https://doi.org/10.4334/JKCI.2021.33.3.227

박조범(Cho-Bum Park) ; 김용혁(Yong-Hyok Kim) ; 전유빈(Yu-Bin Jun) ; 김재홍(Jae Hong Kim) ; 류득현(Deug-Hyun Ryu)

Lightweight aggregate concrete has the advantage of weight reduction in concrete structures. However, it exhibits different properties compared with ordinary concrete because of its high absorption rate. Generally, compressive strength is the most important factor in concrete quality, but a durability evaluation should be considered to verify the medium- and long-term stability of a concrete structure. In this study, durability evaluation for concrete was progressed by hydrous conditions of lightweight aggregate compared with natural aggregate. The results showed that internal moisture in lightweight aggregate greatly reduced the relative dynamic elastic modulus in accordance with the freeze-thaw cycle, and this requires countermeasures. In carbonation tests, resistance to carbonation was better than that of natural aggregate due to the W/B reduction effect, as the lightweight aggregate absorbed the concrete mixing water. In chloride solution tests, results were similar to the carbonation tests. Concrete using oven-dried lightweight aggregate yielded the best results, but air-dried lightweight aggregate did not differ from natural aggregate. For the above-mentioned reasons there is no problem with durability of concrete using none pre-wetting lightweight aggregate, meaning the usability of lightweight aggregate can be extended, and this will increase its demand.

https://doi.org/10.4334/JKCI.2021.33.3.235

김선웅(Sun-Woong Kim) ; 박완신(Wan-Shin Park) ; 장영일(Young-Il Jang) ; 김선우(Sun-Woo Kim) ; 윤현도(Hyun-Do Yun)

Medium-scale earthquakes have been occurring in Korea more and more frequently. As buildings have become larger, revisions have been made to seismic design guidelines, and research on lateral force resisting systems has been broadly conducted to improve resisting performance. As a seismic resisting system, a coupled shear wall system is a representative structural system employed to resist lateral shear force under wind or seismic load. A link beam in the coupled shear wall system can transfer most of the overturning moment by the coupling action between the wall and the link beam. However, the coupling beams in a coupled shear wall system must possess adequate strength and stiffness to effectively resist lateral loads due to the framing action of them. In order to meet the required performance, such a coupling beam is densely laid out with a diagonal bundle reinforcing bar and stirrup. The detailing of the reinforcement is overall quite complicated and incurs problems in its installation. This study investigated the strength characteristics of composite link beams with alternative details. The test variables of this study were the reinforcement method of diagonal reinforcement and the spacing of the stirrup. The results showed that the average capacities of the Concrete link beam (CCB) specimen group exceeded the estimated values of the ACI 318-19 specification.

https://doi.org/10.4334/JKCI.2021.33.3.245

양근혁(Keun-Hyeok Yang) ; 문주현(Ju-Hyun Mun)

This study assesses the load-resistance grade of lightweight concrete insulation panels (ET-panels) made using bottom ash aggregates and air foams and reinforced with wire meshes on the basis of the evaluation of their flexural and shear performances. Six ET-panel specimens were prepared with variations of foam volume ratios () and longitudinal reinforcement ratios () and tested under a top two-point loading system. Test results showed that the wire meshes were promising in distributing flexural and diagonal shear cracks, thereby enhancing the flexural and shear strengths of the ET-panel. The displacement ductility ratio () of the ET-panel was comparable to that observed in conventional normal-weight concrete beams, when does not exceed twice the minimum longitudinal reinforcement ratios () of beams specified in KCI 2017. The flexural and shear strengths of an ET-panel can be conservatively estimated by the procedure of KCI 2017. Overall, all the ET-panel specimens satisfied the requirements for the Class 1 load-resistance recommended in KS F 4736.

https://doi.org/10.4334/JKCI.2021.33.3.253

김태훈(Tae-Hoon Kim) ; 엄기영(Ki-Young Eum) ; 고태훈(Tae-Hoon Koh) ; 신현목(Hyun-Mock Shin)

This paper presents an analytical prediction of seismic performance of reinforced concrete bridge piers with lap splices, using a fiber beam-column element with a plastic hinge model. The fiber hysteresis rule of the beam-column element is derived from the uniaxial constitutive relations of concrete and reinforcing steel fibers. Inelastic deformation in a plastic hinge region results in plastic rotation. The plastic hinge mainly depends on nonlinear characteristics such as lap splices. In particular, the bond-slip behavior of lap spliced reinforcing bars, dominantly developed with the occurrence of cracking at the end face in a column, is taken into account by defining the relationship between the steel stress and the bond-slip. The proposed numerical method for seismic performance assessment of reinforced concrete bridge piers with lap splices is verified by comparison with reliable experimental and analytical results.

https://doi.org/10.4334/JKCI.2021.33.3.263

심소현(Sohyun Shim) ; 김률리(Ryulri Kim) ; 홍진영(Jinyoung Hong) ; 최하진(Hajin Choi) ; 정시영(Si-Young Jung)

We propose a cooling water circulation system for diamond grinding in order to reduce environmental pollution generated by conventional grinding methods. Conventional grinding normally uses 3,000~4,500 kg of cooling water per 200 m2, leading to contaminated water leakage and delays to construction due to exceeding the contaminated water collection storage limit. In our proposed method, the contaminated water generated by the cutting process is immediately collected on site, and the water can be recycled as cooling water through the processes of filtration, treatment, and circulation. The developed system is composed of a primary purification device capable of filtering concrete sludge, a secondary purification device that stores and circulates purified water, and a micro grinder. In order to evaluate its performance, the developed system was applied five times in a field test, and comparison was made with a conventional method. Specifically, the water quality, cutting oil consumption, and carbon footprint were analyzed. It was confirmed that the generated contaminated water can be treated as industrial water grade and that the amount of cutting oil used and carbon dioxide emissions can be reduced by 90 % or more compared with the conventional method.

