• Computers and Concrete
• /
• v.18 no.5
• /
• pp.1053-1063
• /
• 2016

As concrete is most usable material in construction industry it's been required to improve its quality. Nowadays, nanotechnology offers the possibility of great advances in construction. For the first time, the nonlinear buckling of straight concrete columns armed with single-walled carbon nanotubes (SWCNTs) resting on foundation is investigated in the present study. The column is modelled with Euler-Bernoulli beam theory. The characteristics of the equivalent composite being determined using the Mori-Tanaka model. The foundation around the column is simulated with spring and shear layer. Employing nonlinear strains-displacements, energy methods and Hamilton's principal, the governing equations are derived. Differential quadrature method (DQM) is used in order to obtain the buckling load of structure. The influences of volume percent of SWCNTs, geometrical parameters, elastic foundation and boundary conditions on the buckling of column are investigated. Numerical results indicate that reinforcing the concrete column with SWCNTs, the structure becomes stiffer and the buckling load increases with respect to concrete column armed with steel.

• Wind and Structures
• /
• v.30 no.5
• /
• pp.451-463
• /
• 2020

Two-dimensional numerical simulations are conducted at a low Reynolds number Re = 100 to investigate the near wake of three identical circular cylinders that are arranged in an equilateral triangular configuration. The incident angle of the three-cylinder configuration with respect to incoming flow is varied from θ = 0° to 60°, while the spacing between adjacent cylinders (L) covers a wide range of L/D = 1.25-7.0, where D is diameter of the cylinder. Typical flow structures in the near wake of the three-cylinder configuration are identified, including a single Karman vortex street, bistable flip-flopping near wake, anti-phase and/or in-phase vortex shedding, shear layer reattachment, and vortex impingement, depending on the configuration (L/D, θ). The behavior of Strouhal number (St) is discussed in detail, echoing the distinct structures of near wake. Furthermore, fluid forces on the individual cylinders are examined, which, though highly depending on (L/D, θ), exhibit a close correlation to the near wake behavior.

• Computers and Concrete
• /
• v.17 no.5
• /
• pp.567-578
• /
• 2016

As concrete is most usable material in construction industry it's been required to improve its quality. Nowadays, nanotechnology offers the possibility of great advances in construction. For the first time, the nonlinear buckling of straight concrete columns armed with single-walled carbon nanotubes (SWCNTs) resting on foundation is investigated in the present study. The column is modelled with Euler-Bernoulli and Timoshenko beam theories. The characteristics of the equivalent composite being determined using mixture rule. The foundation around the column is simulated with spring and shear layer. Employing nonlinear strains-displacements, energy methods and Hamilton's principal, the governing equations are derived. Differential quadrature method (DQM) is used in order to obtain the buckling load of structure. The influences of volume percent of SWCNTs, geometrical parameters, elastic foundation and boundary conditions on the buckling of column are investigated. Numerical results indicate that reinforcing the concrete column with SWCNTs, the structure becomes stiffer and the buckling load increases with respect to concrete column armed with steel.

• Advances in nano research
• /
• v.2 no.4
• /
• pp.199-210
• /
• 2014

Carbon nanotubes have exceptional mechanical, thermal and electrical properties, and are considered for high performance structural and multifunctional composites. In the present study, the natural frequencies of aligned single walled carbon nanotube (CNT) reinforced composite beams are obtained using shear deformable composite beam theories. The Ritz method with algebraic polynomial displacement functions is used to solve the free vibration problem of composite beams. The Mori-Tanaka method is applied to find the composite beam mechanical properties. The continuity conditions are satisfied among the layers by modifying the displacement field. Results are found for different CNT diameters, length to thickness ratio of the composite beam and different boundary conditions. It is found that the use of smaller CNT diameter in the reinforcement element gives higher fundamental frequency for the composite beam.

