• Geomechanics and Engineering
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• 제14권5호
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• pp.459-466
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• 2018

By conducting uniaxial loading cycle tests on the coal rock with outburst proneness, the dilatation characteristics at different loading rates were investigated. Under uniaxial loading and unloading, the lateral deformation of coal rock increased obviously before failure, leading to coal dilatation. Moreover, the post-unloading recovery of the lateral deformation was rather small, suggesting the onset of an accelerated failure. As the loading rate increased further, the ratio of the stress at the dilatation critical point to peak-intensity increased gradually, and the pre-peak volumetric deformation decreased with more severe post-peak damage. Based on the laboratory test results, the lateral deformation of the coals at different depths in the #1302 isolated coal pillars, Yangcheng Coal Mine, was monitored using wall rock displacement meter. The field monitoring result indicates that the coal lateral displacement went through various distinct stages: the lateral displacement of the coals at the depth of 2-6 m went through an "initial increase-stabilize-step up-plateau" series. When the coal wall of the working face was 24-18 m away from the measuring point, the coals in this region entered the accelerated failure stage; as the working face continued advancing, the lateral displacement of the coals at the depth over 6 m increased steadily, i.e., the coals in this region were in the stable failure stage.

• 대한치과교정학회지
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• 제46권5호
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• pp.310-322
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• 2016

Objective: The aim of this study was to determine the optimal loading conditions for pure intrusion of the six maxillary anterior teeth with miniscrews according to alveolar bone loss. Methods: A three-dimensional finite element model was created for a segment of the six anterior teeth, and the positions of the miniscrews and hooks were varied after setting the alveolar bone loss to 0, 2, or 4 mm. Under 100 g of intrusive force, initial displacement of the individual teeth in three directions and the degree of labial tilting were measured. Results: The degree of labial tilting increased with reduced alveolar bone height under the same load. When a miniscrew was inserted between the two central incisors, the amounts of medial-lateral and anterior-posterior displacement of the central incisor were significantly greater than in the other conditions. When the miniscrews were inserted distally to the canines and an intrusion force was applied distal to the lateral incisors, the degree of labial tilting and the amounts of displacement of the six anterior teeth were the lowest, and the maximum von Mises stress was distributed evenly across all the teeth, regardless of the bone loss. Conclusions: Initial tooth displacement similar to pure intrusion of the six maxillary anterior teeth was induced when miniscrews were inserted distal to the maxillary canines and an intrusion force was applied distal to the lateral incisors. In this condition, the maximum von Mises stresses were relatively evenly distributed across all the teeth, regardless of the bone loss.

• 한국지반공학회논문집
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• 제33권2호
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• pp.17-26
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• 2017

해상구조물, 송전탑 등을 지지하는 말뚝기초는 바람, 조류, 파랑 등의 영향으로 횡방향 반복하중을 지배적으로 받으며, 이는 말뚝 주변 지반에 영구수평변위를 발생시켜 구조물의 안정성 및 기능성을 저해한다. 본 연구에서는 횡방향 반복하중에 의해 발생하는 말뚝의 영구수평변위를 평가하기 위하여, 서로 다른 세 가지 상대밀도(40%, 70%, 90%)로 조성된 건조 및 포화 모래지반에서 모형말뚝시험을 수행하였다. 모형시험 결과, 모든 시험조건에서 말뚝에 재하 된 횡방향 반복하중은 말뚝 주변 지반에 영구수평변위를 발생시켰다. 누적된 영구수평변위의 크기는 말뚝에 재하되는 횡방향 반복하중의 크기 및 재하횟수가 증가함에 따라 증가하였지만, 1회 재하로 인하여 발생되는 영구수평변위의 증가량은 점차 감소하였다. 또한, 말뚝에 발생하는 영구수평변위는 지반의 상대밀도가 클수록 작게 발생하고, 지반이 포화되면 크게 발생되는 것으로 평가되었다. 추가적으로, 누적 영구수평변위를 최초 재하 시 발생한 영구수평변위로 정규화한 영구수평변위를 평가하였으며, 이를 모래지반의 상대밀도, 횡방향 반복하중의 재하횟수에 관한 식으로 나타내었다.

