• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.719-727
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• 2008

The tensile and bond performance of GFRP rebar are different from those of conventional steel reinforcement. It requires some studies on concrete members reinforced with GFRP reinforcing bars to apply it to concrete structures. GFRP has some advantages such as high specific strength, low weight, non-corrosive nature, and disadvantage of larger deflection due to the lower modulus of elasticity than that of steel. Bridge deck is a preferred structure to apply FRP rebars due to the increase of flexural capacity by arching action. This paper focuses on the behavior of concrete bridge deck reinforced with newly developed GFRP rebars. A total of three real size bridge deck specimens were made and tested. Main variables are the type of reinforcing bar and reinforcement ratio. Static test was performed with the load of DB-24 level until failure. Test results were compared and analyzed with ultimate load, deflection behavior, crack pattern and width.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.105-112
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• 2023

Steel fiber reinforced concrete (SFRC) exhibits enhanced strength and superior energy dissipation capacity compared to normal concrete, and it can also reduce crack propagation and fragmentation of concrete even when subjected to blast loads. In this study, the parameters defining failure surface and damage function of the K&C concrete nonlinear model were proposed to be applied for the properties of SFRC in LS-DYNA. Single element analysis has been conducted to validate the proposed parameters in the K&C model, which provided very close simulations on the compressive behavior of SFRC. In addition, blast analysis was performed on SFRC columns with different volume fractions of steel fibers, and the blast resistance of SFRC columns was quantitatively analyzed with Korea Occupational Safety & Health Agency (KOSHA) guidelines.

• Journal of the Korean GEO-environmental Society
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• v.15 no.1
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• pp.53-62
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• 2014

In Korea, in general, separation distance between existing parallel tunnels was set at two to five times as distant as the diameter of the tunnels according to ground conditions. Recently, however, actual applicability of closely spaced parallel tunnels whose distance between tunnel centers was shorter than the diameter has increased due to environmental damages resulting from massive cutting, restriction in purchase of required land, and maintenance of linear continuity. In particular, when the pillar width of tunnel decreases, the safety of pillars affects behaviors of the tunnel and therefore the need for diverse relevant studies has emerged. However, research so far has been largely confined to analysis of behavior characteristics of pillars, or parameters affecting design, and actually applicable and quantitative data have not been presented. Accordingly, in order to present a stability evaluation method which may maximally reflect construction conditions of spots, this study reflected topographical and stratigraphic characteristics of the portal part with the highest closeness between the tunnels, simulated multi-layer conditions with rock mass and complete weathering, and assessed the degree of effect the stability of pillars had on the entire tunnels through numerical analysis according to changes in pillar width by ground strength. This study also presented composite analysis result on ground surface settlement rates, interference volume rates, and average strength to stress and a formula, which may be applicable to actual work, to evaluate safety rates of closely spaced parallel tunnel pillars and minimum pillar width by ground strength based on failure criteria by Hoek-Brown (1980).

• Journal of the Microelectronics and Packaging Society
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• v.24 no.3
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• pp.71-76
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• 2017

The electrical behavior and flexibility of the screen printed Ag circuits were investigated with infrared radiation sintering times and sintering temperatures. Electrical resistivity and radio frequency characteristics were evaluated by using the 4 point probe measurement and the network analyzer by using cascade's probe system, respectively. Electrical resistivity and radio frequency characteristics means that the direct current resistance and signal transmission properties of the printed Ag circuit. Flexibility of the screen printed Ag circuit was evaluated by measuring of electrical behavior during IPC sliding test. Failure mode of the Ag printed circuits was observed by using field emission scanning electron microscope and optical microscope. Electrical resistivity of the Ag circuits screen printed on Pl substrate was rapidly decreased with increasing sintering temperature and durations. The lowest electrical resistivity of Ag printed circuit was up to $3.8{\mu}{\Omega}{\cdot}cm$ at $250^{\circ}C$ for 45 min. The crack length arisen within the printed Ag circuit after $10{\times}10^4$ sliding numbers was 10 times longer than that of after $2.5{\times}10^4$ sliding numbers. Measured insertion loss and calculated insertion loss were in good agreements each other. Insertion loss of the printed Ag circuit was increased with increasing the number of sliding cycle.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.299-306
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• 2019

In this study, a model experiment that simulates the behaviour of the ground composed of several compacted layer was intended to measure the loosened area in the event of a ground cavity through a LAD (Loosened area detector). It was confirmed that the size of the cone diameter was affected by the ground composed of fine grain + granulated soil layered through the model soil. In order to select the appropriate cone type, a scale effect experiment was conducted. From the test results, a micro-cone was chosen for the most suitable indoor model experiment. In the case of applying LAD in this study, the loosening condition of the ground was determined by the rapid change in penetration resistance caused by the difference in the boundary surface and relative density due to the compaction of the ground for indoor model testing. The range of loosened area occurring in the cavity was estimated through the penetration resistance characteristics on the ground, and the failure area was identified through the reduction rate of penetration resistance in the loosening area.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.6
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• pp.65-72
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• 2016

