• Magazine of the Korea Concrete Institute
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• 제8권6호
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• pp.223-234
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• 1996

The purpose of this paper is to present an analysis method by using the finite element method which can exactly analyze load-deflection relationships, crack propagations. and stresses and strains of reinforcements, tendons, and concrete in behaviors of elastic. inelastic and ultimate ranges of reinforced and prestressed concrete slabs under monotonically increasing loads. For t h i s purpose, the m a t e r i a l and geometric nonlinearities are taken into account in this study. The total Lagrangian formulation based upon the simplified Von Karman strain expressions is used to take into account the geometric nonlinearities of the structure. The material nonlinearities are taken into account by comprising the tension, compression. and shear models of cracked concrete and models for reinforcements and tendons in the concrete : and also a so-called smeared crack model is incorporated. The reinforcements and t,endons are assumed to be in a uniaxial stress state and are modelled as smeared layers of equivalent thickness. For the verification of application and validity of the method proposed in this paper, several numerical examples are analyzcd and compared with experimental results. As a result, this method can successfully predict the nonlinear and inelastic behaviors throughout the fracture of reinforced and prestressed concrete slabs.

• The Journal of Korean Academy of Prosthodontics
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• 제34권3호
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• pp.632-649
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• 1996

The purpose of this study was to examine, by the method of 3-dimentional finite element analysis. how infraocclusion affected the stress distribution in surrounding bone and osseointegrated prosthesis. The 3-dimentional finite element mandibular models were made, in which the first and second molars were removed and the two osseointegrated implants were placed in the first and second molar sites and implant supported fixed prostheses were constructed. Analysis of equivalent stress and displacement induced by strong occlusion or infraocclusion was performed under vertical or inclined distributed loads. The results were as follows; 1. Under vertical load of 50N or 500N, the model in which infraocclusion had not been allowed showed greater stress on implants and the supporting bone than on natural teeth. 2. In the model in which infraocclusion of $30{\mu}m$ had been allowed, implant-prosthesis on the molars had no contact with opposing teeth under vertical load of 50N, However with the same allowed infraocclusion and the model under vertical load of 500N, implant prosthesis on the second molar had contact with opposing teeth, and stress distribution occured properly on natural teeth and implants. 3. Under $45^{\circ}$ inclined load, the model in which infraocclusion had not been allowed showed greater stress on implants and the supporting bone than on natural teeth. There was greater stress in the case of $45^{\circ}$ inclined load than in the case of vertical load. 4. Under $45^{\circ}$ inclined load of 50N or 500N, the model in which infraocclusion of $30{\mu}m$, had been allowed showed no occlusal contact on the implants and occlusal contact on the natural teeth. 5. In partially edentulous cases with implant supported prosthesis, we can prevent excessive load on implants by allowing infraocclusion.

• Journal of the Korea institute for structural maintenance and inspection
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• 제7권3호
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• pp.215-222
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• 2003

Recently the deep and large excavations are performed near the existing buildings in urban areas for the practical use of underground space. The earth pressure due to the excavation are varied according to the conditions of ground, the depth of excavation, the construction methods, and the method of supporting the earth pressure etc.. In this study, not only the behavior of axial load and distribution of earth pressure on the flexible wall according to stage excavation depth but also magnitude and distribution of lateral deformation, and the equivalent earth pressure from strut axial loads were analyzed by the results measured from instruments such as, load cells, strain gauges, and in-situ inclinometer, on the field of subway construction. According to the results of this study in the case of stage excavation the earth pressure of soft clayey soil is compounded with Terzaghi-Peck and Tschebotarioff.

