• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.201-210
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• 2023

This study is to evaluate the ductility strengthening effect of aramid fiber sheets on piloti-type structures. Two piloti-type structure specimens were prepared and tested under statical cyclic lateral loads. The ductility strengthening effect was validated from the analysis of lateral load-displacement relationship, displacement ductility ratio, work damage index and torsion behavior. Test results showed that the post-peak behavior of piloti-type structures with columns strengthened with aramid fiber sheets tended to be ductile resulting from preventing shear failure and minimizing torsion due to the effective lateral confinement of column concrete by aramid fiber sheet. Consequently, the displacement ductility ratio and work damage index of piloti-type structures with columns with strengthened with aramid fiber sheets were 4.63 and 42.81 times higher than those of non strengthened piloti-type structures.

• Computers and Concrete
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• v.20 no.4
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• pp.369-380
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• 2017

The effects of the vertical component of a ground motion on the earthquake performances of semi-ductile high-rise R/C structures were investigated in the present study. Linear and non-linear time-history analyses were conducted on an existing in-service R/C building for the loading scenarios including and excluding the vertical component of the ground motion. The ratio of the vertical peak acceleration to the horizontal peak acceleration (V/H) of the ground motion was adopted as the main parameter of the study. Three different near-source earthquake records with varying V/H ratio were used in the analyses. The linear time-history analyses indicated that the incorporation of the vertical component of a ground motion into analyses greatly influences the vertical deflections of a structure and the overturning moments at its base. The lateral deflections, the angles of rotation and the base shear forces were influenced to a lesser extent. Considering the key indicators of vertical deflection and overturning moments determined from the linear time-history analysis, the non-linear analyses revealed that the changes in the forces and deformations of the structure with the inclusion of the vertical ground motion are resisted by the shear-walls. The performances and damage states of the beams were not affected by the vertical ground motion. The vertical ground motion component of earthquakes is markedly concluded to be considered for design and damage estimation of the vertical load-bearing elements of the shear-walls and columns.

• Advances in nano research
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• v.16 no.3
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• pp.217-229
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• 2024

This paper presents results of visual analysis of cracks formation and propagation of concretes made of quaternary binders (QBC). A composition of the two most commonly used mineral additives, i.e. fly ash (FA) and silica fume (SF) in combination with nanosilica (nS), has been proposed as a partial replacement of the cement. The principal objective of the present study is to achieve information about the effect of simultaneous incorporation of three pozzolans as partial replacement to the OPC on the fracture processes in concretes made from quaternary binders (QBC). The modern and precise non-contact measurement method (NCMM) via digital image correlation (DIC) technique was used, during the studies. In the course of experiments it was established that the substitution of OPC with three pozzolans including the nanoadditive in FA+SF+nS FA+SF+nS combination causes a clear change of brittleness and behavior during fractures in QBCs. It was found that the shape of cracks in unmodified concrete was quasi-linear. Substitution of the binder by SCMs resulted in a slight heterogeneity of the structure of the QBC, including only SF and nS, and clear heterogeneity for concretes with the FA additive. In addition, as content of FA rises throughout each of QBC series, material becomes more ductile and shows less brittle failure. It means that an increase in the FA content in the concrete mix causes a significant change in fracture process in this composite in comparison to concrete with the addition of silica modifiers only.

• Structural Engineering and Mechanics
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• v.39 no.4
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• pp.599-620
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• 2011

The investigation on possible causes of failures related to documented collapses is a complicated issue, primarily due to the scarcity and inadequacy of information available. Although several studies have tried to understand which are the inherent structural deficiencies or circumstances associated to failure of the main structural elements in a reinforced concrete frame, to the authors knowledge a uniform approach for the evaluation building static vulnerability, does not exist yet. This paper investigates, by means of a detailed case study, the potential failure mechanisms of an existing reinforced concrete building. The linear elastic analysis for the three-dimensional building model gives an insight on the working conditions of the structural elements, demonstrating the relevance of a number of structural faults that could sensibly lower the structure's safety margin. Next, the building's bearing capacity is studied by means of parametric nonlinear analysis performed at the element's level. It is seen that, depending on material properties, concrete strength and steel yield stress, the failure hierarchy could be dominated by either brittle or ductile mechanisms.

• Journal of Powder Materials
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• v.25 no.4
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• pp.291-295
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• 2018

A conductive additive is prepared by dispersing multi-walled carbon nanotubes (MWCNTs) on Cu powder by mechanical milling and is distributed in epoxy to enhance its electrical conductivity. During milling, the MWCNTs are dispersed and partially embedded on the surface of the Cu powder to provide electrically conductive pathways within the epoxy-based composite. The degree of dispersion of the MWCNTs is controlled by varying the milling medium and the milling time. The MWCNTs are found to be more homogeneously dispersed when solvents (particularly, non-polar solvent, i.e., NMP) are used. MWCNTs gradually disperse on the surface of Cu powder because of the plastic deformation of the ductile Cu powder. However, long-time milling is found to destroy the molecular structure of MWCNTs, instead of effectively dispersing the MWCNTs more uniformly. Thus, the epoxy composite film fabricated in this study exhibits a higher electrical conductivity than 1.1 S/cm.

