• Journal of the Korean Society for Heat Treatment
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• v.37 no.2
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• pp.58-65
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• 2024

In the present study, the effect of annealing condition on the microstructures and mechanical properties of the cold-rolled CoCrFeMnNi high entropy alloys were studied. Annealing treatment was performed under six different temperatures. Microstructural analyses confirmed that annealing below 800℃ resulted in the formation of intermetallic sigma (σ) phase within face-centered cubic (FCC) matrix, and this σ phase has beneficial effects on the formation of fine-grained structures through retardation of grain growth and recrystallization due to Zener pinning effect. This led to the enhanced yield strength and tensile strength of ~646 and ~855 MPa, respectively. The microstructures annealed above 800℃ demonstrated single FCC phase, and fully-recrystallized single FCC microstructure resulted in a slight increase in ductility with a considerable decrease in strength. The evolution of mechanical properties, such as strength, ductility, and strain hardening exponent, will be discussed.

• Journal of the Korean Geosynthetics Society
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• v.14 no.4
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• pp.105-115
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• 2015

In this study, to understand mechanical characteristic of hybrid reinforced concrete by PVA-fiber 6 mm and PP-fiber 50 mm, which are organic fiber replaced macro-fiber with PP-fiber, four mixed Hybrid Organic Fibers Reinforced Concrete (HFRC) is compared with one mixed plain concrete without fiber reinforcement. Volume portion of the fibers are limited under one percent. The result presents that hybrid reinforcement of the organic fibers cannot maximize stiffness and ductility behavior of the steel fiber reinforcement. however, in comparison to plain concrete, it is confirmed that meaningful relation between toughness index and equivalent flexural strength with advanced ductility behavior. Also, in the case of concrete hybrid reinforced by organic fiber, when the volume portion of the fiber increases, ductility also increases. PP-fiber, which is macro fiber, has more effect on the flexural behavior of concrete than PVA-fiber, which is micro fiber, does. The result also shows that it decrease chloride penetration in chloride penetration test.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.113-121
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• 2015

Building using masonry accounts for most of the smaller houses in Korea but due to brittle behavior and low ductility the frequency of usage has decreased in recent years. Despite this, this form of building has been gaining attention overseas for its low cost in construction and environment-friendliness of the materials. As such, many studies are being conducted to resolve the disadvantages in structure. This study produced an specimen for masonry-filled wall and the intersection to confirm the difference in structural movement depends on the existence or lack of expansion joint and verified the reinforcement effect from inserting a connecting steel item (steel plate, stainless steel twist bar). The experiment results show that the specimen with a steel plate inserted saw an increase in durability and an improvement in the strength of the specimens, while the specimen that had stainless steel twists bar inserted saw an increase in ductility that did not cause brittle failure, indicating that the reinforcement effects of inserting a connecting steel item are effective.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.467-473
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• 2002

The purpose of this study is to investigate the inelastic behavior and ductility capacity of reinforced concrete frame subjected to cyclic lateral load and to provide result for developing improved seismic design criteria. A computer program named RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology) for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. The strength increase of concrete due to the lateral confining reinforcement has been taken into account to model the confined concrete. In boundary plane at which each member with different thickness is connected local discontinuous deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel. The proposed numerical method for the inelastic behavior and ductility capacity of reinforced concrete frame subjected to cyclic lateral load is verified by comparison with reliable experimental results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.1
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• pp.147-155
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• 1999

The purpose of this study is to investigate the strength and ductility of reinforced concrete columns subject to axial load experimentally for several variables of reinforcements and propose foundational research date for reinforcement design of column. In the test a total of eleven specimens, which are all $20{\times}20{\times}60cm$ in size and differently reinforced with steel plate, has been used. The main variables of reinforcement considered in the test are the width of steel plate, the thickness of steel plate. Based on the test results, the effect of the main variables on the strength and ductility of reinforced concrete column have been scrutinized. The strength of reinforced concrete columns are that C-2 series on strengthed with 2mm thickness steel plate are smaller than C-4 series on strengthed with 4mm steel plate. Thick steel plate of reinforced expected utilizer than the other on strength increase and specimens to be large width steel plate of each system are the utiltzer on strength increase. Ductility of C-0 specimen is 1.60, C-2 series is 2.38, C-4 series 2.63 Compare efficiency of ductility increase with each specimens, in narrow width condition (2cm, 4cm) C-2 series is more efficiency, in wide width condition (8cm, 10cm) C-4 series is more efficiency.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.7
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• pp.139-146
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• 2019

This study examined the effect of various arrangement methods for forming peripheral closed hoops in the jacket section on the axial behavior of section enlargement strengthening columns. Four types of peripheral closed hoops arranged in the jacket section were prepared as follows: 1) Closed connection of prefabricated bar units (column P); 2) V-clip installation across the overlapped legs of channel-type bars (column V); 3) Use of glass fiber mesh for an alternative of steel bars (column F); and 4) combination of prefabricated bar units and glass fiber mesh (column PF). The V-clip is designed to form the closed hoops in the jacket section using the overlapped channel-type bars, preventing the opening of the channel bar legs. The glass fiber mesh is to examine the feasibility to apply for closed hoops in the jacket section as an alternative for steel bars, considering the easy construction. In the jacket section of all the strengthened columns, V-ties were arranged for supplementary ties, avoiding the interruption of the existing column. The axial stiffness and strength of the strengthened columns were insignificantly affected by the arrangement methods of closed hoops in the jacket section. The axial ductility ratio of the strengthened columns P, V, and PF was enhanced more than twice of that measured in the non-seismic existing column. However, the column F exhibited a lower ductility than the other strengthened columns because of the fracture of the mesh at the ultimate strength of the column. The V-clip approach was favorable to enhance the ductility of the strengthened column, preventing the opening of the legs of channel-type bars.

