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CONTENTS
Volume 15, Number 4, October 2013
 

Abstract
In order to study the degradation and damage behavirs of steel frame welded connections, two series of tests in references with different connection constructions were carried out subjected to various cyclic loading patterns. Hysteretic curves, degradation and damage behaviours and fatigue properties of specimens were firstly studied. Typical failure modes and probable damage reasons were discussed. Then, various damage index models with variables of dissipative energy, cumulative displacement and combined energy and displacement were summarized and applied for all experimental specimens. The damage developing curves of ten damage index models for each connection were obtained. Finally, the predicted and evaluated capacities of damage index models were compared in order to describe the degraded performance and failure modes. The characteristics of each damage index model were discussed in depth, and then their distributive laws were summarized. The tests and analysis results showed that the loading histories significantly affected the distributive shapes of damage index models. Different models had their own ranges of application. The selected parameters of damage index models had great effect on the developing trends of damage curves. The model with only displacement variable was recommended because of a more simple form and no integral calculation, which was easier to be formulated and embedded in application programs.

Key Words
welded connection of steel frame; degradation and damage behaviours; low-cycle fatigue; damage index model; failure mode

Address
1) Meng Wang: School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China;
2) Yongjiu Shi, Yuanqing Wang and Jun Xiong: Department of Civil Engineering, Tsinghua University, Beijing 100084, China;
3) Hong Chen: Architectural Design and Research Institute, Tsinghua University, Beijing 100084, China.

Abstract
Conoidal shells are doubly curved stiff surfaces which are easy to cast and fabricate due to their singly ruled property. Application of laminated composites in fabrication of conoidal shells reduces gravity forces and mass induced forces compared to the isotropic constructions due to the high strength to weight ratio of the material. These light weight shells are preferred in the industry to cover large column free open spaces. To ensure design reliability under service conditions, detailed knowledge about different behavioral aspects of conoidal shell is necessary. Hence, in this paper, static bending, free and forced vibration responses of composite conoidal shells are studied. Lagrange\'s equation of motion is used in conjunction with Hamilton\'s principle to derive governing equations of the shell. A finite element code using eight noded curved quadratic isoparametric elements is developed to get the solutions. Uniformly distributed load for static bending analysis and three different load time histories for solution of forced vibration problems are considered. Eight different stacking sequences of graphite-epoxy composite and two different boundary conditions are taken up in the present study. The study shows that relative performances of different shell combinations in terms of static behaviour cannot provide an idea about how they will relatively behave under dynamic loads and also the fact that the points of occurrence of maximum static and dynamic displacement may not be same on a shell surface.

Key Words
conoidal shell; composite material; finite element method; forced vibration; Newmark\'s method

Address
Kaustav Bakshi and Dipankar Chakravorty: Civil Engineering Department, Jadavpur University, Kolkata- 700032, India.

Abstract
In the present study, the thermal buckling behavior of functionally graded sandwich plates is studied using a new hyperbolic displacement model. Unlike any other theory, the theory is variationally consistent and gives four governing equations. Number of unknown functions involved in displacement field is only four, as against five in case of other shear deformation theories. This present model takes into account the parabolic distribution of transverse shear stresses and satisfies the condition of zero shear stresses on the top and bottom surfaces without using shear correction factor. Material properties and thermal expansion coefficient of the sandwich plate faces are assumed to be graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are assumed as uniform, linear and non-linear temperature rises across the thickness direction. The results reveal that the volume fraction index, loading type and functionally graded layers thickness have significant influence on the thermal buckling of functionally graded sandwich plates.

Key Words
new plate theory; thermal buckling; functionally graded plate; volume fraction index

Address
1) Fatima Zohra Kettaf and Mohamed Benguediab: Departement de Genie Mecanique, Faculte de Technologie, Universite 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: Laboratoire des Materiaux et Hydrologie, Universite de Sidi Bel Abbes, Faculte de Technologie, BP 89 Cite Ben M\'hidi 22000 Sidi Bel Abbes, Algerie;
4) Abdelouahed Tounsi: Departement de Genie Civil, Faculte de Technologie, Universite Sidi Bel Abbes, Algerie.

Abstract
A new-styrofoam-concrete composite sandwich slab with function of heat insulation is designed. Four full-scale simply supported composite sandwich slabs with different shear connectors are tested. Parameters under study are the thickness of the concrete, the height of profiled steel sheeting, the influence of shear connectors including the steel bars and self-drilling screws. Experimental results showing that four specimens mainly failed in bending failure mode; the shear connectors can limit the longitudinal slippery between the steel profiled sheeting and the concrete effectively and thus guarantee the good composite action and cooperative behavior of two materials. The ultimate sagging bending resistance can be determined based on plastic theory. This new composite sandwich slab has high sagging bending resistance and good ductility. Additionally, these test results help the design and application of this new type of composite sandwich slab.

Key Words
composite sandwich slabs; re-entrant trough profiled steel sheeting; shear connectors; bending-bearing capacities; experimental research; bending failure

Address
P.Z. Cao, Y.F. Lu and Kai Wu: College of Civil and Transportation Engineering, Hohai University, Nanjing, Jiangsu, P.R. China.

Abstract
In this study simply supported nonlinear Euler-Bernoulli beams resting on linear elastic foundation and subjected to the axial loads is investigated. A new kind of analytical technique for a non-linear problem called He\'s Energy Balance Method (EBM) is used to obtain the analytical solution for non-linear vibration behavior of the problem. Analytical expressions for geometrically non-linear vibration of Euler-Bernoulli beams resting on linear elastic foundation and subjected to the axial loads are provided. The effect of vibration amplitude on the non-linear frequency and buckling load is discussed. The variation of different parameter to the nonlinear frequency is considered completely in this study. The nonlinear vibration equation is analyzed numerically using Runge-Kutta 4th technique. Comparison of Energy Balance Method (EBM) with Runge-Kutta 4th leads to highly accurate solutions.

Key Words
elastic foundation; nonlinear vibration; analytical method; Runge-Kutta 4th

Address
1) Mehran Javanmard: Department of Civil Engineering, University of Zanjan, Zanjan, Iran;
2) Mahdi Bayat: Department of Civil Engineering, Zanjan Branch, Islamic Azad University, Zanjan, Iran;
3) Alireza Ardakani: Faculty of Engineering and Technology, Imam Khomeini International University, Qazvin, Iran.

Abstract
This paper deals with the multi-objective optimization of tire reinforcement structures such as the tread belt and the carcass path. The multi-objective functions are defined in terms of the discrete-type design variables and approximated by artificial neutral network, and the sensitivity analyses of these functions are replaced with the iterative genetic evolution. The multi-objective optimization algorithm introduced in this paper is not only highly CPU-time-efficient but it can also be applicable to other multi-objective optimization problems in which the objective function, the design variables and the constraints are not continuous but discrete. Through the illustrative numerical experiments, the fiber-reinforced tire belt structure is optimally tailored. The proposed multi-objective optimization algorithm is not limited to the tire reinforcement structure, but it can be applicable to the generalized multi-objective structural optimization problems in various engineering applications.

Key Words
fiber-reinforced composite structure; generalized evolutionary optimization; discrete-type multi-objective optimization; genetic algorithm; artificial neural network

Address
1) J.R. Cho, J.H. Lee and S.B. Lee: School of Mechanical Engineering, Pusan National University, Busan 609-735, Korea;
2) J.R. Cho: Research and Development Institute of Midas IT, Gyeonggi 463-400, Korea;
3) K.W. Kim: R&D Center of Kumho Tire Co. Ltd., Gwangju 500-757, Korea.


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