• Structural Engineering and Mechanics
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• v.81 no.3
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• pp.281-292
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• 2022

This study aimed to analyze the dynamic punching shear performance of slab-column joints under cyclic loads with the use of double-hooked end (5D) steel fibers. Structural systems such as slab-column joints are widely found in infrastructures. The susceptibility to collapse of such structures when submitted to seismic loads is highly dependent on the structural performance of the slab-column connections. For this reason, the punching capacity of reinforced concrete (RC) structures has been the subject of a great number of studies. Steel fibers are used to achieve a certain degree of ductility under seismic loads. In this context, 5D steel hooked fibers provide high levels of fiber anchoring, tensile strength and ductility. However, only limited research has been carried out on the performance under cyclic loads of concrete structural members containing steel fibers. This study covers this gap with experimental testing of five different full-scale subassemblies of RC slab-column joints: one without punching reinforcement, one with conventional punching reinforcement and three with 5D steel fibers. The subassemblies were tested under cyclic loading, which consisted of applying increasing lateral displacement cycles, such as in seismic situations, with a constant axial load on the column. This set of cycles was repeated for increasing axial loads on the column until failure. The results showed that 5D steel fiber subassemblies: i) had a greater capacity to dissipate energy, ii) improved punching shear strength and stiffness degradation under cyclic loads; and iii) increased cyclic loading capacity.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.835-842
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• 2005

This paper presents an experimental investigation of bond-strengthening hooks as a new method to increase bond strength along flexural reinforcing bars in reinforced concrete (RC) beams and columns. The RC members, which consisted of 1,300 MPa-class spirals as shear reinforcement, often suffered from bond splitting failure. The proposed method attempts to increase confining stiffness around the flexural bars by placing U-shaped hooks and to prevent premature bond splitting failure. Twelve specimens with varied amounts and sizes of the hooks were prepared to verify the strengthening effectiveness under monotonic and cyclic loading conditions. The test result indicated that the hooks increased the bond strength along the flexural bars although the strengthening effectiveness was limited by effective reinforcement ratio $P_{be}$. This limit is determined by size of stress-transmitting zones of concrete around anchors of the hooks. Anchors of the hooks are recommended to be longer than twelve times the hook diameter and inserted deeper than a quarter of the member depth (D/4). Proposed design equations provide modest estimates of the shear strengths.

• Steel and Composite Structures
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• v.45 no.3
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• pp.389-408
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• 2022

Residual capacity is defined as the load carrying capacity of an RC column after undergoing severe damage. Evaluation of residual capacity of RC columns is necessary to avoid damage initiation in RC structures. The central aspect of the current research is to propose an empirical formula to estimate the residual capacity of RC columns after undergoing severe damage. This formula facilitates decision making of whether a replacement or a repair of the damaged column is adequate for further use. Available literature mainly focused on the simulation of explosion loads by using simplified pressure time histories to develop residual capacity of RC columns and rarely simulated the actual explosive. Therefore, there is a gap in the literature concerning general relation between blast damage of columns with different explosive loading conditions for a reliable and quick evaluation of column behavior subjected to blast loading. In this paper, the Arbitrary Lagrangian Eulerian (ALE) technique is implemented to simulate high fidelity blast pressure propagations. LS-DYNA software is utilized to solve the finite element (FE) model. The FE model is validated against the practical blast tests, and outcomes are in good agreement with test results. Multivariate linear regression (MLR) method is utilized to derive an analytical formula. The analytical formula predicts the residual capacity of RC columns as functions of structural element parameters. Based on intensive numerical simulation data, it is found that column depth, longitudinal reinforcement ratio, concrete strength and column width have significant effects on the residual axial load carrying capacity of reinforced concrete column under blast loads. Increasing column depth and longitudinal reinforcement ratio that provides better confinement to concrete are very effective in the residual capacity of RC column subjected to blast loads. Data obtained with this study can broaden the knowledge of structural response to blast and improve FE models to simulate the blast performance of concrete structures.

• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.821-826
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• 2008

This study evaluated spalling and internal temperature distribution after elevated temperatures test for high strength concrete ($f_{ck}=60\;MPa$) column member with various polypropylene fiber volume fractions. The ISO-834 time-temperature curve was used for measurement of fire resistance properties. As the result of test, average internal temperature results indicated to low temperature in increased polypropylene fiber volume fraction. But, the highest internal temperature results show that does not difference in proportion of polypropylene fiber volume fractions.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.233-240
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• 2013

In this study, experimental research was carried out to evaluate and improve the seismic performance of high strength R/C interior beam-column joints regions using advanced reinforcing detailings and high ductile fiber-reinforced mortar. Five specimens of retrofitted the beam-column joint regions using advanced reinforcing detailings and high ductile fiber-reinforced mortar were constructed and tested for their retrofitring performances. Specimens designed by retrofitting the interior beam-column joint regions (IJIR series) of existing reinforced concrete building showed a stable mode of failure and an increase in load-carrying capacity. Specimens of IJIR series, designed by the retrofitting of advanced reinforcing detailings and high ductile fiber-reinforced mortar in reinforecd beam-column joint regions increased its maximum load carrying capacity by 114.2~123.5% and its energy dissipation capacity by 1.55~1.85 times in comparison with the standard specimen of SIJC with a displacement ductility of 5.

