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CONTENTS
Volume 22, Number 4, March10 2006
 

Abstract
Solutions to the problems of structural parameter estimation from modal response using least-squares minimization of force or displacement residuals are generally sensitive to noise in the response measurements. The sensitivity of the parameter estimates is governed by the physical characteristics of the structure and certain features of the noisy measurements. It has been shown that the regularization method can be used to reduce effects of the measurement noise on the estimation error through adding a regularization function to the parameter estimation objective function. In this paper, we adopt the regularization function as the Euclidean norm of the difference between the values of the currently estimated parameters and the a priori parameter estimates. The effect of the regularization function on the outcome of parameter estimation is determined by a regularization factor. Based on a singular value decomposition of the sensitivity matrix of the structural response, it is shown that the optimal regularization factor is obtained by using the maximum singular value of the sensitivity matrix. This selection exhibits the condition where the effect of the a priori estimates on the solutions to the parameter estimation problem is minimal. The performance of the proposed algorithm is investigated in comparison with certain algorithms selected from the literature by using a numerical example.

Key Words
parameter estimation; measurement noise; estimation errors; regularization; singular value decomposition.

Address
Department of Civil Engineering, Chulalongkorn University, Phayathai Road, Pathumwan, Bangkok 10330, Thailand

Abstract
Experimental studies on the behaviors of box-shape steel reinforced concrete (SRC) composite beams were conducted. Seven 1:3 scale model composite beams were tested to failure. Each of the beams was simply supported at the ends and two concentrated loads were applied at the one-third span and two-thirds span respectively. Experimental results indicate that the flexural strength can be enhanced when the ratio of flexural reinforcements and flange thickness of the shape steel are increased; the shear strength is enhanced with increase of web thickness of the shape steel. Insignificant effects of concrete in the box-shape steel are found on improving the flexural strength and shear strength of the box-shape SRC composite beams, thus concrete inside the box-shape steel can be saved, and the weight of the SRC beams can be decreased. Shear studs can strengthen the connection and co-work effects between the shape steel and the concrete and enhance the shear strength, but stud design for the composite beams should be further improved. Formulas for flexural and shear strength of the composite beams are proposed, and the calculated results are in good agreement with the experimental results. In general, the box-shape SRC composite beam is a kind of ductile member, and suitable for extensive engineering application.

Key Words
steel reinforced concrete (SRC); experimental study; ultimate strength; box-shape steel; composite beam.

Address
Chun Yang and Jian Cai; Department of Civil Engineering, South China University of Tech., Guangzhou 510640, P. R. China
Yi Wu; Department of Civil Engineering, Guangzhou University, Guangzhou 510405, P. R. China
Jiangang He and Haifeng Chen; Guangzhou Civil Architecture Research & Design Institute, Guangzhou 510055, P. R. China

Abstract
The problem of very large deflection of a circular cantilever arc device subjected to inward or outward polar force is studied. An exact elliptic integral solution is derived for the two cases and the results are checked using large displacement finite element analysis via the ANSYS package by performing a new novel modeling simulation technique for this problem. Excellent agreements have been obtained between the exact analytical solution and the numerical approach.
From this study, a design chart for engineers is developed to predict the required value for the inward polar force for the device to switch on for a given angle forming the circular arc (o). This study has several interesting applications in mechanical engineering, integrated circuit technology. nanotechnology and especially in microelectromechanical systems (MEMs) such as a MEM circular device switch subjected to attractive or repulsive magnetic forces due to the attachments of two magnetic poles at the fixed and at the free end of the circular cantilever arc switch device.

Key Words
ANSYS; circular cantilever arc; elastica; elliptic integral; polar force.

