• Computers and Concrete
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• v.32 no.4
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• pp.425-438
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• 2023

In this article, the performance of steel fiber-reinforced concrete (SFRC) flat slabs was investigated numerically. The influence of flexural steel reinforcement, steel fiber content, concrete compressive strength, and slab thickness were discussed. The numerical model was developed using ATENA-Gid, user-friendly software for non-linear structural analysis for the evaluation and design of reinforced concrete elements. The numerical model was calibrated based on eight experimental tests selected from the literature to validate the actual behavior of steel fiber in the numerical analysis. Then, a parametric study of 144 specimens was generated and discussed the impact of various parameters on the punching shear strength, and statistical analysis was carried out. The results showed that slab thickness, steel fiber content, and concrete compressive strength positively affect the punching shear capacity. The fib Model Code 2010 for specimens without steel fibers and the model of Muttoni and Ruiz for SFRC specimens presented a good agreement with the results of this study.

• Proceedings of the Korean Fiber Society Conference
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• 1996.10a
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• pp.423-426
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• 1996

• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.159-168
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• 2011

In the present study, an improved design method was developed for the punching shear strength of interior slabcolumn connections and column footings with and without shear reinforcement. In the evaluation of the punching shear strength, the possible failure mechanisms of the connections and column footings were considered. The considered failures modes were inclined tensile cracking of concrete, yielding of shear re-bars, and concrete crushing of compression zone/strut. The punching shear applied to the concrete critical section was assumed to be resisted mainly by the compression zone. The punching shear strength of the concrete compression zone was evaluated based on the material failure criteria of the concrete subjected to the compressive normal stress and shear stress. For verification of the proposed design method, its prediction was compared with the existing test results. The result showed that the proposed method predicted the strengths of the test specimens better than the current design methods of the KCI code for both the shear reinforced and unreinforced cases.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.1
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• pp.121-129
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• 2007

The aim of this study is to investigate punching shear strength of exterior connections in the flat plate structure with rectangular column. To inspect the effect of column aspect ratios on the punching shear behavior, eight specimens for exterior connection were made and tested. In this experimental program the length of critical perimeter was kept constant, while column aspect ratio varied from 2.0 to 4.5. Two levels of concrete strength and slab reinforcement ratio were also considered. As the column aspect ratio increased, the punching shear strengths are decreased. The decrement of punching shear strength was small in specimens with high aspect ratio of column.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.31-38
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• 2011

In this study, in order to observe the behaviors of fiber reinforced polymer (FRP) strengthened and steel fiber reinforced concrete specimens for impact and static loads, flexural and punching tests were performed. For the one-way flexural and two-way punching tests, concrete specimens with the dimensions of $50{\times}100{\times}350$ mm and $50{\times}350{\times}350$ mm were fabricated, respectively. The steel fiber reinforced concrete specimens showed much enhanced resistance on two-way punching of static and impact loads. In addition the FRP strengthening system provided the outstanding performance under a punching load. Because of a large tensile strength and toughness of ultra high performance concrete (UHPC), the UHPC specimens retrofitted with FRP showed marginally enhanced strength and energy dissipating capacity.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.213-216
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• 2008

When using the light-weight form with polystyrene on slab, as a result of reducing the weight of slab, the span was increased or size of supporting member for slab was decreased. But capacity of punching shear resistance on the slab using the polystyrene form with plat plate system was deteriorated at critical section around the column. But standard for estimate of internal force did not exist, and established study was insufficient. This study performed the experiment on the punching shear for understanding punching shear force at the slab-column connection using the slab with polystyrene form. The principal variable was size of column, arrangement of polystyrene form and existence of shear reinforcement, and we planned four specimens. From the test, we analysed the crack, failure mode, road-displacement graph and punching shear strength, and capacity of punching shear resistance for slab using the polystyrene form was understood.

• Journal of agriculture & life science
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• v.50 no.5
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• pp.217-224
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• 2016

In this study, performance of a developed automatic punching machine considering the planting density of soybeans was evaluated in the case of the operation speed of 0.18-0.28 m/s. The performance demonstrated a rate of 320-500 ㎡/h, 260-400 ㎡/h, and 210-330 ㎡/h for the 0.20 m, 0.25 m, and 0.30 m soybean planting density, respectively. One hundred percent punching capacity was confirmed in 30 mm distance between the ground and the blade. Additionally, in the 50 mm distance condition, the performance of round, square, and hexagonal blades were observed in the range of 16.7-25.2%, 33.0-42.3%, and 54.5-100.0%, respectively. Above all, the hexagonal blade with a 60° edge angle had the most superior cutting quality demonstrating a smooth and soft cutting plane of the plastic.

• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.361-367
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• 2014

This paper investigates the punching shear strength of lightweight aggregate concrete (LWAC) slabs through a series of experimental study. Five full scale slabs were constructed using normal concrete and four different types of LWAC. Each lightweight aggregate (LWA) used in this study had different sources (clay, shale, or slate) and shapes (crushed or spherical shape). Based on the test results, the effect of the lightweight aggregates (LWA) on the punching shear behavior was investigated. From the test results, it was found that the punching shear failure surface of LWAC slab with spherical shape coarse aggregate was less inclined than that with crushed shape coarse aggregate, which resulted in an increase of the area of the shear failure surface. As a result, it leads to the increased punching shear strength of the slab. On the other hand, the failure surfaces of LWAC slab with crushed shape coarse aggregate and normal coarse aggregate were inclined similarly. Finally, the test results of this study were compared with the punching shear strength obtained from current design models, such as ACI and CEB-FIP, to examine the validation of current design model to predict the punching shear strength of the LWAC slab.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.221-231
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• 2011

Thinner and lighter structural members can be designed by utilizing the high stiffness and toughness, and high compressive strength of UHPC(ultra high performance concrete), which reaches up to 200MPa. The punching shear capacity of UHPC was investigated in this paper aiming for the application of UHPC to bridge decks. Six square slabs were fabricated and punching shear test was performed under fixed boundary condition. Different thicknesses of test slabs, which were 40mm and 70mm, were selected. The shape ratio of loading plates were ranged between 1.0~2.5. 40mm thickness slabs showed longer softening region after the peak load and, on the other hand, 70mm thickness slabs revealed a more brittle shear failure. Experimental results were analyzed using various existing punching shear predicting equations. Ductal$^{(R)}$ equation and JSCE equation better predicted for 40mm slabs, and Harajli et al. equation and ACI-Ductal$^{(R)}$ equation better suited for 70mm slabs. Nevertheless generally they didn't well predict the test results. A new punching shear equation which was derived based on the actual failure mechanism was proposed. The proposed equation appeared to better predict the punching shear strength of UHPC than other available equations.

• The Korean Journal of Mycology
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• v.49 no.3
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• pp.295-302
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• 2021

The effect of punching treatment on bags containing sawdust medium for the stable production of fruiting bodies of Lentinula edodes 'Hwadam' was investigated. After spawn inoculation, the sawdust medium temperature and CO₂ concentration reached 27.0-28.8℃ on the 23^rd day of incubation, and 14.0-15.6% on the 16^th day of incubation, respectively, decreasing thereafter. The O₂ concentration showed an opposite pattern to the CO₂ concentration. As the number of punching treatments on the medium increased during the incubation period, the lightness value decreased, and conversely, the color difference and weight loss rate increased. There was no difference in the cultivation period according to the punching treatment. As the punching treatment increased on the sawdust medium, the fruiting body yield increased; a three-time punching treatment produced the best yield with 605.7 g. Thus, proper punching treatment on a sawdust medium during the incubation period can increase the number of fruiting bodies and yield.