• Journal of Korean Society of Steel Construction
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• 제18권2호
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• pp.173-180
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• 2006

The seismic responses of a building are affected by the base soil conditions. In this study, linear time-history seismic analysis and nonlinear pushover static seismic analysis were performed to estimate the base shear forces of 3-, 5-, and 7-story steel buildings, considering the rigid and soft soil conditions. Foundation soil stiffness, based on the equivalent static stiffness formula, is used for the damper, one of the Link elements in SAP 2000. The base shear forces of the steel buildings, estimated through time-history analysis using the general-purpose structural-analysis program of SAP 2000, were compared with those calculated using the domestic seismic design code, the UBC-97 design response spectrum. and pushover static nonlinear analysis. The steel buildings designed for gravity and wind loads showed elastic responses with a moderate earthquake of 0.11 g, while the elastic soft-soil layer increased the displacement and the base shear force of the buildings due to soil-structure interaction and soil amplification. Therefore, considering the characteristics of the soft-soil layer, it is more reasonable to perform an elastic seismic analysis of a building's structure during weak or moderate earthquakes.

• Journal of the Korea Convergence Society
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• 제10권11호
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• pp.297-302
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• 2019

A-pillar is closely related to safety for the purpose of protecting the bodies of passengers by mitigating the impact that may be caused by the vehicle being overturned while driving. Therefore, the A-pillar should protect these parts from a variety of dynamic loads. This study result is thought to contribute for the strength and durability of A-pillar by designing two types of parts before making this product and analyzing the product which thickness is adjusted for the light weight of vehicle. If this study result is practically applied to the parts of A-pillar in a car, it is considered that the damage can be protected by the durability verification of design. By utilizing the data of analysis and design on the strength and durability of automotive A-pillar in this study, the esthetic sense can be given by being grafted onto the real automotive part.

• Computers and Concrete
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• 제21권6호
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• pp.717-726
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• 2018

Concrete pipelines are the most efficient and safe means for gas and oil transportation over a long distance. The use of nano materials and nono-engineering can be considered for enhancing concrete pipelines properties. the tests show that $SiO_2$ nanoparticles can improve the mechanical behavior of concrete. Moreover, severe hazard for pipelines is seismic ground motion. Over the years, scientists have attempted to understand pipe behavior against earthquake most frequently via numerical modeling and simulation. Therefore, in this paper, the dynamic response of underwater nanocomposite submerged pipeline conveying fluid is studied. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via Classic shell theory and Hamilton's principle. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. As well, the effect of external fluid is modeled with an external force. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite. 1978 Tabas earthquake in Iran is considered for modelling seismic load. The dynamic displacement of the structure is extracted using differential quadrature method (DQM) and Newmark method. The effects of different parameters such as $SiO_2$ nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios, internal and external fluid pressure and earthquake intensity are discussed on the seismic response of the structure. From results obtained in this paper, it can be found that the dynamic response of the pipe is increased in the presence of internal and external fluid. Furthermore, the use of $SiO_2$ nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제41권4호
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• pp.417-428
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• 2021

Since future maintenance cost estimation of infrastructure involves uncertainty, it is important to make use of a failure prediction model. However, it is difficult for local governments to develop accurate failure prediction models applicable to infrastructure due to a lack of budget and expertise. Therefore, this study estimated the life expectancy of asphalt road pavement of national highways using the Bayesian Markov Mixture Hazard model. In addition, in order to accurately estimate life expectancy, environmental variables such as traffic volume, ESAL (Equivalent Single Axle Loads), SNP (Structural Number of Pavement), meteorological conditions, and de-icing material usage were applied to retain reliability of the estimation results. As a result, life expectancy was estimated from at least 13.09 to 19.61 years by region. By using this approach, it is expected that it will be possible to estimate future maintenance cost considering local failure characteristics.

