• Journal of the Korea Concrete Institute
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• v.24 no.5
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• pp.585-596
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• 2012

In this study, the flexural characteristics of reinforced polymer concrete T-beams strengthened with GFRP, typically used for bridges and parking structures, are investigated. A method to determine the flexural failure mode of reinforced polymer concrete T-beams comprised of compression failure (CF), tension failure (TF), and fiber sheet failure (FF) for different levels of GFRP strengthening is proposed. Moreover, the present study provides a formula to calculate the design flexural strength for each failure mode. In reinforced polymer concrete T-beams strengthened with GFRP, an ideal failure mode can be achieved when the failure occurs in the following order: 1) yield of steel reinforcement, 2) failure of GFRP, and 3) compression failure of concrete. In the case of FF mode, due to GFRP failure before the polymer concrete crushing in compression region, a concept of equivalent rectangular block based on the ultimate limit state of concrete should not be used. Thus, this study suggests an idealized stress-strain curve for polymer concrete and finds parameters for stress block, ${\alpha}$ and ${\beta}$ based on the strain distribution in polymer concrete. Furthermore, the present study suggests an aspect ratio of 2.5 by examining the compressive stress distribution and design flexural strength characteristics for different aspect ratio of T-beams. This study also provides a design flexural strength formula, and validates its acceptability based on experiment and theoretical analysis.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.941-946
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• 2002

Short reinforced concrete bridge piers are particularly susceptible to shear failure as a consequence of the high shear/moment ratio and conservatism in the flexural strength design of existing RC bridge pier, which were constructed before 1992. In addition, shear failure is brittle and involves rapid strength degradation. Inelastic shear deformation is thus unsuitable for ductile seismic response. It is, however, believed that there are not many experimental research works for shear failure of the existing RC bridge pier in Korean peninsula subjected to earthquake motions. The object of this research is to evaluate the seismic performance of existing circular RC bridge piers by the quasi-static test. Existing RC bridge piers were moderate seismically designed in accordance with the conventional provisions of Korea Highway Design Specification. This study has been performed to verify the effect of aspect ratio (column height-diameter ratio). Quasi-static test has been done to investigate the physical seismic performance of RC bridge piers, such as lateral force-displacement hysteric curve, envelope curve etc.

• Steel and Composite Structures
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• v.11 no.5
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• pp.391-402
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• 2011

It is clear from the former researches on reinforced concrete filled steel tubular (RCFT) structures that RCFT structures have higher strength and deformation capacity than concrete filled steel tubular (CFT) structures. However, in the case of actual applications to large-scaled structures, the thin-walled steel tube must be used from the view point of economic condition. Therefore, in this study, compression tests of RCFT columns which were made by thin-walled steel tube or small load-sharing ratio in cooperation with high strength concrete were carried out, meanwhile corresponding tests of CFT, reinforced concrete (RC), pure concrete and steel tube columns were done to compare with RCFT. By the a series of comparison and analysis, characteristics of RCFT columns were clarified, and following conclusions were drawn: RCFT structures can effectively avoided from brittle failure by the using of reinforcement while CFT structures are damaged due to the brittle failure; with RCFT structures, excellent bearing capacity can be achieved in plastic zone by combining the thin-walled steel tube with high strength concrete and reinforcement. The smaller load-sharing ratio can made the reinforcement play full role; Combination of thin-walled steel tube with high strength concrete and reinforcement is effective way to construct large-scaled structures.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.2
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• pp.125-132
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• 2011

The rupture of an expansion tube is mainly affected by the expansion ratio and the external shape of the punch used to expand the tube. In order to prevent the tube from rupture, the effect of the external shape of the punch should be considered in the design. The aim of this paper is to confirm the effect of key design parameters of the punch on rupture of the tube using a finite element analysis with a ductile damage model. The results of the analysis indicated that the expansion ratio of the tube was mainly affected by variation of the radius of the punch. However, the rupture was more affected by variation of the punch angle than the radius of the punch. The existence of a specific punch angle at which rupture did not occur, even if the radius of the punch was increased, was found from the results.

• Steel and Composite Structures
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• v.22 no.3
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• pp.663-675
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• 2016

The effects of slenderness ratio, eccentricity and column slope on the load-carrying capacities and failure modes of variable and uniform concrete filled steel tubular (CFST) latticed columns under axial and eccentric compression were investigated and compared in this study. The results clearly show that all the CFST latticed columns with variable cross section exhibit an overall failure, which is similar to that of CFST latticed columns with a uniform cross section. The load-carrying capacity decreases with the increase of the slenderness ratio or the eccentricity. For 2-m specimens with a slenderness ratio of 9, the ultimate load-carrying capacity is increased by 3% and 5% for variable CFST latticed columns with a slope of 1:40 and 1:20 as compared with that of uniform CFST latticed columns, respectively. For the eccentrically compressed variable CFST latticed columns, the strain of the columns at the loading side, as well as the difference in the strain, increases from the bottom to the cap, and a more significant increase in strain is observed in the cross section closer to the column cap.

