• Structural Engineering and Mechanics
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• v.35 no.5
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• pp.555-570
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• 2010

Shallow fixed arches have a nonlinear primary equilibrium path with limit points and an unstable postbuckling equilibrium path, and they may also have bifurcation points at which equilibrium bifurcates from the nonlinear primary path to an unstable secondary equilibrium path. When a shallow fixed arch is subjected to a central step load, the load imparts kinetic energy to the arch and causes the arch to oscillate. When the load is sufficiently large, the oscillation of the arch may reach its unstable equilibrium path and the arch experiences an escaping-motion type of dynamic buckling. Nonlinear dynamic buckling of a two degree-of-freedom arch model is used to establish energy criteria for dynamic buckling of the conservative systems that have unstable primary and/or secondary equilibrium paths and then the energy criteria are applied to the dynamic buckling analysis of shallow fixed arches. The energy approach allows the dynamic buckling load to be determined without needing to solve the equations of motion.

• Proceedings of the KSR Conference
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• 2001.05a
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• pp.295-302
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• 2001

The lateral stability of curved continuous welded rail (CWR) is studied fur buckling prevention. This study includes the influences of vehicle induced loads on the thermal buckling behavior of straight and curved CWR tracks. quasi-static loads model is assumed to determine the uplift region, which occurs due to the vertical track deformation induced by wheel loads of vehicle. Parametric numerical analyses are performed to calculate the upper and lower critical buckling temperatures of CWR tracks. The parameters include track lateral resistance, track curvature, longitudinal stiffness, tie-ballast friction coefficient, axle load, truck center spacing, and the ratio of lateral to vertical vehicle load. This study provides a guideline for the improvement or stability for dynamic buckling in on tracks.

• Journal of Korean Association for Spatial Structures
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• v.20 no.4
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• pp.149-158
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• 2020

The governing equation for a dome-type shallow spatial truss subjected to a transverse load is expressed in the form of the Duffing equation, and it can be derived by considering geometrical non-linearity. When this model under constant load exceeds the critical level, unstable behavior is appeared. This phenomenon changes sensitively as the number of free-nodes increases or depends on the imperfection of the system. When the load is a periodic function, more complex behavior and low critical levels can be expected. Thus, the dynamic unstable behavior and the change in the critical point of the 3-free-nodes space truss system were analyzed in this work. The 4-th order Runge-Kutta method was used in the system analysis, while the change in the frequency domain was analyzed through FFT. The sinusoidal wave and the beating wave were utilized as the periodic load function. This unstable situation was observed by the case when all nodes had same load vector as well as by the case that the load vector had slight difference. The results showed the critical buckling level of the periodic load was lower than that of the constant load. The value is greatly influenced by the period of the load, while a lower critical point was observed when it was closer to the natural frequency in the case of a linear system. The beating wave, which is attributed to the interference of the two frequencies, exhibits slightly more behavior than the sinusoidal wave. And the changing of critical level could be observed even with slight changes in the load vector.

• Journal of Korean Society of Steel Construction
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• v.12 no.6
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• pp.727-736
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• 2000

The present study investigates the influences of vehicle induced loads on the thermal buckling behavior of straight and curved continuous welded rail (CWR) tracks. Quasi-static loads model is assumed to determine the uplift region, which occurs due to the vertical track deflection induced by wheel loads of vehicle. The lateral loads of vehicle induced by weight, the speed, the superelevation and curvature of track, and other dynamic vehicle track interaction, are included in the ratio of lateral to vertical vehicle load. Parametric numerical analyses are perfomed to calculate the upper and lower critical buckling temperatures of CWR tracks, and the comparison between the results of this work and the previous results without vehicle is also included.

• Steel and Composite Structures
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• v.27 no.6
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• pp.691-702
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• 2018