• 한국지반환경공학회 논문집
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• 제13권9호
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• pp.17-29
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• 2012

각종 연직배수재가 설치된 연약지반의 전단강도, 지반변형의 특성을 조사하기 위해 우리나라 서해안과 남해안 지역에서 계측관리가 실시된 13개 연약지반현장 200개소에서 계측자료를 수집하였다. 먼저 연약지반의 침하량과 측방변위량과의 관계를 성토 초기 단계, 성토 완료 단계 및 성토 완료 후 단계의 세 단계로 구분하여 조사하였다. 다음으로 성토압과 성토고가 연약지반의 비배수전단강도와 어떤 관계에 있는가를 조사하였다. 검토결과, 침하의 증가량에 대한 수평변위의 증가량은 성토 초기 단계에서는 작았으나 점차 증가하여 성토 완료 단계에서 가장 크게 발생되었다. 그러나 성토 완료 후에도 침하량은 계속 증가하고 있었으며 수평변위는 거의 수렴하였으므로 대부분의 측방유동은 성토시공 중에 발생되었다. 침하량증분에 대한 수평변위증분의 비는 성토 초기 단계에서 20% 정도로 Tavenas et al.(1979)이 제시한 값과 일치하였으나 성토 완료 단계에서는 Tavenas et al.(1979)이 제시한 값의 절반 정도인 50%밖에 나타나지 않았다. 그리고 성토 완료 후 단계에서는 1%에서 9% 사이로 아주 작게 발생되어 Tavenas et al.(1979)이 제시한 값과 상당한 차이를 보였다. 모든 현장에서 설계성토고가 초기비배수강도 상태에서의 항복성토고보다 높은 상태였으므로, 연약지반 속에 전단변형 내지 전단파괴가 발생될 것이 예상되었다. 그러나 강도가 증가된 후에는 모든 현장에서 설계 성토고가 항복성토고보다 낮게 되어 안전한 성토시공이 가능하였던 것으로 판단된다. 도로성토시공을 안전하게 실시하기 위해서는 성토하중이 초기비배수전단강도의 5.14배가 넘지 않도록 하여야 하며 증가된 비배수전단강도의 3.0배 이하가 되도록 설계하여야 한다.

• 대한치과교정학회지
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• 제46권2호
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• pp.87-95
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• 2016

Objective: We evaluated the effects of tooth displacement on frictional force when conventional ligating lingual brackets (CL-LBs), CL-LBs with a narrow bracket width, and self-ligating lingual brackets (SL-LBs) were used with initial leveling and alignment wires. Methods: CL-LBs (7th Generation), CL-LBs with a narrow bracket width (STb), and SL-LBs (In-Ovation L) were tested under three tooth displacement conditions: no displacement (control); a 2-mm palatal displacement (PD) of the maxillary right lateral incisor (MXLI); and a 2-mm gingival displacement (GD) of the maxillary right canine (MXC) (nine groups, n = 7 per group). A stereolithographic typodont system and artificial saliva were used. Static and kinetic frictional forces (SFF and KFF, respectively) were measured while drawing a 0.013-inch copper-nickel-titanium archwire through brackets at 0.5 mm/min for 5 minutes at $36.5^{\circ}C$. Results: The In-Ovation L exhibited lower SFF under control conditions and lower KFF under all displacement conditions than the 7th Generation and STb (all p < 0.001). No significant difference in SFF existed between the In-Ovation L and STb for a 2-mm GD of the MXC and 2-mm PD of the MXLI. A 2-mm GD of the MXC produced higher SFF and KFF than a 2-mm PD of the MXLI in all brackets (all p < 0.001). Conclusions: CL-LBs with narrow bracket widths exhibited higher KFF than SL-LBs under tooth displacement conditions. CL-LBs and ligation methods should be developed to produce SFF and KFF as low as those in SL-LBs during the initial and leveling stage.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1999년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall
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• pp.396-403
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• 1999

This experimental study investigates the hysterestic behavior of traditional timber frames subjected to lateral loads. Prototype frames for this study were selected from one of typical national treasures for timber structures in Korea. For simplicity roof structures and braket systems were excluded from specimens and the joint behavior of beam-to-column system were presumed to have crucial effect on their global behavior. The experimental observation showed stiffness degradation and slip after experiencing initial yield and the first cycle at a new larger displacement due to inherent gaps in traditional timber connection and gradual indentation of interfaces, The cyclic behaviors of all specimens were similar to those os modern timber frames with bolt and nail connections. Additional structural members such as an upper beam and clay-filled wall increased the initial stiffness strength and energy dissipation. It is expected that collapse of Korean traditional timber frames under lateral load is mainly caused from P-$\Delta$ effects rather than local member failure.

