• 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.

• Structural Monitoring and Maintenance
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• v.9 no.3
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• pp.259-270
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• 2022

This study explores the use of the recently developed "strain-sensing smart skin" (S⁴) method for noncontact strain measurements on cement-based samples. S⁴ sensors are single-wall carbon nanotubes dilutely embedded in thin polymer films. Strains transmitted to the nanotubes cause systematic shifts in their near-infrared fluorescence spectra, which are analyzed to deduce local strain values. It is found that with cement-based materials, this method is hampered by spectral interference from structured near-infrared cement luminescence. However, application of an opaque blocking layer between the specimen surface and the nanotube sensing film enables interference-free strain measurements. Tests were performed on cement, mortar, and concrete specimens with such modified S⁴ coatings. When specimens were subjected to uniaxial compressive stress, the spectral peak separations varied linearly and predictably with induced strain. These results demonstrate that S⁴ is a promising emerging technology for measuring strains down to ca. 30 𝜇𝜀 in concrete structures.

• Steel and Composite Structures
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• v.42 no.4
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• pp.447-458
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• 2022

Cold-formed steel (CFS) sections are thin-walled, therefore, more susceptible to different types of geometric imperfections. Global type of geometric imperfections has a significant impact on the load-carrying capacity of flexural members. This paper reports an experimental study that discusses the influence of global imperfections on the flexural response of CFS built-up I-beams composed of two lipped channels, with simply supported ends, under four-point loading. Global imperfections of magnitude over eight times the maximum permissible ones were induced in the specimens, leading to their distress. Using various simple stiffening schemes, the capacity and stiffness of the distressed specimens were improvised. The performance comparisons were made based on the maximum loads resisted, flexural stiffnesses offered, and failure modes experienced by the specimens. As experimental data on such distressed specimens are currently lacking in the literature, the test results of the present study will provide the necessary data needed by future researchers to numerically extend this study further, which will help in the development of necessary design guidelines for the same. The stiffening schemes significantly improved the structural efficiency of distressed specimens in terms of strength and stiffness, by over 60%. As a result, an effective and time-saving solution to such realistic structural engineering problems is given.

• Steel and Composite Structures
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• v.43 no.6
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• pp.689-706
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• 2022

Thin-walled square concrete-filled double steel tubular (CFDST) columns composed of the inner circular tube filled with concrete can be used to carry the large axial loads or strengthen existing CFST columns in composite constructions. This paper reports an experimental program carried out on short square CFDST columns loaded concentrically. The influences of important column parameters on the post-buckling performance of such columns are investigated. Test results exhibit that the inner circular tube significantly improves the ultimate loads and the ductility of such columns compared to conventional concrete-filled steel tubular (CFST) and double-skin CFST (DCFST) columns with an inner void. A mathematical model developed is used to simulate the ultimate strengths and load-strain curves of such columns loaded axially. Furthermore, the ultimate strengths of such columns are predicted using existing codified design models for conventional CFST columns as well as the formulas proposed by previous researchers and compared against a large database comprising 500 CFDST columns. Lastly, an accurate artificial neural network model is developed for the practical applications of such columns under axial loading.

• Structural Engineering and Mechanics
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• v.87 no.6
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• pp.541-554
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• 2023

An unbraced cantilever beam subjected to loads which cause bending about the major axis may buckle in a flexuraltorsional mode by deflecting laterally and twisting. For the efficient design of these structures, design engineers require a simple accurate equation for the elastic flexural-torsional buckling load. Existing solutions for the flexural-torsional buckling of cantilever beams have mainly been derived by numerical methods which are tedious to implement. In this research, an attempt is made to derive a theoretical equation by the energy method using different buckled shapes. However, the results of a finite element flexural-torsional buckling analysis reveal that the buckled shapes for the lateral deflection and twist rotation are different for cantilever beams. In particular, the buckled shape for the twist rotation also varies with the section size. In light of these findings, the finite element flexural-torsional buckling analysis was then used to derive simple accurate equations for the elastic buckling load and moment for cantilever beams subjected to end point load, uniformly distributed load and end moment. The results are compared with previous research and it was found that the equations derived in this study are accurate and simple to use.

• Computers and Concrete
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• v.31 no.5
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• pp.371-384
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• 2023

Precast roofing systems employing prestressed elements often serve as smart structural solutions for the construction of industrial buildings. The precast concrete elements usually employed are highly engineered, and often consist in thin-walled members, characterised by a complex behaviour in fire. The present study was carried out after a fire event damaged a precast industrial building made with prestressed beam and roof elements, and non-prestressed curved barrel vault elements interposed in between the spaced roof elements. As a consequence of the exposure to the fire, the main elements were found standing, although some locally damaged and distorted, and the local collapse of few curved barrel vault elements was observed in one edge row only. In order to understand and interpret the observed structural performance of the roof system under fire, a full fire safety engineering process was carried out according to the following steps: (a) realistic temperature-time curves acting on the structural elements were simulated through computational fluid dynamics, (b) temperature distribution within the concrete elements was obtained with non-linear thermal analysis in variable regime, (c) strength and deformation of the concrete elements were checked with non-linear thermal-mechanical analysis. The analysis of the results allowed to identify the causes of the local collapses occurred, attributable to the distortion caused by temperature to the elements causing loss of support in early fire stage rather than to the material strength reduction due to the progressive exposure of the elements to fire. Finally, practical hints are provided to avoid such a phenomenon to occur when designing similar structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.575-582
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• 2010

