• 대한기계학회논문집A
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• 제25권4호
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• pp.629-636
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• 2001

In order to investigate the possibility of impact punching in brittle materials, an experimental setup was developed. In the setup, a long bar as a punch was used to apply the impact load to the specimen plate and measure the applied impact force during the impact punching process. Impact punching tests with various shape of punches were performed in soda-lime glass and silicon wafer under a different level of contact pressure. The damage appearance after the impact punching was examined according to the applied contact pressure. The minimum contact pressure required for a complete punching in glass specimens without development of radial cracks around the punched hole was sought at each condition. The minimum contact pressure increased with increasing the thickness of specimens and decreasing the end radius of punches. The profile of impact forces was measured during the impact punching experiment, and it could explain well the behavior of the punching process in brittle material plates. The measured impact force increased with increasing the contact pressure applied to the plates.

• 콘크리트학회논문집
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• 제23권1호
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• pp.31-38
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• 2011

이 연구에서는 FRP와 강섬유로 보강한 콘크리트 시편의 충격하중과 정적하중에서의 거동을 보기 위해 휨 실험과 펀칭 실험을 수행하였다. 1방향 휨 실험과 2방향 펀칭 실험에서 콘크리트 시편은 각각 $50{\times}100{\times}350$ mm와 $50{\times}350{\times}350$ mm의 크기로 제작하였다. 0.75% 혼입률의 강섬유 보강 콘크리트는 2방향 충격하중 및 정적하중에서 높은 저항 성능을 보였다. 일반 콘크리트와 강섬유 보강 콘크리트에서 FRP 보강은 높은 성능 증가를 보였다. 초고성능 콘크리트는 콘크리트 자체가 가지고 있는 높은 인장강도와 인성으로 인해, CFRP로 보강한 경우 강도와 에너지 소산 능력이 크게 증가하지 않았다.

• Computers and Concrete
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• 제20권6호
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• pp.731-738
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• 2017

Reinforced concrete flat plates consist of slabs supported directly on columns. The absence of beams makes these systems attractive due to advantages such as economical formwork, shorter construction time, less total building height with more clear space and architectural flexibility. Punching shear failure is usually the governing failure mode of flat plate structures. Punching failure is brittle in nature which induces more vulnerability to this type of structure. To analyze the flat plate behavior under punching shear, twelve finite element models of flat plate on a column with different parameters have been developed and verified with experimental results. The maximum range of variation of punching stress, obtained numerically, is within 10% of the experimental results. Additional finite element models have been developed to analyze the influence of integrity reinforcement, clear cover and column reinforcement. Variation of clear cover influences the punching capacity of flat plate. Proposed finite element model can be a substitute to mechanical model to understand the influence of clear cover. Variation of slab thickness along with column reinforcement has noteworthy impact on punching capacity. From the study it has been noted that integrity reinforcement can increase the punching capacity as much as 19 percent in terms of force and 101 percent in terms of deformation.

• Structural Engineering and Mechanics
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• 제89권4호
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• pp.363-374
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• 2024

Significant changes have been made to estimate the punching shear capacity for edge column-slab joints in the latest editions of most current codes. The revised equations account for axial forces as well as moments conveyed to columns from slabs, which have a substantial impact on the punching resistance of such joints. Many key design parameters, such as reinforcement-ratio, concrete strength, size-effect, and critical-section perimeter, were treated differently or even ignored in various code provisions. Consequently, wide ranges of predicted punching shear strength were detected by applying different code formulas. Therefore, it is essential to assess the various current Codes' design-equations. Because of the similarity in estimated outcomes, only the ACI, EC, and SNiP are used in this study to cover a wide range of estimation ranges from highly conservative to unconservative. This paper is devoted to analyzing the techniques in these code provisions, comparing the estimated punching resistance with available experimental data, and finally developing efficient models predicting the punching capacity of edge column-slab connections. 63 samples from past investigations were chosen for validation. To appropriately predict the punching shear, newly updated equations for ACI and SNiP are provided based on nonlinear regression analysis. The proposed equations'results match the experimental data quite well.

• 한국정밀공학회지
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• 제20권5호
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• pp.156-163
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• 2003

In order to investigate the possibility of punching process of brittle material by ball impact, the effects of sealing materials about impact damage of soda-lime glass by small spheres were evaluated experimentally. The using of sealing materials in the development of perfect cone crack was more effective than no using of sealing materials. At the sealing materials condition, in the case of 5mm-thick specimen, Copper and PMMA sealing were more effective in producing a perfect cone formation than the other sealing materials. And in the case of 8mm-thick specimen, Aluminum sealing was most effective in producing a perfect cone formation. The impact velocity range over which perfect cones were formed was influenced by both the thickness of specimen and sealing materials. By a proper selection of sealing materials, the application fur industrial technology for hole (or nozzle) punching process of brittle materials is expected.