• Steel and Composite Structures
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• 제1권2호
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• pp.201-212
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• 2001

In order to investigate the effect of the loading rate on the mechanical behavior of SRC shearwalls, we conducted the lateral loading tests on the 1/3 scale model shearwalls whose edge columns were reinforced by H-shaped steel. The specimens were subjected to the reversed cyclic lateral load under a variable axial load. The two types of loading rate, 0.01 cm/sec for the static loading and 1 cm/sec for the dynamic loading were adopted. The failure mode in all specimens was the sliding shear of the in-filled wall panel. The edge columns did not fail in shear. The initial lateral stiffness and lateral load carrying capacity of the shearwalls subjected to the dynamic loading were about 10% larger than those subjected to the static loading. The effects of the arrangement of the H-shaped steel on the lateral load carrying capacity and the lateral load-displacement hysteresis response were not significant.

• 한국지반공학회논문집
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• 제26권11호
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• pp.63-73
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• 2010

해상풍력발전기의 기초로 사용되는 단말뚝은 풍력과 파랑하중에 의해 큰 크기의 반복수평하중을 받는다. 본 연구에서는 모래지반에서 반복수평하중을 받는 항타말뚝의 거동 특성을 조사하기 위해서 가압토조와 길이가 다른 3개의 모형말뚝을 이용해서 모형말뚝재하시험을 수행하였다. 실험결과에 따르면 하중의 최초 재하는 그 이후에 가해지는 반복재하보다 말뚝의 수평변위를 크게 발생시키고, 반복하중의 재하횟수가 증가함에 따라 1회 재하로 인해 발생하는 말뚝의 수평변위량은 감소하는 것으로 나타났다. 하중의 한방향 반복재하는 말뚝의 영구수평변위를 재하방향으로 증가시킨 반면, 양방향 반복재하는 최초 재하방향과 반대방향으로 말뚝의 영구수평변위를 증가시켰다. 그리고 반복 하중으로 인한 말뚝의 영구수평변위는 지반의 상대밀도가 감소하거나 말뚝에 가해지는 반복하중의 크기가 커질수록 급격히 증가하였고, 지반의 토압계수나 말뚝의 근입길이 변화에는 크게 영향을 받지 않았다. 또한 모형실험의 결과에 근거해서 하중이 한방향으로 반복재하될 때 말뚝의 영구수평변위와 영구회전각을 예측할 수 있는 산정식을 제안하였다.

• 한국안전학회지
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• 제16권1호
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• pp.59-64
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• 2001

Even though there is a guideline for the required strength of pipe support in inspection, it does not mean the nominal strength which can be used for the form work design. And, Concrete Specification defines that the pipe support should be designed according to the steel design guidelines but the design details are not provided, such as buckling length and the sectional modulus, etc. For the better prediction of strength of pipe support, the slenderness ratio of support which reflects the boundary condition should be considered. In this paper, the elastic buckling formula based on the slenderness is derived. The formula contains the strength reduction factor that consider the strength deduction caused by initial lateral deformation and is 0.65 consistently regardless of boundary conditions. And the coefficient of effective buckling length is calculated from the experiment.

• Structural Engineering and Mechanics
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• 제41권1호
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• pp.43-65
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• 2012

The primary objective of this study was to identify concrete contribution to the initial shear strength of reinforced concrete (RC) hollow columns under lateral loading. Seven large-scale RC rectangular hollow column specimens were tested under monotonic or cyclic lateral loads. The most important design parameter was column length-to-depth aspect ratio ranging between 1.5 and 3.0, and the other test variables included web area ratio, hollow section ratio, and loading history. The tests showed that the initial shear strength reduced in a linear pattern as the column aspect ratio increased, and one specimen tested under cyclic loading achieved approximately 83% of the shear strength of the companion specimen under monotonic loading. Also, several pioneering shear models proposed around the world, all of which were mainly based on tests for columns with solid sections, were reviewed and compared with the test results of this study, for their possible applications to columns with hollow sections. After all, an empirical equation was proposed for concrete contribution to the initial shear strength of RC hollow columns based on fundamental mechanics and the test results.