• International Journal of Concrete Structures and Materials
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• v.18 no.3E
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• pp.199-205
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• 2006

The composite frame system with reinforced concrete column and steel beam can be improved in its structural efficiency by complementing the shortcomings of the two systems. The system, however, has many inherent problems in practical design and construction process due to the dissimilarities of the materials. Considering these circumstance, this research aims for the development of a composite structural system which connects the steel beams to the R/C columns with higher structural safety and economy. Basically, the proposed connection system is composed of four split tees, structural angles reinforced by a stiffener, high strength steel rods, connecting plates and shear plates. Structural tests have been carried out to investigate the moment transfer mechanism 1Tom the beam flange to steel rods or connecting plates through the structural angle reinforced by a stiffener. The four prototype specimens have been tested until the flange of the beam reached a plastic state. The test results indicated that no distinct material dissimilarities between concrete and steel have been detected for the proposed hybrid beam-column connection system and that the stress transfer through the structural angle between the beam flange and steel rods or connecting plates was very encouraging.

• Steel and Composite Structures
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• v.39 no.3
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• pp.337-352
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• 2021

The study presented experimental and numerical investigation on the seismic performance of steel reinforced concrete (SRC) L-shaped column- reinforced concrete (RC) beam joints. Various parameters described as steel configuration form, axial compressive ratio, loading angle, and the existence of slab were examined through 4 planar joints and 7 spatial joints. The characteristics of the load-displacement response included the bearing capacity, ductility, story drift ratio, energy-dissipating capacity, and stiffness degradation were analyzed. The results showed that shear failure and flexural failure in the beam tip were observed for planar joints and spatial joint, respectively. And RC joint with slab failed with the plastic hinge in the slab and bottom of the beam. The results indicated that hysteretic curves of spatial joints with solid-web steel were plumper than those with hollow-web specimens. The capacity of planar joints was higher than that of space joints, while the opposite was true for energy-dissipation capacity and ductility. The high compression ratio contributed to the increase in capacity and initial stiffness of the joint. The elastic and elastic-plastic story deformation capacity of L-shaped column frame joints satisfied the code requirement. A design formula of joint shear resistance based on the superposition theory and equilibrium plasticity truss model was proposed for engineering application.

• International Journal of High-Rise Buildings
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• v.8 no.3
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• pp.201-209
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• 2019

This paper presents a structural design of the "(Tentative Name) Toranomon Hills Residential Tower" which is currently under construction in Tokyo. The building is a reinforced concrete high-rise residential complex building with 54 stories above ground, 4 basement levels, and a building height of about 220 m. It is a requirement to provide the highest grade of residence in Japan, and in terms of the structural design, it is required to provide wide and comfortable spaces with high seismic performance. These requirements are satisfied by providing a total of 774 vibration control walls of two types. Also, to further improve the structural performance, steel fibers at the rate of 1.0vol% are provided in the ultra-high strength concrete used in the column members.

• Journal of Korean Society of Steel Construction
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• v.11 no.2 s.39
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• pp.191-199
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• 1999

This paper is the first step on the study of the industrialization of the mid-story steel building structures. The purpose of this study is to investigate the structural behavior of concrete-filled square steel tubular column to H-beam connections using angles and high tension bolts. The tests are carried out with five types of specimens under static loading and the main parameter is the thickness of angles. Yield-line theory which obtains connection strength by way of the lowest value based on upper-limit theory is applied to predict strength formulas.

• Journal of the Society of Disaster Information
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• v.20 no.2
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• pp.411-418
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• 2024

Purpose: This study aims to develop brand new bolt fastening type of seismic retrofit using high tensile alloy materials for existing reinforced concrete columns. Method: A T-type cross-sectional seismic retrofit made of SUS304 and SS275, and the high-tensile bolt of SCM435 was analyzed for the effect of material properties on seismic performance through bending test. Result: The experiment using SUS304 shows a 7% higher maximum strength and 22% higher yield strength and shows a higher compressive stress of 360MPa. In addition, the change in the neutral axis is also smaller. Conclusion: Seismic retrofit using SUS304 is considered to be better in terms of yield strength, tensile strength, neutral axis change, and ductility, and it is considered necessary to experiment with RC column real experiments in future studies.