• Computers and Concrete
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• v.15 no.2
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• pp.305-319
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• 2015

On mesoscopic level, concrete can be treated as a three-phase composite material consisting of mortar, aggregates and interfacial transition zone (ITZ) between mortar and aggregate. A lot of research has confirmed that ITZ plays a crucial role in the mechanical fracture process of concrete. The aim of the present study is to propose a numerical method on mesoscale to analyze the failure mechanism of reinforced concrete (RC) structures under mechanical loading, and then it will help precisely predict the damage or the cracking initiation and propagation of concrete. Concrete is meshed by means of the Rigid Body Spring Model (RBSM) concept, while the reinforcing steel bars are modeled as beam-type elements. Two kinds of RC members, i.e. subjected to uniaxial tension and beams under bending, the fracture process of concrete and the distribution of cracks, as well as the load-deflection relationships are investigated and compared with the available test results. It is found that the numerical results are in good agreement with the experimental observations, indicating that the model can successfully simulate the failure process of the RC members.

• Structural Engineering and Mechanics
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• v.80 no.6
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• pp.737-747
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• 2021

The objective of seismic resilience is to maintain or rapidly restore the function of a building after an earthquake. An efficient tilt mechanism at the member level is crucial for the restoration of the main structure function; however, the damage resistance of the members should be the main focus. In this study, through a comparison with the classical Flamant theory of local loading in the elastic half-space, an elastomechanical solution for the axial-stress distribution of a reinforced-concrete (RC) rocking column was derived. Furthermore, assuming that the lateral displacement of the rocking column is determined by the contact surface rotation angle of the column end and bending and shear deformation of the column body, the load-lateral displacement mechanical model of the RC rocking column was established and validated through a comparison with finite-element simulation results. The axial-compression ratio and column-end strength were analyzed, and the results indicated that on the premise of column damage resistance, simply increasing the axial-compression ratio increases the lateral loading capacity of the column but is ineffective for improving the lateral-displacement capacity. The lateral loading and displacement of the column are significantly improved as the strength of the column end material increases. Therefore, it is feasible to improve the working performance of RC rocking columns via local reinforcement of the column end.

• Computers and Concrete
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• v.3 no.1
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• pp.17-28
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• 2006

Replacement of actual stress distribution in a reinforced concrete (RC) flexural member with a simpler geometrical shape, which maintains magnitude and location of the resultant compressive force, is an acceptable conceptual trick. This concept was originally perfected for normal strength concrete. In recent years, high strength concrete (HSC) has been introduced and widely used in modern construction. The stress block parameters require updating to account for special features of HSC in the design of flexural members. In future, more varieties of concrete may be developed and a corresponding design procedure of RC flexural members will be required. The usual practice is to conduct large number of experiments on various sizes of specimen and then evolve an empirical relation. This paper presents a numerical procedure through which the stress block parameters can be numerically derived for a given strain ratio variation. The material model for concrete is presented and computational procedure is described. This procedure is illustrated with several variations of strain ratio. The advantages of numerical procedure are that it costs less and it can be used with new material models for any new variety of concrete.

• Structural Monitoring and Maintenance
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• v.10 no.2
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• pp.133-154
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• 2023

Obscured structural members are mostly under-evaluated during condition assessment due to lack of visual inspection capability. Insufficient information about the integrity of these structural members poses a significant risk for public safety. Time domain reflectometry (TDR) is a novel approach in structural health monitoring (SHM). Ordinary coaxial cables "as is" without a major modification are not suitable for SHM with TDR. The objective of this study is to propose a practical and cost-effective modification approach to commercially available coaxial cables in order to use them as a "cable sensor" for damage detection with the TDR equipment for obscured structural members. The experimental validation and assessment of the proposed modification approach was achieved by conducting 3-point bending tests of the model piles as a representative obscured structural member. It can be noted that the RG59/U-6 and RG6/U-4 cable sensors expose higher strain sensitivity in comparison with non-modified "as is" versions of the cables used. As a result, the cable sensors have the capability of sensing both the presence and the location of a structural damage with a maximum aberration of 3 cm. Furthermore, the crack development can be monitored by the RG59/U-6 cable sensor with a simple calibration.

• Journal of Korean Association for Spatial Structures
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• v.22 no.1
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• pp.41-49
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• 2022

In the case of columns in buildings with soft story, the concentration of stress due to the difference in stiffness can damage the columns. The irregularity of buildings including soft story requires retrofit because combined load of compression, bending, shear, and torsion acts on the structure. Concrete jacketing is advantageous in securing the strength and stiffness of existing members. However, the brittleness of concrete make it difficult to secure ductility to resist the large deformation, and the complicated construction process for integrity between the existing member and extended section reduces the constructability. In this study, two types of Steel Grid Reinforcement (SGR), which are Steel Wire Mesh (SWM) for integrity and Steel Fiber Non-Shrinkage Mortar (SFNM) for crack resistance are proposed. One reinforced concrete (RC) column with non-seismic details and two columns retrofitted with each different types of proposed method were manufactured. Seismic performance was analyzed for cyclic loading test in which a combined load of compression, bending, shear, and torsion was applied. As a result of the experiment, specimens retrofitted with proposed concrete jacketing method showed 862% of maximum load, 188% of maximum displacement and 1,324% of stiffness compared to non-retrofitted specimen.

