• Computers and Concrete
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• v.14 no.2
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• pp.109-125
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• 2014

The force transfer mechanism in positive moment continuity details for prestressed concrete girder bridges is investigated in this paper using a three-dimensional detailed finite element model. Positive moment reinforcement in the form of hairpin bars as recommended by the National Cooperative Highway Research Program Report No 519 is incorporated in the model. The cold construction joint that develops at the interface between girder ends and continuity diaphragms is also simulated via contact elements. The model is then subjected to the positive moment and corresponding shear forces that would develop over the service life of the bridge. The stress distribution in the continuity diaphragm and the axial force distribution in the hairpin bars are presented. It was found that due to the asymmetric configuration of the hairpin bars, asymmetric stress distribution develops at the continuity diaphragm, which can be exacerbated by other asymmetric factors such as skewed bridge configurations. It was also observed that when the joint is subjected to a positive moment, the tensile force is transferred from the girder end to the continuity diaphragm only through the hairpin bars due to the lack of contact between the both members at the construction joint. As a result, the stress distribution at girder ends was found to be concentrated around the hairpin bars influence area, rather than be resisted by the entire girder composite section. Finally, the results are used to develop an approach for estimating the cracking moment capacity at girder ends based on a proposed effective moment of inertia.

• Journal of the Korean Society of Safety
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• v.15 no.3
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• pp.57-65
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• 2000

The stress corrosion crack growth is simulated assuming a small axial surface crack inside a S/G tube. Internal pressure and residual stresses are considered as applied forces. Stress intensity factors along crack front, variation of crack shape and crack growth rate are obtained and discussed. It is noted that the aspect ratio of the crack is not depend on the initial crack shape but depend on the residual stress distribution.

• Computers and Concrete
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• v.26 no.6
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• pp.547-563
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• 2020

In this paper, the influence of axial compression ratio on the mechanical properties of new type joints of side span of rectangular concrete-filled steel tubular column-H-type steel beam is studied. Two new types of side-span joints of rectangular concrete-filled steel tubular column-H-type steel beam are designed and quasi-static tests of five new type joints with 1:2 scale reduction ratios are performed. The axial compression ratio of joint JD1 is 0.3, 0.4 and 0.5, and the axial compression ratio of joint JD2 is 0.3 and 0.5. In the joint test, different axial forces were applied to the top of the column according to different axial compression ratios, and low-cyclic reciprocating load was applied on the beam. The stress and strain distribution, beam and column deformation, limit state, failure process, failure mechanism, stiffness degradation, ductile deformation and energy dissipation capacity of the joint were measured and analyzed. The results show that: with the increase of axial compression ratio, the ultimate bearing capacity of the joint decreases slightly, the plastic deformation decreases, and the stiffness and ductility decrease. According to the energy dissipation curve of the specimen, the equivalent damping coefficient also increases with the increase of axial compression ratio in a certain range, indicating that the increase of axial compression ratio can improve the seismic performance of the joint to a certain extent. The finite element method is used to simulate the joint test, and the test results are in good agreement with the simulation results.

• Structural Engineering and Mechanics
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• v.54 no.4
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• pp.809-827
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• 2015

In this paper, seismic energy response of inelastic steel structures under earthquake excitations is investigated. For this purpose, a numerical procedure based on nonlinear dynamic analysis is developed by considering material, geometric and connection nonlinearities. Material nonlinearity is modeled by the inversion of Ramberg-Osgood equation. Nonlinearity caused by the interaction between the axial force and bending moment is also defined considering stability functions, while the geometric nonlinearity caused by axial forces is described using geometric stiffness matrix. Cyclic behaviour of steel connections is taken into account by employing independent hardening model. Dynamic equation of motion is solved by Newmark's constant acceleration method in the time history domain. Energy response analysis of space frames is performed by using this proposed numerical method. Finally, for the first time, the distribution of the different energy types versus time at the duration of the earthquake ground motion is obtained where in addition error analysis for the numerical solutions is carried out and plotted depending on the relative error calculated as a function of energy balance versus time.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1043-1044
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• 2011

This paper discusses the electromagnetic and mechanical design considerations to improve the design accuracy and power to mass ratio of multi-stack axial flux permanent magnet synchronous generator (AFPMSG). Design accuracy of multi-stack AFPMSG for direct drive wind turbine application is improved by considering magnetic flux leakages and fringing effect. FEM structural analysis is utilized to increase power to mass ratio of three-stack AFPMSG by reducing the rotor yoke thickness considering magnetic and centrifugal forces and Von Mises stress distribution.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.2
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• pp.131-134
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• 2011

In this study, we propose an optimal design and new fabrication method for a slim tactile sensor. Slim tactile sensor can detect 3-axial forces and has suitable flexibility for intelligent robot fingers. To amplify the contact signal, a unique table-shaped structure was attempted. A new layer-by-layer fabrication process for polymer micromachining that can make a 3D structure by using a sacrificial layer was proposed. A table-shaped epoxy sensing plate with four legs was built on top of a flexible polymer substrate. The plate can convert an applied force to a concentrated stress. Normal and shear forces can be detected by combining responses from metal strain gauges embedded in the polymer substrate. The optimal positions of the strain gauges are determined using the strain distribution obtained from finite element analysis.

