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Journal of the Korea Concrete Institute

Journal AbbreviationJ Korea Inst. Struct. Maint. Insp.
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  • Korea Citation Index(KCI)

국내 청소년시설 대상 유지관리기반 안전점검 및 안전성 평가 연구 Assessment of Degree and Safety Inspection Based on Maintenance Level in domestic Youth Training Facility

https://doi.org/10.11112/jksmi.2020.24.3.1

이정석(Jeong-Seok Lee)

Recent the number, size and accident on Youth Training Facility have increased annually. Also, the discussion and interest relation to safety and maintenance of youth culture and education. This study asserts the necessity and importance of present condition and characteristic based on Youth Training Facility in domestic. Therefore, Results of this study, it is appeared that very vulnerable to improve safety and maintenance in them. Accordingly, The purpose of this study is to investigate the current status for the whole youth facilities. second it estimate on main damage and defect of them for the period four years.

H 파일과 프리캐스트 콘크리트로 형성된 벽체의 횡저항성능에 대한 실험적 연구 An Experimental Study on Lateral Load Resistance of a Wall Structure composed of Precast Concrete and H-Pile

https://doi.org/10.11112/jksmi.2020.24.3.9

서동주(Dong-Joo Seo) ; 강덕만(Duk-Man Kang) ; 이현기(Hyun-Gee Lee) ; 문도영(Do-Young Moon)

The purpose of this study was to evaluate lateral load resistance of a wall structure composed of precast concrete wall and H-Pile. This type of structure can be used for noise barrier foundation or retaining wall. Mock-up specimens having actual size were designed and fabricated. The lateral design load is 54.6kN. The H-pile length for the test specimen is 1.5m for simulating behavior of actual wall structure has 6.5m H-pile in the field, which is determined from theoretical study. Lateral displacements and strains of wall and H-pile were monitored and cracking in precast concrete wall inspected during the test. Load and deformation capacity of test specimens was compared with design capacity. The comparisons demonstrated that this type of structures, precast concrete wall and H-pile, can resist enough to lateral design load.

딥러닝을 이용한 경량혼합토의 일축압축강도 예측 시스템 Predictive System for Unconfined Compressive Strength of Lightweight Treated Soil(LTS) using Deep Learning

https://doi.org/10.11112/jksmi.2020.24.3.18

박보현(Bohyun Park) ; 김두기(Dookie Kim) ; 박대욱(Dae-Wook Park)

The unconfined compressive strength of lightweight treated soils strongly depends on mixing ratio. To characterize the relation between various LTS components and the unconfined compressive strength of LTS, extensive studies have been conducted, proposing normalized factor using regression models based on their experimental results. However, these results obtained from laboratory experiments do not expect consistent prediction accuracy due to complicated relation between materials and mix proportions. In this study, deep neural network model(Deep-LTS), which was based on experimental test results performed on various mixing conditions, was applied to predict the unconfined compressive strength. It was found that the unconfined compressive strength LTS at a given mixing ratio could be resonable estimated using proposed Deep-LTS.

비용효율을 고려한 자기 충전형 콘크리트의 CCD 실험설계법 및 가중 다목적성 기반 다목적설 계최적화(MODO) Muti-Objective Design Optimization of Self-Compacting Concrete using CCD Experimental Design and Weighted Multiple Objectives considering Cost-Effectiveness

https://doi.org/10.11112/jksmi.2020.24.3.26

도정윤(Jeongyun Do)

Mixture design of self-compacting concrete is a typical multi-criteria decision making problem and conventional mixture designs are based on the low level engineering method like trials and errors through iteration method to satisfy the various requirements. This study concerns with performing the straightforward multiobjective design optimization of economic SCC mixture considering relative importances of the various requirements and cost-effectives of SCC. Total five requirements of 28day compressive strength, filling ability, segregation stability, material cost and mass were taken into consideration to prepare the objective function to be formulated in form of the weighted-multiobjective mixture design optimization problem. Economic SCC mixture computational design can be given in a rational way which considering material costs and the relative importances of the requiremets and from the result of this study it is expected that the development of SCC mixtue computational design and the consequent univeral concrete material design optimization methodology can be advanced.

