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CONTENTS
Volume 14, Number 4, April 2013
 

Abstract
The web-encased steel-concrete composite (WESCC) beam is a new developed steel-concrete composite beam. Experiments of six simply supported WESCC beam specimens were conducted. The effects of the shear-span ratio and steel section type were all investigated on the static behaviors such as failure modes, failure mechanism and bearing capacity. The experimental results denoted that all specimens failed in bending mode and the degree of combination between the bottom armor plate of steel shape and concrete were very well without any evident slippage, which demonstrated that the function of bottom armor plate and web were fully exerted in the WESCC beams. It could be concluded the WESCC beams have high stiffness, high load carrying capacity and advanced ductility. The design methods are proposed which mainly consist the bearing capacity calculation of bending and flexural rigidity. The calculation results of the bearing capacity and deflection which take the shear deflection into account are in agreement with the experimental results. The design methods are useful for design and application of the innovative composite beams.

Key Words
composite beams; experiment study; mechanical behavior; bearing capacity; flexural rigidity; shear deflection

Address
(1) Gang Zhu, Yong Yang, Jianyang Xue: College of Civil Engineering, Xi'an University of Arch. and Tech., Shaan Xi, Xi'an, 710055, P.R. China;
(2) Gang Zhu, China Haisum Engineering Co. Ltd., Shanghai, 200031, P.R. China;
(3) Jianguo Nie: Department of Civil Engineering, Tsinghua University, Beijing, 100084, P.R. China.

Abstract
In this paper, the nonlinear cylindrical bending behavior of functionally graded nanocomposite plates reinforced by single-walled carbon nanotubes (SWCNTs) is studied using an efficient and simple refined theory. This theory is based on assumption that the in-plane and transverse displacements consist of bending and shear components in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments. The material properties of SWCNTs are assumed to be temperature-dependent and are obtained from molecular dynamics simulations. The material properties of functionally graded carbon nanotube-reinforced composites (FG-CNTCRs) are assumed to be graded in the thickness direction, and are estimated through a micromechanical model. The fundamental equations for functionally graded nanocomposite plates are obtained using the Von-Karman theory for large deflections and the solution is obtained by minimization of the total potential energy. The numerical illustrations concern the nonlinear bending response of FG-CNTRC plates under different sets of thermal environmental conditions, from which results for uniformly distributed CNTRC plates are obtainedas comparators.

Key Words
functionally graded materials; nanocomposites; nonlinear behavior; refined plate theory

Address
K. Bakhti, A. Kaci, A.A. Bousahla, M.S.A. Houari, A. Tounsi and E.A. Adda Bedial: Laboratoire des Materiaux et Hydrologie, Universite de Sidi Bel Abbes, Algerie; A. Kaci: Universitaire Mustapha Stambouli, Mascara, Algerie

Abstract
Structures consisting of concrete and steel parts, which are irregular in damping ratios are investigated. This investigation is a code-based seismic design of such structures. Several practical difficulties encountered, due to inherent differences in the nature of dynamic response of each part, and the different damping ratios of the two parts. These structures are irregular in damping ratios and have complex modes of vibration so that their analysis cannot be handled with the readily available commercial software. Therefore, this work aims to provide simple yet sufficiently accurate constant values of equivalent damping ratios applied to the whole structure for handling the damping irregularity of such structures. The results show that the equivalent damping ratio changes with the height of the building and the kind of the structural system, but it is constant for all accelerations values. Thus, available software SAP2000 applied for seismic analysis, design and the provisions of existing seismic codes. Finally, evaluation of different kinds of structural system used in this research to find the most energy dissipating one found by finding the best value of quality coefficient.

Key Words
mixed structure; SAP2000; quality coefficient; damping coefficient; equivalent damping coefficient; better seismic energy dissipating

Address
Ahmed Abdelraheem Farghaly: Civil and Architecture Building Department, Faculty of Industrial Education, Sohag University, Egypt

Abstract
Damage in structures often leads to failure. Thus it is very important to monitor structures for the occurrence of damage. When damage happens in a structure the consequence is a change in its modal parameters such as natural frequencies and mode shapes. Artificial Neural Networks (ANNs) are inspired by human biological neurons and have been applied for damage identification with varied success. Natural frequencies of a structure have a strong effect on damage and are applied as effective input parameters used to train the ANN in this study. The applicability of ANNs as a powerful tool for predicting the severity of damage in a model steel girder bridge is examined in this study. The data required for the ANNs which are in the form of natural frequencies were obtained from numerical modal analysis. By incorporating the training data, ANNs are capable of producing outputs in terms of damage severity using the first five natural frequencies. It has been demonstrated that an ANN trained only with natural frequency data can determine the severity of damage with a 6.8% error. The results shows that ANNs trained with numerically obtained samples have a strong potential for structural damage identification.

Key Words
artificial neural networks (ANNs); finite element; damage detection; backpropagation algorithm; natural frequency

Address
S.J.S. Hakim and H. Abdul Razak: StrucHMRS Group, Department of Civil Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

Abstract
Aim of this paper is to apply to a steel truss bridge a methodology that takes into account the consequences of extreme loads on structures, focusing on the influence that the loss of primary elements has on the structural load bearing capacity. In this context, the topic of structural robustness, intended as the capacity of a structure to withstand damages without suffering disproportionate response to the triggering causes while maintaining an assigned level of performance, becomes relevant. In the first part of this study, a brief literature review of the topics of structural robustness, collapse resistance and progressive collapse takes place, focusing on steel structures. In the second part, a procedure for the evaluation of the structural response and robustness of skeletal structures under impact loads is presented and tested in simple structures. Following that, an application focuses on a case study bridge, the extensively studied I-35W Minneapolis steel truss bridge. The bridge, which had a structural design particularly sensitive to extreme loads, recently collapsed for a series of other reasons, in part still under investigation. The applied method aims, in addition to the robustness assessment, at increasing the collapse resistance of the structure by testing alternative designs.

Key Words
consequence-based design; structural robustness; collapse resistance; progressive collapse; skeletal structures; steel truss bridge; alternative design

Address
Pierluigi Olmati and Konstantinos Gkoumas: Faculty of Engineering, Sapienza University of Rome, Via Eudossiana 18, 00184, Rome, Italy; Francesca Brando and Liling Cao: Thornton Tomasetti, 51 Madison Ave., New York, N.Y. 10010-1603, United States

Abstract
This paper deals with multiobjective optimization of symmetrically laminated composite truncated circular conical shells subjected to external uniform pressure load and thermal load. The design objective is the maximization of the weighted sum of the critical buckling load and fundamental frequency. The design variable is the fibre orientations in the layers. The performance index is formulated as the weighted sum of individual objectives in order to obtain optimal solutions of the design problem. The first-order shear deformation theory (FSDT) is used in the mathematical formulation of laminated truncated conical shells. Finally, the effect of different weighting factors, length-to-radius ratio, semi-cone angle and boundary conditions on the optimal design is investigated and the results are compared.

Key Words
laminated composite truncated conical shells; multiobjective optimization; frequency; buckling

Address
Umut Topal: Karadeniz Technical University, Of Faculty of Technology, Department of Civil Engineering, Trabzon, Turkey


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