• Journal of the Korean Society for Railway
• /
• v.19 no.3
• /
• pp.331-340
• /
• 2016

Wheel load, design velocity, traffic amount (MGT), stiffness and thickness of sub-layers of asphalt concrete track are selected as performance design parameters in this study. A pseudo-static wheel load computed considering the dynamic amplification factor (DAF) based on the design velocity of the KTX was applied to the top of asphalt concrete track for full three dimensional structural analysis using the ABAQUS program. Tensile strains at the bottom of the asphalt concrete layer and vertical strains at the top of the subgrade were computed from the structural FEA with different combinations of performance parameter values for one asphalt concrete track section. Utilizing the computed structural analysis results such as the tensile strains and the vertical strains, it was possible to develop design graphs to investigate proper track sections for different combination of the performance parameters including wheel load, design velocity, traffic amount(MGT), stiffness and thickness of asphalt concrete layers for any given design life. By analyzing the proposed design graphs for asphalt concrete track, it was possible to propose simple design tables that can be used by engineers for the effective and fast design of track.

• Journal of the Korea Concrete Institute
• /
• v.15 no.3
• /
• pp.454-461
• /
• 2003

This study addressed a procedure to carry out an experimental study on a behavior of simple and continuous concrete beams. For this purpose, sample concrete beams were fabricated and sensors for the measurement of strains and deflections were attached both on the surface of the beams and inside them. Two types of sensors were used to measure strains associated with loading: electric resistance strain sensors and fiber optic sensors. Displacement gauges were also attached on the bottoms of beams to investigate the behavior of beams more rationally. The behavior of the beams was then evaluated throughout the results measured from different sensors while they were subject to steady loading up to failure. From results of this study, it was found that concurrent use of sensors and displacement gauges is helpful in investigating the behavior of concrete beams more effectively. Especially, combined-type strain sensors specifically fabricated in this experiment were found not to be affected by the occurrence of cracks so significantly and to be very effective in monitoring strains of concrete structure. It was also observed that beams show nonlinear force-displacement relationship and reinforcing bars take charge of resisting the external force once cracks occur in concrete beams.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.11 no.4
• /
• pp.381-390
• /
• 2023

In this study, the mechanical performance of concrete exposed to chloride ion penetration was investigated. And a compressive stress-strain model was presented. CaCl₂ solution was added when mixing concrete to simulate long-term chloride ion penetration, and the concentration of chlorine ions was set to 0, 1, 2, and 4 % based on the weight of the binder. To investigate the compressive stress-strain curve after the peak stress of concrete, the compressive strength was measured by displacement control. When the chlorine ion concentration was 1 %, peak stress increased, but when the chlorine ion concentration was 2 % or more, peak stress decreased. In the case of peak strain, no trend according to chloride ion concentration was observed at 7 days. At 28 days, peak strain decreased as the chloride ion concentration increased. A compressive stress-strain curve model based on the Popovics model was presented using changes in peak stress and peak strain at 28 days. Microstructure analyses were performed to investigate the cause of the decrease in mechanical performance as the concentration of chlorine ions increased. It was confirmed that as the concentration of chlorine ion increased, Friedel's salt increased and portlandite decreased.

• Journal of the Korea Concrete Institute
• /
• v.18 no.3 s.93
• /
• pp.361-370
• /
• 2006

The results of previous tests by many researchers have been compiled to evaluate the flexural strength of steel-fiber reinforced concrete beams. Existing prediction equations for flexural strength of such beams were examined, and a new equation based on mechanical and empirical observations, was proposed. In other words, the constitutive models for steel fiber reinforced concrete(SFRC) were proposed, which incorporate compressive and tensile strength. A steel model might also exhibit stain-hardening characteristics. Predictions based on the model are compared with the experimental data. For the collection of tests, a variation of the Henager equations, modified to apply to fiber-reinforced concrete beams, provided reliable estimates of flexural strength. The proposed equations accounted for the influence of fiber-volume fraction, fiber aspect ratio, concrete compressive strength and flexural steel reinforcement ratio. The proposed equations gave a good estimation for 129 flexural specimens evaluated.

