• Journal of Korean Association for Spatial Structures
• /
• v.1 no.2 s.2
• /
• pp.93-100
• /
• 2001

A stress-strain relationship for reinforced concrete membrane elements subjected to reversed cyclic loading is quite different to that of concrete cylinder subjected to uniaxial compression. The compressive strength of cracked concrete membrane elements is reduced by cracking due to tension in the perpendicular direction. Based on the three reinforced concrete panel tests, a softened stress-strain curve of concrete subjected to reversed cyclic loading is proposed. The proposed model consists of seven stages in the compressive zones and six stages in the tensile zones. The proposed model is verified by comparing to the test results.

• Computers and Concrete
• /
• v.5 no.3
• /
• pp.243-260
• /
• 2008

The present article summarises the fundamental characteristics of concrete behaviour which underlie the formulation of an engineering finite element model capable of realistically predicting the behaviour of (plain or reinforced) concrete structural forms in a wide range of problems ranging from static to impact loading without the need of any kind of re-calibration. The already published evidence supporting the proposed formulation is complemented by four additional typical case studies presented herein; for each case, a comparative study is carried out between numerical predictions and the experimental data which reveals good agreement. Such evidence validates the material characteristics upon which the FE model's formulation is based and provides an alternative explanation regarding the behaviour of structural concrete and how it should be modelled which contradicts the presently (widely) accepted assumptions adopted in the majority of FE models used to predict the behaviour of concrete.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05b
• /
• pp.1-4
• /
• 2005

This research is to present experimental materials model of high strength concrete for prediction of fire safety of structural members based on physical properties of materials during heating up to 800$^{circ}C$. The following conclusions are drawn from this study. First of all, between 100 to 200 $^{circ}C$, the physical models of concrete such as specific heat and thermal conductivity, show visible degradation, regardless of concrete strength. Second, between 300 to 600$^{circ}C$, the physical models of the 29MPa and 49MPa concrete show degradation continually at these temperatures. Finally, beyond 600$^{circ}C$, the physical models of 49MPa strength concrete show larger degradation than 29MPa strength concrete due to rise of pore pressure and melting of the interface between aggregate and cement paste.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.30 no.5A
• /
• pp.443-462
• /
• 2010

The strut-tie model approach has proven to be effective in the ultimate analysis and design of structural concrete with disturbed regions. For the reliable analysis and design by the approach, however, the effective strength of concrete struts must be determined accurately. In this study, the validity of the effective strength of concrete struts, presented by the several design codes and many researchers including the author, was examined through the ultimate strength analysis of 24 reinforced concrete panels, 275 reinforced concrete deep beams, and 218 reinforced concrete corbels by using the conventional linear strut-tie model approach of current codes. The present study shows that the author's approach, resulting in an accurate and consistent evaluation of the ultimate strength of the panels, deep beams, and corbels, may reflect rationally the effects of primary variables including the types of strut-tie model and structural concrete, the conditions of load and geometry, and the strength of concrete in the strut-tie model analysis and design of structural concrete.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.17 no.6
• /
• pp.575-586
• /
• 2015

In NATM tunnel, the Ground-Lining Interaction model(GLI model) had been proposed a one of the numerical analysis as the ground load estimation method of the concrete lining. But this model was not applied with the interface mechanism between the ground and the support member or concrete lining. Therefor in this study, it is implemented as a model for closer than actual states that the interface element applied to the existing GLI model. And the modified GLI formula is proposed with the ground load estimation that is from the numerical results for each ground and rock cover conditions. Based on the numerical results, the ground load acting on concrete lining is reduced to ave. 88~106% in case of IV ground condition and ave. 47~57% in case of weathered soil condition comparing with the existing GLI model. It can be anticipated that the results obtained from this study can be applied to an estimation of the ground load on the concrete lining modeled like as real states, consistent and economical design.

• Journal of the Korea Concrete Institute
• /
• v.15 no.3
• /
• pp.433-442
• /
• 2003

This paper presents a hypoplastic model for three-dimensional analysis of concrete structures under monotonic, cyclic, proportional and non-proportional loading. The constitutive model is based on the concept of equivalent uniaxial strains that allows the assumed orthotropic model to be described via three equivalent uniaxial stress-strain curves. The characteristics of these curves are obtained from the ultimate strength surface in the principal stress space based on the Willam-Warnke curve. A cap model is added to consider loading along or near the hydrostatic axis. The equivalent uniaxial curve is based on the Popovics and Saenz models. The post-peak behavior is adjusted to account for the effects of confinement and to describe the change in response from brittle to ductile as the lateral confinement increases. Correlation studies with available experimental tests are presented to demonstrate the model performance. Tests with monotonic loading on specimens under constant lateral confinement are considered first, followed by biaxial and triaxial tests with cyclic loads. The triaxial test example considers non-proportional loading.

