https://doi.org/10.4334/JKCI.2019.31.5.419

최지훈(Ji-Hun Choi) ; 최승재(Seung-Jai Choi) ; 김태균(Tae-Kyun Kim) ; 이태희(Tae-Hee Lee) ; 김장호(Jang-Ho Jay Kim)

Recently, the construction trend is to build larger and slender structures all over the world. In order to construct the required structures, prestressed concrete (PSC) construction method is an only viable option, which requires an evaluation of prestress tendons. Recently, many researches were performed on the evaluation for PS tendons. Implementation of the PS tendons is done to precisely understand prestress loss along the full length of PS tendons. Therefore, in this paper, long-term loss in normal and high strength tendons were measured experimentally. To evaluate the long-term loss of prestressed concrete members, long-term loss tests were carried out on 18 m PSC girder specimens. PS tendons used in the specimens were two types of steel strand. SWPC 7B (Type B) is a strand with tensile strength of 1,860 MPa, while SWPC 7D (Type D) is a strand with tensile strength of 2,400 MPa. The PS loss data were measured of two years. The experimental results can be used as basic research references to formulate constitutive models of PS tendons, which can be used to calibrate simulation tools of full-scale PSC structural behavior.

https://doi.org/10.4334/JKCI.2019.31.5.429

황용하(Yong-Ha Hwang) ; 양근혁(Keun-Hyeok Yang) ; 심재일(Jae-Il Sim) ; 최용수(Yong-Soo Choi)

The objective of the present study is to examine the significance and limitation of a V-clip developed to prevent the opening of overlapped channel-type hoops in the jacket section of section enlargement strengthening columns. Five full-scale columns were tested under concentric axial loads. Test results revealed that, until ultimate failure of strengthed columns, no opening of the overlapped legs of the channel-type hoops and supplementary V-ties was observed in the jacket section with the developed V-ties and V-clips. The axial ductility ratios of the strengthened columns with V-ties and V-clips were as much as 1.66 times higher when compared with that measured in the existing non-seismic column. In addition, the strengthened columns with V-ties and V-clips exhibited 1.42 times higher axial ductility than those of counterpart columns without V-clips of the same details. Overall, the proposed supplementary V-ties and V-clips possess the potential to enhance the ductility of section enlargement strengthening columns, satisfying the seismic design details of code provision in the jacket section.

https://doi.org/10.4334/JKCI.2019.31.5.437

양기윤(Ki-Yun Yang) ; 송종걸(Jong-Keol Song) ; 김재석(Jae-Suk Kim)

The current regulatory guidelines and design criteria for nuclear power plant (NPP) structures, it's call for reflection of the embedment effect which is consider the separation of the lateral soil and the structure in the soil-structure interaction (SSI) analysis of partially embedded structures. To reflect this, a fragmentary criteria was proposing that is suggesting that the non-contact with a part of the embedding depth is assumed, or the effective stiffness by embedding is reduced by changing the characteristics of the soil. In order to evaluate the current embedment effect criteria, SSI analysis was performed considering 3 types of embedment conditions, 6 types of generic soil models, and 5 types of structural models. For the SSI analysis, the ACS SASSI program using the flexible volume substructure method was used, and the artificial acceleration time history which conforms to the NPP design criteria was used for the design input motion. As a result of the SSI analysis, the floor response spectra of the structure and the relative displacement of the each floor to the foundation were analyzed and the embedment effect was evaluated. From the results of the analysis, it can be observed that the possibility of conservative design is increased when applying the embedment effect guidelines according to the current Nuclear Regulatory Guidelines.

https://doi.org/10.4334/JKCI.2019.31.5.449

성한석(Han-Suk Sung) ; 강현구(Thomas H.-K. Kang)

Recently, the number of earthquake occurrences in Korea has been rapidly increasing. For low-to-mid-rise buildings with masonry-infilled reinforced concrete frames, application of novel seismic retrofit methods is urgently needed. In this study, concrete frames and masonry-infilled walls were reinforced using composite materials such as GFRP (Glass Fiber-Reinforced Polymer) panels, GFRP bars, polyurea and/or polymer blocks; structural performance of specimens was verified by cyclic lateral loading tests in accordance with ACI 374.2R-13. Test results showed that the maximum strength for lateral loads improved due to the novel retrofit methods. The retrofit methods effectively prevented severe destruction of specimens because the composite materials effectively redistributed the stress applied to specimens and increased the integrity of frames and masonry-infilled walls. As a result, this method is expected to be a retrofitting option to reduce direct and indirect casualties caused by earthquakes.

https://doi.org/10.4334/JKCI.2019.31.5.459

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

As the lightweight aggregate used to reduce the weight of concrete has a high absorption rate, low density, and reduced liquidity in the concrete, pre-wetting is performed on the lightweight aggregate, but it is very difficult to have a uniform moisture content. In this study, concrete was tested on an air dried (ad) lightweight aggregate without pre-wetting, and concrete using natural aggregate was compared with concrete using a crude lightweight aggregate to analyze its characteristics according to the moisture conditions. The results of the experiment show that absorption of combined water resulted in a more fluid loss than natural aggregate concrete, and that the series of oven dried (od) lightweight aggregates with no moisture content. Overall, the w/b reduction effect of lightweight aggregate absorption increased, and the compressive strength was higher than that of natural aggregate concrete, but the elastic modulus factor of the aggregate itself was also reduced. Therefore, it is deemed that the pre-wetting method performed to enhance the demand of lightweight aggregates and that it also used in air dried state.

