• Journal of computational fluids engineering
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• v.11 no.4 s.35
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• pp.75-80
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• 2006

Navier-Stokes simulation of the flow in a micro viscous pump is carried out. The micro viscous pump consists of a rotating circular rotor placed in a two dimensional channel. All simulation is carried out by using a finite volume approach, at the Reynolds number of 0.5, to study the performance of the micro viscous pump. Length of channel of the pump is varied to simulate the effects of the pumping load. Numerical solutions show that the net flow of the pump is realized by two counter rotating vortices formed on both sides of the rotor. The volume flow rate of the pump is decreased as length of the channel is increased, while the static pressure difference across the rotor is increased. The static pressure difference across the rotor is observed to be inversely proportional to the volume flow rate as inertia effects are negligibly small. The efficiency of the pump is found to reach a maximum when two counter rotating vortices on both sides of the rotor becomes to merge forming an outer enveloping vortex.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.7
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• pp.749-753
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• 2013

Hydraulic systems are used to transform mechanical energy and fluid energy into each other. Its applications are very wide over the whole industries such as automobiles, public works, rockets, machine tools, construction heavy equipments, airplaces and so on. They are hydraulic pumps that transform energy in the systems. In this study, with basic operation principles as a start point, I tried to understand how the rotating radius of a piston affects the lubrication characteristics in more practical conditions, a swash-plate with tilt angle zero capable of rotating motion and other devices was used. In this paper, a slipper was located on 45mm eccentricity from the center of a swash-plate. As a result, through this experiment, it was found that the rotating radius of a piston affects load capacity, leakage flow and lubrication characteristics and it is one of the important parts for improving the pump efficiency.

• Advances in concrete construction
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• v.6 no.1
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• pp.1-13
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• 2018

An experimental investigation has been carried out on the use of an environmentally sustainable material, bamboo, in the construction of precast concrete structural wall panels. The strength and behaviour of three prototype bamboo reinforced concrete wall panel specimens under two-way in-plane action was studied. The specimens with varying aspect ratio and thinness ratio were tested to fail under a uniformly distributed in-plane load applied at an eccentricity of t/6. The aspect ratio of the specimens considered includes 1.667, 1.818 and 2 and the thinness ratio includes 12.5, 13.75 and 15. The influence of aspect ratio and thinness ratio of bamboo reinforced concrete wall panels, on its strength and behaviour was discussed. Varnished and sand blasted bamboo splints of 20 mm width and thickness varying from 8 to 15 mm were used as reinforcement in concrete. Based on the study, an empirical equation was developed considering the geometrical parameters of bamboo reinforced concrete wall panels for predicting its ultimate strength under two way in-plane action.

• Computers and Concrete
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• v.10 no.4
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• pp.331-347
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• 2012

This paper describes the varying material model, the analysis method and the software development for reinforced concrete circular columns confined by spiral or hoop transverse steel reinforcement and subjected to eccentric loading. The widely used Mander model of concentric loading is adapted here to eccentric loading by developing an auto-adjustable stress-strain curve based on the eccentricity of the axial load or the size of the compression zone to generate more accurate interaction diagrams. The prediction of the ultimate unconfined capacity is straight forward. On the other hand, the prediction of the actual ultimate capacity of confined concrete columns requires specialized nonlinear analysis. This nonlinear procedure is programmed using C-Sharp to build efficient software that can be used for design, analysis, extreme event evaluation and forensic engineering. The software is equipped with an elegant graphics interface that assimilates input data, detail drawings, capacity diagrams and demand point mapping in a single sheet. Options for preliminary design, section and reinforcement selection are seamlessly integrated as well. Improvements to KDOT Bridge Design Manual using this software with reference to AASHTO LRFD are made.

• Earthquakes and Structures
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• v.13 no.1
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• pp.1-8
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• 2017

This article is all about using the MR damper with an external lever system for mitigation torsional and transitional lateral displacements by using of PID control algorithm. The torsional modes are so destructive and can be varied during an earthquake therefore, using a semi-active control system mostly recommended for them. In this paper the corner lateral displacement of each floor obtains and then it equivalents in a solid member and it connects to an MR damper, which relies to a rigid structure to reduce the response. An MR damper is a semi-active control system, which can absorb a lot of energy by injecting current to it. This amount of current is very low and needs low power supply, but it increases the amount of damper force, rather than inactive systems like viscous dampers. This paper will show the appropriate algorithm for current injection into MR damper when the eccentricity of the load is changed by using of Bouc-Wen and Bingham's methods and illustrates the coincidence of them.

• Structural Engineering and Mechanics
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• v.74 no.3
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• pp.445-455
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• 2020

Shear lag phenomenon has long been taken into consideration in various structural codes; however, the AISC provisions have not proposed any specific equation to calculate the shear lag ratio in some cases such as fillet-welded connections of front-to-front double channel sections. Moreover, those equations and formulas proposed by structural codes are based on the studies that were conducted on riveted and bolted connections, and can be applied to single channel sections whilst using them for fillet-welded double channels would be extremely conservative due to the symmetrical shape and the fact that bending moments will not develop in the gusset plate, resulting in less stress concentration. Numerical models are used in the present study to focus on parametric investigation of the shear lag effect on fillet-welded tension connection of double channel section to a gusset plate. The connection length, the eccentricity of axial load, the free length and the thickness of gusset plate are considered as the key factors in this study. The results are then compared to the estimates driven from the AISC-LRFD provisions and alternative equations are proposed.