In recent years, several rapid-mold-heating techniques that can be used for the injection molding of thin-walled parts or micro/nano structures have been developed. High-frequency induction heating, which involves heating by electromagnetic induction, is an efficient method for the rapid heating of mold surfaces. The present study proposes an integrated numerical model of the high-frequency induction heating process and the resulting injection molding process. To take into account the effects of thermal boundary conditions in induction heating, we carry out a fully integrated numerical analysis that combines electromagnetic field calculation, heat transfer analysis, and injection molding simulation. The proposed integrated simulation is extended to the injection molding of a thin-wall part, and the simulation results are compared with the experimental findings. The validity of the proposed simulation is discussed according to the ways of the boundary condition imposition.

• Smart Structures and Systems
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• v.8 no.1
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• pp.139-155
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• 2011

Polymeric thin-film assemblies whose bulk electrical conductivity and mechanical performance have been enhanced by single-walled carbon nanotubes are proposed for measuring strain and corrosion activity in metallic structural systems. Similar to the dermatological system found in animals, the proposed self-sensing thin-film assembly supports spatial strain and pH sensing via localized changes in electrical conductivity. Specifically, electrical impedance tomography (EIT) is used to create detailed mappings of film conductivity over its complete surface area using electrical measurements taken at the film boundary. While EIT is a powerful means of mapping the sensing skin's spatial response, it requires a data acquisition system capable of taking electrical impedance measurements on a large number of electrodes. A low-cost wireless impedance analyzer is proposed to fully automate EIT data acquisition. The key attribute of the device is a flexible sinusoidal waveform generator capable of generating regulated current signals with frequencies from near-DC to 20 MHz. Furthermore, a multiplexed sensing interface offers 32 addressable channels from which voltage measurements can be made. A wireless interface is included to eliminate the cumbersome wiring often required for data acquisition in a structure. The functionality of the wireless impedance analyzer is illustrated on an experimental setup with the system used for automated acquisition of electrical impedance measurements taken on the boundary of a bio-inspired sensing skin recently proposed for structural health monitoring.

• The Korean Journal of Pesticide Science
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• v.2 no.1
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• pp.40-45
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• 1998

An antagonistic fungus inhibiting growth of various phytopathogenic fungi was isolated from greenhouse soils and identified. Mophological features of fruiting structures on potato dextrose agar and colorless globose to ovate heavy walled hyaline cells from the vegetative mycelium grown on MY20 agar indicate that this antagonist is Aspergillus terreus. The antagonistic activity is due to the production of antifungal compounds. An antifungal compound was purified from its culture filtrate using chloroform extraction, column chromatography, and thin layer chromatography. The purified antibiotic was effective to various phytopathogenic fungi and identified as butyrolactone I. $ED_{50}$ values measured by petri-plate assay through effective dosage(ED)-probit analysis were 9.7, 13.7, 23.3, 42.6 and 102.7 ppm on Botrytis cinerea, Rhizoctonia solani, Pythium ultimum, Phytophthora capsici, and Fusarium oxysporum, respectively.

• Journal of Power System Engineering
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• v.15 no.1
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• pp.24-31
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• 2011

Rectangular box type structures are used in many fields of civil, mechanical and marine engineering. Especially, Most ship structures are often in contact with inner or outer fluid, like ballast, fuel and stem tanks. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance with exciting force of engine and propeller. Vibration characteristics of these thin walled tanks in contact with fluid near engine and propeller are strongly affected by added mass of containing fluid. Therefore it is essentially important to estimate the added mass effect to predict vibration of the tanks. Many authors have studied vibration of rectangular tanks containing fluid. Few research on dynamic interaction among tank walls filled with fluid are reported in the vibration of rectangular tanks recently. In case of rectangular tanks, structural coupling between adjacent panels and effect of vibration modes of multiple panels on added mass of water have to be considered. In the previous report, a numerical analysis is performed for the coupling effect between panels of a tank on added mass of containing fluid, the effect of structural constraint between panels on each vibration mode for fluid region, and mode characteristics in accordance with changing breadth of the plates by using finite element method for plates and boundary element method for fluid region. In this paper, the coupling effect between panels of a tank on added mass of containing fluid, the effect of structural constraint between panels on each vibration mode for fluid region, and mode characteristics in accordance with changing length, thickness, and boundary condition of the plates are investigated numerically and discussed.