• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.11
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• pp.416-424
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• 2019

In Korea, press concrete in basements is mainly applied using plain concrete. This system has undesirable defects such as cracks caused by plastic shrinkage and irregular temperature distribution. To solve this problem, metal lath and fibers have been used in the past. However, they have not been effective in controlling cracks. This study analyzed the reduction of plastic shrinkage cracking for press concrete using various admixtures in a basement has been. In the air contents test, the specimens with various admixtures showed air contents similar to plain concrete (4.5±1.5%). The specimens using silica fume, super plasticizer agent, and SBR showed higher compressive strength by about 10-15% than plain concrete. Cracking decreased when the MC, super plasticizer, and SBR were added. When MC was used in the concrete, the plastic shrinkage did not occur.

• Advances in concrete construction
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• v.1 no.1
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• pp.103-119
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• 2013

The applicability of limit analysis methods in design and assessment of concrete structures generally requires a certain plastic deformation capacity. The latter is primarily provided by the ductility of the reinforcement, being additionally affected by the bond properties between reinforcing steel and concrete since they provoke strain localization in the reinforcement at cracks. The bond strength of reinforcing bars is not only governed by concrete quality, but also by construction details such as bar ribbing, bar spacing or concrete cover thickness. For new concrete structures, a potentially unfavorable impact on bond strength can easily be anticipated through appropriate code rules on construction details. In existing structures, these requirements may not be necessarily satisfied, consequently requiring additional considerations. This two-part paper investigates in a theoretical study the impacts of the most frequently encountered construction details which may not satisfy design code requirements on bond strength, steel strain localization and plastic deformation capacity of cracked structural concrete. The first part introduces basic considerations on bond, strain localization and plastic deformation capacity as well as the fundamentals of the Tension Chord Model underlying the further investigations. It also analyzes the impacts of the hardening behavior of reinforcing steel and concrete quality. The second part discusses the impacts of construction details (bar ribbing, bar spacing, and concrete cover thickness) and of additional structure-specific features such as bar diameter and crack spacing.

• Proceedings of the Korea Concrete Institute Conference
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• 1990.10a
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• pp.19-22
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• 1990

Based on the design concept of a "Strong Column - Weak Beam" in the design of reinforced concrete, recently, a design method which moves the plastic hinging zone of a specific length away from the column face, has been proposed for reducing the degradation of stiffness and strength in the beam-column joint. To analyze reinforced concrete structures designed by this method. It is necessary to establish the analytical model which can simulate the hysteretic behavior depended on the initial positions and enlargements of plastic hinges. In this paper, by the numerical assumptions and the regression of experimental results, an analytical model is proposed. To estimate the accuracy of this model, some example analyses are conducted and compared with experimental results. From these comparision. It is shown that the proposed model is a good to predict the behavior of members subjected go cyclic loads.lic loads.

• KCI Concrete Journal
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• v.13 no.2
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• pp.67-74
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• 2001

In this study, a numerical model for the simulation of reinforced concrete columns subject to cyclic loading is presented. The model consists of three separate models representing concrete, reinforcing steel bars and bond-slip between a reinforcing bar and ambient concrete. The concrete model is represented by the plane stress plastic-damage model and quadrilateral finite elements. The nonlinear steel bar model embedded in truss elements is used for longitudinal and transverse reinforcing bars. Bond-slip mechanism between a reinforcing bar and ambient concrete is discretized using connection elements in which the hysteretic bond-slip link model defines the bond stress and slip displacement relation. The three models are connected in finite element mesh to represent a reinforced concrete structure. From the numerical simulation, it is shown that the proposed model effectively and realistically represents the overall cyclic behavior of a reinforced concrete column. The present plastic-damage concrete model is observed to work appropriately with the steel bar and bond-slip link models in representing the complicated localization behavior.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.2 s.42
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• pp.29-36
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• 2005

The purpose of this study is to investigate the inelastic behavior of reinforced concrete bridge columns with unbonding of main reinforcements at plastic hinge region. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. The effect of unbonding of main reinforcements at plastic hinge region has been also taken into account to model the concrete and reinforcing steel. The proposed numerical method for the inelastic behavior of reinforced concrete bridge columns with unbonding of main reinforcements at plastic hinge region is verified by comparison with reliable experimental results.

• Steel and Composite Structures
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• v.32 no.5
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• pp.657-670
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• 2019

This paper proposes a one-dimensional fiber beam element model taking account of materially non-linear behavior, benefiting the highly efficient elastic-plastic analysis of girders with shear-lag effects. Based on the displacement-based fiber beam-column element, two additional degrees of freedom (DOFs) are added into the proposed model to consider the shear-lag warping deformations of the slabs. The new finite element (FE) formulations of the tangent stiffness matrix and resisting force vector are deduced with the variational principle of the minimum potential energy. Then the proposed element is implemented in the OpenSees computational framework as a newly developed element, and the full Newton iteration method is adopted for an iterative solution. The typical materially non-linear behaviors, including the cracking and crushing of concrete, as well as the plasticity of the reinforcement and steel girder, are all considered in the model. The proposed model is applied to several test cases under elastic or plastic loading states and compared with the solutions of theoretical models, tests, and shell/solid refined FE models. The results of these comparisons indicate the accuracy and applicability of the proposed model for the analysis of both concrete box girders and steel-concrete composite girders, under either elastic or plastic states.