• Interaction and multiscale mechanics
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• v.5 no.2
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• pp.91-104
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• 2012

There is relatively little numerical study on the behavior of eccentrically loaded high strength rectangular concrete-filled steel tubular (CFST) slender beam-columns with large depth-to-thickness ratios, which may undergo local and global buckling. This paper presents a multiscale numerical model for simulating the interaction local and global buckling behavior of high strength thin-walled rectangular CFST slender beam-columns under eccentric loading. The effects of progressive local buckling are taken into account in the mesoscale model based on fiber element formulations. Computational algorithms based on the M$\ddot{u}$ller's method are developed to obtain complete load-deflection responses of CFST slender beam-columns at the macroscale level. Performance indices are proposed to quantify the performance of CFST slender beam-columns. The accuracy of the multiscale numerical model is examined by comparisons of computer solutions with existing experimental results. The numerical model is utilized to investigate the effects of concrete compressive strength, depth-to-thickness ratio, loading eccentricity ratio and column slenderness ratio on the performance indices. The multiscale numerical model is shown to be accurate and efficient for predicting the interaction buckling behavior of high strength thin-walled CFST slender beam-columns.

• Journal of Korean Society of Steel Construction
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• v.22 no.5
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• pp.497-509
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• 2010

Five concrete-encased steel columns using high-strength steel($f_{ys}$=801MPa) and high-strength concrete($f_{ck}$=97.7MPa) were tested to investigate the eccentric axial load-displacement relationship. Test parameters included the type, yield strength, and spacing of lateral reinforcement, and also the eccentricity of axial load. To analyze the behavior of the column specimens, the nonlinear sectional analysis using strain-compatibility and confinement effect was performed. To examine the applicability of existing design codes for the composite sections using high-strength materials, the test results were also compared with the predictions by the nonlinear analysis and the design codes. The confinement effect of lateral reinforcement increased the ductility of concrete, and the moment capacity of the column specimens increased with the ductility of concrete. The prediction by the nonlinear analysis gave good agreement with the test results. On the other hand, the ACI 318 neglecting lateral confinement effect underestimated the strength of the column specimens, and the Eurocode 4 using complete plastic capacity of steel section overestimated.

• Structural Engineering and Mechanics
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• v.72 no.5
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• pp.631-642
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• 2019

The objective of the present study is to examine the flexural behavior of two-span post-tensioned lightweight aggregate concrete (LWAC) beams using unbonded tendons and the reliability of the design provisions of ACI 318-14 for such beams. The parameters investigated were the effective prestress and loading type, including the symmetrical top one-point, two third-point, and analogous uniform loading systems. The unbonded prestressing three-wire strands were arranged with a harped profile of variable eccentricity. The total length of the beam, measured between both strand anchorages, was 11000 mm. The test results were compared with those compiled from simply supported LWAC one-way members, wherever possible. The ultimate load capacity of the present beam specimens was evaluated by the collapse mechanism of the plasticity theorem and the nominal section moment strength calculated following the provision of the ACI 318-14. The test results showed that the two-span post-tensioned LWAC beams had lower stress increase (Δf_ps) in the unbonded tendons than the simply supported LWAC beams with a similar reinforcement index. The effect of the loading type on Δf_ps and displacement ductility was less significant for two-span beams than for the comparable simply supported beams. The design equations for Δf_ps and Δf_ps proposed by ACI 318-14 and Harajli are conservative for the present two-span post-tensioned LWAC beams, although the safety decreases for the two-span beam, compared to the ratios between experiments and predictions obtained from simply supported beams.

• Steel and Composite Structures
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• v.8 no.6
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• pp.491-510
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• 2008

This paper presents a plan and guidelines that were drawn for Korean based research carried out on the fire-resistance of CFT columns. This research was carried out by reviewing the Korean regulations related to the fire-resistance of CFT columns and examining studies which had been made in Korea as well as overseas. The first phase of the study plan was to compare the fire-resistance of square CFT columns without fire protection (obtained through fire-resistance tests and numerical analyses) with estimated values (obtained through fire-resistance design formulas proposed in Korea and overseas). This comparison provided conclusions as outlined below. Fire-resistance tests conducted in this study proved that, when the actual design load is taken into consideration, square CFT columns without fire protection are able to resist a fire for more than one hour. A comparison was made of test and analysis results with the fire-resistance time based on the AIJ code, the AISC design formula and the estimation formula suggested for Korea. The results of this comparison showed that the test and analysis results for specimens SAH1, SAH2-1, SAH2-2 and SAH3 were almost identical with the AIJ code, the AISC design formula and estimation formula. For specimens SAH4 and SAH5, the estimation formula was more conservative than the AIJ code and the AISC design formula. It was necessary to identify the factors that have an influence on the fire-resistance of CFT columns without fire protection and to draw fire-resistance design formulas for these columns. To achieve this, it is proposed that numerical analyses and tests be conducted in order to evaluate the fire-resistance of circular CFT columns, the influence of eccentricity existing as an additional factor and the influence of the slenderness ratio of the columns. It is also suggested that the overall behavior of CFT structures without fire protection within a fire be evaluated through analysis simulation.