• Wind and Structures
• /
• v.26 no.4
• /
• pp.205-214
• /
• 2018

In this paper, the thermo-mechanical buckling characteristics of functionally graded (FG) size-dependent Timoshenko nanobeams subjected to an in-plane thermal loading are investigated by presenting a Navier type solution for the first time. Material properties of FG nanobeam are supposed to vary continuously along the thickness according to the power-law form and the material properties are assumed to be temperature-dependent. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. The nonlocal governing equations are derived based on Timoshenko beam theory through Hamilton's principle and they are solved applying analytical solution. According to the numerical results, it is revealed that the proposed modeling can provide accurate critical buckling temperature results of the FG nanobeams as compared to some cases in the literature. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as material distribution profile, small scale effects and aspect ratio on the critical buckling temperature of the FG nanobeams in detail. It is explicitly shown that the thermal buckling of a FG nanobeams is significantly influenced by these effects. Numerical results are presented to serve as benchmarks for future analyses of FG nanobeams.

• Advances in aircraft and spacecraft science
• /
• v.2 no.4
• /
• pp.403-425
• /
• 2015

This work is focused on the definition and the analysis of both complete and incomplete similitudes for the dynamic responses of thin shells. Previous numerical and experimental investigations on both structural and structural-acoustic systems motivated this further analysis, mainly centred on the incomplete (distorted) similitudes. These similitudes and the associated scaling laws are defined by using the classical modal approach (CMA) and by invoking also the Energy Distribution Approach (EDA) in order to take into account both the cinematic and energetic items. The whole procedure is named SAMSARA: Similitude and Asymptotic Models for Structural-Acoustic Research and Applications. A brief summary of the procedure is herein given and the attention is paid to the analytical models of thin stiffened and unstiffened cylindrical shells. By using the well-known smeared model, the stiffened cylinder equations are used as general framework to analyse the possibility to define exact (replicas) or distorted similitudes (avatars). Despite the extreme simplicity of the proposed models, the results are really encouraging. The final aim is to define equivalent models to be used in laboratory measurements.

• Structural Engineering and Mechanics
• /
• v.31 no.1
• /
• pp.75-91
• /
• 2009

It is known that retaining walls were severely damaged as well in the most recent earthquakes having occurred in the countries in the active seismic belts of the world. This damage can be ascribed to the calculation methods used for the designs of retaining walls in the event of their constructions and employment having been accurately carried out. Generally simplified pseudo-static methods are used in the analysis of retaining walls with analytical methods and soil-structure interaction are not considered. In view of these circumstances, in this article by taking soil interaction into consideration, linear and nonlinear behaviours of retaining walls are analyzed with the assistance of LUSAS which is one of the structural analysis programs. This investigations are carried out per LUSAS which employs the finite element method as to the Erzincan (1992) Earthquake North-South component and the obtained findings are compared with the ones obtained from the method suggested in Eurocode-8, which is still effective today, and Mononobe-Okabe method. Not only do the obtained results indicate the distribution and magnitude of soil pressures are depend on the filling soil but on the foundation soil as well and nonlinear effects should be considered in designs of these walls.

• Journal of Soil and Groundwater Environment
• /
• v.20 no.4
• /
• pp.22-30
• /
• 2015

For the preliminary investigations of the bioclogging on groundwater artificial recharge system, studies for conditions and analytical methods of biofilm formation on sediments were performed. Based on the tested results, following conditions were determined for biofilm formation on batch process: optimum period for biofilm formation (30 days), the proper inoculating water (pond water), medium (minimum salt medium with 0.1% yeast extract). Procedures for the measurement of ATP and DHA were also determined. Biomass extract was used for ATP measurement, while sediment itself for DHA. Effects of metals on the biofilm formation were investigated under the determined conditions. Different sensitivities and orders were found depending on tested metals and measurement methods. In general, biomass measurement by ATP and viable cell count showed higher sensitivity than that of DHA. Following toxicity orders were also appeared for ATP and viable cell: Cu ≈ Cd > As(III).

• Steel and Composite Structures
• /
• v.16 no.3
• /
• pp.325-337
• /
• 2014

The strength and buckling problem of a five layer sandwich beam under axial compression or bending is presented. Two faces of the beam are thin aluminium sheets and the core is made of aluminium foam. Between the faces and the core there are two thin binding glue layers. In the paper a mathematical model of the field of displacements, which includes a share effect and a bending moment, is presented. The system of partial differential equations of equilibrium for the five layer sandwich beam is derived on the basis of the principle of stationary total potential energy. The equations are analytically solved and the critical load is obtained. For comparison reasons a finite element model of the beam is formulated. For the case of bended beam the static analysis has been performed to obtain the stress distribution across the height of the beam. For the axially compressed beam the buckling analysis was carried out to determine the buckling load and buckling shape. Moreover, experimental investigations are carried out for two beams. The comparison of the results obtained in the analytical and numerical (FEM) analysis is shown in graphs and figures. The main aim of the paper is to present an analytical model of the five layer beam and to compare the results of the theoretical, numerical and experimental analyses.