• Structural Engineering and Mechanics
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• v.69 no.6
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• pp.651-665
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• 2019

Past earthquakes have shown that appropriately designed and detailed buildings with shear walls have great performance such a way that a considerable portion of inelastic energy dissipation occurs in these structural elements. A plastic hinge is fundamentally an energy diminishing means which decrease seismic input energy through the inelastic deformation. Plastic hinge development in a RC shear wall in the areas which have plastic behavior depends on the ground motions characteristics as well as shear wall details. One of the most generally used forms of structural walls is flanged RC wall. Because of the flanges, these types of shear walls have large in-plane and out-of-plane stiffness and develop high shear stresses. Hence, the purpose of this paper is to evaluate the main characteristics of these structural components and provide a more comprehensive expression of plastic hinge length in the application of performance-based seismic design method and promote the development of seismic design codes for shear walls. In this regard, the effects of axial load level, wall height, wall web and flange length, as well as various features of earthquakes, are examined numerically by finite element methods and the outcomes are compared with consistent experimental data. Based on the results, a new expression is developed which can be utilized to determine the length of plastic hinge area in the flanged RC shear walls.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.118-121
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• 2000

CFRD (Concrete Faced Rockfill Dam) face slab concrete has a much capability to occur crack due to drying shrinkage, hydration heat and bas compaction etc. Because of crack of concrete induce structural problem and decrease durability of concrete, it is need to reduce crack of concrete. This is an experimental study to analyze the Control Property of Plastic Shrinkage Crack for CFRD face slab concrete. For this purpose, it was investigated and analyzed the engineering properties of plain concrete and using admixtures (polypropylene fiber, fly-ash) according to test result As the result, it was found that crack width and area of concrete using admixtures less than of plain concrete.

• Journal of the Korea Institute of Building Construction
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• v.7 no.3
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• pp.83-90
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• 2007

This study is to investigate the effects of nylon(NY) and cellulose(CEL) fiber contents on the mechanical properties of the concrete. The results were summarized as following. Test showed that increase of NY and CEL fiber contents decreased fluidity of fresh concrete, so the loss of the fluidity would be considered when they were over added. Air contents were slight increased, but they satisfied the target air content. Bleeding capacity of concrete containing fiber significantly was declined. In addition, concrete containing higher amounts of fiber retarded setting time remarkably. Plastic shrinkage crack was reduced with the use of fiber due to increasing fiber contents and changing fiber classes, and NY fibers to prevent the plastic shrinkage crack effectively. Compressive and tensile strength of almost specimens were increased when air contents of the fresh concrete were fixed according to fiber contents, and flexural strength was increased according to fiber contents. For the impact strength of specimens, the specimen containing $0.6kg/m^3$ of NY fibers, showed the most favorable impact strength, The fiber reinforced concrete using NY fibers exhibited superior mechanical performance, and it was considered that $0.6kg/m^3$ of was desirable as the most favorable adding amount.

• Advances in concrete construction
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• v.14 no.2
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• pp.79-92
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• 2022

The amount and configuration of transverse reinforcement are known as critical parameters that significantly affect the lateral confinement of concrete, the ductility capacity, and the plastic hinge length of RC columns. Based on test results, this study investigated the effect of the three variables on structural indexes such as neutral axis depth, lateral expansion of concrete, and ductility capacity. Five reinforced concrete column specimens were tested under cyclic flexure and shear while simultaneously subjected to a constant axial load. The columns were reinforced by two types of reinforcing steel: rectangular hoops and spiral type reinforcing bars. The variables in the test program were the shape, diameter, and yield strength of transverse reinforcement. The interactive influence of the amount of transverse reinforcement on the structural indexes was evaluated. Test results showed that when amounts of transverse reinforcement were similar, and yield strength of transverse reinforcement was 600 MPa or less, the neutral axis depth of a column with spiral type reinforcing bars was reduced by 28% compared with that of a column reinforced by existing rectangular hoops at peak strength. While the diagonal elements of spiral-type reinforcing bars significantly contributed to the lateral confinement of concrete, the strain of diagonal elements decreased with increases of their yield strength. It was confirmed that shapes of transverse reinforcement significantly affected the lateral confinement of concrete adjacent to plastic hinges. Transverse reinforcement with a yield strength exceeding 600 MPa, however, increased the neutral axis depth of normal-strength concrete columns at peak strength, resulting in reductions in ductility and energy dissipation capacity.