Address
Department of Civil Engineering, Faculty of Engineering, Hashemite University, Zarqa 13115, Jordan

Abstract
Most existing concrete structures in Taiwan are considered nonductile due to insufficient transverse reinforcement and poor detailing of frame elements. Such features are fairly typical for buildings constructed prior to 1997, at which time the local building code was revised based on ACI 318-95. Among these structures, many contain perimeter or partition walls made of concrete or clay brick for architectural purposes. These walls, though treated as non-structural components in common design practice, could affect the structural behavior of the buildings during an earthquake. To study the behavior of such structures under seismic load, experiments were conducted on concrete frames of various configurations to show the force-deformation relationships, damage patterns, and other characteristics of the frames. For further interest, similar units with columns jacketed by carbon-fiber-reinforced-polymer (CFRP) were also tested to illustrate the effectiveness of this technique in the retrofit of concrete frames.

Key Words
CFRP; infill; nonductile frame; seismic retrofit.

Address
Chao-Hsun Huang and Yu-Chi Sung; Department of Civil Engineering, National Taipei University of Technology, 1, Sec. 3, Chung Hsiao E. Rd., Taipei 106, Taiwan
Chi-Hsin Tsai; Futai Engineering Co., 6F, 19-5 San Chong Rd., Taipei 115, Taiwan

Abstract
A new method called fuzzy factor method for the stationary stochastic response analysis of fuzzy truss with global fuzzy structural parameters is presented in this paper. Considering the fuzziness of the structural physical parameters and geometric dimensions simultaneously, the fuzzy correlation function matrix of structural displacement response in time domain is derived by using the fuzzy factor method and the optimization method, the fuzzy mean square values of the structural displacement and stress response in the frequency domain are then developed with the fuzzy factor method. The influences of the fuzziness of structural parameters on the fuzziness of mean square values of the displacement and stress response are inspected via an example and some important conclusions are obtained. Finally, the example is simulated by Monte-Carlo method and the results of the two methods are close, which verified the feasibility of the method given in this paper.

Key Words
fuzzy truss; stationary stochastic excitation; fuzzy correlation function matrix of displacement response; fuzzy factor method; fuzzy mean square values of structural dynamic response.

Address
J. Ma and J. J. Chen; School of Electromechanical Engineering, Xidian University, Xi?n 710071, P. R. China
W. Gao; School of Mechanical and Manufacturing Engineering, The University of New South Wales,
Sydney, NSW2052, Australia
Y. Y. Zhao; School of Electromechanical Engineering, Xidian University, Xi?n 710071, P. R. China

Abstract
The dynamic instability characteristics of laminated composite stiffened shell panels subjected to in-plane harmonic edge loading are investigated in this paper. The eight-noded isoparametric degenerated shell element and a compatible three-noded curved beam element are used to model the shell panels and the stiffeners respectively. As the usual formulation of degenerated beam element is found to overestimate the torsional rigidity, an attempt has been made to reformulate it in an efficient manner. Moreover the new formulation for the beam element requires five degrees of freedom per node as that of shell element. The method of Hill? infinite determinant is applied to analyze the dynamic instability regions. Numerical results are presented to demonstrate the effects of various parameters like shell geometry, lamination scheme, stiffening scheme, static and dynamic load factors and boundary conditions, on the dynamic instability behaviour of laminated composite stiffened panels subjected to in-plane harmonic loads along the boundaries. The results of free vibration and buckling of the laminated composite stiffened curved panels are also presented.

Key Words
buckling; composite stiffened shell panels; degenerated curved beam element; degenerated shell element; dynamic instability; finite element method; in-plane load and vibration.

Address
S. N. Patel and P. K. Datta; Department of Aerospace Engineering, I.I.T. Kharagpur, Kharagpur-721 032, India
A. H. Sheikh; Department of Ocean Engineering and Naval Architecture, I.I.T. Kharagpur, Kharagpur-721 032, India

Abstract
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Key Words
shallow foundations; fluid-structure-soil interaction; plasticity; pipelines; macroelement; strain hardening plasticity.

Address
Centre for Offshore Foundation Systems, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia

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