• Steel and Composite Structures
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• v.32 no.3
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• pp.411-422
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• 2019

Six shear-critical square tubed steel reinforced concrete (TSRC) columns using the high-strength concrete ($f_{cu,150}=86.6MPa$) were tested under constant axial and lateral cyclic loads. The height-to-depth ratio of the short column specimens was specified as 2.6, and the axial load ratio and the number of shear studs on the steel shape were considered as two main parameters. The shear failure mode of short square TSRC columns was observed from the test. The steel tube with diagonal stiffener plates provided effective confinement to the concrete core, while welding shear studs on the steel section appeared not significantly enhancing the seismic behavior of short square TRSC columns. Specimens with higher axial load ratio showed higher lateral stiffness and shear strength but worse ductility. A modified ACI design method is proposed to calculate the nominal shear strength, which agrees well with the test database containing ten short square TSRC columns with shear failure mode from this study and other related literature.

• Structural Engineering and Mechanics
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• v.72 no.4
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• pp.469-477
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• 2019

The understanding of tool-rock interaction mechanism is of high essence for improving the rock breaking efficiency and optimizing the drilling parameters in mechanical rock breaking. In this study, the tool-rock interaction models of indentation and cutting are carried out by employing the discrete element method (DEM) to examine the rock failure modes of various brittleness rocks and critical indentation and cutting depths of the ductile to brittle failure mode transition. The results show that the cluster size and inter-cluster to intra-cluster bond strength ratio are the key factors which influence the UCS magnitude and the UCS to BTS ratio. The UCS to BTS strength ratio can be increased to a more realistic value using clustered rock model so that the characteristics of real rocks can be better represented. The critical indentation and cutting depth decrease with the brittleness of rock increases and the decreasing rate reduces dramatically against the brittleness value. This effort may lead to a better understanding of rock breaking mechanisms in mechanical excavation, and may contribute to the improvement in the design of rock excavation machines and the related parameters determination.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.257-265
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• 2016

The failure behavior of reinforced concrete beams is governed by the mechanical relationships between the shear span-to-effective depth ratio, flexural reinforcement ratio, load and support conditions, and material properties. In this study, two simple indeterminate strut-tie models which can reflect all characteristics of the failure behavior of reinforced concrete beams were proposed. The proposed models are effective for the beams with shear span-to-effective depth ratio of less than 3. For each model, a load distribution ratio, defined as the fraction of load transferred by a truss mechanism, is also proposed to help structural designers perform the rational design of the beams by using the strut-tie model approaches of current design codes. In the determination of the load distribution ratios, the effect of the primary design variables including shear span-to-effective depth ratio, flexural reinforcement ratio, and compressive strength of concrete was reflected through numerous material nonlinear analysis of the proposed indeterminate strut-tie models. In the companion paper, the validity of the proposed models and load distribution ratios was examined by applying them to the evaluation of the failure strength of 335 reinforced concrete beams tested to failure by others.

• Journal of the Korean GEO-environmental Society
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• v.7 no.5
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• pp.57-66
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• 2006

In this study, the centrifuge model tests were carried out to evaluate the stress concentration ratio, the deformation modes of piles and the ground movement in clay deposit improved by SCP and GCP piles with changing the replacement ratio(20%, 40%, 60%) under flexible loading. Based on the results obtained, it was shown that the stresses acting on GCP was larger than those acting on SCP with the same replacement ratio. It was evaluated that the average stress concentration ratio of soft clay ground improved by GCP was slightly larger than that of SCP when the replacement ratio is 40%. Only expansion failure occurred in GCP, whereas SCP showed the expansion and shear failure simultaneously.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.403-408
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• 2003

The objective of this study is to understand the variables affected the confinement for the transverse reinforcement of the reinforced concrete structural walls with the T-shaped cross section subjected to cyclic lateral loads. The structural performance of T-shaped walls was advanced by the transverse reinforcement which restrained the concrete subjected to compressive stress. If the arrangement of transverse reinforcement was not suitable for the confinement, T-shaped walls happened the brittle failure by web crushing or bucking of vertical reinforcement at the compression zone. It is necessary to confine transverse reinforcement in order to prevent the these failure. But the location of neutral axis and the magnitude of ultimate strain vary according to the section shape, a ratio of axial load, a ratio of wall cross sectional area to the floor-plan area, an aspect ratio and the reinforcement ratio. Therefore, the objective of this research is to grasp the location of neutral axis and the range which needs for the confinement of transverse reinforcement through the results of the sectional analysis which varies the ratio of axial load and the ratio of vertical reinforcement.