• Journal of the Korea Concrete Institute
• /
• v.20 no.4
• /
• pp.477-486
• /
• 2008

External bonding of carbon fiber reinforced plastic sheets has recently emerged as a popular method for strengthening reinforced concrete structures. The behavior of CFRP-strengthened RC structure is often controlled by the behavior of the interface between CFRP sheets and concrete. In this study, a review of models on bond strength, bond-slip, and interfacial stresses has been first carried out. Then a new bond-slip model is proposed. The proposed bond-slip model has bilinear ascending regions and exponential descending region derived from modifications mode on the conventional bilinear bond-slip model. The comparison of the results with those of existing experiment researches on bond-slip models indicate good agreements.

• Structural Engineering and Mechanics
• /
• v.63 no.3
• /
• pp.371-384
• /
• 2017

Ultra high performance concrete (UHPC) has recently been applied as an alternative to conventional concrete in construction due to its extremely high compressive and tensile strength, and enhanced durability. However, up to date, there has been insufficient information regarding the confinement behavior of UHPC columns. Therefore, this study aims to perform an assessment of axial stress-strain model for UHPC confined by circular steel tube stub columns. The equations for calculating the confined peak stress and its corresponding strain of confined concrete in existing models suggested by Johansson (2002), Sakino et al. (2004), Han et al. (2005), Hatzigeorgiou (2008) were modified based on the regression analysis of test results in Schneider (2006) in order to increase the prediction accuracy for the case of confined UHPC. Furthermore, a new axial stress-strain model for confined UHPC was developed. To examine the suitability of the modified models and the proposed model for confined UHPC, axial stress-strain curves derived from the proposed models were compared with those obtained from previous test results. After validating the proposed model, an extensive parametric study was undertaken to investigate the effects of diameter-to-thickness ratio, steel yield strength and concrete compressive strength on the complete axial stress-strain curves, the strength and strain enhancement of UHPC confined by circular steel tube stub columns.

• Computers and Concrete
• /
• v.8 no.3
• /
• pp.343-355
• /
• 2011

This paper presented the model to predict the chloride diffusion coefficient in tension zone of plain concrete under flexural cyclic load. The fictitious crack based analytical model was used together with the stress degradation law in cracked zone to predict crack growth of plain concrete beams under flexural cyclic load. Then, under cyclic load, the chloride diffusion, in the steady state and one dimensional regime, through the tension zone of the plain concrete beam, in which microcracks were formed by a large number of cycles, was simulated with assumptions of continuously straight crack and uniform-size crack. The numerical analysis in terms of the chloride diffusion coefficient, $D_{tot}$, normalized $D_{tot}$, crack width and crack length was issued as a function of the load cycle, N, and load level, SR. The nonlinear model as regarding with the chloride diffusion coefficient in tension zone and the load level was proposed. According to this model, the chloride diffusion increases with increasing load level. The predictions using model fit well with experimental data when we adopted suitable crack density and tortuosity parameter.

• Journal of Korean Association for Spatial Structures
• /
• v.20 no.3
• /
• pp.81-89
• /
• 2020

As the damage caused by earthquakes gradually increases, seismic retrofitting for existing public facilities has been implemented in Korea. Several types of structural analysis methods can be used to evaluate the seismic performance of structures. Among them, for nonlinear dynamic analysis, the hysteresis model must be carefully applied because it can significantly affect the behavior. In order to find a hysteresis model that predicts rational behavior, this study compared the experimental results and analysis results of the existing non-seismic reinforced concrete frames. For energy dissipation, the results were close to the experimental values in the order of Pivot, Concrete, Degrading, and Takeda models. The Concrete model underestimated the energy dissipation due to excessive pinching. In contrast, the other ones except the Pivot model showed the opposite results with relatively little pinching. In the load-displacement curves, the experimental and analysis results tended to be more similar when the column axial force was applied to columns.