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CONTENTS
Volume 19, Number 1, January10 2005
 

Abstract
The expertise required in the judicious use of nonlinear finite element (FE) packages for design-assistance purposes is not widely available to the average engineer, whose sole aim may be to obtain an estimate for a single design parameter, such as the limit load capacity of a structure. Such a parameter may be required for the design of a proposed reinforced concrete (RC) floor slab or bridge deck with a given set of geometrical and material details. This paper outlines a procedure for developing design-assistance equations for carrying out such predictions for partially restrained RC slabs under uniformly distributed loading condition, based on a database of FE results previously generated from a large number of

Key Words
finite elements; partially restrained RC slabs; FE-based equations; limit load prediction; numerical modeling; design assistance tools; FE predictions.

Address
O. O. Olufemi and K. L. Cheung;
School of Engineering and Physical Sciences, University of Aberdeen, AB24 3UE, U.K.
K. M. A. Hossain; Department of Civil Engineering, Ryerson University, Toronto, Ontario, Canada M5B 2K3

Abstract
A method is presented to detect and assess the structural damage from changes in natural frequencies using Genetic Algorithm (GA). Using the natural frequencies of the structure, it is possible to formulate the inverse problem in optimization terms and then to utilize a solution procedure employing GA to assess the damages. The technique has been applied to a cantilever beam and a plane frame, each one with different damage scenario to study the efficiency of the developed algorithm. A laboratory tested data has been used to verify the proposed algorithm. The study indicates the potentiality of the developed code to solve a wide range of inverse identification problems in a systematic way. The outcomes show that this method can detect and estimate the amount of damages with satisfactory precision.

Key Words
genetic algorithm; damage assessment; inverse problem; finite element method; natural frequency; stiffness reduction factor.

Address
Department of Civil Engineering, Indian Institute of Technology, Guwahati 781039, India

Abstract
The linearized buckling problem is considered for an isotropic clamped-clamped cylindrical shell with an oblique end. A theoretical solution based on the Budiansky shell theory is developed, and numerical results are determined using the differential quadrature method. In formulating the solutions, the surface of the shell is developed onto a plane, and the resulting irregular domain is then mapped, using blending functions, onto a square parent domain. The analysis is carried out in the parent domain. Convergence, validation, and parametric studies are conducted for a uniform external pressure loading. Results determined are compared with finite element results. The paper ends with an appropriate set of conclusions.

Key Words
stability; cylindrical shell; differential quadrature method; finite element method.

Address
Department of Mechanical Engineering, University of Ottawa, Ottawa, Canada K1N 6N5

Abstract
In several design codes and specifications, simplified formulae and diagrams are given for determining the buckling lengths of frame columns. It is shown that these formulae may yield rather erroneous results in certain cases. This is due to the fact that, the code formulae utilise only local stiffness distributions. In this paper, a simplified procedure for determining approximate values for the buckling loads of multi-storey frames is developed. The procedure utilises lateral load analysis of frames and yields errors in the order of 10%, which may be considered suitable for design purposes. The proposed procedure is applied to several numerical examples and it is shown that all the errors are in the acceptable range and on the safe side.

Key Words
buckling load; buckling length; effective length; sway mode; unbraced frames; isolated subassembly; multi-storey frames; design codes.

Address
Faculty of Civil Engineering, Istanbul Technical University, Maslak 34469, Istanbul, Turkey

Abstract
For the spatially coupled free vibration analysis of shear deformable thin-walled non- symmetric curved beam subjected to initial axial force, an exact dynamic element stiffness matrix of curved beam is evaluated. Firstly equations of motion and force-deformation relations are rigorously derived from the total potential energy for a curved beam element. Next a system of linear algebraic equations are constructed by introducing 14 displacement parameters and transforming the second order simultaneous differential equations into the first order simultaneous differential equations. And then explicit expressions for displacement parameters are numerically evaluated via eigensolutions and the exact 14 ?14 dynamic element stiffness matrix is determined using force-deformation relations. To demonstrate the accuracy and the reliability of this study, the spatially coupled natural frequencies of shear deformable thin-walled non-symmetric curved beams subjected to initial axial forces are evaluated and compared with analytical and FE solutions using isoparametric and Hermitian curved beam elements and results by ABAQUS\' shell elements.

Key Words
thin-walled; curved beam; dynamic stiffness matrix; free vibration; shear deformation.

Address
Department of Civil and Environmental Engineering, Sungkyunkwan University, Cheoncheon-Dong, Jangan-Ku, Suwon 440-746, S. Korea

Abstract
The standard practice is to seismically qualify the safety related equipment and structural components used in the nuclear power plants. Among several qualification approaches the qualification by the analysis using finite element (FE) method is the most common approach used in practice. However the predictions by the FE model for a structure is known to show significant deviations from the dynamic behaviour of

Key Words
modal test; FE modelling; model updating; seismic analysis.

Address
Jyoti K. Sinha and A. Rama Rao;
Vibration Laboratory, Reactor Engineering Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
R. K. Sinha; Reactor Design and Development Group, Bhabha Atomic Research Centre, Mumbai 400 085, India

Abstract
The suboptimal control rule is introduced in structural control implementation as an alternative over the optimal control because the optimal control may require large amount of processing time when applied to complex structural control problems. It is well known that any time delay in structural control implementation will cause un-synchronized application of the control forces, which not only reduce the effectiveness of an active control system, but also cause instability of the control system. The effect of time delay on the displacement and acceleration responses of building structures is studied when the suboptimal control rule is adopted. Two examples are given to show the effectiveness of the suboptimal control rule. It is shown through the examples that the present method is easy in implementation and high in efficiency and it can significantly reduce the time delay in structural control implementation without significant loss of performance.

Key Words
suboptimal control; optimization; structural control; time delay; vibration; earthquake simulation.

Address
J. Y. Xu; Department of Civil Engineering, Wuhan University of Technology, Wuhan 430070, P.R. China
Q. S. Li; Department of Building and Construction, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong
G. Q. Li; Department of Civil Engineering, Wuhan University of Technology, Wuhan 430070, P.R. China
(School of Engineering and Science, Swinburne University of Technology, John Street, Howthorn, Victoria 3122, Australia)
J. R. Wu and J. Tang; Department of Building and Construction, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong


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