate. As a main variable, the unit binder content varied from $325kg/m^3$ to $425kg/m^3$ at a space of $25kg/m^3$. The test results revealed that AA foamed concrete has considerable potential for practical applications when the unit binder content is close to $375kg/m^3$, which achieves the minimum quality requirements specified in KS F 4039 and ensures economic efficiency. In addition, lifecycle assessment demonstrated the reduction in the environmental impact profiles of all specimens relative to typical ordinary portland cement foamed concrete as follows: 99% for photochemical oxidation potential, 87~89% for global warming potential, 78~82% for abiotic depletion, and 70~75% for both acidification potential and human toxicity.

개구부 폭과 깊이 변화에 따른 철근콘크리트 깊은 보의 파괴모드 및 내력 평가에 관한 연구

양근혁,이영호,은희창,정헌수 대한건축학회 2003 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.23 No.1(구조계)

The purpose of this study is to investigate the failure mode and the shear strength of reinforced concrete deep beams with rectangular openings. Fourteen deep beams which shear span-to-depth ratio(a/h) is 0.5 were tested and an equation to predict the ultimate shear strength of deep beams with rectangular openings was established by the test results.