Service life evaluation for RC Structures exposed to chloride attack is very important, however the previous two methods(deterministic and probabilistic method) show a big difference. The paper presents a service life simulation using deterministic and probabilistic method with time-dependent diffusion coefficient. Three different cases are considered for diffusion coefficient, concrete cover depth, and surface chloride content respectively, and then the PDF(probability of durability failure) and the related service life are obtained. Through adopting time-dependent diffusion, the discrepancy between the two methods can be reduced, which yields reasonable service life. When diffusion coefficient increases from $2.5{\times}10^{-12}m^2/sec$ to $7.5{\times}10^{-12}m^2/sec$, the service life decreases to 25.5~35.6% level, and cover depth does from 75 mm to 125 mm, it increases to 267~311% level as well. In the case of surface chloride content from $5.0kg/m^3$ to $15.0kg/m^3$, it changes to 40.9~54.5%. The effect of cover depth is higher than the others by 8~10 times and also implies it is a key parameter to service life extension.

• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.99-107
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• 2004

Anisotropic characteristics of deformation are important to understand the particular behavior in the pre-failure state of soils. Recent experiments show that cross-anisotropic moduli of granular soils can be expressed by functions of normal stresses in the corresponding directions, which is closely linked to micromechanical characteristics of particles. Granular soils are composed of a number of particles so that the force-displacement relationship at each contact point governs the macroscopic stress-strain relationship. Therefore, the micromechanical approach in which the deformation of granular soils is regarded as a mutual interaction between particle contacts is one of the best ways to investigate the anisotropic elastic deformation of soils. In this study, a numerical program based on the theory of micromechanics is developed. Generalized contact model for the irregular contact surface of soil particles is adopted to represent the force-displacement relationship in each contact point far the realistic prediction of anisotropic moduli. To evaluate the model parameters, a set of analytical solutions of anisotropic elastic moduli is derived in the isotropic stress condition. A detailed procedure to determine the model parameters is proposed with emphasis on the practical applicability of micromechanical program to analyze the elastic behavior of the granular soils.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.2
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• pp.485-495
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• 2017

A development of underground space is very useful solution to slove problem occurred from ground surface enlargement in urban areas due to the growth of population, tunnelling is the most popular way and widely used. Researches regarding tunneling-induced pile-soil interactive behaviour have been conducted by many researchers. A study on pile axial force distribution due to tunnelling through laboratory model test, however, is being rarely carried out. In this study, therefore, authors investigate ground behaviour due to tunnelling below grouped pile subjected vertical load as well as pile axial force distribution. A concept of volume loss is used to express tunnel excavation, which is normally applied to 1~2% for tunnelling in soft ground. In this study, however, 10% of that applied to investigate failure mechanism. As a result of laboratory model test, a decrease of pile axial force occurs at 1.5% of volume loss, settlement of grouped pile is 1.2~4.7 times greater than the adjacent ground surface one. Ground deformations at 1.5% of volume loss are measured using Close Range Photogrammetry and compared with results from numerical analysis.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.581-592
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• 2016

Tensile constitutive stress-strain model of steel fiber reinforced concrete (SFRC) in fib MC2010 was investigated. In order to model tensile behavior of SFRC, three point loading flexural tests were conducted on notched small beams according to BE-EN-14651. Design parameters for the constitutive model were determined from the flexural tests. Flexural test and finite element analysis were conducted on large SFRC beam without steel reinforcements and compared with each other. In addition, parametric study on the effect of compressive and tensile model, and characteristic length on flexural behavior of the SFRC beam was conducted also. In results, pre-peak load-displacement curves from the FE analysis was close to experimental curves but significant difference was shown in post-peak behavior. The reason of the difference is originated from the fact that the fiber distribution and orientation were not being properly considered in the MC2010 model. This study shows that modification and detail explanations on the orientation factor K in MC2010 might require to better reproduce the behaviour of large scale SFRC beams.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.2
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• pp.119-128
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• 2016

In a performance-based design, the structural safety is estimated from pre-defined damage states and corresponding damage indices. Both damage states and damage indices are well defined for above-ground structures, but very limited studies have been performed on underground structures. In this study, we define the damage states and damage indices of a cut-and-cover box tunnel which is one of typical structures used in metro systems, under a seismic excitation from a series of inelastic frame analyses. Three damage states are defined in terms of the number of plastic hinges that develop within the structure. The damage index is defined as the ratio of the elastic moment to the yield moment. Through use of the proposed index, the inelastic behavior and failure mechanism of box tunnels can be simulated and predicted through elastic analysis. In addition, the damage indices are linked to free-field shear strains. Because the free-field shear strain can be easily calculated from a 1D site response analysis, the proposed method can be readily used in practice. Further studies are needed to determine the range of shear strains and associated uncertainties for various types of tunnels and site profiles. However, the inter-linked platform of damage state - damage index - shear wave velocity - shear strain provides a novel approach for estimating the inelastic response of tunnels, and can be widely used in practice for seismic designs.