• Computers and Concrete
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• v.4 no.5
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• pp.403-424
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• 2007

The investigation of corrosion effects on the tensile behavior of reinforced concrete (RC) members is very important in region prone to high corrosion conditions. In this article, an experimental study concerning corrosion effects on tensile behavior of RC members is presented. For this purpose, a comprehensive experimental program including 58 cylindrical reinforced concrete specimens under various levels of corrosion is conducted. Some of the specimens (44) are located in large tub containing water and salt (5% salt solution); an electrical supplier has been utilized for the accelerated corrosion program. Afterwards, the tensile behavior of the specimens was studied by means of the direct tension tests. For each specimen, the tension stiffening curve is plotted, and their behavior at various load levels is investigated. Average crack spacing, loss of cross-section area due to corrosion, the concrete contribution to the tensile response for different strain levels, and maximum bond stress developed at each corrosion level are studied, and their appropriate relationships are proposed. The main parameters considered in this investigation are: degree of corrosion ($C_w$), reinforcement diameter (d), reinforcement ratio (${\rho}$), clear concrete cover (c), ratio of clear concrete cover to rebar diameter (c/d), and ratio of rebar diameter to reinforcement percentage ($d/{\rho}$).

• Steel and Composite Structures
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• v.47 no.1
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• pp.19-36
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• 2023

An experimental study of eleven PVC-FRP Confined Concrete (PFCC) column-Reinforced Concrete (RC) beam joints reinforced with Core Steel Tube (CST) under axial compression is carried out. All specimens are designed in accordance with the principle of "weak column and strong joint". The influences of FRP strips spacing, length and steel ratio of CST, height and stirrup ratio of joint on mechanical behavior are investigated. As the design anticipated, all specimens are destroyed by column failure. The failure mode of PFCC column-RC beam joint reinforced with CST is the yielding of longitudinal steel bars, CST and stirrups of column as well as the fracture of FRP strips and PVC tube. The ultimate bearing capacity decreases as FRP strips spacing or joint height increases. The effects of other three studied parameters on ultimate bearing capacity are not obvious. The strain development rules of longitudinal steel bars, PVC tube, FRP strips, column stirrups and CST are revealed. The effects of various studied parameters on stiffness are also examined. Additionally, an influence coefficient of joint height is introduced based on the regression analysis of test data, a theoretical formula for predicting bearing capacity is proposed and it agrees well with test data.

• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.499-511
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• 2019

In this study, the axial compressive behavior of novel quadruple C-channel built-up cold-formed steel columns with different slenderness ratio was investigated, using the experimental and numerical analysis. The axial compressive capacity and failure modes of the columns were obtained and analyzed. The finite element models considering the geometry, material and contact nonlinearity were developed to simulate and analyze the structural behavior of the columns further. There was a great correlation between the numerical analyses and test results, which indicated that the finite element model was reasonable and accurate. Then influence of, slenderness ratio, flange width-to-thickness ratio and screw spacing on the mechanical behavior of the columns were studied, respectively. The tests and numerical results show that due to small slenderness ratio, the failure modes of the specimens are generally local buckling and distortional buckling. The axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns decrease with the increase of maximum slenderness ratio. When the screw spacing is ranging from 150mm to 450mm, the axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns change little. The axial compressive capacity of quadruple C-channel built-up cold-formed steel columns increases with the decrease of flange width-thickness ratio. A modified effective length factor is proposed to quantify the axial compressive capacity of the quadruple C-channel built-up cold-formed steel columns with U-shaped track in the ends.

• Steel and Composite Structures
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• v.35 no.1
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• pp.13-27
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• 2020

To investigate the stress-strain relation of PVC-FRP Confined Concrete (PFCC) column with RC ring beam joint subjected to eccentric compression, the experiment of 13 joint specimens, which were designed with principle of "strong joint and weak column", were presented. Several variable parameters, such as reinforcement ratio, width and height of ring beam, FRP strips spacing and eccentricity, were considered. The specimens were eventually damaged by the crushing of concrete, the fracture of PVC tube and several FRP strips. With the FRP strips spacing or eccentricity increased, the ultimate carrying capacity of specimens declined. The strain of FRP strips and axial strain of PVC tube decreased as FRP strips spacing decreased. The decrease of eccentricity would slow down the development of strain of FRP strips and axial strain of PVC tube. The slope of stress-strain curve of PFCC column decreased as FRP strips spacing or eccentricity increased. The ultimate strain of PFCC column reduced as FRP strips spacing increased, while the effect of eccentricity on the ultimate strain of PFCC was not distinct. Considering the influence of eccentricity on the stress-strain relation, a modified stress-strain model for conveniently predicting the weak PFCC column and strong RC ring beam joint under eccentric compression was proposed and it was in good agreement with the experimental data.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.383-399
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• 2020

Optimizing the spacing of the disc cutter is a key element in the design of the TBM cutter head, which determines the drilling performance of the TBM. The full-scale linear cutting test is known as the most reliable and accurate test for calculating the spacing of the disc cutter, but it has the disadvantage of costly and time-consuming for the full-scale experiment. In this study, through the numerical analysis study based on the discrete element method, the tendency between Specific Energy-S/P ratio according to uniaxial compression strength and penetration depth of rock was analyzed, and the optimum spacing of 17-inch disc cutter was derived. To examine the appropriateness of the numerical analysis model, the rolling force acting on the disc cutter was compared and reviewed with the CSM model. As a result of numerical analysis for the linear cutting test, the rolling force acting on the disc cutter was analyzed to be similar to the rolling force derived from the theoretical formula of the CSM model. From the numerical analysis on 5 UCS cases (50 MPa, 70 MPa, 100 MPa, 150 MPa, 200 MPa), it is found that the range of the optimum spacing of the disc cutter decreases as the rock strength increases. And it can be concluded that 80~100 mm of disc cutter spacing is the optimum range having minimum specific energy regardless of rock strength. This tends to coincide with the optimal spacing of previously reported disk cutters, which underpins the disk cutter spacing calculated through this study.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.231-239
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• 2003

