• Fire Science and Engineering
• /
• v.26 no.1
• /
• pp.80-88
• /
• 2012

This study evaluates the fire resisting capacity of the beam of the legal fire resistance construction, which establishes the Article 3 of the Regulations on Escape and Fire Resistance of Buildings. There are a total of five structures that we consider as legal fire resistance constructions, however, this study has a primary target of the reinforced concrete beam, and tests the fire-resistant performance depend on the covering depth of reinforce concrete. The results showed that it meets the three hours, the maximum statutory fire resistance time, if it was a load ratio of 0.5 and covering depth of 40 cm. Steel framed mortar beam is legal fire resistance structure that it was possessed three hours fire resistance performance, if it was a load ratio of 0.4 and covering depth of 60 mm.

• Journal of Korean Society of Steel Construction
• /
• v.15 no.1
• /
• pp.1-8
• /
• 2003

In locations where the cost of concrete is relatively high or in situations where the weight of concrete members has to be kept to a minimum, it may be more economical to use hollow reinforced concrete vertic al members. Hollow reinforced concrete colun-ms with a low axial load, a moderate longitudinal steel percentage and a reasonably thick wall were found to perform in a ductile manner at the flexural strength, similar to solid columns. Hollow reinforced concrete columns with a high axial load, a high longitudinal steel percentage, and a thin wall were found, however, to behave in a brittle manner at the flexural strength, since the neutral axis is forced to occur away from the inside face of the tube towards the section centroid and, as a result, crushing of concrete occurs near the unconfined inside face of the section. If, however, a steel tube is placed near the inside face of a circular hollow column, the column can be expected not to fail in a brittle manner through the disintegration of the concrete in the compression zone. A design recommendation and example through the moment-curvature analysis program for curvature ductility are herein presented. A theoretical moment-curvature analysis for reinforced concrete columns, indicating the available flexural strength and ductility, can be conducted, providing that the stress-strain relation for the concrete and steel are known. In this paper, a unified stress-stain model for confined concrete by Mander is developed foi members with circular sections.

• Steel and Composite Structures
• /
• v.20 no.1
• /
• pp.127-145
• /
• 2016

Composite column design is strongly influenced by the computation of the critical buckling load, which is very sensitive to the effective flexural stiffness (EI) of the column. Because of this, the behaviour of a composite column under lateral loading and its response to deflection is largely determined by the EI of the member. Thus, prediction models used for composite member design should accurately mirror this behaviour. However, EI varies due to several design parameters, and the implementation of high-strength materials, which are not considered by the current composite design codes of practice. The reliability of the design methods from six codes of practice (i.e., AS 5100, AS/NZS 2327, Eurocode 4, AISC 2010, ACI 318, and AIJ) for composite columns is studied in this paper. Also, the reliability of these codes of practice against a serviceability limit state criterion are estimated based on the combined use of the test-based statistical procedure proposed by Johnson and Huang (1997) and Monte Carlo simulations. The composite columns database includes 100 tests of circular concrete-filled tubes, rectangular concrete-filled tubes, and concrete-encased steel composite columns. A summary of the reliability analysis procedure and the evaluated reliability indices are provided. The reasons for the reliability analysis results are discussed to provide useful insight and supporting information for a possible revision of available codes of practice.

• Journal of Korean Society of Steel Construction
• /
• v.29 no.6
• /
• pp.411-422
• /
• 2017

In this study, to investigate the seismic performance of beam-column joints using concrete-encased and -filled circular steel tube(CEFT) columns, two types of tests were performed: (1) column - flange tension test and (2) beam - column joint cyclic load test. In column - flange tension test, test parameters were concrete encasement and connection details: flange width and strengthening rebar. Five specimens were tested to investigate the load-carrying capacity and the failure mode. Test results showed that increase of flange width from 200mm to 350mm result in increase of connection strength and stiffness by 61% and 56%, respectively. Structural performances were further improved with addition of tensile rebars by 35% and 92%, respectively. In cyclic loading test, three exterior beam-column joints were prepared. Test parameters were strengthening details including additional tensile rebars, thickened steel tube, and vertical plate connection. In all joint specimens, flexural yielding of beam was occurred with limited damages in the connection regions. In particular, flexural capacity of beam-column joint was increased due to additional load transfer through tube - beam web connection. Also, connection details such as increase of tube thickness and using vertical plate connection were effective in improving the resistance of panel zone.

