• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.729-735
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• 2008

For well-constructed concrete, its service life is a long period and it has an enough durability performance. For cracked concrete, however, it is clear that cracks should be a preferential channel for the penetration of aggressive substance such as chloride ions accoding to author's previous researches. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study to deal with the effect of different types of surface treatment system, which are expected to seal the concrete and the cracks to chloride-induced corrosion in particular. In this study, it is examined the effect of surfaced treated systems such as penetrant, coating, and their combination on chloride penetration through microcracks. Experimental results showed that penetrant can't cure cracks. However, coating and combined treatment can prohibit chloride penetration through cracks upto 0.06 mm, 0.08 mm, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6A
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• pp.861-872
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• 2008

Concrete-filled glass fiber reinforced polymer tubes are often used for marine structures with the benefit of good durability and high resistance against corrosion under severe chemical environment. Current research presents results of a comprehensive experimental investigation on the behavior of axially loaded circular concrete-filled glass fiber reinforced polymer tubes. This paper is intended to examine several aspects related to the usage of glass fiber fabrics and filament wound layers used for outer shell of piles subjected to axial compression. The objectives of the study are as follows: (1) to evaluate the effectiveness of filament winding angle of glass fiber layers (2) to evaluate the effect of number of GFRP layers on the ultimate load and ductility of confined concrete (3) to evaluate the effect of loading condition of specimens on the effectiveness of confinement and failure characteristics as well, and (4) to propose a analytical model which describes the stress-strain behavior of the confined concrete. Three different types of glass fiber layers were chosen; fabric layer, ${\pm}45^{\circ}$ filament winding layer, and ${\pm}85^{\circ}$ filament winding layer. They were put together or used independently in the fabrication of tubes. Specimens that have various L:D ratios and different diameters have also been tested. Totally 27 GFRP tube specimens to investigate the tension capacity, and 66 concrete-filled GFRP tube specimens for compression test were prepared and tested. The behavior of the specimens in the axial and transverse directions, failure types were investigated. Analytical model and parameters were suggested to describe the stress-strain behavior of concrete under confinement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6A
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• pp.965-976
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• 2006

A realistic lifetime seismic-reliability based approach is unavoidable to perform Life-Cycle Cost (LCC)-effective optimum design, maintenance, and retrofitting of structures against seismic risk. So far, though a number of researchers have proposed the LCC-based seismic design and retrofitting methodologies, most researchers have only focused on the methodological point. Accordingly, in most works, they have not been quantitatively considered critical factors such as the effects of seismic retrofit, maintenance, and environmental stressors on lifetime seismic reliability assessment of deteriorating structures. Thus, in this study, a systemic lifetime seismic reliability analysis methodology is proposed and a program HPYER-DRAIN2DX-DS is developed to perform the desired lifetime seismic reliability analysis. To demonstrate the applicability of the program, it is applied to an example bridge with or without seismic retrofit and maintenance strategies. From the numerical investigation, it may be positively stated that HYPER-DRAIN2DX-DS can be utilized as a useful numerical tool for LCC-effective optimum seismic design, maintenance, and retrofitting of bridges.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2A
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• pp.301-310
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• 2006

Carbon fiber reinforced polymer (CRFP) materials are well suited to the rehabilitation of civil engineering structures due to their corrosion resistance, high strength to weight ratio and high stiffness to weight ratio. Their application in the field of the rehabilitation of concrete structures is increased due to the vast number of bridges and buildings in need of strengthening. However, RC members, strengthened with externally bonded CFRP plates, happened to collapse before reaching the expected design failure load. Therefore, it is necessary to develop the new strengthening method to overcome the problems of previous bonded strengthening method. This problems can be solved by prestressing the CFRP plate before bonding to the concrete. In this study, a total of 21 specimens of 3.3 m length were tested by the four point bending method after strengthening them with externally bonded CFRP plates. The CFRP plates were bonded without prestress and with various prestress levels ranging from 0.4% to 0.8% of CFRP plate strain. All specimen with end anchorage failed by a plate fracture regardless of the prestress levels while the specimen without end anchorage failed by the separation of the plate from the beam due to premature debonding. The cracking loads was proportionally related to the prestress levels, but the maximum loads of specimens strengthened with prestressed CFRP plates were insignificantly affected by the prestress levels.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.691-697
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• 2008

Coating the high tension bolted frictional joint has been generally allowed for anti-corrosion purpose. However in case of painting on paying surface of the high tension bolt, the influence on a slip strength of the joint depending on precision of painting has remained controversial. The study thus was intended to identify the slip behavior on high tension bolted frictional joint when applying ceramic painting, which has been currently developed. A slip test was conducted on a high tension bolted frictional joint specimen on which ceramic painting has been applied and a slip load and slip coefficient were measured. Based on result, the safety and usability of ceramic painting-applied high tension bolted frictional joint was evaluated. As a result, a difference to some extent by specimen in terms of load-displacement when a slip occurred was observed but an average slip coefficient appeared to have exceeded 0.4, which is the design frictional coefficient set forth in the specification. To secure the safety and usability of ceramic painting-applied high tension bolted frictional joint, it's necessary to establish the standard for painting as well as to revise the relevant specification.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.753-759
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• 2006