• 시큐리티연구
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• 제31호
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• pp.187-207
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• 2012

본 연구는 태권도의 기본동작인 주춤서기 자세에서의 주먹 지르기 동작을 3차원 입체영상분석을 통해 유형별로 운동학적 변인인 시간, 속도, 각도, 각속도, 각가속도 등을 분석하여 유형별 특성을 알아보고 올바른 주먹 지르기 동작의 지도방법을 제시하고자 하였다. 이를 위해 대학교 경호무도 태권도 경호무도시범단 3인을 대상으로 실시하였고 다음과 같은 결론은 도출 하였다. 1. 지르기 동작 수행시간 : 각 유형(Type)별 주춤서기 자세에서 주먹 지르기 동작 수행시간은 1구간에서 $0.24{\pm}0.07s$와 $0.42{\pm}0.08s$로 유형(Type)1의 주먹 지르기 동작 수행시간이 빠르게 나타났지만 전체 수행시간에 대한 구간별 비율은 유형(Type)2의 테이크 백(take back)이 더 짧은 것으로 나타났다. 2. 선속도 및 선가속도 변인 : 각 유형(Type)의 국면별 선속도는 모두 다르지만 가장 높은 선속도는 각 유형(Type)의 임팩트 순간 이라 할 수 있으며, 유형(Type)2의 임팩트 순간인 3국면에서 가장 높은 선속도가 나타났다. 3. 관절각 변인 : 유형(Type)별 주먹 지르기 동작이 관절의 각은 임팩트 국면인 유형(Type)1의 주먹 지르기 동작과 유형(Type)2의 주먹 지르기 동작에서 외형적으로 큰 차이가 나지 않지만 유형 (Type)2의 주먹 지르기 동작이 관절각의 변화가 다양해 역동적인 자세를 취하고 있다. 4. 각속도 및 각가속도 변인 : 유형(Type)1의 주먹 지르기 동작이 임팩트 순간인 3국면의 고관절, 견관절, 손목관절 의 각속도는 각각 $0.79{\pm}0.02deg/s$, $0.91{\pm}0.04deg/s$, $5.24{\pm}0.09deg/s$ 로 나타났으며, 유형(Type)2의 주먹 지르기 동작이 임팩트 순간인 4국면의 고관절, 견관절, 손목관절의 각속도는 각각 $1.32{\pm}0.03deg/s$, $0.21{\pm}0.03deg/s$, $4.98{\pm}0.08deg/s$로 나타났다. 유형(Type)2의 임팩트 순간인 3국면의 오른쪽 손목관절의 각가속도의 변화를 보면 $176.24{\pm}1.11deg/s^2$로 유형(Type)1의 임팩트 순간의 각가속도 보다 더 큰 속도의 변화를 보였다.

• Elastomers and Composites
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• 제57권4호
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• pp.157-164
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• 2022

Representative bulletproof materials, such as aramid or ultra-high molecular weight polyethylene(UHMWPE), have excellent strength and modulus in the plane direction but are very vulnerable to forces applied in the thickness direction. This paper reports a study on the effects of reinforcement in the thickness direction when bulletproof composite fabrics are prepared to improve their performance. Aramid and UHMWPE fabrics were combined using the film-bonding, needle-punching, or stitching methods and then subjected to low-velocity projectile and ball-drop impact tests. The results of the low-velocity projectile test indicated that the backface signature(BFS) decreased by up to 29.2% in fabrics obtained via the film-bonding method. However, the weight of the film-bonded fabric increased by approximately 23% compared with that obtained by simple lamination, and the fabric stiffened on account of the binder. Flexibility, light weight for wearability, and excellent bulletproof performance are very important factors in the development of bulletproof materials. When the needle-punching method was used, the BFS increased as the fibers sustained damage by the needle. When the composite fabrics were combined by stitching, no significant difference in weight and thickness was observed, and the BFS showed similar results. When a diagonal stitching pattern was employed, the BFS decreased as the stitching density increased. By contrast, when a diamond stitching pattern was used, the fabric fibers were damaged and the BFS increased as the stitching density increased.

• Structural Engineering and Mechanics
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• 제53권3호
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• pp.455-479
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• 2015

This paper presents a numerical analysis of reinforced concrete slabs under missile impact loading. The specimen used for the numerical simulation was tested by the Technical Research Center of Finland. LS-DYNA, commercial available software, is used to analyze the model. The structural components of the reinforced concrete slab, missile, and their contacts are fully modeled. Included in the analysis is material nonlinearity considering damage and failure. The results of analysis are then verified with other research results. Parametric studies with different longitudinal rebar ratios, shear bar ratios, and concrete strengths are conducted to investigate their influences on the punching behavior of slabs under the impact of a missile. Finally, efficient designs are recommended.

• Computers and Concrete
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• 제32권4호
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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.

• Computers and Concrete
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• 제6권2호
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• pp.109-132
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• 2009

This paper presents finite element impact analysis for the design of Structurally Dissipating Rock-shed (SDR), an innovative design of reinforced concrete rock-shed. By using an appropriate finite element impact algorithm, the SDR structure is modelled in a simplified but efficient way. The numerical results are firstly verified through comparisons with the results of the experiments recently realized by ESIGEC and TONELLO I.C. It is shown that, using this impact algorithm, it is possible to correctly predict the SDR structural behaviour under different rock-fall impact conditions. Moreover, the numerical results show that the slab centre is the critical impact location for reinforced concrete slab design. The impact analyses have thus been focused on the impacts at the slab centre for the SDR structural optimization. Several series of parametric studies have been carried out with respect to load cases and engineering parameters choices. These numerical results support the robustness of the new SDR concept, and serve to optimize SDR structure and improve its conventional engineering design, especially for ensuring the slab punching shear resistance.