• Journal of the Korean Society for Railway
• /
• v.18 no.3
• /
• pp.175-185
• /
• 2015

Generally, in the train area, switch tracks have required high reliability because this system is directly associated with derailment. Especially, switch tracks of Maglev vehicles must be moved in terms of the whole geometric characteristics, in which the bogies are encased in the switch track. For this reason, switch track was constructed with steel lighter than concrete girders. But, the steel switch track was weak because of structural vibration as well as structural deformation. Therefore, it is important to predict the levitation stability when a vehicle passes over flexible switch track. The aims of this paper are to develop a coupled dynamic model to describe the relationship between a Maglev vehicle and switch track and to predict the levitation stability. In order to develop the coupled dynamic model, a three dimensional vehicle model was developed based on multibody dynamics; a switch model was made using the modal superposition method. And, the developed model was verified using comparison measured data.

• The korean journal of orthodontics
• /
• v.14 no.2
• /
• pp.203-215
• /
• 1984

This experiment was performed to explore the effect of electric currents and orthodontic forces on bone $PGE_2$ content and orthodontic tooth movement on cats. Stainless steel electrodes were connected a power pack consisting of five miniature batteries, a transistor, and a resistor. The current $(10{\pm}2{\mu}A)$ was provided by a constant source encased in a palatal acrylic plate. In first experiment, the cathode was placed mesial to the right maxillary canine tooth and the anode was positioned distal to the tooth, Sham electrodes were placed new the left cuspid, to serve as control. Nine cats were divided into three groups evenly. Groups of three animals were treated with electric currents only-for 1, 3 and 7 days, respectively. In second experiment, electric currents and the orthodontic forces of about 80 gm were applied to the right maxillary canine, and the orthodontic forces only were applied to the left maxillary canine. 3 groups of three cats each were treated in this experiment-for 1, 3 and 7 days, respectively. Alveolar bone samples were obtained from sites of tension and compression as well as from contralateral sites. Bone samples were extracted by homogenization in $40\%$ ethanal. The supernatant partitioned twice with 2 volumes of petroleum ether to remove neutral lipids and the aqueous supernatant partitioned in ethyl acetate. After drying the solvent, $PGE_2$ was measured by radioimmunoassay technique. The obtained results were as follows. 1. Teeth treated with combined force and electricity moved faster than those treated with force alone. 2. Alveolar bone $PGE_2$ content of electric stimulation was increased at both electrodes. 3. Alveolar bone $PGE_2$ content of mechanical stimulation at compression sites was gradually increased at all time period. At tension site, $PGE_2$ content increased after 1 day of mechanical stimulation remained elevated at all time period. 4. Alveolar bone $PGE_2$ content of compression sites was increased more than that of tension sites from mechanical stimulation as well as electrical stimulation.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.24 no.1
• /
• pp.97-107
• /
• 2020

In this study, finite element analysis was carried out through the finite element analysis program (ANSYS) to investigate the fire resistance of composite columns in fire. Transient heat transfer analysis and static structural analysis were performed according to ASTM E 119 heating curve and axial force ratio 0.7, 0.6, 0.5 by applying stress-strain curves according to temperature, and loading heating experiments were carried out under the same conditions. In addition, the nominal compressive strength of the composite column according to the heating time according to the standard(Eurocode 4) was calculated and expressed as the axial force ratio and compared with the analytical and experimental values. Through the analysis, As a result of finite element analysis, the fire resistance time was 180 minutes and similar value to the experimental value was obtained, whereas the fire resistance time 150 minutes and 60 minutes were derived from the axial force ratios 0.6 and 0.7. In addition, it was confirmed that the fire resistance time according to the axial force ratio calculated according to the reference equation (Eurocode 4) was lower than the actual experimental value. However, it was confirmed that the standard(Eurocode 4) was higher than the experimental value at the axial force ratio of 0.7. Accordingly, it is possible to confirm the fire resistance characteristics(time-axial force ratio relationship) of the SRC column at high axial force, and to use the experimental and anaylsis data of the SRC column as the data for verification based on Eurocode.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.31 no.6
• /
• pp.367-372
• /
• 2018

Defects in aging infrastructures such as pre-stressed concrete bridges and cable bridges can cause a collapse of the entire structure. Defects, however, are often located inside of the structures that they are not visible from the outside. For example, in PSC bridges, because reinforcement steels are encased by exterior covers, corrosion and void on the reinforcement steel cannot be detected with a visual inspection. Therefore, in this paper, a new non-destructive evaluation(NDE) method that can detect defects inside of structures is presented. The new method utilizes sending of electrical signals, a method often utilized in electrical engineering to detect any discontinuities on power cables. In order to confirm the applicability and accuracy of the method, some experiments were conducted in the laboratory. And to overcome the hardship of conducting experiments on real structures due to their enormous size, simualtions were conudcted using a commercial program, COMSOL. The results of the experiments were analyzed and compared to confirm the accuracy of the simualtions.