• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.23 no.3
• /
• pp.315-323
• /
• 2010

Five concrete compressive stress-strain models have been analyzed to check the validity of the strength method for determining the nominal moment of strengthened members using commercially available computer language. The results show that the concrete stress-strain models do not influence on the flexural analysis. The moment of a strengthened member obtained from the flexural analysis at concrete compressive strain reaching 0.003 is well agreed with nominal moment using the strength method. The flexural analysis results show that when the steel reinforcement, FRP ratio, FRP failure strain, and concrete failure compressive strain are relatively lower, the strength method overestimates the flexural capacity of the strengthened members.

• Journal of the Korea Concrete Institute
• /
• v.25 no.6
• /
• pp.593-599
• /
• 2013

The unrestrained shrinkage strain of alkali-activated (AA) slag concrete was examined and compared with design equations specified in code provisions and empirical equations proposed by Yang et al. The main parameters investigated were the water-to-binder ratio (W/B), unit water content and fine aggregate-to-total aggregate ratio (S/a). Test results revealed that shrinkage strain of AA slag concrete is nearly proportional to the W/B ratio, whereas its time function is independent of the W/B ratio. The shrinkage strain of AA slag concrete increased significantly when the unit water content is above $185kg/m^3$, whereas it is marginally affected by the S/a ratio. The design equation of ACI 209 considerably overestimates the shrinkage behavior of AA slag concrete, whereas CEB-FIP equation tends to underestimate the shrinkage at the age more than 28 days. The empirical equation of Yang et al. is in better agreement with test results, showing that values of mean and standard deviation of error coefficients obtained from each specimen are 016 and 0.07, respectively.

• Journal of the Korea Concrete Institute
• /
• v.15 no.1
• /
• pp.69-77
• /
• 2003

One directional and biaxial tension tests of 13 reinforced concrete panels were conducted to derive a constitutive law of concrete. Based on the test results, a model equation is derived for the stress-strain relationship of concrete in tension. Main test variables are reinforcement ratio and the load ratio applied in two directions. In addition a failure envelope of concrete in tension-tension region is suggested based on the initial crack occurrence. Test results show that the concrete carries substantial tensile stress even after cracking occurrence. However, the application of this proposed stress-strain relationship for concrete is limited to the case where the direction of reinforcement coincides with the direction of the applied principal stresses.

• Journal of Sensor Science and Technology
• /
• v.10 no.6
• /
• pp.304-309
• /
• 2001

A Fiber optic strain sensor for the measurement of the internal strain of a concrete specimen was developed. This sensor was a 11 mm Fiber-optic Fabry-Perot interferometer attached inside a stainless steel pipe of 2 mm diameter. The fabricated strain sensors were embedded in a reinforced concrete structure of $100{\times}100{\times}500\;mm^3$ size and were measured the internal strain of a concrete structure when the external pressure was applied to the structure. For a field application, the strain sensors were attached on the bottom of a real bridge and dynamic loading test were executed. In the test, they showed good sensitivity as a deformation sensor and capability of remote monitoring.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.341-344
• /
• 2008

In this paper, the effect of flame cutting order of tendons on the concrete stress was investigated experimentally. For this, the three slab specimens with 14 tendons were cast and tested. During the detensioning, the longitudinal and transversal strain were measured. Test results showed that the measured strains of transversal stirrups were varied by the cutting order.

• Journal of the Korea Concrete Institute
• /
• v.13 no.3
• /
• pp.251-260
• /
• 2001

It is required to evaluate the axial strain of reinforced concrete beams in order to predict the ductility of reinforced concrete beams subjected to reversed cyclic loading. A model was proposed to determine the axial strains In reinforced concrete beams by analysing the behavior of reinforced concrete sections and comparing with published test results. The proposed axial strain model inclusively reflected four kinds of paths : Path 1-steel bar in an elastic stage or a unloading region; Path 2-after flexural yielding; Path 3-a slip region; and Path 4-a reversing loading region. The equations to predict the axial strains of each path were proposed. The proposed equations took into account the effects of the loading program. Comparison of axial strains between experimental results and the results from proposed equations showed to be in a good agreement with experimental results.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.30 no.4A
• /
• pp.383-389
• /
• 2010

The concrete structural design provisions in Korea are based on ultimate strength design. Up to service load stage, it is assumed a linear stress-strain relation, but there is no stress-strain relationship for a concrete material from service load stage to limat state. According to the current provisions, an independent method is provided for the each calculation of deflection and crack width. In EC2 provisions based on limit state design, however, a stress-strain relationship of concrete is provided. Thereby, it is able to calculate a strength as well as a deflection directly from concrete stress-strain relationship. In this paper the moment-curvature relationship is directly calculated from a material law using equilibrium and compatibility conditions. Then strength and deflection are formulated. These results are compared with the values from the current provisions in Korea. From the results, the deflection based on a moment-curvature relationship is well agreed with experimental results and it is appeared that the deflection after the yielding of steel is also possible.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.253-256
• /
• 2008

Although researches on the beams strengthened with Fiber reinforced Polymers (FRPs) have recently been conducted around the world, there are few researches on the beams with FRPs under a sustained load. This paper presents the behavior of the beams with Carbon Fiber Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) under a sustained load during 300 days. Strains of steel and FRP reinforcement were measured in order to investigate the behavior of the beams. Additionally, Adjusted Effective Modulus Method (AEMM) and Ghali and Farve's method were used to predict increase in the stress and strain caused by creep and shrinkage. Through the experiment, it was found that the beam with CFRP is more effective than the beam with GFRP in terms of flexural strengthening. Compared with analytical results, it was indicated that strains of tension steels were overestimated, whereas strains of compression steels were underestimated.

• Magazine of the Korea Concrete Institute
• /
• v.16 no.4 s.81
• /
• pp.70-77
• /
• 2004

콘크리트 구조물에 대한 많은 기준들의 요건에 따르면, 휨을 받는 철큰 콘크리트(RC) 보의 압축부에서의 응력은 일반적으로 일축의 응력-변형을 관계를 이용하여 계산한다. 이와 같은 접근은 가끔씩 압축력을 받는 콘크리트에서 부서짐이 발성할 때 보의 구조적 거동을 재현하지 못할 수 있다. 결과적으로, RC 구조물의 지지력과 그들의 연성은 근사적으로 평가된다. 본 논문에서는 압축을 받고 있는 콘크리트의 postpeak 거동은 활동면을 이용하여 모델링되었다. 이 활동 면의 모멘트-곡률곡선에서 연화부분에 그 원인이 있다. 제안된 활동현상의 수학적 표현은 압축력을 받는 콘크리트(즉, 연화부분의 거동이 압축영역의 크기와 변형률구배(곡배)에 의존하는)에 있어서 특정한 응력-변형률 관계를 정의하는 것이 얼마나 어려운지를 보여주고 있다.

• Journal of the Korea Concrete Institute
• /
• v.13 no.2
• /
• pp.130-138
• /
• 2001

This paper presents on the shear behavior prediction of reinforced concrete beams using Transformation Angle Truss Model (TATM). The TATM can evaluate the stress-strain relationships for cracked concrete by transforming stresses and strains for principal plane into those over the crack surfaces. This proposed analytical method simplifies the Fixed Angle Softened Truss Model (FA-STM) and removes the limitation of applicability of the FA-STM. The shear.strength and strain of reinforced concrete beams are predicted by using the TATM. For the verification of proposed method, experimental results of reinforced concrete beams were compared with theoretical results by the TATM, FA-STM and Rotating Angle Softened Truss Model (RA-STM).