• Advances in nano research
• /
• v.4 no.2
• /
• pp.85-111
• /
• 2016

In this paper, the classical and non-classical boundary conditions effect on free vibration characteristics of functionally graded (FG) size-dependent nanobeams are investigated by presenting a semi analytical differential transform method (DTM) for the first time. Three kinds of mathematical models, namely; power law (P-FGM), sigmoid (S-FGM) and Mori-Tanaka (MT-FGM) distribution are considered to describe the material properties in the thickness direction. The nonlocal Eringen theory takes into account the effect of small size, which enables the present model to become effective in the analysis and design of nanosensors and nanoactuators. Governing equations are derived through Hamilton's principle and they are solved applying semi analytical differential transform method. The good agreement between the results of this article and those available in literature validated the presented approach. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as small scale effects, spring constant factors, various material compositions and mode number on the normalized natural frequencies of the FG nanobeams in detail. It is explicitly shown that the vibration of FG nanobeams is significantly influenced by these effects. Numerical results are presented to serve as benchmarks for future analyses of FG nanobeams.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.23 no.1
• /
• pp.31-42
• /
• 2019

In this study, the results of an analytical investigation on the seismic behavior of two residential 4-story bearing wall buildings with pilotis, each of which has symmetric or unsymmetric wall arrangement at their piloti level, are presented. The dynamic characteristics and lateral resistance of the piloti buildings were investigated through linear elastic and nonlinear static analyses. According to the results, the analytical natural period of vibration of the piloti buildings were significantly shorter than the fundamental period calculated in accordance with KBC 2016. In the initial elastic behavior, the walls resisting in-plane shear contributed to the lateral stiffness and strength, while the contribution of columns resisting flexural moments in double curvature was limited. However, after the shear cracking and yielding of the walls occurred, the columns significantly contributed to the residual strength and ductility. Based on those investigations, design recommendations of low-rise bearing wall buildings with piloti configuration are given.

• Steel and Composite Structures
• /
• v.51 no.3
• /
• pp.325-335
• /
• 2024

Yielding dampers exhibit varying cyclic behavior based on their geometry. These dampers not only increase the energy dissipation of the structure but also increase the strength and stiffness of the structure. In this study, parametric investigations were carried out to explore the impact of angled U-shape damper (AUSD) dimensions on its cyclic behavior. Initially, the numerical model was calibrated using the experimental specimen. Subsequently, analytical equations were presented to calculate the yield strength and elastic stiffness, which agreed with the experimental results. The outcomes of the parametric studies encompassed ultimate strength, effective stiffness, energy dissipation, and equivalent viscous damper ratio (EVDR). These output parameters were compared with similar dampers. Also, the magnitude of the effect of damper dimensions on the results was investigated. The results of parametric studies showed that the yield strength is independent of the damper width. The length and thickness of the damper have the greatest effect on the elastic stiffness. Reducing length and width resulted in increased energy dissipation, effective stiffness, and ultimate strength. Damper width had a more significant effect on EVDR than its length. On average, every 5 mm increase in damper thickness resulted in a 3.6 times increase in energy dissipation, 3 times the effective stiffness, and 3 times the ultimate strength of the model. Every 15 mm reduction in damper width and length increased energy dissipation by 14% and 24%, respectively.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.23 no.3
• /
• pp.243-249
• /
• 2013

Objectives: This study assessed the status of domestic industrial hygiene laboratories using data from on-site investigation for revision of quality control systems in 2012-2013. Methods: The target laboratories were 60 industrial hygiene laboratories chosen by random selection and nationwide distribution which had participated in on-site investigations for revision of quality control systems from March 2012 to August 2013. The investigation was performed on-site following standard quality control procedures. The score between each group was compared using Mann-Whitney and Kruskal-Wallis tests, and the correlation between analytical career, sex, academic major of analyst and score of analytical performance was expressed as Spearman's rank correlation coefficient. Results: The assessment revealed that the items to be improved, in sequence, were effort at staff training (score 65.5), ability to calculate data (score 73.4), establishment of internal quality control guidelines (score 75.7), laboratory facilities (score 77.1), degree of understanding and skill at gas chromatography (score 77.1). Analysis performance showed a positive correlation with career of analyst (r=0.56, p<0.01). Conclusions: The practice of on-site investigation for quality control systems showed the current status of industrial hygiene laboratories in the first trial. There were many laboratories which needed improvement and development of analytical systems. This assessment can provide information for the systematic operation and improvement of facilities at each laboratory. Further practice of this investigation will lead to a proficiency testing and accreditation system for autonomous quality control as is the practice in many countries, rather than mandatory practice by legal regulation.

• Journal of Korean Society of Steel Construction
• /
• v.25 no.6
• /
• pp.613-622
• /
• 2013

Numerous water gates have been constructed and are under construction for the control of water level because, due to the topographical characteristics of mountainous area, many small size rivers are developed in Korean peninsula. Among the water gates, movable water gates are more efficient to control water level than the fixed water gates. By the field application of the movable water gates, many problems associated with the fixed water gates have been mitigated. The problems include the bottom water pollution, the change of habitats for the riparian organisms, etc. This is the reason to increase the field application of movable water gates. In the paper we present the result of analytical investigation pertaining to the structural behavior of multistage overturning movable water gate which is one of the movable water gates. In the analytical investigations, the finite element analysis on the constructed water gate has been conducted for illustration purposes and it was found that the multistage movable water gate is much better than the fixed and/or existing movable water gates in the point of structural and environmental performances.