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CONTENTS
Volume 15, Number 2, August 2013
 

Abstract
This paper presents the experimental results of axially loaded stub columns of slender steel hollow square section (SHS) strengthened with carbon fiber reinforced polymers (CFRP) sheets. 9 specimens were fabricated and the main parameters were: width-thickness ratio (b /t), the number of CFRP ply, and the CFRP sheet orientation. From the tests, it was observed that two sides would typically buckle outward and the other two sides would buckle inward. A maximum increase of 33% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b /t = 100 transversely. Also, stiffness and ductility index (DI) were compared between un-retrofitted specimens and retrofitted specimens. Finally, it was shown that the application of CFRP to slender sections delays local buckling and subsequently results in significant increases in elastic buckling stress. In the last section, a prediction formula of the ultimate strength developed using the experimental results is presented.

Key Words
FRP; CFRP; Steel hollow section (SHS); slender section; retrofit; elastic buckling; reduction factor

Address
(1) Jai-woo Park: Gayoon Construction. Co. Ltd., 9-91, Hwayang-dong, Gwangjin-gu, Seoul, 143-130, Republic of Korea
(2) Jung-han Yoo: School of Architecture, Seoul National University of Science & Technology, 232 Gongreung-ro, Nowon-gu, Seoul, 139-743, Republic of Korea.

Abstract
In this study, an electrolyzing device for the production of metal powders was designed and fabricated. The production of copper powders was performed using a variety of current densities, anode-cathode distances and power removal times. The effect of these parameters on powder particle size and shape was determined. Particle size was measured using a laser diffraction unit while the powder shape was determined by SEM. Experimental results show that an increase in current density leads to a decrease in powder particle size. In addition particle shape changed from globular dendritic to acicular dendritic with increasing the current density. Distance between the cathode and anode also showed a similar influence on powder particle size and shape. An increase in time of powder removal led to an increase in powder particle size, as the shape changed from acicular dendritic to globular dendritic.

Key Words
metallurgy, electrolytic copper powder, current density, powder particle size and shape

Address
(1) Mustafa Boz: Technical Education Faculty (Metal Education), Karabuk University, Karabuk, Turkey;
(2) Masood Hasheminiasari: Faculty of Engineering (Metallurgical and Materials), Colorado School of Mines, Colorado, USA.

Abstract
The thermal creep is one of the major factors causing the buckle of steel columns in the fire events. But, few related studies have been reported to evaluate the factors affecting the thermal creep of steel column experimentally or numerically. In this study a series of Fire-resistant steel columns with three different slenderness ratios under a sustained load are tested under a uniform temperature up to six hours in order to evaluate the creep upon three selected factors, temperature, applied load, and column slenderness. Based on experimental results, a proposed creep strain rate model is established as the function of a single parameter of the load ratio of temperature LR(T) to determine the buckling time of steel column due to creep. Furthermore it is found that the creep can be neglected when LR(T) is smaller than 0.77.

Key Words
thermal creep; load ratio; elevated temperature; steel columns

Address
Kuo-Chen Yang and Zong-Han Yu: National Kaohsiung First University of Science and Technology, Department of Construction Engineering, Kaohsiung, 824, Taiwan.

Abstract
The super convergent laminated composite beam element is newly derived for the lateral stability analysis. For this, a theoretical model of the laminated composite beams is developed based on the first-order shear deformation beam theory. The present laminated beam takes into account the transverse shear and the restrained warping induced shear deformation. The second-order coupling torque resulting from the geometric nonlinearity is rigorously derived. From the principle of minimum total potential energy, the stability equations and force-displacement relationships are derived and the explicit expressions for the displacement parameters are presented by applying the power series expansions of displacement components to simultaneous ordinary differential equations. Finally, the member stiffness matrix is determined using the force-displacement relationships. In order to show accuracy and superiority of the beam element developed by this study, the critical lateral buckling moments for bisymmetric and monosymmetric I-beams are presented and compared with other results available in the literature, the isoparametric beam elements, and shell elements from ABAQUS.

Key Words
failure criterion; three-point bending; damage; laminated composite; interface

Address
(1) Nam-Il Kim: Department of Architectural Engineering, Sejong University, 98 Kunja dong, Kwangin Ku, Seoul 143-747, Republic of Korea;
(2) Dong-Ho Choi: Department of Civil and Environmental Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-Ku, Seoul, 133-791, Republic of Korea.

Abstract
The study of the tensile strength of composite materials is far more complex than analysis of the properties of elasticity and plasticity. Indeed, during mechanical loading, micro-cracks in the matrix, the fibers break, debonding of the interfaces are created. The failure process of composites is of great diversity and cannot be described if even we know: the strength criterion of each individual component, the state of stress and strain in the material, the propagation phenomena cracks in the structure and nature of the interface between the matrix and the reinforcement. This information is only partially known and the obtained by the analysis of a stress limit beyond which there is destruction of the material is almost impossible. To partially process the issue, a solution lies in a mesoscopic approach of seeking a law to locate the ultimate strength of the material for a plane stress state. Tests on rectangular plates in bending PEEK/APC2 and T300/914 three were made and this in order to validate our approach, the calculation has been implemented in a nonlinear finite element code (Castem 2000), in order to make comparison with the numerical results. The results show good agreement between numerical simulation and the two materials; however, it would be interesting to consider other phenomena in the criterion.

Key Words
failure criterion; three-point bending; damage; laminated composite; interface

Address
Mokaddem Allel, Alami Mohamed and Boutaous Ahmed: Faculty of Science, Department of Physics, U.S.T.O., BP 1505 Oran, Algeria.

Abstract
This paper presents an analytical solution to the thermomechanical bending analysis of functionally graded sandwich plates by using a new hyperbolic shear deformation theory in which the stretching effect is included. The modulus of elasticity of plates is assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. The effects of functionally graded material (FGM) layer thickness, volume fraction index, layer thickness ratio, thickness ratio and aspect ratio on the deflections and stresses of functionally graded sandwich plates are investigated.

Key Words
thermomechanical; analytical modelling; functionally graded material; stretching effect

Address
(1) Hayat Saidi, Abdelouahed Tounsi and El Abbas Adda Bedia: Laboratoire des Materiaux et Hydrologie, Universite de Sidi Bel Abbes, Faculte de Technologie, BP 89 Cite Ben M\'hidi 22000 Sidi Bel Abbes, Algerie;
(2) Mohammed Sid Ahmed Houari and Abdelouahed Tounsi: Laboratoire des Structures et Materiaux Avances dans le Genie Civil et Travaux Publics, Universite de Sidi Bel Abbes, Faculte de Technologie, BP 89 Cite Ben M\'hidi 22000 Sidi Bel Abbes, Algerie;
(3) Abdelouahed Tounsi: Departement de Genie Civil, Faculte de Technologie, Universite Sidi Bel Abbes, Algerie.


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