This paper presents experimental and analytical results of fiber reinforced polymer (FRP) confined steel tubular columns under transverse impact loads. Influences of applied impact energy, thickness of FRP jacket and impact position were discussed in detail, and then the impact responses of FRP confined steel tubes were compared with bare steel tubes. The test results revealed that the FRP jacket contributes to prevent outward buckling deformation of steel at the clamped end and inward buckling of steel at the impact position. For the given applied impact energy, specimens wrapped with one layer and three layers of FRP have the lower peak impact loads than those of the bare steel tubes, whereas specimens wrapped with five layers of FRP exhibit the higher peak impact loads. All the FRP confined steel tubular specimens displayed a longer duration time than the bare steel tubes under the same magnitude of impact energy, and the specimen wrapped with one layer of FRP had the longest duration time. In addition, increasing the applied impact energy leads to the increase of peak impact load and duration time, whereas increasing the distance of impact position from the clamped end results in the decrease of peak impact load and the increase of duration time. The dynamic analysis software Abaqus Explicit was used to simulate the mechanical behavior of FRP confined steel tubular columns, and the numerical results agreed well with the test data. Analytical solution for lateral displacement of an equivalent cantilever beam model subjected to impact load was derived out. Comparison of analytical and experimental results shows that the maximum displacement can be precisely predicted by the present theoretical model.

• Composites Research
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• v.35 no.4
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• pp.269-276
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• 2022

In this paper, a composite stiffened panel was fabricated using a three-dimensional weaving method that can reduce the risk of delamination, and mechanical properties such as buckling load and natural frequency were investigated. The preform of the stringer and skin of the stiffened panel were fabricated in one piece using T800 grade carbon fiber and then, resin (EP2400) was injected into the preform. The compression test and natural frequency measurement were performed for the stiffened panel, and the results were compared with the finite element analyses. In order to compare the performance of 3D weaving structures, the stiffened panels with the same configuration were fabricated using UD and 2D plain weave (fabric) prepregs. Compared to the tested buckling load of the 3D woven panel, the buckling loads of the stiffened panels of UD prepreg and 2D plain weave exhibited +20% and -3% differences, respectively. From this study, it was confirmed that the buckling load of the stiffened panel manufactured by 3D weaving method was lower than that of the UD prepreg panel, but showed a slightly higher value than that of the 2D plain weave panel.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.2
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• pp.250-263
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• 2001

The up and down speed of heddle frames that produce woven cloth by insertion of weft yarns between warp yarns has been increased recently much for productivity improvement, which induces higher inertial stresses and vibrations in the heddle frame. the heddle frame is required to reduce its mass because the heddle frame contributes the major portion of the stresses in the heddle frames during accelerating and decelerating. Conventional aluminum heddle frames have fatigue life of around 5 months at 550rpm due to their low fatigue flexural strength as well as low bending stiffness. In this work, since carbon/epoxy composite materials have high specific fatigue strength(S/p), high specific modulus(E/p), high damping capacity and sandwich construction results in lower deflections and higher buckling resistance, the sandwich structure composed of carbon/epoxy composite skins and polyurethane foam were employed for the high-speed heddle frame. The design map for the sandwich beams was accomplished to determine the optimum thickness and the stacking sequences for the heddle frames. Also the effects of the number of ribs on the stress of the heddle frame were investigated by FEM analyses. Finally, the high-speed heddle frames were manufactured with sandwich structures and the static and dynamic properties of the aluminum and the composite heddle frames were tested and compared with each other.

• Steel and Composite Structures
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• v.45 no.1
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• pp.83-100
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• 2022

Timber is one of the few natural, renewable building materials and glulam is a type of engineering wood product. In the present work, timber-based braces are applied for retrofitting midrise Special Moment Resisting Frame (SMRF) using two types of timber base braces (Timber base glulam, and hybrid Timber-Steel-BRB) as alternatives for retrofitting by traditional steel bracings. The improving effects of adding the bracings to the SMRF on seismic characteristics of the frame are evaluated using load-bearing capacity, energy dissipation, and story drifts of the frame. For evaluating the retrofitting effects on the seismic performance of SMRF, a five-story SMRF is considered unretofitted and retrofitted with steel-hollow structural section (HSS) brace, Glued Laminated Timber (Glulam) brace, and hybrid Timber-Steel BRB. Using OpenSees structural analyzer, the performance are investigated under pushover, cyclic, and incremental loading. Results showed that steel-HSS, timber base Glulam, and hybrid timber-steel BRB braces have more significant roles in energy dissipation, increasing stiffness, changing capacity curves, reducing inter-story drifts, and reducing the weight of the frames, compared by steel bracing. Results showed that Hybrid BRB counteract the negative post-yield stiffness, so their use is more beneficial on buildings where P-Delta effects are more critical. It is found that the repair costs of the buildings with hybrid BRB will be less due to lower residual drifts. As a result, timber steel-BRB has the best energy dissipation and seismic performance due to symmetrical and stable hysteresis curves of buckling restrained braces that can experience the same capacities in tension and compression.