https://doi.org/10.4334/JKCI.2021.33.3.271

정현진(Hyun-Jin Jung) ; 이상화(Sanghwa Lee) ; 김세호(Seho Kim) ; 안효준(Hyojoon An) ; 이종한(Jong-Han Lee)

The number of earthquakes in Korea is gradually increasing, and recent earthquakes in Gyeongju and Pohang caused serious damage to piloti structures, a common structural type in Korea. Therefore, this study evaluated the seismic safety of a piloti structure following seismic reinforcement of hoop rebar and the design of a column isolation device. The isolation device was designed at the bottom and also at the top of a column in consideration of repair and replacement. Eigenvalue analysis showed little difference in natural frequency according to the seismic design of hoop rebar but a reduction in the first natural frequency by approximately 15~21 % with the installation of the isolation device. The maximum displacement also decreased by approximately 20~22 % and the maximum stress by 43~73 %, depending on the position of the installed device. Compared with seismic reinforcement of the piloti structure with hoop rebar, the isolation device absorbed displacement induced by an earthquake within its allowable range, which results in simultaneously reducing structural displacement and the seismic load transmitted to the structure.

https://doi.org/10.4334/JKCI.2021.33.3.279

운드람 나디앙자브(Undram Nadianjav) ; 하상수(Sangsu Ha) ; 뭉크투브신 오치버드(Munkhtuvshin Orchirbud) ; 최동욱(Donguk Choi)

Fabric-reinforced cementitious matrix (FRCM) composite is an emerging technology that can be applied to the repair and strengthening of RC members. Polyparaphenylene benzobisoxazole (PBO) fiber fabric was used along with green, high-strength mortar that comprised PBO-FRCM. The objective was to propose basic design parameters through mechanical characterization of a PBO-FRCM system. Three different types of test were conducted: a uniaxial test of tensile specimens; an interlaminar shear test of composite short beams; and a pull-off test of thin FRCM placed on top of normal strength concrete. Tensile test results showed that the tensile properties of the PBO fabric governed the tensile behavior. The nominal tensile strength of the FRCM cross section was 6.12 MPa at 2.15 % strain of the composite material. The short beam strength of 2.07 MPa was determined by the interlaminar shear test performed following ASTM D2344M. In the pull-off test, different failure modes were observed, including tensile failure at the PBO fiber mesh plane in the thin FRCM, interface failure in the tension between the FRCM and the concrete substrate, and tensile failure of the substrate concrete. The average strength of all pull-off tests was 3.69 MPa. Design values were suggested based on current test results of the PBO-FRCM.

https://doi.org/10.4334/JKCI.2021.33.3.289

장범수(Beom Soo Jang) ; 김재현(Jae Hyun Kim) ; 최승호(Seung-Ho Choi) ; 김강수(Kang Su Kim) ; 황진하(Jin-Ha Hwang) ; 최석동(Suk Dong Choi)

In this study, precast concrete (PC) wide girders were developed to secure economic efficiency by reducing the amount of slab volume resulting from enabling to shorten the span length of slab. A total of three PC wide girder-column joint specimens were fabricated with different details of reinforcing bars penetrating beams and columns in the joint region. Reversed cyclic loading tests were then conducted to evaluate structural performance, from which the lateral behavior of all the specimens were compared in detail. In addition, seismic performance of the proposed PC wide girder-column joints was quantitatively evaluated based on the acceptance criteria of the ACI 374 report.

https://doi.org/10.4334/JKCI.2021.33.3.299

임영철(Young-Chul Lim)

This study aims to evaluate the effect of reinforcement according to the measurement location in the measuring of electrical resistivity in concrete structures. The Apparent Resistivity rate (AR rate) based on the Resistivity Estimation Model (REM) was used for quantitative analysis of the measurement position and the angle of an electrode in the apparent resistivity measurement. It was confirmed that the measurement sensitivity of the apparent resistivity varies depending on the above conditions. In order to examine the applicability of the AR rate, the concrete resistivity was estimated from the apparent resistivity measured in a reinforced concrete specimen. This concrete resistivity was applied to the AR rate to calculate the estimated apparent resistivity. As a result, it was found that although the internal conditions of the concrete had an influence on the measurement results, the estimated apparent resistivity well represented the trend of the measured apparent resistivity.

https://doi.org/10.4334/JKCI.2021.33.3.307

이병재(Byung-Jae Lee) ; 김규형(Kyu Hyoung Kim) ; 김윤용(Yun-Yong Kim)

In order to study the applicability of fine aggregate recycled from waste concrete as a concrete aggregate, the effects of coating materials and application methods on the absorption rate of fine aggregate were investigated. In addition, material properties, including flow and strength, of mortar produced with recycled fine aggregate were examined. From absorption rate tests, acrylic resin coating was the most effective in reducing the absorption rate, and vacuum impregnation was the most effective coating method. As a result of density tests, the KS standard requirement was satisfied in all coating conditions. In contrast, sieving test results were outside the range of the grading curve for sodium silicate and polydimethylsiloxane. The absorption characteristics over time of uncoated recycled fine aggregate showed a high initial absorption rate, whereas coated recycled fine aggregate showed a similar tendency of absorption rate over time as a natural aggregate. From a flow test of mortar, it was found that as the replacement rate of washed coated recycled fine aggregate for recycled fine aggregate increased, the amount of superplasticizer required to achieve a flow of 200 mm decreased. In the strength tests, the mix using ISO standard sand and the mix using 100 % washed coated recycled fine aggregate showed similar strength characteristics. This indicates the applicability of coated recycled fine aggregate.