탄산화에 노출된 GGBFS 콘크리트의 콜드 조인트 및 하중 재하를 고려한 확률론적 내구수명 해석 Probabilistic Service Life Analysis of GGBFS Concrete Exposed to Carbonation Cold Joint and Loading Conditions

https://doi.org/10.11112/jksmi.2020.24.3.39

김태훈(Tae-Hoon Kim) ; 권성준(Seung-Jun Kwon)

Carbonation is a deterioration which degrades structural and material performance by permitting CO2 and corrosion of embedded steel. Service life evaluation through deterministic method is conventional, however the researches with probabilistic approach on service life considering loading and cold joint effect on carbonation have been performed very limitedly. In this study, probabilistic service life evaluation was carried out through MCS (Monte Carlo Simulation) which adopted random variables such as cover depth, CO2 diffusion coefficient, exterior CO2 concentration, and internal carbonatable materials. Probabilistic service life was derived by changing mean value and COV (Coefficient of variation) from 100 % to 300 % and 0.1 ~ 0.2, respectively. From the analysis, maximum reduction ratio (47.7%) and minimum reduction ratio (11.4%) of service life were obtained in cover depth and diffusion coefficient, respectively. In the loading conditions of 30~60% for compressive and tensile stress, GGBFS concrete was effective to reduce cold joint effect on carbonation. In the tensile condition, service life decreased linearly regardless of material types. Additionally service life rapidly decreased due to micro crack propagation in the all cases when 60% loading was considered in compressive condition.

장기 재령 GGBFS 콘크리트의 염화물 확산 거동 평가 및 확률론적 염해 내구수명 해석 Evaluation of Chloride Diffusion Behavior and Analysis of Probabilistic Service Life in Long Term Aged GGBFS Concrete

https://doi.org/10.11112/jksmi.2020.24.3.47

윤용식(Yong-Sik Yoon) ; 김태훈(Tae-Hoon Kim) ; 권성준(Seung-Jun Kwon)

In this study, three levels of W/B(Water to Binder) ratio (0.37, 0.42, 0.47) and substitution ratio of GGBFS (Ground Granulated Blast Furnace Slag) rate (0 %, 30 %, 50 %) were considered to perform RCPT (Rapid Chloride Diffusion Test) at the 1,095 aged day. Accelerated chloride diffusion coefficient and passed charge of each concrete mixture were assessed according to Tang's method and ASTM C 1202, and improving behaviors of durability performance with increasing aged days are analyzed based on the test results of previous aged days from the preceding study. As the age of concrete increases, the passed charge and diffusion coefficient have been significantly reduced, and especially the concrete specimens containing GGBFS showed a significantly more reduction than OPC(Ordinary Portland Cement) concrete specimen by latent hydraulic activity. In the case of OPC concrete’s results of passed charge, at the 1,095 days, two of them were still in the "Moderate" class. So, if only OPC is used as the binder of concrete, the resistance performance for chloride attack is weak. In this study, the time-parameters () were derived based on the results of the accelerated chloride diffusion coefficient, and the deterministic and probabilistic analysis for service life were performed by assuming the design variable as a probability function. For probabilistic service life analysis, durability failure probabilities were calculated using Monte Carlo Simulation (MCS) to evaluate service life. The service life of probabilistic method were lower than that of deterministic method, since the target value of PDF (Probability of Durability Failure) was set very low at 10 %. If the target value of PDF suitable for the purpose of using structure can be set and proper variability can be considered for each design variable, it is believed that more economical durability design can be made.