• Journal of the Korea Concrete Institute
• /
• v.21 no.1
• /
• pp.75-84
• /
• 2009

An analytical model for predicting the shear strength of prestressed concrete beams without shear reinforcement was developed, on the basis of the existing strain-based shear strength model. It was assumed that the compression zone of intact concrete in the cross-section primarily resisted the shear forces rather than the tension zone. The shear capacity of concrete was defined based on the material failure criteria of concrete. The shear capacity of the compression zone was evaluated along the inclined failure surface, considering the interaction with the compressive normal stress. Since the distribution of the normal stress varies with the flexural deformation of the beam, the shear capacity was defined as a function of the flexural deformation. The shear strength of a beam was determined at the intersection of the shear capacity curve and the shear demand curve. The result of the comparisons to existing test results showed that the proposed model accurately predicted the shear strength of the test specimens.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2010.05a
• /
• pp.105-106
• /
• 2010

FBG temperature sensor and strain sensor has been used to monitoring shrinkage and temperature of concrete cable-stayed girder bridge site in its casting early age, The monitoring method using this study is expected to used a practical method.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.5
• /
• pp.135-142
• /
• 2022

In this study, lap spliced ultra-high strength reinforced concrete beams were tested and the code criteria for calculating the lap splice length which was affected by the transverse reinforcement and concrete covering performance were reviewed. The main variables for test were set as fiber volume fraction and transverse reinforcing bar arrangement to improve the confining performance of the concrete cover. The change of the confining performance of concrete cover according to the increase in the fiber mixing amount at 1% and 2% volume ratio was examined, and D10 stirrups with a spacing of 100 mm were placed in the lap spliced region. As a result of the test, the specimens confined by the stirrups showed a sudden drop of load bearing capacity with horizontal cracking at the position of tensile longitudinal reinforcement. However, horizontal cracks were not appeared at the location of longitudinal reinforcement for the specimens with steel fiber. And these specimens showed gradual decrease of load bearing capacity after experiencing peak load. In particular, it was found that the strain at the position of the tensile longitudinal reinforcements of the specimens to which the mixing ratio of 2% was applied exceeds the yield strain. As a result of measuring the strain on the concrete surface, it was found that the fiber was more effective in preventing damage to the concrete surface than the stirrups for short lap spliced region.

• Journal of the Korea Concrete Institute
• /
• v.16 no.4 s.82
• /
• pp.501-509
• /
• 2004

The proposed model can predict the compressive behaviors of concrete confined with fiber reinforced polymer (FRP) jacket. To model confining concrete by FRP jackets, the hypoelasticity-based constitutive law of concrete In tri-axial stress states has been presented. The increment of strength of concrete has been determined by the failure surface of concrete in tri-axial states, and its corresponding peak strain is computed by the strain enhancement factor that is proposed in the present study, Therefore, the newly proposed model is a load-dependent confinement model of concrete wrapped by FRP jackets to compare the previous models which are load-independent confinement models. The behavior of FRP jackets has been modeled using the mechanics of orthotropic laminated composite materials in two-dimension. The developed model is implemented into the incremental analysis of compressive tests. The verification study with several different experiments shows that the model is able to adequately capture the behavior of the compression test by including better estimations of the axial responses as well as the lateral response of FRP-confined concrete cylinders.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.3 s.55
• /
• pp.225-231
• /
• 2009

This study introduces the CFTA girder(Concrete-Filled and Tied Steel Tubular Arch Girder) which is a combined structural system of traditional CFT, arch, and prestress structures. Static load tests and structural behavior analyses were carried out for a 25m long CFTA girder. In the analysis, each load of 58kN, 88kN, 148kN, 207kN,and 298kN was applied incrementally at the positions of 1.0 m distances in both directions from the center of the girder. On each test, strain and displacement were measured. Linear static FEM analyses using Strand7 code were also performed to check the structural stability and to investigate the effects of prestressing(${\pm}$20%) and material property(Young's modulus) on the displacement and strain. The results of this study are summarized as follows: the initial strain & displacement under selfweight and prestressing were influenced with the variation of prestressing, but they were mainly effected only by Young's modulus when additional loads were applied.

• Magazine of the Korea Concrete Institute
• /
• v.14 no.3
• /
• pp.18-23
• /
• 2002

구조재료로써 콘크리트의 물리적 특성은 강재와는 달리 시간 의존적이라고 할 수 있다. 즉, 타설 후 재령이 경과함에 따라 압축강도와 탄성계수가 증가함은 물론, 콘크리트 내의 수분이 대기 상태로 증발하면서 부재가 수축하는 건조수축 및 외력의 증감없이 변형률이 증가하는 크리프 특성 등을 가지고 있다. 또한, 콘크리트는 시멘트의 수화반응에 의해 시공초기에 재료의 온도가 급격히 상승하는 발열특성도 동시에 가지고 있다. 이러한 특성들은 구조물의 설계시 무시할 수 없으며, 각 시공단계 및 완성단계의 구조물의 응력에 커다란 영향을 미치게 된다.(중략)