To predict service life of concrete structures exposed to chloride attack, surface chloride concentration, diffusion coefficient of chloride ion, and chloride corrosion threshold value in concrete, are used as important factors. Of these, as the diffusion coefficient of chloride ion for concrete is strongly influenced by concrete quality and environmental conditions of structures and may significantly change the service life of structures, it is considered as the most important factor for service life prediction. The qualitative factors affecting the penetration and diffusion of chloride ion into concrete are water-cement (W/C) ratio, age, curing conditions, chloride ion concentration of given environment, wet and dry conditions, etc. In this paper the influence of W/C ratio and curing conditions on the diffusion characteristics of chloride ion in concrete was investigated through the chloride ion diffusion test. In the test, the voltages passing through the diffusion cell were measured by accelerated test method using potential difference, and then with the consideration of IR drop ratio the diffusion coefficient of chloride ion for concrete with different W/C ratios were estimated by Andrade's model. Furthermore, under different curing conditions formulas for the estimation of the diffusion coefficient of chloride ion have been proposed by the regression analysis considering the effect of W/C ratio and age.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.513-521
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• 2006

Many studies have been conducted on the high tension bolt friction connection in the view of the field practice. Those effort, however, unfortunately have not been appropriately applied in the design specifications. Recently, particularly for steel bridges, rationalization of design takes greater attention from designers and hence, demand on rationalization of high tension connection becomes more significant. The purpose of this study is to suggest direction for the rationalization of high tension bolt connection and to also provide fundamental information for the improvement of the design specifications. In order to accomplish the purposes, the design specifications in Korea was analyzed and compared with other specification from abroad, and was studied one of the most important factors including slip coefficient, and the specifications on the size of bolt holes. The effect of over-sized bolt hole and the reduction of axial force on bolt was evaluated through the experimental studies on the slippage of the high tension bolt connections. Other research topics included herein includes the difference of slip coefficients, the effect of over-sized bolt holes and the gap distance of members, and the application of filler plate and corrosion protected bolts. From the research results, it is known that the specifications in Korea apply a constant slip coefficient with respect to the contacted surface conditions while various coefficients are available depending on the contacted surface conditions. Therefore, it is recommended that the specifications in Korea also develop and detail the slip coefficient which can appropriately take account of the variation of the contacted surface conditions. It is also suggested that the limitation abroad on the over-sized bolt hole may be applied for enhancing the effectiveness of construction.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6A
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• pp.977-988
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• 2006

The goal of this study is to develop a realistic methodology for determination of the Life-Cycle Cost (LCC)-effective optimal seismic retrofit and maintenance strategy of deteriorating bridges. The proposed methodology is based on the concept of minimum LCC which is expressed as the sum of present value of seismic retrofit costs, expected maintenance costs, and expected economic losses with the constraints such as design requirements and acceptable risk of death. The proposed methodology is applied to the LCC-effective optimal seismic retrofit and maintenance strategy of a steel bridge considered as a example bridge in the accompanying study, and various conditions such as corrosion environments and Average Daily Traffic Volumes (ADTVs) are considered to investigate the effects on total expected LCC. In addition, to verify the validity of the developed methodology, the results are compared with the existing methodology. From the numerical investigation, it may be positively expected that the proposed methodology can be effectively utilized as a practical tool for the decision-making of LCC-effective optimal seismic retrofit and maintenance strategy of deteriorating bridges.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.71-83
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• 2009

Shotcrete is an important primary support for tunnelling in rock. The quality control of shotcrete is a core issue in the safe construction and maintenance of tunnels. Although shotcrete may be applied well initially onto excavated rock surfaces, it is affected by blasting, rock deformation and shrinkage and can debond from the excavated surface, causing problems such as corrosion, buckling, fracturing and the creation of internal voids. This study suggests an effective non-destructive evaluation method of the tunnel shotcrete bonding state applied onto hard rocks using the impact-echo (IE) method and ground penetration radar (GPR). To verify previous numerical simulation results, experimental study carried out. Generally, the bonding state of shotcrete can be classified into void, debonded, and fully bonded. In the laboratory, three different bonding conditions were modeled. The signals obtained from the experimental IE tests were analyzed at the time domain, frequency domain, and time-frequency domain (i.e., the Short- Time Fourier transform). For all cases in the analyses, the experimental test results were in good agreement with the previous numerical simulation results, verifying this approach. Both the numerical and experimental results suggest that the bonding state of shotcrete can be evaluated through changes in the resonance frequency and geometric damping ratio in a frequency domain analysis, and through changes in the contour shape and correlation coefficient in a time-frequency analysis: as the bonding state worsens in hard rock condition, the autospectral density increases, the geometric damping ratio decreases, and the contour shape in the time-frequency domain has a long tail parallel to the time axis. The correlation coefficient can be effectively applied for a quantitative evaluation of bonding state of tunnel shotcrete. Finally, the bonding state of shotcrete can be successfully evaluated based on the process suggested in this study.

• The Journal of Korean Academy of Prosthodontics
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• v.61 no.3
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• pp.234-244
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• 2023

Tooth wear refers to the loss of dental hard tissue caused by various physiological and pathological causes, and excessive pathological wear can cause complications such as pathological changes in dimensions, occlusal disharmony, loss of function, and aesthetic problems. The cause of tooth wear can be caused by attrition, abrasion, corrosion and abfraction, and it is known to act in a multifactorial etiology in interocclusal activity. In patients with excessive pathological wear, it is important to determine whether or not the vertical dimension of occlusion is reduced, and complete oral rehabilitation should be achieved with the adaptation of the neuromuscular and temporomandibular joint through accurate diagnosis and analysis. The patient in this case was a 63-year-old male patient, who presented discomfort to cold beverage due to severe tooth wear. After analysis of the patient's vertical dimension of occlusion, a full mouth rehabilitation was performed with increasing vertical dimension of occlusion. The goal of treatment was to improve the occlusal plane with the equal-intensity contact of all teeth, harmonious anterior guidance and immediate disclusion of all posterior contacts. After rehabilitation, the patient was satisfied with function and esthetic appearance.