• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.89-95
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• 2006

This paper proposes a modified method of Latin Hypercube sampling to reduce the variance of statistical parameters in uncertainty analysis of concrete structures. The proposed method is a modification of Latin Hypercube sampling method. This analysis method uses specifically modified tables of random permutations of ranked numbers. In addition, the Spearman coefficient is used to make modified tables. Numerical analysis is carried out to predict the uncertainty of axial shortening in prestressed concrete bridge. Statistical parameters obtained from modified Latin Hypercube sampling method and conventional Latin Hypercube sampling method are compared and evaluated by a numeric analysis. The results show that the proposed method results in a decrease in the variance of statistical parameters. This indicates the method is efficient and effective in the uncertainty analysis of complex structural system such as prestressed concrete bridges.

• Journal of the Korean Society for Nondestructive Testing
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• v.11 no.2
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• pp.22-31
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• 1991

Various types of ultrasonic techniques have been used for the estimation of compressive strength of concrete structures. However, conventional ultrasonic velocity method using only longitudial wave cannot be determined the compressive strength of concrete structures with accuracy. In this paper, by using the introduction of multiple parameter, e. g. velocity of shear wave, velocity of longitudinal wave, attenuation coefficient of shear wave, attenuation coefficient of longitudinal wave, combination condition, age and preservation method, multiple regression analysis method was applied to the determination of compressive strength of concrete structures. The experimental results show that velocity of shear wave can be estimated compressive strength of concrete with more accuracy compared with the velocity of longitudinal wave, accuracy of estimated error range of compressive strength of concrete structures can be enhanced within the range of ${\pm}$10% approximately.

• Computers and Concrete
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• v.18 no.5
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• pp.951-968
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• 2016

In this study, pullout capacities of post-installed deformed bars anchored in low strength concrete using different bonding materials are investigated experimentally. The experimental study was conducted under outdoor and indoor conditions; on the beams of an actual reinforced concrete building and on concrete bases constructed at Istanbul Technical University (ITU). Ready-mixed cement based anchorage mortar with modified polymers (M1), ordinary cement with modified polymer admixture (M2), and epoxy based anchorage mortar with two components (E) were used as bonding material. Furthermore, test results are compared with the predictions of current analytical models. Findings of the study showed that properly designed cement based mortars can be efficiently used for anchoring deformed bars in low quality concrete. It is important to note that the cost of cement based mortar is much lower with respect to conventional epoxy based anchorage materials.

• Computers and Concrete
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• v.5 no.6
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• pp.559-572
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• 2008

The effects of fly ash and superplasticizer (SP) on workability of concrete are quite difficult to predict because they are dependent on other concrete ingredients. Because of high complexity of the relations between workability and concrete compositions, conventional regression analysis could be not sufficient to build an accurate model. In this study, a workability model has been built using artificial neural networks (ANN). In this model, the workability is a function of the content of all concrete ingredients, including cement, fly ash, blast furnace slag, water, superplasticizer, coarse aggregate, and fine aggregate. The effects of water/binder ratio (w/b), fly ash-binder ratio (fa/b), superplasticizer-binder ratio (SP/b), and water content on slump were explored by the trained ANN. This study led to the following conclusions: (1) ANN can build a more accurate workability model than polynomial regression. (2) Although the water content and SP/b were kept constant, a change in w/b and fa/b had a distinct effect on the workability properties. (3) An increasing content of fly ash decreased the workability, while raised the slump upper limit that can be obtained.

• Structural Engineering and Mechanics
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• v.13 no.3
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• pp.241-260
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• 2002

The effect of shear coupled with axial force variation on the inelastic seismic behaviour of reinforced concrete bridge piers is investigated in this paper. For this purpose, a hysteretic axial-shear interaction model was developed and implemented in a nonlinear finite element analysis program. Thus, flexure-shear-axial interaction is simulated under variable amplitude reversed actions. Comparative studies for shear-dominated reinforced concrete columns indicated that a conventional FE model based on flexure-axial interaction only gave wholly inadequate results and was therefore incapable of predicting the behaviour of such members. Analysis of a reinforced concrete bridge damaged during the Northridge (California 1994) earthquake demonstrated the importance of shear modelling. The contribution of shear deformation to total displacement was considerable, leading to increased ductility demand. Moreover, the effect of shear with axial force variation can significantly affect strength, stiffness and energy dissipation capacity of reinforced concrete members. It is concluded that flexure-shear-axial interaction should be taken into account in assessing the behaviour of reinforced concrete bridge columns, especially in the presence of high vertical ground motion.