• Structural Engineering and Mechanics
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• v.38 no.6
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• pp.697-714
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• 2011

Assessing the ductility of reinforced concrete sections and members has been a complex and intractable problem for many years. Given the complexity in estimating ductility, members are often designed specifically for strength whilst ductility is provided implicitly through the use of ductile steel reinforcing bars and by ensuring that concrete crushing provides the ultimate limit state. As such, the empirical hinge length and neutral axis depth approaches have been sufficient to estimate ductility and moment redistribution within the bounds of the test regimes from which they were derived. However, being empirical, these methods do not have a sound structural mechanics background and consequently have severe limitations when brittle materials are used and when concrete crushing may not occur. Structural mechanics based approaches to estimating rotational capacities and rotation requirements for given amounts of moment redistribution have shown that FRP plated reinforced concrete (RC) sections can have significant moment redistribution capacities. In this paper, the concept of moment redistribution in beams is explained and it is shown specifically how an existing RC member can be retrofitted with FRP plates for both strength and ductility requirements. Furthermore, it is also shown how ductility through moment redistribution can be used to maximise the increase in strength of a member. The concept of primary and secondary hinges is also introduced and it is shown how the response of the non-hinge region influences the redistribution capacity of the primary hinges, and that for maximum moment redistribution to occur the non-hinge region needs to remain elastic.

• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.433-442
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• 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 Korean Society of Environmental Restoration Technology
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• v.20 no.6
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• pp.35-50
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• 2017

This study is to see the recovery effect of the Deltacon method by investigating the amount of sand deposition, the topographical cross section and the vegetation structure; and to derive the effective recovery method of coastal erosion area. The target areas of this study include Jinri coastal dune, Bajireum coastal dune and Seopori coastal dune in Deokjeok-do Island, Ongjin-gun, Incheon. In order to assess the current status of the coastal erosion area recovery, the soil profile structure map was prepared on the site and then the amount of sand deposition within 1m was calculated indoors. The vegetation recovery status of the costal erosion area was assessed via the analyses of the topographical profile structure and the plant community structure, and we aim to derive the effective recovery plan of the Deltacon method with the results. With the Deltacon method, structures with ductile material, special non-woven fabric bags filled with soil and vegetation can be performed therefore the structuralstability and prevention of sand erosion can be achieved. The amounts of sand deposition of Bajireum coastal dune, Seopori costal dune and Jinri costal dune were calculated $0.98{\sim}2.54m^3$, $1.02{\sim}2.96m^3$, and $0.27{\sim}0.75m^3$, respectively, and it is considered that the costal erosion recovery is actively performed for Bajireum costal dune and Seopori costal dune. The analysis results of vegetation structures by topography show that the installation of the send collecting net in steep areas has been highly effective and the Deltacon-constructed target areas have been restored to vegetation and the costal dune, which is similar to the natural dune. The investigation of the plant community structure in Deokjeok-do Island costal dune, Incheon displayed similar research results of the existing costal dune flora and confirmed the emergence of Lathyrus japonicus, Carex kobomugi, Elymus mollis, Vitex rotundifolia, and Calystegia soldanella and others. In order to carry out further effective recovery with the Deltacon method, improvements to rootage of herbaceous vegetation are needed in areas without foredune herbaceous vegetation, and continuos maintenance & management monitoring of connected windbreak forest to costal dunes are also necessary.

• Journal of Korean Society of Steel Construction
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• v.25 no.1
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• pp.93-102
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• 2013

This paper describes the experimental study on the structural behavior of the vertical plane connection between a reinforced concrete wall and a steel plate concrete wall under out-of-plane flexural loads. The specimen was tested under a dynamic test with the use of cyclic loads. As a result of the test, ductile failure mode of vertical bars was shown under a push load and the failure load was more than that of the nominal strength of the specimen. However, the shear failure mode of the connection was confirmed in case of a pull test and thus demonstrates a need for a shear reinforcement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5A
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• pp.267-275
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• 2012

This paper describes the experimental study on the structural behavior of the joint plane between a RC(Reinforced Concrete) wall and a SC(Steel Plate Concrete) wall under out-of plane flexural loads and in-plane shear loads. The test specimens were produced with L and I shape to assess efficiently flexural and shear behavior of the structures. In order to consider dynamic loads such as earthquake, cyclic loading tests were carried out. As results of the out-of plane flexural tests, ductile failure mode of vertical bars was shown under a push load and the failure load was more than nominal strength of the specimen. And the latter test was performed to verify the variation which was composition presence of horizontal bars in the SC member. The test results showed that capacity of the specimens was more than their nominal strength regardless of composition presence of horizontal bars.