• Korean Journal of Metals and Materials
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• v.48 no.5
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• pp.394-400
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• 2010

The effects of oxidation behavior on the hot ductility of plain carbon steels were investigated at various temperatures in order to simulate the continuous casting process more precisely, in which the process undergoes in air atmosphere rather than Ar atmosphere. The high temperature oxidation behavior and scale morphology of the carbon steels exposed to the air and Ar atmosphere at various temperatures were also investigated in order to assess the mechanism of the RA value decreasing in an air atmosphere. The RA values obtained from the air atmosphere were marked below 45% by the test temperature, except for over 1000${^{\circ}C}$, with the RA values remaining in low values in both the low and high temperature region, at which the RA values generally recovered in the Ar atmosphere. The surface roughness of the specimen was developed by external and internal oxidation when the specimen was deformed in an air atmosphere at high temperature, with the result being the stress concentrated at the roughness of the specimen surface, resulting in low RA values. The hot ductility in the air atmosphere was found to be likely controlled by the oxidation rate instead of the microstructures corresponding to test temperatures.

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.3
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• pp.105-116
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• 2022

Seismic demand on nonstructural components (NSCs) is highly dependent on the coupled behavior of a combined supporting structure-NSC system. Because of the inherent complexities of the problem, many of the affecting factors are inevitably neglected or simplified based on engineering judgments in current seismic design codes. However, a systematic analysis of the key affecting factors should establish reasonable seismic design provisions for NSCs. In this study, an idealized 2-DOF model simulating the coupled structure-NSC system was constructed to analyze the parameters that affect the response of NSCs comprehensively. The analyses were conducted to evaluate the effects of structure-NSC mass ratio, structure, and NSC nonlinearities on the peak component acceleration. Also, the appropriateness of component ductility factor (R_p) given by current codes was discussed based on the required ductility capacity of NSCs. It was observed that the responses of NSCs on the coupled system were significantly affected by the mass ratio, resulting in lower accelerations than the floor spectrum-based response, which neglected the interaction effects. Also, the component amplification factor (a_p) in current provisions tended to underestimate the dynamic amplification of NSCs with a mass ratio of less than 15%. The nonlinearity of NSCs decreased the component responses. In some cases, the code-specified R_p caused nonlinear deformation far beyond the ductility capacity of NSCs, and a practically unacceptable level of ductility was required for short-period NSCs to achieve the assigned amount of response reduction.

• Earthquakes and Structures
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• v.23 no.5
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• pp.473-491
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• 2022

The research investigates experimentally the effect of confinement on structural behavior at the ends of beam-column in reinforced concrete (RC) frames. In the experimental study, five specimens consisting of 1/3-scaled RC frames having single-bay, representing the traditional deficiencies of existing buildings constructed without receiving proper engineering service is investigated. The RC frame specimens were produced to represent most of the existing buildings in Turkey that have damage potential. To decrease the probable damage to the existing buildings exposed to earthquakes, the carbon Textile Reinforced Mortar (TRM) strengthening technique (fully wrapping) was used on the ends of the RC frame elements to increase the energy dissipation and deformation capacity. The specimens were tested under reversed cyclic lateral loading with constant axial loads. They were constructed satisfying the weak column-strong beam condition and consisting of low-strength concrete, such as compressive strength of 15 MPa. The test results were compared and evaluated considering stiffness, strength, energy dissipation capacity, structural damping, ductility, and damage propagation in detail. Comprehensive investigations of these experimental results reveal that the strengthening of a brittle frame with fully-TRM wrapping with non-anchored was effective in increasing the stiffness, ductility, and energy dissipation capacities of RC bare frames. It was also observed that the frame-only-retrofitting with an infill wall is not enough to increase the ductility capacity. In this case, both the frame and infill wall must be retrofitted with TRM composite to increase the stiffness, lateral load carrying, ductility and energy dissipation capacities of RC frames. The presented strengthening method can be an alternative strengthening technique to enhance the seismic performance of existing or moderately damaged RC buildings.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.743-752
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• 2006

Confined concrete has enhanced strength and ductility compared with unconfined strength. Cause of these merits of confined concrete, many researches have been performed for confining effects of concrete and been studied in many fields. Although many researches about concrete confined by FRP sheets have been studied recently, it is difficult to apply concrete confined by FRP in real structures because FRP is a brittle material. In this study, the enhanced strength and ductility of concrete which is confined by steel tubes or steel plates were investigated. Fifty one specimens were tested and each specimen has different confining condition. Test results showed enhanced ductility and strength of confined concrete and concrete models were suggested under various confining conditions by regression of experimental data.