콘크리트 하수관거 보수용 초속경 수중불분리 모르타르의 재료적 특성 Material Properties of Ultra Rapid Hardening Mortar for Repairing Sewage Treatment Concrete Pipes

https://doi.org/10.11112/jksmi.2020.24.3.57

이병재(Byungjae Lee) ; 이선목(Sunmok Lee) ; 방진욱(Jin-wook Bang) ; 김윤용(Yun-yong Kim)

Among the sewage pipes installed in Korea, the length of concrete pipes exceeding 20 years is 66,334 km (42.5%). Deteriorated concrete sewer pipes need to be repaired due to the leakage of internal sewage, which causes problems such as sink holes by expanding the cavity around the pipeline. In this study, we tried to apply anti-washout underwater mortar with ultra rapid hardening cement and segregation reducing agent to sewage pipe repair. As a result of the setting time test, the final set time was delayed by up to 172% by incorporating segregation reducing agent. In the test for measuring the degree of mortar segregation in water, it was measured at pH 12 or less under all mixing conditions. In addition, the suspension amount was measured to be 50 mg / l or less to satisfy the KCI-AD102 standard by incorporating a segregation reducing agent. In terms of the average value of mortar compressive strength, by incorporating segregation reducing agent, the strength of the specimens produced in air was more than 80% of that of the specimens produced in water. Conversely, the bond strengths of the specimens produced in water were measured to be higher than those of the specimens produced in air. Water resistance was evaluated by measuring water absorption and water permeability. Water absorption and water permeability were reduced by 42.6% and 36.6%, respectively, by mixing segregation reducing agent.

건축기준 완화를 위한 순환골재 콘크리트 적용 시의 품질 특성 연구 A Study on the Quality Properties When Applying Recycled Aggregate Concrete for the Construction Standard Mitigation

https://doi.org/10.11112/jksmi.2020.24.3.63

우경섭(Gyeong-Sub Woo) ; 김정호(Jung-Ho Kim) ; 이세현(Sea-Hyun Lee) ; 오중근(Jung-Keun Oh)

The volume of construction waste material from the entire waste material volume in Korea is approximately 47.3% to take the biggest ratio, and from them, the waste concrete takes up approximately 62.8% that recycling is an urgent issue to address. Therefore, the government recommends more diverse and broader facilitation of the recycled aggregate in order to promote recycling the construction waste materials. In addition, when using concrete recycled aggregate in building, building standard such as floor area ratio and building height are being mitigation. The standard is a condition that mitigation the floor area ratio by up to 15% when using up to 25% of concrete recycled aggregate. Therefore, this study reviewed the relaxation of construction of construction standards when using concrete recycled aggregate in order to actively recommend the use of concrete recycled aggregate. And using the recycled coarse aggregate among the recycled aggregate, the appropriate mixing time in the batch plant according to the substitution rate was derived. In addition, using recycled aggregate admixture in order to improve the drying shrinkage, did comparative analysis about physical and mechanical property of concrete.

IoT 기반 비접촉 초음파 측정 시스템 개발 및 적용 Development and application of IoT-based contactless ultraosonic system

https://doi.org/10.11112/jksmi.2020.24.3.70

김지환(Jihwan Kim) ; 홍진영(Jinyoung Hong) ; 김률리(Rrulri Kim) ; 우욱용(Ukyong Woo) ; 최하진(Hajin Choi)

The main objective of this research to develop an IoT based wireless contactless ultrasonic system (ICUS) and its application to concrete structure. The developed system consists of 16 mems, 2Mhz digitizer, amplifying circuit, FPGA, and wifi module, enabling to measure leaky surface waves from concrete specimens without physical coupling process and wires. Multi-channel analysis is performed to improve the accuracy of data analysis, and the velocity of leaky surface waves and acoustics are derived. Field inspection of railroad concrete sleepers is conducted to evaluate the performance of the system and to compare the results with conventional ultrasonic pulse velocity (UPV). As a result of the field inspection, UPV was limited to evaluate damages. This is because crack pattern of railroad sleepers is parallel to ultrasonic ray path and accessibility of the railroad at the field is disadvantageous to contact-based UPV. On the other hand, ICUS possibly detect the damages as reduction of dynamic modulus by up to 59% compared to non-damaged specimen.

