• Journal of the Korean Geotechnical Society
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• v.30 no.9
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• pp.41-55
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• 2014

In performing seismic analysis of tunnels, it is a common practice to ignore the rock joints and to assume that the rock mass surrounding the tunnel is continuous. The applicability of this assumption has not yet been validated in detail. This study performs a series of pseudo-static discrete element analyses to evaluate the effect of rock joint on the seismic response of tunnels. The parameters considered are joint intersection location, joint spacing, joint stiffness, joint dip, and interface stiffness. The results show that the joint stiffness has the most critical influence on the tunnel response. The tunnel response increases with the spacing, resulting in localized concentration of moment and shear stress. The response of the tunnel is the lowest for joints dipping at $45^{\circ}$. This is because large shear stresses result in rotation of the principal planes by $45^{\circ}$. In summary, the weathered and smooth, vertical or horizontal, and widely spaced joint set will significantly increase the tunnel response under seismic loading. The tunnel linings are shown to be most susceptible to damage due to induced shear stress, and therefore should be checked in the seismic design.

• Journal of the Korean GEO-environmental Society
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• v.19 no.9
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• pp.5-12
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• 2018

The foundation of the multi-span greenhouse structures is designed with small shallow concrete foundation considering mainly the vertical load. However, recently, due to an abnormal climate such as strong wind, horizontal load and up-lift load over design strength are applied to the foundation, causing safety problems of the greenhouse foundation. In order to reasonably evaluate the safety of greenhouse foundations, rotational and pullout stiffness expressed by the ground-foundation interaction should be evaluated, which also affects the safety of the upper structural members. In this study, three representative basic foundation types were selected by classifying greenhouse standards in Korea according to the shape, and the horizontal loading tests and theoretical calculation were performed for each foundation type. As a result of the comparison and analysis of the test and calculation, it was found that rotational resistance of the foundation is different according to the ratio of the contact area between the foundation and ground when the conditions of the foundation - ground contact surface and the mechanical properties of the ground are the same.

• Journal of Navigation and Port Research
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• v.28 no.1
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• pp.1-8
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• 2004

The final goal of this research is to establish the relative dangerousness D/B for factors on seakeeping performance. This D/B is, essential to develope the seakeeping performance evaluation system built-on-ship. The system is composed of the apparatus for measuring a vertical acceleration to be generated by the ship's motions, computer for calculating the synthetic seakeeping performance index and monitor for displaying the evaluating diagram of navigational safety of ship. In this paper, a methodology on the establishment of the relative dangerousness D/B for factors on seakeeping performance is presented by a numerical simulations, playing an important role on the algorithm of the program for calculating the synthetic seakeeping performance index. Finally, It is investigated whether the relative dangerousness D/B can be realized an accurate values according to the loading conditions, weather conditions, wave directions and present ship's speed of a model ship.

• Restorative Dentistry and Endodontics
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• v.19 no.2
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• pp.549-567
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• 1994

Restoration of severly damaged teeth after endodontic treatment had been an interest to many dentists, and it is a fact that there have been lots of studies about it. In these days, although we have used Para-Post, pins, threaded steel post, cast gold post and core, and so on, as a method of restoration frequently, it has been in controversy with the influence of them on the teeth and surrounding periodontal tissue. In this study, we assume that the crown of the upper incisor have severly damaged, so, after the root canal therapy, 4 types of restoration had been carried out; 1) coronal-radicular amalgam restoration, 2) after setting up the Para-Post, restore with composite resin core only, 3) after setting up the Para-Post; restore with amalgam core, then cover with the PPM crown 4) after setting up the Para-Post, restore with composite core, then cover with the PPM crown. After restoration, in order to observe the concentration of stress at internal portion of the teeth and the sourrounding periodontal tissue, developing a 2-dimensional finite element model of labiopalatal section, then loading forces from 3 direction - direction of 45 degrees from lingual side near the incisal edge, horizontal direction from labial height of contour, vertical direction at the incisal edge-were applied. The analyzed results were as follows: 1. Stress of the normal central incisor was concentrated on the dentin aroundpulp chamber, labiocervical portion of a tooth and root apex, but with the alveolar bone, in the case of load from the direction of 45 degrees from lingual side near the incisal edge showed remarkable concentration of stress: 2. Coronal-radicular amalgam technique -showed less concentration of stress on the root and surrounding periodontal tissue than the restoration with the Para-Post. 3. The von Mises equivalent stress on the Para-Post showed maximum value at root-core junction rather than both ends and model with PPM restoration with amalgam core showed the least concentration of stress. Only the force from horizontal direction showed large shear stress on internal portion of the root, root apex and alveolar bone. 4. PPM crown with composite core rarely showed the concentration of stress on root and periodontal tissue. 5. As for alveolar bone, remarkable shear stress was concentrated on labial and palatal side by horizontal load.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.191-200
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• 1999

The shear behavior of simply supported reinforced concrete deep beams subject to concentrated loads has been scrutinized experimentally to verify the influence of the structural parameters such as concrete strength, shear span-depth ratio, and web reinforcements. A total of 42 reinforced concrete deep beams with compressive strengths of 250 kg/$cm^2$ and 500 kg/$cm^2$ has been tested at the laboratory under one or two-point top loading. The shear span-depth ratio have been taken as three types of 0.4, 0.8 and 1.2, and the horizontal and vertical shear reinforcements ratio, ranging from 0.0 to 0.57 percent respectively. In the tests, the effects of the shear span-depth ratio, concrete strength and web reinforcements on the shear strength and crack initiation and propagation have been carefully checked and analyzed. From the tests, it has been observed that the failures of all specimens were due to shear and the shear behaviors of specimens were greatly affected by inclined cracks from the load application points to the supports in shear span. The load bearing capacities have changed significantly depending on the shear span ratio, and the efficiency of horizontal shear reinforcements were increased as the shear span-depth ratio decreased. The test results have been analyzed and compared with the formulas proposed by previous researchers and the design equation from the code. While the shear strengths obtained from the tests showed around 1.4 and 1.9 times higher than the values calculated by CIRIA guide and the domestic code, they were closely coincident with the formulas given by de Paiva's equation.

