• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.345-351
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• 2017

This study evaluated the effectiveness of V-shaped ties as an alternative to the supplementary crossties specified in ACI 318-14 on the flexural ductility of reinforced concrete columns. From column specimens tested under constant axial loads and reversed cyclic lateral loads, the mode of failure and lateral load-lateral displacement relationship were measured according to the variation of the applied axial load levels. After the columns reached the peak lateral load capacity, the $90^{\circ}$ hooks of the crossties gradually opened, which eventually caused premature buckling of the longitudinal reinforcement and severe crushing of the core concrete, whereas no V-ties were extracted from the core concrete until the column failure. As a result, the cumulative work damage indicators up to 80% of the peak lateral load for V-tie columns under the axial load level of 0.2, 0.4, and 0.55 was as much as 2.4, 2.3, and 5.2 times higher, respectively, than those of the companion crosstie columns. The superiority of the V-ties to the conventional crossties in enhancing the flexural ductility of columns became more prominent as the axial load level increases.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.1-10
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• 2012

This paper presents an experimental result and suggests the confinement effect of headed cross tie in reinforced concrete(RC) columns subjected to cycling horizontal loads under constant axial load. Five RC columns specimens were manufactured, taking confined type of transverse reinforcement, whether or not using cross tie, end detail of cross tie (hooked or headed), and axial stress in column as major variables, Cyclic horizontal load applied to the columns under constant axial stress and the effect of cross tie to structural capacity of column was evaluated from the test. The column without cross tie failed showing bending deformation of hoop with crack in core concrete at low horizontal load while the column with cross tie showed quite improved strength and ductility by suppressing bending deformation of hoop as well as buckling of longitudinal bar at once even after crack in core concrete. At high lateral displacement, the column with hooked cross tie showed the failure pattern loosing the confining force of cross tie since the $90^{\circ}$ hooked part of cross tie was stretched out and the cracked core concrete lumps were came off. However, the column with headed cross tie showed very stable behavior since the head of cross tie effectively confined the hoop and longitudinal bars even at high lateral displacement.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.357-366
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• 2010

This paper presents experimental results about shear wall with various lateral reinforcement details in boundary elements. The research objective is to study the structural behavior of shear wall with boundary column confined by rectangular spiral hoops and headed cross ties developed to improve workability in the fabrication of boundary columns. These two details can be fabricated in a factory and put together on-site after being delivered so that the construction work may be reduced. Main parameters in the experimental study were the types of hoop and cross tie: rectangular spiral hoop and headed cross tie vs. standard hoop and cross tie with hook. Four half scaled shear wall specimens with babel shape were made and tested by applying horizontal cyclic load under constant axial force, 10% of nominal compressive strength of concrete. Based on the test result, it was shown that the shear wall with rectangular spiral hoop and headed cross tie in boundary columns has structural capacity compatible with conventional shear wall. The specimen SW-Hh which has bigger hoop bar and higher volumetric ratio of transverse reinforcements than other showed improved energy dissipating characteristic but it presented a rapid reduction of strength after peak point. The results indicates that, it is necessary to consider volumetric ratio of transverse reinforcements as well as hoop space in designing of shear wall with boundary columns for improved strength and ductility.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.81-88
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• 2018

The present study evaluated the effective arrangement approach of transverse reinforcement in the jacket section for seismic strengthening of reinforced concrete columns. To simulate the full-scale columns, the section dimensions were determined as $450{\times}450mm$ for non-seismic existing columns and $750{\times}750mm$ for section enlargement strengthening columns. Over-lapped channel-shape bars and prefabricated bar units were proposed for closed-hoops in the jacket section, and conventional cross-ties anchored into existing columns and V-ties were considered for the supplementary ties. Test results showed that the axial capacity of the existing column and section enlargement columns with over-lapped channel-shape hoops was similar to the nominal strength calculated using ACI 318-14 procedure whereas the section enlargement column with prefabricated bar units possessed 1.25 times higher axial capacity than the nominal prediction. Furthermore, the axial ductility ratio of the section enlargement column with prefabricated bar unit was 139% higher than that of the existing column despite the potential size effect on ductility of concrete. Thus, it can be concluded that the developed prefabricated bar unit technique is practically useful for preventing the premature buckling of longitudinal reinforcement and confining core concrete in the section enlargement strengthening columns.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.207-214
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• 2015

This study examined the feasibility of wire ropes as lateral reinforcement at the boundary element of heavyweight concrete shear walls. The spacing of the wire ropes varied from 60 mm to 120 mm at an interval of 30 mm, which produces the volumetric index of the lateral reinforcement of 0.126~0.234. The wire ropes were applied as a external hoop and/or internal cross-tie. Five shear wall specimens were tested to failure under constant axial load and cyclic lateral loads. Test results showed that with the increase of the volumetric index of the lateral reinforcement, the ductility of shear walls tended to increase, whereas the variation of flexural capacity of walls was minimal. The flexural capacity of shear walls tested was slightly higher than predictions determined from ACI 318-11 procedure. The displacement ductility ratio of shear walls with wire ropes was higher than that of shear wall with the conventional mild bar at the same the volumetric index of the lateral reinforcement. In particular, the shear walls with wire rope index of 0.233 achieved the curvature ductility ratio of more than 16 required for high-ductility design.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.1
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• pp.57-64
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• 2022

This study investigated the structural performance of the RC boundary beam-wall system subjected to axial loads that required lesser construction quantity and smaller floor height in comparison with the conventional RC transfer girder system. Four specimens of 1/2 scale were constructed, and their peak strengths under axial loads and failure characteristics were compared and analyzed. Test parameters included the ratio of the lower to the upper wall length, lower wall thickness, and stirrup details of the lower wall. In addition, three-dimensional nonlinear finite element analysis was performed to verify the effectiveness of the boundary beam-wall system. The peak strength of each specimen was similar to the nominal axial strength of the lower wall, indicating that the axial load was transferred smoothly from the upper to the lower wall. The contribution of the lower wall cross-section was high if the ratio of the lower to the upper wall length was small; the contribution was low if the out-of-plane eccentricity existed in the lower wall. The specimen with smaller stirrup distance and cross-ties in the lower wall showed higher initial stiffness and peak load than other specimens.