슬립폼 방식으로 제작된 역리브 프리캐스트 슬래브의 구조거동에 대한 실험적 연구 Experimental Study on Structural Behavior of Inverted Multi-Tee Precast Slabs Manufactured by Slipformer

https://doi.org/10.11112/jksmi.2020.24.3.80

최석동(Choi, Seokdong) ; 김민석(Kim, Min-Seok) ; 김강수(Kim, Kang Su) ; 홍성엽(Hong, Sung Yub) ; 한선진(Han, Sun-Jin)

In the fabrication process of inverted multi-tee (IMT) slabs, concrete has to be poured twice due to its shape, which is a huge disadvantage as a precast member. To overcome this, a new technique for manufacturing IMT slabs using a slipform method has been recently developed. In this study, flexural and shear tests were carried out to investigate the structural performances of inverted multi-tee (IMT) slabs manufactured using slipform method. To this end, one flexural specimen and two shear specimens with topping concrete were fabricated, and their failure modes and crack patterns, and the slips that occurred between the precast slab and topping concrete were measured and analyzed in detail. In addition, the flexural and shear strengths of the specimens were evaluated by utilizing the structural design code, and a shear strength estimation method, which is suitable for composite IMT slabs with different concrete properties, was proposed for practical design. The IMT slab satisfied the nominal flexural strength calculated by the current design code, and the proposed method provided a good estimation of the shear strength of the specimens.

EIS를 이용한 아크 금속용사 표면처리기법이 적용된 강재의 콘크리트 내 부식 거동에 관한 실험적 연구 An Experimental Study on Corrosion Behavior in Steel of Concrete Applied with Arc Metal Spray Method Surface Treatment Technology Using EIS

https://doi.org/10.11112/jksmi.2020.24.3.87

윤창복(Chang-Bok Yoon) ; 박장현(Jang hyun Park) ; 이한승(Han-Seung Lee)

As an experimental study on the corrosion behavior of steel materials to which ATMS method using EIS was applied in concrete, immersion of Ca(OH)2 saturated aqueous solution and NaCl aqueous solution simulating the environment inside concrete The corrosion behavior was tested. The equivalent circuit was derived through the analysis of the Nyquist plot, and the interfacial resistance and the polarization resistance of the Ca(OH)2 aqueous solution were compared, and Al ATMS was the best interfacial resistance and Zn ATMS was the best polarization resistance. After burying ATMS steel material of cement mortar, the initial immersion impedance measurement value was the highest in the Zn ATMS test body in the impedance measurement by the immersion time by immersing it in the NaCl aqueous solution. , Al ATMS test piece has the highest impedance and is highly reliable. This is because Al, which has a high ionization tendency, is continuously oxidized in a strong alkaline environment to form a film and protect the steel from permeation of chlorine ions.

천연 제올라이트의 분말도와 치환율이 시멘트모르타르의 화학반응 및 물리적 특성에 미치는 영향에 관한 연구 Study on the Effect of Fineness and Substitution Rate of Natural Zeolites on Chemical Reaction and Physical Properties of Cement Mortar

https://doi.org/10.11112/jksmi.2020.24.3.96

윤창복(Chang-Bok Yoon) ; 이한승(Han-Seung Lee)

As a basic study for the application of natural zeolite as a concrete admixture, the compressive strength, activity factor, Ca(OH)2 quantitative analysis and XRD experiments were investigated. It is thought that SiO2, which is abundant in natural zeolite, affects the strength development by reacting with the hydration product of cement in all specimens in which natural zeolite was added according to powder level and substitution rate. As the substitution rate increases, the compressive strength decreases, which is considered to be due to the decrease in the amount of C3S and C2S minerals in the clinker, which affects the strength expression compared to the cement content of the reference mortar. The XRD crystal structure did not show a significant difference from the reference mortar, and it was confirmed that the Z2-10 (Blaine: 15,600cm² / g) specimen with 10% substitution of natural zeolite was the best among the experimental levels. Substitution amount for use as concrete admixture is 10% substitution is most ideally seen.