• Journal of the Korea Institute of Building Construction
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• v.22 no.1
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• pp.11-21
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• 2022

Currently, in the domestic construction industry, the free web method has been emerging as a potential solution to the shortage of skilled workers due to the prolonged COVID-19 crisis, as it helps in securing economic feasibility through shortening the construction period and reducing labor costs. To consider one part of the construction method, in this study, the bending behavior according to the load was evaluated for the SY slope-type beam formwork, which was manufactured at a factory, assembled with rebar, brought into the site, and then poured into the site. For the SY Beam standard cross-sectional shape, a cross-sectional dimensional width of 400mm and depth 600mm determined through structural modeling using the MIDAS GEN program were applied. A total of 6 specimens were made with a member length of 5,000mm, 5 specimens and one RC specimen in the comparison group were manufactured in real-size format using the thickness of the steel plate(0.8, 1.0, 1.2mm) as a variable, and bending experiments were performed. In the bending test, the steel plate deck showed high initial stiffness and maximum strength as it yielded, which showed that it sufficiently contributed to the flexural strength. It is judged that additional analysis and experimental studies for 1.05, 1.1, and 1.15mm are needed to derive the appropriate steel plate thickness and the method for calculating the tensile force contribution of the steel plate to secure the manufacturing, construction and economic feasibility of SY Beam in the future.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.563-570
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• 2016

The composited structural member in which two or more materials having different stress-strain relationships (steel & concrete) has increased greatly in recent years. This paper presents the experimental results of flexural capacity of the composited H-Pile subjected to bending moment. Eight composited beams were tested under direct loading condition using the frame tester. Based on the experimental results it is noted that flexural capacity of composited H-Pile increased about 20~30% and ductility ratio significantly increased. Limit state analysis of the specimens was conducted and the result shows that flexural strength by limit state analysis is conservative.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.26-33
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• 2018

This paper presents experimental and analytical results on flexural behavior of flexural members made of SIFCON. Twelve SIFCON beams were subjected to bending tests and their flexural behavior was evaluated. Experimental variables included steel fiber type, presence of tensile reinforcement, and height of section. The specimens using Type-B steel fibers, which had better pullout resistance than Type-A steel fibers, showed flexural failure behavior without shear failure. The aspect ratio of steel fiber had a great influence on the behavior of SIFCON beams without tensile steel, however the effect on the behavior of SIFCON beams was negligible. In addition, the flexural strength equation for SIFCON was proposed in the study. The mean and standard deviation of the ratios of the predicted value to the experimental value are 1.02 and 0.04, respectively. Therefore, the proposed flexural strength equation can be useful for the design and performance evaluation of SIFCON beam.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.594-605
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• 2003

Pinching is an important property of reinforced concrete member which characterizes its cyclic behavior. In the present study, numerical studies were performed to investigate the characteristics of pinching behavior and the energy dissipation capacity of flexure-dominated reinforced concrete members. By investigating existing experiments and numerical results, it was found that flexural pinching which has no relation with shear action appears in RC members subject to axial compression force. However, members with specific arrangement and amount of re-bars, have the same energy dissipation capacity regardless of the magnitude of the axial force applied even though the shape of the cyclic curve varies due to the effect of the axial force. This indicates that concrete as a brittle material does not significantly contribute to the energy dissipation capacity though its effect on the behavior increases as the axial force increases, and that energy dissipation occurs primarily by re-bars. Therefore, the energy dissipation capacity of flexure-dominated member can be calculated by the analysis on the cross-section subject to pure bending, regardless of the actual compressive force applied. Based on the findings, a practical method and the related design equations for estimating energy dissipation capacity and damping modification factor was developed, and their validity was verified by the comparisons with existing experiments. The proposed method can be conveniently used in design practice because it accurately estimates energy dissipation capacity with general design parameters.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.46-55
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• 2021

Concrete structures can cause various problems as the number of common years increases when exposed to external extreme climate conditions. Among these problems, freezing and thawing occur due to the action of extreme climate factors such as heavy rain and heavy snow, which have become the most problematic in recent years. In this study, we present a rapid freezing and thawing test method of concrete in the air, referring to KS F 2456, as Seoul exhibits very dry weather during the period of freezing and thawing. Concrete test specimens and RC beams were fabricated to perform rapid freezing and thawing of 0, 100, 200, and 300 cycles, and the performance evaluation confirmed the degradation of each subject in material and member units. The design strength of 24 MPa, which performs rapid freezing and thawing in the air up to 300 cycles, decreases by 5.24 MPa (21%), and as rapid freezing and thawing in the air increases the stress burden on reinforced concrete bending members, reducing the energy absorption (dissipation) ability of structures due to earthquakes.