• KCI Concrete Journal
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• v.14 no.4
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• pp.139-144
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• 2002

Concrete filled FRP tube has lately attracted attention as the member that can substitute the conventional reinforced concrete. Glass fiber and carbon fiber are some of available materials for FRP tube. Carbon tube is filament wound with specified winding angle to meet the appropriate capacity demands. Confinement effect of carbon tube is varied according to winding angle. In this study, a total 4 of large scale circular specimens of 30cm diameter and 60cm height is tested. To estimate the effect of winding angle and thickness of carbon tube on the increased confined compressive strength, the test tube are wound with $\pm45^{\circ}\;and\;\pm30^{\circ}$ with two types of thickness, 2mm and 3mm, respectively. It is shown that effectively increased confined strength and ductility are observed from the specimens with $\pm45^{\circ}$ winding angle than $\pm30^{\circ}$ winding angle. Increasing thickness is not as effective as adjusting winding angle for the confinement of concrete core.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.461-464
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• 2003

Portland Cement Concrete (PCC) pavements have the advantage of durability and superior surface friction when compared to most dense-graded asphalt. However, data collected to date generally show PCC pavements to create more noise than asphaltic surfaces. As the results of research, surfaces of exposed aggregate, tining and grooving concrete pavements appear to provide better noise quality characteristics as well as good frictional characteristics and durability. In this paper, several methods of texturing were considered to reduce tire/pavement noise. As the results of this paper, PCC pavements with special texturing have superior surface friction as well as noise reductions when compared to conventional PCC pavement. Especially, Exposed Aggregate Concrete (EAC) surface appears to provide better noise quality characteristics. Conclusively, if overall noise and safety are considered simultaneously, EAC pavement that provides satisfactory friction as well as better noise reductions is suggested.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.671-679
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• 2010

The construction of concrete track for the first time in Korea gives lots of meanings to civil engineering in various aspects. Settlement level needs to be kept minimal for the safety of the track. Concrete track has different structural characteristics comparing to conventional ballast track, so load distribution in concrete track is also different. Since it is the first time to build concrete track, there are very few experience and data available on the subject. Therefore it is important to evaluate how much load is transferred to the ground due to the running vehicle in concrete track and to determine the optimal thickness of layers. In this research, 9 individual earth pressure cells were installed at OOOk930 site in 2nd stage of Kyungbu high speed railway during under construction. The in-situ pressure data were measured at each layers during pump-car and locomotive were moving on the high speed railway surface.

• Structural Engineering and Mechanics
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• v.63 no.2
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• pp.217-223
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• 2017

Glass fiber reinforced gypsum panels (GFRG) are hollow panels made from modified gypsum plaster and reinforced with chopped glass fibers. The hollow cores of panels can be filled with in-situ concrete/reinforced concrete or insulation material to increase the structural strength or the thermal insulation, respectively. GFRG panels are unfilled when used as partition walls. As load bearing walls, the panels are filled with M 20 grade concrete (reinforced concrete filling) in order to resist the gravity and lateral loads. The study was conducted in two stages: First stage involves formulation of the alternate light weight mix by conducting experimental investigations to obtain the optimum combination of phosphogypsum and shredded thermocol. In the second stage the alternate mixes are filled in GFRG panels and experimental investigations are conducted to compare the performance against panels filled with conventional M 20 mix.

• Computers and Concrete
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• v.20 no.1
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• pp.1-10
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• 2017

This paper focuses on the mesh-size dependency in numerical simulations of reinforced concrete (RC) structures subjected to blast loading. A tensile failure criterion that can minimize the mesh-dependency of simulation results is introduced based on the fracture energy theory. In addition, conventional plasticity based damage models for concrete such as the CSC model and the HJC model, which are widely used for blast analyses of concrete structures, are compared with the orthotropic model that adopts the introduced tensile failure criterion in blast tests to verify the proposed criterion. The numerical predictions of the time-displacement relations at the mid-span of RC beams subjected to blast loading are compared with experimental results. The analytical results show that the numerical error according to the change in the finite element mesh size is substantially reduced and the accuracy of the numerical results is improved by applying a unique failure strain value determined by the proposed criterion.