https://doi.org/10.4334/JKCI.2019.31.5.467

윤용식(Yong-Sik Yoon) ; 임희섭(Hee-Seob Lim) ; 권성준(Seung-Jun Kwon)

Concrete structures in marine environments are degraded not only when they are immersed in sea water, but also by chloride ions from tidal and splash areas. It is well known that GGBFS (Ground Granulated Blast Furnace Slag) improves the pore structure in concrete through latent hydraulic activity and chloride resistance by considerable absorption of free chlorine ions. In this paper, marine environment exposure tests are performed considering three levels of water to binder ratio (W/B) and two levels of GGBFS replacement ratio. Three cases of exposure conditions (immersion zone, tidal zone, and splash zone) and three levels of exposure period (180 days, 365 days, and 730 days) are considered. In all cases, the lower the concrete W/B is and the higher the substitution ratio of GGBFS is, the lower the apparent chloride diffusion coefficient is. Also, at 730 days of exposure, the diffusion coefficient in GGBFS concrete decreases to 16 % of that in OPC concrete. Considering the effects of exposure conditions, high apparent chloride diffusion coefficient is evaluated in order of tidal zone, immersion zone, and splash zone for GGBFS concrete.

https://doi.org/10.4334/JKCI.2019.31.5.475

성민규(Min-Kyu Seong) ; 천성철(Sung-Chul Chun)

Since reinforcing bars are mainly subjected to tension, research on anchorage in compression is very limited. It is not necessary to consider the influence of the rear-cover in development in tension. However, anchorage strength of compressive bars should be evaluated considering the influence of the rear-cover, because failure can be caused by side-cover or rear-cover concrete breakout. In this study, experiments on anchorages of reinforcing bars in compression terminated within exterior beam-column joint was carried out with rear-cover thickness as the main experimental parameter. Experimental results show that the contribution of the bearing for compression anchorage increases as the thickness of the rear-cover increases. When sufficient rear-cover thickness is secured, relative slip between reinforcing bars and concrete is reduced, thereby increasing the bond strength. Due to the favorable influence of the rear-cover, it is economical to make the embedding length as short as possible, within a range of embedment length to column width ratio of 0.56 to 0.72, because within this range similar anchorage strength was developed.

https://doi.org/10.4334/JKCI.2019.31.5.485

지구배(Gu-Bae Ji) ; 김희재(Hee-Jae Kim) ; 양근혁(Keun-Hyeok Yang)

The objective of this study is to propose empirical models to straightforwardly assess the CO2 emission and environmental impact of bottom ash aggregate concrete (BAAC). The system investigated for these assessments was based on Korean lifecycle inventory from cradle to preconstruction, which includes consistent materials, transportation and production phases. On the basis of analyzing a database including 90 datasets for BAAC, the CO2 emission and environmental impacts for each category were empirically formulated in the following forms: 1.0B for CO2 emissions, and α1B for each environmental impact, where B is the unit cement content. The experimental constant α1 can be determined to be 5×10-8 for global warming, 2×10-8 for photochemical oxidant creation, 1×10-9 for acidification, 7×10-10 for eutrophication, 2×10-10 human toxicity, 2×10-8 for abiotic resource depletion, 9×10-8 for total impact.

https://doi.org/10.4334/JKCI.2019.31.5.493

이무(Mao Li) ; 김진만(Jin-Man Kim)

The hybridization of different types of fibers may play an important role in the control of cracks and the production of high-performance concrete. This paper reports experimental results on mechanical properties and fiber distribution conditions of a fiber reinforced cementitious composite. In particular, pulverized rapid cooling ladle furnace slag is used as cementitious material instead of ordinary Portland cement. Consequently, mixtures with 1 % of steel fiber exhibit maximum flexural strength improvements of 30 % when compared with the plain mixtures. Moreover, image analysis was conducted to obtain experimental data of the orientation and distribution of the embedded steel fibers. With the specific mixing process and binder material, the steel fiber exhibits an average angle in the range of 58.1~62.5° to the friction section.

https://doi.org/10.4334/JKCI.2019.31.5.505

이용준(Yong-Jun Lee) ; 김형국(Hyeong-Gook Kim) ; 김민준(Min-Jun Kim) ; 이진섭(Jin-Seop Lee) ; 김길희(Kil-Hee Kim)

In this study, flexural and shear tests with height of section as variable was conducted to evaluate the structural performances of prestressed concrete hollow core slabs (HCS) produced by extrusion. Eighteen HCS specimens were fabricated and four-point bending test on HCS specimens was conducted. Test results showed that the ratio of analytical to experimental results for flexural strength and shear strength averaged 1.01~1.04 and 1.47~1.86, respectively. It was confirmed that the HCS specimens tested in this study have sufficient structural performances that exceed requirements recommended by the design codes KCI 2017 and ACI 318-14. Moreover, the flexural strength values of the HCS specimens were 1.63~1.77 times higher than the cracking moment and satisfied the ductility qualifications of the crack grade recommended by the design codes.