• 대한치과의사협회지
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• 제53권6호
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• pp.418-426
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• 2015

The appropriate occlusion is one of the most important factors for the long-term success of implant and its restorations. The purpose of this review is to investigate and define occlusal considerations to reduce failure of implant prostheses. The physiological movement of implants is markedly lower than that of natural teeth and they also lack in occlusal sensitivity. Proper occlusal pattern may be assigned to compensate for the biological disadvantages and occlusal contacts must be formed where the cantilever effect is minimized. Moreover, the long-term success of implants after osseointegration can be assured by reducing early occlusal loading to avoid implant overloading and selecting appropriate occlusion material. Occlusal overload was brought by the number and location of occlusal contacts, which are under the clinician's control. The concept of implant occlusion is based on the concepts derived from traditional prosthetics. Moreover, there are few evidence on the concept or design of implant occlusion. Several occlusal design was recommended for implant prosthesis. Mutually protected occlusion, group function occlusion and bilateral balance occlusion was recommended for the specific types of implant restorations. This article reviews proper design of occlusion for implant restoration and offers occlusion strategy clinically.

• 한국CDE학회논문집
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• 제19권1호
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• pp.1-11
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• 2014

In the initial design stage, the technology for estimating and managing the weight of a floating offshore structure, such as a FPSO (Floating, Production, Storage, and Off-loading unit) and an offshore wind turbine, has a close relationship with the basic performance and the price of the structure. In this study, using the genetic programming (GP), being used a lot in the approximate estimating model and etc., the weight estimation model of the floating offshore structure was studied. For this purpose, various data for estimating the weight of the floating offshore structure were collected through the literature survey, and then the genetic programming method for developing the weight estimation model was studied and implemented. Finally, to examine the applicability of the developed model, it was applied to examples of the weight estimation of a FPSO topsides and an offshore wind turbine. As a result, it was shown that the developed model can be applied the weight estimation process of the floating offshore structure at the early design stage.

• 한국유체기계학회 논문집
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• 제20권2호
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• pp.63-68
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• 2017

This paper predicts the rotordynamic force coefficients of tilting pad journal bearings (TPJBs) with ball-socket pivot and compares the predictions to the published test data obtained under load-between-pad (LBP) configuration. The present TPJB model considers the pivot stiffness calculated based on the Hertzian contact stress theory. Due to the compliance of the pivot, the predicted journal eccentricity agree well with the measured journal center trajectory for increasing static loads, while the early prediction without pivot model consideration underestimates it largely. The predicted pressure profile shows the significant pressure development even on the unloaded pads along the direction opposite to the loading direction. The predicted stiffness coefficients increase as the static load and the rotor speed increase. They agree excellently with test data from open literature. The predicted damping coefficients increase as the static load increases and the rotor speed decreases. The prediction underestimates the test data slightly. In general, the current predictive model including the pivot stiffness improves the accuracy of the rotordynamic performance predictions when compared to the previously published predictions.

• Journal of Periodontal and Implant Science
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• 제32권1호
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• pp.69-87
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• 2002

Implant material, implant design, surface quality, status of the bone, surgical technique, and implant loading conditions were regarded as prerequisites for osseointegration which is a prime condition for implant success. The aim of this review paper was to investigate the survival rate of single implants in relation to the prerequisites for osseointegration. Fifty-eight papers reporting survival rates of single implants were selected by use of the 'PubMed' and hand searching. The survival rate of single implants were assessed with reference to factors influencing osseointegration. The results showed that single implants in general showed a high survival rate except a few failures in certain extreme conditions and early stages. Those failures and complications such as screw loosening and esthetic problem were almost solved with the development of implant components and surgical techniques and a better understanding of biology around a single implant. Single-tooth implant-replacement is now considered as a reliable and predictable treatment option for a single missing tooth and its application seems to expand to compromised situations which were previously thought to be impossible for single implant therapy.

• Advances in concrete construction
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• 제3권2호
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• pp.127-143
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• 2015

Steel fibre reinforced concrete (SFRC) is an anisotropic material due to the random orientation of the fibres within the cement matrix. Fibres under different inclination angles provide different strength contribution of a given crack width. For that the pull-out response of inclined fibres is of great importance to understand SFRC behaviour, particularly in the case of fibres with hooked ends, which are the most widely used. The paper focuses on the numerical modelling of the pull-out response of this kind of fibres from high-strength cementitious matrix in order to study the effects of different inclination angles of the fibres to the load-displacement pull-out curves. The pull-out of the fibres is studied by means of accurate three-dimensional finite element models, which take into account the nonlinearities that are present in the physical model, such as the nonlinear bonding between the fibre and the matrix in the early stages of the loading, the unilateral contact between the fibre and the matrix, the friction at the contact areas, the plastification of the steel fibre and the plastification and cracking of the cementitious matrix. The bonding properties of the fibre-matrix interface considered in the numerical model are based on experimental results of pull-out tests on straight fibres.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2018-2025
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• 2002