• Journal of Climate Change Research
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• 제6권3호
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• pp.185-191
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• 2015

This study presents an estimate of on-site surface fuel loadings composed of coarse woody debris (CWD) using $5^{th}$ National Forest Inventory (NFI) data in South Korea. We classified CWD data into forest type, region and decay class, and used conversion factors by decay class and tonne of oil equivalent developed in the country. In 2010, the total wildfire fuel load of CWD was estimated as 8.9 million TOE; those of coniferous, deciduous and mixed forests were 3.5 million TOE, 2.8 million TOE and 2.6 million TOE, respectively. Gangwon Province had the highest wildfire fuel load of CWD (2.3 million TOE), whereas Seoul exhibited the lowest wildfire fuel load of CWD (0.02 million TOE). Wildfire fuel loads of CWD were estimated as 2.9 million TOE, 1.9 million TOE, 2.4 million TOE and 1.7 million TOE for decay classes I, II, III and IV, respectively. The total wildfire fuel load of CWD corresponded to the calorific value of 8.2 million tons crude oil, 2.46% of that of living trees. Proportionate to the growing stock, total wildfire fuel load of CWD was in a broad distinction by region, while its TOE $ha^{-1}$ was not. This implies that there is no need to establish different guidelines by region for management of CWD. The results of this work provide a baseline study for scientific policy guidelines on preventing wildfires by proposing CWD as wildfire fuel load.

• Earthquakes and Structures
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• 제15권6호
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• pp.617-627
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• 2018

After earthquakes FRP sheets are often used for the rehabilitation of damaged Reinforced Concrete (RC) beamcolumn connections. Connections with minor to moderate damage are often dealt with by applying FRP sheets after a superficial repair of the cracks using resin paste or high strength mortar but without infusion of thin resin solution under pressure into the cracking system. This technique is usually adopted in these cases due to the fast and easy-to-apply procedure. The experimental investigation reported herein aims at evaluating the effectiveness of repairing the damaged beam-column connections using FRP sheets after a meticulous but superficial repair of their cracking system using resin paste. The investigation comprises experimental results of 10 full scale beam-column joint specimens; five original joints and the corresponding retrofitted ones. The repair technique has been applied to RC joints with different joint reinforcement arrangements with minor to severe damage brought about by cyclic loading for the purposes of this work. Aiming at quantitative concluding remarks about the effectiveness of the repair technique, data concerning response loads, loading stiffness and energy absorption values have been acquired and commented upon. Furthermore, comparisons of damage index values and values of equivalent viscous damping, as obtained during the test of the original specimens, with the corresponding ones observed in the loading of the repaired ones have also been evaluated and commented. Based on these comparisons, it is deduced that the technique under investigation can be considered to be a rather satisfactory repair technique for joints with minor to moderate damage taking into account the rapid, convenient and easy-to-apply character of its application.

• Wind and Structures
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• 제29권4호
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• pp.247-270
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• 2019

Wind-resistant design of existing cooling tower structures overlooks the impacts of rainfall. However, rainstorm will influence aerodynamic force on the tower surface directly. Under this circumstance, the structural response of the super-large cooling tower (SLCT) will become more complicated, and then the stability and safety of SLCT will receive significant impact. In this paper, surrounding wind fields of the world highest (210 m) cooling tower in Northwest China underthree typical wind velocities were simulated based on the wind-rain two-way coupling algorithm. Next, wind-rain coupling synchronous iteration calculations were conducted under 9 different wind speed-rainfall intensity combinations by adding the discrete phase model (DPM). On this basis, the influencing laws of different wind speed-rainfall intensity combinations on wind-driving rain, adhesive force of rain drops and rain pressure coefficients were discussed. The acting mechanisms of speed line, turbulence energy strength as well as running speed and trajectory of rain drops on structural surface in the wind-rain coupling field were disclosed. Moreover, the fitting formula of wind-rain coupling equivalent pressure coefficient of the cooling tower was proposed. A systematic contrast analysis on its 3D distribution pattern was carried out. Finally, coupling model of SLCT under different working conditions was constructed by combining the finite element method. Structural response, buckling stability and local stability of SLCT under different wind velocities and wind speed-rainfall intensity combinations were compared and analyzed. Major research conclusions can provide references to determine loads of similar SLCT accurately under extremely complicated working conditions.