• Structural Monitoring and Maintenance
• /
• v.1 no.4
• /
• pp.427-449
• /
• 2014

A hybrid optimization method for the identification of state-space models is presented in this study. Hybridization is succeeded by combining the advantages of deterministic and stochastic algorithms in a superior scheme that promises faster convergence rate and reliability in the search for the global optimum. The proposed hybrid algorithm is developed by replacing the original stochastic mutation operator of Evolution Strategies (ES) by the Levenberg-Marquardt (LM) quasi-Newton algorithm. This substitution results in a scheme where the entire population cloud is involved in the search for the global optimum, while single individuals are involved in the local search, undertaken by the LM method. The novel hybrid identification framework is assessed through the Monte Carlo analysis of a simulated system and an experimental case study on a shear frame structure. Comparisons to subspace identification, as well as to conventional, self-adaptive ES provide significant indication of superior performance.

• Steel and Composite Structures
• /
• v.28 no.4
• /
• pp.415-426
• /
• 2018

This paper presents a multi-layer finite element for buckling and free vibration analyses of laminated beams based on a higher-order layer-wise theory. An N-layer beam element with (9N + 7) degrees-of-freedom is proposed for analyses. Delamination and slip between the layers are not allowed. Element matrices for the single- and multi-layer beam elements are derived by Lagrange's equations. Buckling loads and natural frequencies are calculated for different end conditions and lamina stacking. Comparisons are made to show the accuracy of proposed element.

• Proceedings of the Korean Society of Agricultural Engineers Conference
• /
• 2001.10a
• /
• pp.45-50
• /
• 2001

The purpose of this study was to estimate of soil loss form hillslope using WEPP(Water Erosion Prediction Project) model. WEPP model was developed for predicting soil erosion and deposition, fundamentally based on soil erosion prediction technology. The model for predicting sediment yields from single storms was applied to a tested watershed. Surface runoff is calculated by kinematic wave equation and infiltration is based on the Green and Ampt equation. Governing equations for sediment continuity, detachment, deposition, shear stress in rills, and transport capacity are presented. Tested watershed has an area of 0.6ha, where the runoff and sediment data were collected. The relative error between predicted and measured runoff was $-16.6{\sim}2.2%$, peak runoff was $-15.6{\sim}2.2%$ and soil loss was $-23.9{\sim}356.5%$.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
• /
• 2003.06a
• /
• pp.87-105
• /
• 2003

A new polymer technology commercialized with the name of Core Shell has been developed by Ondeo Nalco Company. Laboratory evaluations have demonstrated that Core Shell polymers produce a floc with high shear resistance, making them the flocculants of choice for modern high-speed paper machines. Core Shell polymers provide significant papermaking benefits, when used as single component or in combination with microparticles. At this time, the new program has been successfully applied on more than 60 paper and board machines across the world. Implementation of Core Shell polymers with or without a microparticle provided better and more stable retention values and improvements in paper quality, system cleanliness and machine runnability.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05a
• /
• pp.438-441
• /
• 2006

Since the behavior of structural members subjected to blast load shows different responses, the effect of impulse as well as peak load should be considered in the damage analysis. The threshold on P-I diagram that causes specific damage level divides the diagram into the failure zone and the non-failure zones. In this study, numerical analysis is performed based on single-degree-of-freedom (SDOF) techniques to generate rational P-I diagram considering material non-linearity and dual failure modes (flexure and direct shear) of RC beams. From the comparison with existing test results it is concluded that proposed numerical method is good to derive failure mode of RC beam under blast load.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.10a
• /
• pp.88-91
• /
• 2004

In this study, a number of natural fiber henequen reinforced polymer matrix composites were successfully fabricated by means of a compression molding technique using chopped henequen fibers surface-treated with different electron beam irradiation (EBI) dosages, thermoplastic poly(butylene succinate), thermosetting unsaturated polyester and phenolic resins. Their interfacial and thermal characteristics were studied in terms of interfacial shear strength, fracture surface, dynamic mechanical properties, dimensional stability, and thermal stability using single fiber microbonding test, SEM, DMA, TMA, and TGA. The results show that their interfacial and thermal properties significantly depend on the intensity of EBl treatment on the natural fiber surface.