It is well known that the strength and the fatigue life of welded steel components are affected extensively by welding residual stresses distributed around their weldments under not only monotonic but also cyclic loads. The externally applied loads are to be superimposed with the welding residual stresses, so that unexpected deformations and failures of the components might occur. These residual stresses are not kept constant, but relaxed or redistributed during in service. Under monotonic loads the relaxation takes place when the sum of external and welding residual stress exceeds locally the yield stress of material used. By the way, it is shown that under cyclic loads the welding residual stress is considerably relieved by the first or the early cycles of loads, and then gradually relaxed with increasing loading cycles. Although many investigations in this field have been carried out, the phenomenon and mechanism of the stress relaxation are still not clear, and there are few comprehensive models to predict amount of relaxed welding residual stress. In this study, the characteristics of the welding residual stress relaxation under monotonic and cyclic loads were investigated, and a model to predict quantitatively amount of welding residual stress relaxation was proposed.

• 한국정밀공학회지
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• 제17권1호
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• pp.145-152
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• 2000

X-ray diffraction method detects change of crystal lattice distance under material surface using diffraction angle 2$\theta$. This technique can be applied to the behavior on slip band and micro crack due to material degradation. The relation between half-value breadth and number of cycle has three stages which constitute rapid decrease in initial number of cycles, slight decrease in middle number of cycles and rapid decrease in final number of cycles. The ratio of half-value breadth takes a constant value on B/B$_{0}$-N diagram with loading condition except early part of fatigue life. The ratio of half-value breadth B/B$_{0}$ with respect to number of cycle to failure N$_{f}$ has linear behavior on B/B$_{0}$-log N$_{f}$ diagram. Therefore, in this paper the estimation of fatigue life by average gradient method has much less estimated mean error than the estimation of fatigue life by log B/B$_{0}$-log N/N$_{f}$ relation.elation.ation.

• Structural Engineering and Mechanics
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• 제15권2호
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• pp.159-180
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• 2003

In this paper spacing and width of flexural cracks in reinforced concrete beams are determined using two-dimensional finite element analysis. At early loading stages on the beam the primary crack spacing is based on the slip length, which is the development length required to resist the steel stress increment that occurs at a cracked section on the formation of the first flexural crack. A semi-empirical formula is presented in this paper for the determination of the slip length for a given beam. At higher load levels, the crack spacing is based on critical crack spacing, which is defined as the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width is calculated as the relative difference in extensions of steel reinforcement and adjacent concrete evaluated at the cracked section. Finally a comparative study is undertaken, which indicates that the spacing and width of cracks calculated by this method agree well with values measured by other investigators.

• Structural Engineering and Mechanics
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• 제69권1호
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• pp.1-10
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• 2019

In the construction of flat plate slabs, which are widely used for tall buildings but have relatively low flexural stiffness, serviceability problems such as excessive deflections and cracks are of great concern. To prevent excessive deflections at service load levels, current design codes require the minimum slab thickness, but the requirement could be unconservative because it is independent on loading and elastic modulus of concrete, both of which have significant effects on slab deflections. In the present study, to investigate the effects of the construction load of shored slabs, reduced flexural stiffness and moment distribution of early-age slabs, and creep and shrinkage of concrete on immediate and time-dependent deflections, numerical analysis was performed using the previously developed numerical models. A parametric study was performed for various design and construction conditions of practical ranges, and a new minimum permissible thickness of flat plate slabs was proposed satisfying the serviceability requirement for deflection. The proposed minimum slab thickness was compared with current design code provisions and numerical analysis results, and it agreed well with the numerical analysis results.

• Smart Structures and Systems
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• 제30권1호
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• pp.17-34
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• 2022

For steel structures, fatigue cracks are critical damage induced by long-term cycle loading and distortion effects. Vision-based crack detection can be a solution to ensure structural integrity and performance by continuous monitoring and non-destructive assessment. A critical issue is to distinguish cracks from other features in captured images which possibly consist of complex backgrounds such as handwritings and marks, which were made to record crack patterns and lengths during periodic visual inspections. This study presents a parametric study on image-based crack identification for orthotropic steel bridge decks using captured images with complicated backgrounds. Firstly, a framework for vision-based crack segmentation using the atrous convolution-based Deeplapv3+ network (ACDN) is designed. Secondly, features on crack images are labeled to build three databanks by consideration of objects in the backgrounds. Thirdly, evaluation metrics computed from the trained ACDN models are utilized to evaluate the effects of obstacles on crack detection results. Finally, various training parameters, including image sizes, hyper-parameters, and the number of training images, are optimized for the ACDN model of crack detection. The result demonstrated that fatigue cracks could be identified by the trained ACDN models, and the accuracy of the crack-detection result was improved by optimizing the training parameters. It enables the applicability of the vision-based technique for early detecting tiny fatigue cracks in steel structures.