Techno Press
Tp_Editing System.E (TES.E)
Login Search


sem
 
CONTENTS
Volume 23, Number 2, May30 2006
 

Abstract
The axisymmetric free vibrations of transversely isotropic magnetoelectroelastic laminated circular plates are studied. Based on the three-dimensional governing equations of magnetoelectroelastic medium, the state space equations of laminated circular plates are obtained. By using the finite Hankel transform and rendering the free terms left by the transform in terms of the boundary quantities, the solutions of the state space equations are given for two kinds of boundary conditions. The frequency equations of the free vibration are derived using the propagator matrix method and the boundary conditions at top and bottom surfaces. By virtue of the inverse Hankel transform, the mode shapes are also determined. Since the solutions strictly satisfy the governing equations in the region and the boundary conditions at the edges, they are the three-dimensionally exact. Finally, the natural frequencies of such plates are tabulated and compared with those of the piezoelectric and elastic plates in the numerical example.

Key Words
magnetoelectroelastic medium; laminated circular plates; free vibration; state space method.

Address
Jiangying Chen; Faculty of Engineering, Ningbo
University, Ningbo 315211, China (Ningbo Institute of Technology, Zhejiang University, Ningbo 315100, China)
Rongqiao Xu; Department of Civil Engineering, Zhejiang University, Hangzhou 310027, China
Xusheng Huang; Faculty of Engineering, Ningbo University, Ningbo 315211, China
Haojiang Ding; Department of Civil Engineering, Zhejiang University, Hangzhou 310027, China

Abstract
This paper provides an insight into the response of non-seismic reinforced concrete (RC) building frames to excitations of different frequencies through experimental investigation. The results of cyclic loading tests of six full-scale RC beam-column sub-assemblies are presented. The tested specimens did not have any transverse reinforcement inside the joint core, and they were subjected to quasi-static and dynamic loading with frequencies as high as 20 Hz. Some important differences between the cyclic responses of non-seismic and ductile RC frames are highlighted. The effect of excitation frequency on the behavior of non-seismic joints is also discussed. In the quasi-static tests, shear deformation of the joint panel accounted for more than 50% of the applied story drift. The test results also showed that higher-frequency excitations are less detrimental than quasi-static cyclic loads, and non-seismic frames can withstand a higher load and a larger deformation when they are applied faster.

Key Words
non-seismic; high-frequency; loading rate; shear failure; joint deformation; residual stiffness.

Address
Rajesh P. Dhakal; Department of Civil Engineering, University of Canterbury, Post bag 4800, Christchurch 8020, New Zealand
Tso-Chien Pan; Protective Technology Research Centre, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798

Abstract
Recent developments in fractal theory suggest that fractal may provide a more realistic representation of characteristics of cementitious materials. In this paper, the roughness of fracture surfaces in cementitious material has been characterized by fractal theory. A systematic experimental investigation was carried out to examine the dependency of fracture parameters on the aggregate sizes as well as the loading rates. Three maximum aggregate sizes (4.76 mm, 12.7 mm, and 19.1 mm) and two loading rates (slow and fast loading rate) were used. A total of 25 compression tests and 25 tension tests were performed. All fracture parameters exhibited an increase, to varying degrees, when aggregates were added to the mortar matrix. The fracture surfaces of the specimens were digitized and analyzed. Results of the fractal analysis suggested that concrete fracture surfaces exhibit fractal characteristics, and the fractal geometry provide a useful tool for characterizing nonlinear fracture behavior of concrete. Fractal dimension D was monotonically increased as maximum aggregate sizes increase. A new fractal fracture model was developed which considers the size and shape of aggregate, and the crack paths in the constituent phases. Detailed analyses were given for four different types of fracture paths. The fractal fracture model can estimate fractal dimension for multiphase composites.

Key Words
fracture; fractal; roughness; aggregate size; loading rate.

Address
Kug Kwan Chang; Architectural Engineering Department, Seoul National University of Technology, Seoul 139-743, South Korea
Yunping Xi; Department of Civil, Environmental and Architectural Engineering, University of Colorado,
Boulder, CO 80309, USA
Y-S Roh; Architectural Engineering Department, Seoul National University of Technology, Seoul 139-743, South Korea

Abstract
In this paper, the dynamic response of a piezoelectric layer with a penny-shaped crack is investigated. The piezoelectric layer is subjected to an axisymmetrical action of both mechanical and electrical impacts. Two kinds of crack surface conditions, i.e., electrically impermeable and electrically permeable, are adopted. Based upon integral transform technique, the crack boundary value problem is reduced to a system of Fredholm integral equations in the Laplace transform domain. By making use of numerical Laplace inversion the time-dependent dynamic stress and electric displacement intensity factors are obtained, and the dynamic energy release rate is further derived. Numerical results are plotted to show the effects of both the piezoelectric layer thickness and the electrical impact loadings on the dynamic fracture behaviors of the crack tips.

Key Words
piezoelectric layer; penny-shaped crack; dynamic energy release rate; dynamic stress intensity factor; axis symmetry.

Address
Department of Mechanics and Engineering Science, Shijiazhuang Railway Institute, Shijiazhuang 050043, P. R. China

Abstract
Determining the hysteretic energy demand and dissipation capacity and level of damage of the structure to a predefined earthquake ground motion is a highly non-linear problem and is one of the questions involved in predicting the structure? response for low-performance levels (life safe, near collapse, collapse) in performance-based earthquake resistant design. Neural Network (NN) analysis offers an alternative approach for investigation of non-linear relationships in engineering problems. The results of NN yield a more realistic and accurate prediction. A NN model can help the engineer to predict the seismic performance of the structure and to design the structural elements, even when there is not adequate information at the early stages of the design process. The principal aim of this study is to develop and test multi-layered feedforward NNs trained with the back-propagation algorithm to model the non-linear relationship between the structural and ground motion parameters and the hysteretic energy demand in steel moment resisting frames. The approach adapted in this study was shown to be capable of providing accurate estimates of hysteretic energy demand by using the six design parameters.

Key Words
neural network; hysteretic energy demand; steel moment resisting frames; back-propagation.

Address
Department of Earthquake and Structural Science, Gebze Institute of Technology, 41400 Gebze-Kocaeli, Turkey

Abstract
An efficient and accurate algorithm is proposed to estimate cable safety factor of suspension bridges satisfying prescribed reliability levels. Uncertainties in the structure and load parameters are incorporated. The proposed algorithm integrates the concepts of the inverse reliability method and deterministic method for assessing cable safety factors of suspension bridges. The unique feature of the proposed method is that it offers a tool for cable safety assessment of suspension bridges, when the reliability level is specified as a target to be satisfied by the designer. After the accuracy and efficiency of the method are demonstrated through two numerical examples, the method is used to estimate cable safety factors of suspension bridges with span length ranging from 2000 to 5000 m. The results show that the deterministic method overestimates cable safety factor of suspension bridges because of neglecting the parameter uncertainty effects. The actual cable safety factor of suspension bridges should be estimated based on the proposed method.

Key Words
inverse reliability method; cable safety factor; suspension bridges; target reliability index; uncertainties.

Address
Department of Bridge Engineering, Tongji University, Shanghai, 200092, China

Abstract
.

Key Words
.

Address
Department of Naval Architecture and Marine Engineering, Chung Cheng Institute of Technology,
National Defense University, Yuansulin, Dashi, Taoyuan, Taiwan 335, Republic of China


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2017 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: info@techno-press.com