Many box girder bridges have been constructed during the past several decades due to their large bending and torsional rigidities as well as aesthetic considerations. However, box girders have shortcoming in that the cross section distorts under an eccentric loading and warps out of the section plane. Therefore, in order to reduce distortional stresses such as distortional warping and transverse bending normal stresses, diaphragms were generally installed in the box girders. Shapes of the diaphragms in steel-box-girder bridges constructed up to date were solid-plate, frame, and truss types. The objectives of this study using parametric study were to evaluate the appropriate stiffness ratio of intermediate diaphragms and then to propose the effective spacing and numbers of intermediate diaphragms based on the evaluated stiffness ratio. Target bridges for this study were straight continuous span bridges with a single-cell steel box section. The parameters for the parametric study were the shape of box section, the span numbers, the equivalent span length, the stiffness of intermediate diaphragms, and the spacing of intermediate diaphragms. From the results of the parametric study, the effective spacing and numbers as well as the stiffness ratio of the intermediate diaphragms will be presented.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.475-482
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• 2014

This paper presents the experimental results concentrically reinforced concrete tension members and compares cracking behavior of amorphous steel fiber and normal steel fiber reinforced concrete members. Two kind of steel fibers were included as a major experimental parameter together with the six cover thickness to bar diameter ratio ($c/d_b$). The presence of amorphous steel fibers effectively controlled the splitting cracks initation and propagation. In the amorphous steel fiber reinforced specimens, no splitting cracks were observed that becomes higher with cover thickness to bar diameter ratio is 2.0. Crack spacing of the each specimens reinforced with amorphous steel fibers and normal steel fibers becomes larger with the increase in cover thickness, and also measured maximum and average crack spacing are significantly smaller than current design code provision. Based on the measured crack spacings, a relationships for predicting the crack spacing is proposed using the measured average crack spacing in amorphous steel fiber reinforced concrete tension members.

• Journal of Korean Society of Transportation
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• v.25 no.4
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• pp.79-87
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• 2007

The interchanges of urban freeways have many problems with traffic operation due to high off-ramp flows and frequent congestion at adjacent intersections. The flow exiting from off-ramps is affected by the operational status and traffic volume conditions of the nearest signalized intersection. As a result, off-ramp flow cannot exit and the queue backs up the freeway mainline when queues from the signalized intersection form up to the junction of the off-ramp and street. The spacing between an off-ramp and an adjacent intersection is likely to determine the traffic conditions at the adjacent intersection. However, the current design guidelines do not consider such a factor. This study is to develop a model calculating the spacing between off-ramps and adjacent intersections considering the signal, traffic, and road conditions. The variables affecting the model in this study are effective green time (g/C), volume-capacity ratio (v/c), the number of lanes, and off-ramp volume. Various scenarios are designed to represent the effects of the variables and the road networks are constructed using VISSIM, which is a common traffic micro-simulation software package. The queue length is derived from VISSIM and this length is considered as the recommended spacing between the off-ramp and the adjacent intersection. Through the simulation analysis, regression models are developed to calculate the queue length reflecting the various conditions such as signals, traffic, and road configurations. The developed model can be used to create road design guidelines to determine the location of off-ramps in the planning stage.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.1
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• pp.18-26
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• 2007

The steady-state aerodynamic characteristics of wings on the formation flight were analyzed using the Vortex Lattice Method. When two wings were at formation flight, the sectional lift coefficient of a rear wing was increased due to a front wing. The result showed that the lift drag ratio increased as the rear wing were placed downward and decreased as the lateral spacing between wings increased. The difference of lift drag ratio between forward wing and rear wing increase as the aspect ratio of wings increased. When a rear wings and a forward wings placed at the same height, wings on the formation flight had the maximum lift drag ratio. The results showed that the benefit of the formation flight increased as the number of wings on the formation flight increased.

• Steel and Composite Structures
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• v.52 no.2
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• pp.121-134
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• 2024

To investigate the compressive behavior of partially encased recycled aggregate concrete (PERAC) stub columns after exposed to elevated temperatures, 22 specimens were tested. The maximum temperature suffered, the replacement ratio of recycled coarse aggregate (RCA), the endurance time and the spacing between links were considered as the main parameters. It was found that the failure mode of post-heated PERAC columns generally matched that of traditional partially encased composite (PEC) columns, but the flange of specimens appeared premature buckling after undergoing the temperature of 400℃ and above. Additionally, the ultimate strength and ductility of the specimens deteriorated with the elevated temperatures and extended heating time. When 400℃< T ≤ 600℃, the strength reduction range is the largest, about 11% ~ 17%. The higher the replacement ratio of RCA, the lower the ultimate strength of specimens. At the temperature of 600℃, the ultimate strength of specimens with the RCA replacement ratio of 50% and 100% is 0.94 and 0.91 times than that of specimens without RCA, respectively. But the specimen with 50% replacement ratio of RCA showed the best ductility performance. And the bearing capacity and ductility of PERAC stub columns were changed for the better due to the application of links. When the RCA replacement ratio is 100%, the ultimate strength of specimens with the link spacing of 100 mm and 50 mm increased 14% and 25% than that of the specimen without links, respectively. Based on the results above, a formula for calculating the ultimate strength of PERAC stub columns after exposure to high temperatures was proposed.