• Steel and Composite Structures
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• v.30 no.5
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• pp.471-481
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• 2019

Beam-columns are structural members subjected to a combination of axial and bending forces. Lateral-torsional buckling is one of the main failure modes. Beam-columns that are bent about its strong axis may buckle out of the plane by deflecting laterally and twisting as the values of the applied loads reach a limiting state. Lateral-torsional buckling failure occurs suddenly in beam-column elements with a much greater in-plane bending stiffness than torsional or lateral bending stiffness. This study intends to establish a unique convenient closed-form equation that it can be used for calculating critical elastic lateral-torsional buckling load of beam-column in the presence of a known axial load. The presented equation includes first order bending distribution, the position of the loads acting transversely on the beam-column and mono-symmetry property of the section. Effects of axial loads, slenderness and load positions on lateral torsional buckling behavior of beam-columns are investigated. The proposed solutions are compared to finite element simulations where thin-walled shell elements including warping are used. Good agreement between the analytical and the numerical solutions is demonstrated. It is found out that the lateral-torsional buckling load of beam-columns with mono-symmetric sections can be determined by the presented equation and can be safely used in design procedures.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3287-3296
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• 1994

For the numerical computation of three-dimensional compressible flow field within a blade row in a centrifugal compressor, a quasi 3-dimensional solver which combines a reversible B-B flow and an irreversible H-S flow using finite element methods was developed. In a reversible B-B flow, the governing coordinates are modified in order to be applied to any type of turbomachinery, and two kinds of stream functions are introduced in order to make the Kutta condition exactly satisfied. In an irreversible H-S flow, the changes of entropy in the irreversible governing equations are determined not by empirical source but by the theoretical treatment of dissipation forces. The dissipation forces are obtained from the distribution of shear stresses in the flow passage which are given from the wall shear stresses using the exponential functions. A more accurate quasi-3-dimensional solver is established where the effect of body forces is involved in the non-axisymmetric H-S flow. Some numerical results obtained from authors' previous studies for axial flow machines assure that the present method is able to predict well as long as the flow is subsonic and not under strong viscous effect.

• Transactions of the Society of Information Storage Systems
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• v.1 no.2
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• pp.169-174
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• 2005

Current information storage devices read/write data on the rotating disk. The axial vibration of a rotating disk should be suppressed for the successful operation of the device. Information storage devices widely used in these days adopt relatively thick disk which is stiff enough to suppress axial vibration under allowable limit. However, the thickness of the disk is going to be thinner and thinner as the small form factor of the devices is getting preferred by the consumer. In this study, a stabilizer system, which is composed with 8 air bearings, is proposed for suppressing the axial vibration of a $95{\mu}m$ thick PC disk in a non-contacting manner. The performance of the stabilizer system is simulated by numerical computation and then confirmed its results through a series of experiment. A thin and flexible disk has various vibration modes when it rotates in high speed. The stabilizer system generates positive as well as negative pressure due to the rotation of flexible disk so that the force due to the pressure distribution pushes and pulls rotating disk in a non-contacting manner. The balance between positive and negative pressure forces can be obtained by adjusting the area and the slope of the air bearing surface. The axial vibration of the flexible disk of 120mm diameter is suppressed successfully from over $1000{\mu}m$ to $30{\mu}m$ peak-to-peak value at the rotational speed of 5,000rpm.

• Wind and Structures
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• v.16 no.6
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• pp.579-601
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• 2013

Interference effects are of considerable concern for group hyperboloidal cooling towers, but evaluation methods and results are different from each other because of the insufficient understanding on the structure behavior. Therefore, the mechanical performance of hyperboloidal cooling tower shell under wind loads was illustrated according to some basic properties drawn from horizontal rings and cantilever beams. The hyperboloidal cooling tower shell can be regarded as the coupling of horizontal rings and meridian cantilever beams, and this perception is beneficial for understanding the mechanical performance under wind loads. Afterwards, the mean external latitude wind pressure distribution, CP(${\theta}$), was artificially adjusted to pursue the relationship between different CP(${\theta}$) and wind-induced responses. It was found that the maximum responses in hyperboloidal cooling tower shell are primarily dominated by the non-uniformity of CP(${\theta}$) but not the local pressure amplitude CP or overall resistance/drag coefficient CD. In all the internal forces, the maximum amplitude of meridian axial tension shows remarkable sensitivity to the variation of CP(${\theta}$) and it's also the controlling force in structure design, so it was selected as an indicator to evaluate the influence of CP(${\theta}$) on responses. Based on its sensitivity to different adjustment parameters of CP(${\theta}$), an comprehensive response influence factor, RIF, was deduced to assess the meridian axial tension for arbitrary CP(${\theta}$).