철근 보강된 콘크리트-ECC 복합보의 휨 거동 Flexural Behavior of Concrete-ECC Composite Beam Reinforced with Steel Rebar

https://doi.org/10.11112/jksmi.2020.24.3.104

현정환(Jung-Hwan Hyun) ; 방진욱(Jin-Wook Bang) ; 이방연(Bang-Yeon Lee) ; 김윤용(Yun-Yong Kim)

The purpose of this study is to investigate the flexural behavior and plastic hinge of reinforced concrete-ECC composite beams. Ordinary portland cement was used as a binder, and high volume fly ash was also used to improve the properties of ECC. An ECC designed in this study showed high tensile strain capacity of 3.0%. Three types of beams were manufactured according to the replacement length of concrete with ECC. From the bending tests, it was found that load-bearing capacity as well as ductility of beam increased with an increase in the replacement length of concrete with ECC. Curvature ductility and plastic hinge length of beam were also increased.

영상신호를 이용한 현수교 행어케이블의 장력 추정 Tension Estimation for Hanger Cables on a Suspension Bridge Using Image Signals

https://doi.org/10.11112/jksmi.2020.24.3.112

김성완(Sung-Wan Kim) ; 윤다운(Da-Woon Yun) ; 박시현(Si-Hyun Park) ; 공민준(Min-Joon Kong) ; 박재봉(Jae-Bong Park)

In suspension bridges, hanger cables are the main load-supporting members. The tension of the hanger cables of a suspension bridge is a very important parameter for assessing the integrity and safety of the bridge. In general, indirect methods are used to measure the tension of the hanger cables of a suspension bridge in traffic use. A representative indirect method is the vibration method, which extracts modal frequencies from the cables’ responses and then measures the cable tension using the cables’ geometric conditions and the modal frequencies. In this study, the image processing technique is applied to facilitate the estimation of the dynamic responses of the cables using the image signal, for which a portable digital camcorder was used due to its convenience and cost-efficiency. Ambient vibration tests were conducted on a suspension bridge in traffic use to verify the validity of the back analysis method, which can estimate the tension of remote hanger cables using the modal frequencies as a parameter. In addition, the tension estimated through back analysis method, which was conducted to minimize the difference between the modal frequencies calculated using finite element analysis of the hanger cables and the measured modal frequencies, was compared with that measured using the vibration method.

모멘트-변형각의 관계를 이용한 SCH80 3인치 강재배관엘보의 한계상태 평가 Limit State Assessment of SCH80 3-inch Steel Pipe Elbows Using Moment-Deformation Angle Relationship

https://doi.org/10.11112/jksmi.2020.24.3.122

김성완(Sung-Wan Kim) ; 윤다운(Da-Woon Yun) ; 정진환(Jin-Hwan Cheung) ; 김성도(Seong-Do Kim)

To conduct probabilistic seismic fragility analysis for nuclear power plants, it is very important to define the failure modes and criteria that can represent actual serious accidents. The seismic design criteria for piping systems, however, cannot fully reflect serious accidents because they are based on plastic collapse and cannot express leakage, which is the actual limit state. Therefore, it is necessary to clearly define the limit state for reliable probabilistic seismic fragility analysis. Therefore, in this study, the limit state of the SCH80 3-inch steel pipe elbow, the vulnerable part of piping systems, was defined as leakage, and the in-plane cyclic loading test was conducted. Moreover, an attempt was made to quantify the failure criteria for the steel pipe elbow using the damage index, which was based on the dissipated energy that used the moment-deformation angle relationship.