• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.7 s.124
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• pp.605-610
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• 2007

In this paper a dynamic behavior(natural frequency) of a cracked cantilever beam subjected to follower force is presented. In addition, an analysis of the flutter and buckling instability of a cracked cantilever beam subjected to a follower compressive load is presented. Based on the Euler-Bernoulli beam theory, the equation of motion can be constructed by using the Lagrange's equation. The vibration analysis on such cracked beam is conducted to identify the critical follower force for flutter instability based on the variation of the first two resonant frequencies of the beam. Besides, the effect of the crack's intensity and location on the flutter follower force is studied. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations.

• Journal of Korean Society of Steel Construction
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• v.18 no.4
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• pp.447-456
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• 2006

In this study, a torsional test for U-type steel box girders was performed to observe the effects of the kind of panel for top lateral walateral bracings on the torsional behavior of the U-type steel girder system. For the structural tests, the test specimen with a two-thirds scale of the system actually constructed in the field was used. In the torsional test to observe the efects of top lateral bracings, the most economical arrangement of the top lateral bracing was found to be the panel width to length ratio of 1:1.5 with the inclined angle of $40^{\circ}$.

• Steel and Composite Structures
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• v.27 no.5
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• pp.545-554
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• 2018

This study presents a novel method of improving the strength and stiffness of cold-formed steel (CFS) beams. Flexural members are primary members in most of the structures. Hence, there is an urgent need in the CFS industry to look beyond the conventional CFS beam sections and develop novel techniques to address the severe local buckling problems that exist in CFS flexural members. The primary objective of this study was to develop new CFS composite beam sections with improved structural performance and economy. This paper presents an experimental study conducted on different CFS composite beams with simply supported end conditions under four point loading. Material properties and geometric imperfections of the models were measured. The test strengths of the models are compared with the design strengths predicted by using Australian/New Zealand Standard for cold-formed steel structures. Furthermore, to ensure high precision testing, a special testing rig was also developed for testing of long span beams. The description of test models, testing rig features and test results are presented here. For better interpretation of results, a comparison of the test results with a hot rolled section is also presented. The test results have shown that the proposed CFS composite beams are promising both in terms of better structural performance as well as economy.

• Structural Engineering and Mechanics
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• v.62 no.6
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• pp.695-702
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• 2017

In this work, a nonlocal zeroth-order shear deformation theory is developed for the nonlinear postbuckling behavior of nanoscale beams. The beauty of this formulation is that, in addition to including the nonlocal effect according to the nonlocal elasticity theory of Eringen, the shear deformation effect is considered in the axial displacement within the use of shear forces instead of rotational displacement like in existing shear deformation theories. The principle of virtual work together of the nonlocal differential constitutive relations of Eringen, are considered to obtain the equations of equilibrium. Closed-form solutions for the critical buckling load and the amplitude of the static nonlinear response in the postbuckling state for simply supported and clamped clamped nanoscale beams are determined.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1063-1071
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• 2008

A piezoceramic unimoph actuator can produce a relatively larger actuation force and actuation displacement when a proper compressive load is applied during operation, because the compressive stress causes material nonlinear behavior in the piezoceramic layer and triggers mechanical buckling. In this paper, we examined effects of the actuator under compression on the flapping angle and aerodynamic force generation capability. Effects of wing shape and passive wing rotation angle on the aerodynamic force production were also investigated. The average vertical force acquired by a 2D CFD simulation for an artificial wing showed a good agreement with the measured one by the experiment.

• Composites Research
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• v.12 no.6
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• pp.65-73
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• 1999

Crippling stress and failure behavior of Z-section graphite/epoxy composite laminated stringers are investigated by the nonlinear finite element method. Stringers are idealized using 9-node laminated shell element. The complete unloading model is introduced into the finite element method for the progressive failure analysis. A modified Riks method is used to trace the post-failure equilibrium path after local buckling. Finite element results are validated with previous experimental results. The results show that the most important parameter affecting the crippling stress of Z-section stringers is the flange width. In terms of stacking sequence. the highest cripping stress is found at the stringer with $[{\pm}45/0/90]s$ lamination.

• Earthquakes and Structures
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• v.17 no.6
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• pp.623-633
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• 2019

A large number of available concrete buildings designed only considering gravity load that require seismic rehabilitation because of failure to meet plasticity criteria. Using steel bracings are a common type of seismic rehabilitation. The eccentric bracings with vertical link reduce non-elastic deformation imposed on concrete members as well as elimination of probable buckling problems of bracings. In this study, three concrete frames of 10, 15, and 20 stories designed only for gravity load have been considered for seismic improvement using performance-based plastic design. Afterwards, nonlinear time series analysis was employed to evaluate seismic behavior of the models in two modes including before and after rehabilitation. The results revealed that shear link can yield desirable performance with the least time, cost and number of bracings of concrete frames. Also, it was found that the seismic rehabilitation can reduce maximum relative displacement in the middle stories about 40 to 80 percent. Generally, findings of this study demonstrated that the eccentric bracing with vertical link can be employed as a suitable proxy to achieve better seismic performance for existing high rise concrete frames.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.922-927
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• 2006

There is a concern with worldwide deterioration of highway bridges, particularly reinforced concrete. The advantages of fibre reinforced plastic(FRP) composites over conventional materials motivate their use in highway bridges for replacement of structures. Recently, an FRP deck has been installed on a state highway, located in New York State, as an experimental project. In this paper, a systematic approach for analysis of this FRP deck bridge is presented. Multi-step linear numerical analyses have been performed using the finite element method to study the structural behavior and the possible failure mechanism of the FRP deck-superstructure system Deck's self-weight and ply orientations at the interface between steel girders and FRP deck are considered in this study. From this research, the results of the numerical analyses were corroborated with field test results. Analytical results reveal several potential failure mechanism for the FRP deck and truss bridge system The results presented in this study may be used to propose engineering design guideline for new and replacement FRP bridge deck structure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.1
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• pp.70-76
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• 2008

Periodic cellular metals (PCMs) are actively being investigated because of their excellent specific strength and stiffness, and multi-functionality such as a heat disperse structure bearing external loading. The Kagome truss PCM has been proved that it has higher resistance to plastic buckling and lower anisotropy than other truss PCMs. In this paper, the out-of-plane compressive responses of the WBK specimens have been measured, theoretically predicted and numerically analyzed. Three specimens of two-layered WBK are fabricated and tested for measuring the responses. The peak stress of compressive behavior and effective elastic modulus are predicted based on the equilibrium equation and elastic energy conservation. Moreover, the structure of the specimen is modeled using the commercial mesh generation code, PATRAN and the finite element analysis for the model under the compression is carried out using the commercial FE code, ABAQUS. Finally, the obtained results are compared with each other to analyze the compressive characteristics of Wire-woven Bulk Kagome (WBK).

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.453-458
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• 2008

Under driving condition, A vehicle experiences various kinds of loads, which brings on the buckling and fracture of suspension systems. Lower control arm (LCA), which consists of 2 bush joints and 1 ball joint connection, is the one of the most important parts in the suspension system. The bush joints absorb the impact load and reduce the vibration from the road. When analyzing the LCA behavior, it is important to understand the material properties and boundary conditions of bushing systems correctly, because of the nonlinearity characteristics of the rubber. In this paper, in order to predict the large scale deformation of the LCA more precisely, three factors are newly suggested, that is, coupling of bush stiffness between translation and rotation, bush extraction force and maximum rotation angle of ball joint. LCA stiffness is estimated by CAE and component test. Analysis and test results are almost same and the validity of considering three factors in LCA analysis is verified.