• Land and Housing Review
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• v.2 no.2
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• pp.163-170
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• 2011

Individual Vacuum Pressure Method (IVPM) is a soft ground improvement technique, in which a vacuum pressure can be directly applied to the vertical drain board to promote consolidation and to strengthen the soft ground. This method does not require surcharge loads, different to embankment or pre-loading method. In this study, the ground improvement efficiency of Individual Vacuum Pressure Method was estimated when suction pressure increases step by step(-20, -40, -60, -80kPa) with different periods. During Individual Vacuum Pressure Method process, surface settlement and pore pressure were monitored, and cone resistance as well as water content were also measured after the completion of Individual Vacuum Pressure Method treatment. From the results, optimum duration of each step of vacuum pressure was determined, and the settlement was calculated using FEM numerical analysis.

• Journal of the Korean Vacuum Society
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• v.16 no.4
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• pp.244-249
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• 2007

Deadweight piston gauge have been widely used as a fundamental instrument of precise pressure measurement because they are robust, accurate, potable, convenient to use and are able to realize the definition of pressure as farce per unit area. Basically, a deadweight piston gauge consists of a piston mounted vertically in a close-fitting cylinder filled with a gas and weights of known mass values. The pressure to be measured is applied to the base of the piston generating an upward vertical force, and is balanced by the downward gravitational force generated by weights. These instruments can be used to measure pressures above 10 kPa because of tare weights including piston. However, using a variable bell-jar pressure method and a newly developed weight loading device we can extend the application range of deadweight piston gauge to lower pressures. In this paper, we present the practical calibration results for two CDGs(Capacitance diaphragm gauge, MKS) with full-scale ranges of 1.33 kPa and 13.3 kPa, respectively.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.51 no.6
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• pp.539-543
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• 2006

Lodging is classified as root lodging caused by the loss of supporting force in the root, bending caused by the deformation of the stem and breaking where the stem breaks down as loads exceeding critical elasticity were applied. This research excluded breaking which is not in a state of equilibrium and tried to partition the level of lodging using an algebraic model in root lodging and stem lodging, or bending. When a vertical load was applied, the deformation of the stem of rice plant showed the form of a quadratic equation. The trace of the panicle neck in the process of lodging was an ellipse-shape. When loading was pure root lodging, the trace of the panicle neck became a circle of which culm length is the radius. When it was a pure stem lodging, the trace of the panicle neck is an ellipse of which major axis is culm length and minor axis is 0.64* culm length. When both stem lodging and root lodging occurred in a natural setting, the partitioning of lodging can be calculated by a formula using eccentricity of an ellipse, S=e*100/0.768(S is the ratio of stem lodging in the whole lodging, e is eccentricity of the ellipse). This method is expected to be useful in simple lodging partitioning. We could also calculate the partitioning of stem lodging and root lodging as units of angles as an accuracy method, by using a straight line calculated by differentiating a quadratic equation of stem deformation at the origin of the coordinates. These two methods for dividing root and stem lodging showed different values. However, each of them showed almost same values with different lodging degree in one plant.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.40-48
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• 2017

RC flat plates may be governed by a serviceability as well as a strength condition, and a construction sequence and its impact on the distributions of gravity loads among slabs tied by shores are decisive factors influencing short and long term behaviors of flat plate. Over-loading and tensile cracking in early-aged slabs significantly increase the deflection of a flat plate system under construction, and a reshoring work may be helpful in reducing slab deflections by controlling the vertical distributions of loads in a multi-shored flat plate system. In this study, a effect of reshoring works on short and long term deflections of flat plate systems are analyzed. The slab construction loads with various reshoring schemes and slab design and construction conditions are defined by a simplified method, and the practical calculation of slab deflections with considering construction sequences and concrete cracking and long term effects is applied. From parametric studies, the reshoring works are verified to reduce slab deflections, and the optimized conditions for the reshoring works and slab design and constructions are discussed.

• Journal of the Korean Geotechnical Society
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• v.31 no.3
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• pp.51-62
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• 2015

Shear behavior obtained by direct shear tests is dependent on shear box and boundary condition. The objective of this study is to analyze problems of conventional direct shear test (type-A) and provide the reliable results by developing type-C direct shear apparatus. Experimental tests are carried out for Ulleung sand by using type-A and -C direct shear devices. The soil specimens, which are prepared at the relative density of 60%, and are applied to vertical confining stresses of 50, 100, 200, 300, and 400 kPa, are sheared at a constant shear strain rate of 0.5 mm/min. By comparing the results obtained by type-A and -C direct shear apparatus under constant normal load (CNL) condition, the performance of new one is verified. In addition, two constrained conditions including constant normal load (CNL) and constant pressure (CP) are applied to type-C one. Experimental results show that type-A direct shear apparatus has some problems such as rotating of loading plate and upper shear box, and the frictional forces between soil and inner wall of upper shear box. Thus, the shear strengths obtained by type-A device are overestimated or underestimated depending on shear box and boundary condition. On the other hand, type-C device produces clear and consistent test results regardless of constrained conditions. This study represents that type-C direct shear apparatus not only can solve the problems of type-A direct shear apparatus but provide the reliable results.