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CONTENTS
Volume 7, Number 5, May 1999
 

Abstract
Sandwich panels comprising steel facings and a polystyrene foam core are increasingly used as roof and wall claddings in buildings in Australia. When they are subjected to loads causing bending and/or axial compression, the steel plate elements of their profiled facing are susceptible to local buckling. However, when compared to panels with no foam core, they demonstrate significantly improved local buckling behaviour because they are supported by foam. In order to quantify such improvements and to validate the use of available design buckling stress formulae, an investigation using finite element analyses and laboratory experiments was carried out on steel plates that are commonly used in Australia of varying yield stress and thickness supported by a polystyrene foam core. This paper presents the details of this investigation, the buckling results and their comparison with available design buckling formulae.

Key Words
local buckling, steel plates, plastic foam core, sandwich panels

Address
Mahendran M, Queensland Univ Technol, Sch Civil Engn, Phys Infrastruct Ctr, Brisbane, Qld 4000, Australia
Queensland Univ Technol, Sch Civil Engn, Phys Infrastruct Ctr, Brisbane, Qld 4000, Australia

Abstract
This paper presents a solution method, which can be regarded as the further extension of the generalized evolutionary method (Zhao et al. 1998a), for the simultaneous optimization of several different natural frequencies of a structure in general and a two dimensional structure in particular. The main function of the present method is to optimize the topology of a structure so as to simultaneously make several different natural frequencies of interest to be of the corresponding different desired values for the target structure. In order to develop the present method, the new contribution factor of an element is proposed to consider the contribution of an element to the gaps between the currently calculated values for the different natural frequencies of interest and their corresponding desired values in a weighted manner. Using this new contribution factor of an element, the most inefficiently used material can be detected and removed gradually from the design domain of a structure. Through applying the present method to optimize two and three different natural frequencies of a two dimensional structure, it has been demonstrated that it is possible and applicable to use the generalized evolutionary method for tackling the simultaneous optimization of several different natural frequencies of a structure in the structural design.

Key Words
simultaneous optimization, several natural frequencies, generalized evolutionary method

Address
Zhao CB, CSIRO, Div Explorat & Min, POB 437, Nedlands, WA 6009, Australia
CSIRO, Div Explorat & Min, Nedlands, WA 6009, Australia
Univ Sydney, Fac Engn, Finite Element Anal Res Ctr, Sydney, NSW 2006, Australia
Victoria Univ Technol, Dept Civil & Bldg Engn, MCMC, Melbourne, Vic 8001, Australia

Abstract
In this paper, different curvature-rates are controlled to highlight the characteristic of viscoplastic response in cyclic bending tests. The curvature-ovalization apparatus, which was designed by Pan et al. (1998), is used for conducting the curvature-controlled experiments on thin-walled tubular specimens for AISl 304 stainless steel under cyclic bending. The results reveals that the faster the curvature-rate implies, the fast degree of hardening of the metal tube. However, the ovalization of the tube cross-section increases when the curvature-rate increases.

Key Words
viscoplastic response, thin-walled tube, cyclic bending, endochronic theory.

Address
Pan WF, Natl Cheng Kung Univ, Dept Engn Sci, Tainan 701, Taiwan
Natl Cheng Kung Univ, Dept Engn Sci, Tainan 701, Taiwan
Tung Fung Jr Coll Technol, Dept Arts Craft, Kao Hsiung Cty, Taiwan

Abstract
In the present study, the thermal buckling analysis of thick anisotropic laminated composite plates is carried out using the finite strip method based on the higher-order shear deformation theory. This theory accounts for the parabolic distribution of the transverse shear strains through the thickness of the plate and for zero transverse shear stresses on the plate surfaces. Therefore, this theory yields improved results over the Mindlin plate theory and eliminates the need for shear correction factors in calculating the transverse shear stiffness. The critical temperatures of simply supported rectangular cross-ply and angle-ply composite laminates are calculated. The effects of several parameters, such as the aspect ratio, the length-to-thickness ratio, the number of plies, fibre orientation and stacking sequence, are investigated.

Key Words
thermal buckling, composite plate, finite strip method.

Address
Cheung MS, Univ Ottawa, Dept Civil Engn, Ottawa, ON K1N 9B4, Canada
Univ Ottawa, Dept Civil Engn, Ottawa, ON K1N 9B4, Canada
Royal Mil Coll Canada, Dept Civil Engn, Kingston, ON K7K 5L0, Canada
Carleton Univ, Dept Civil Engn, Ottawa, ON K1S 5B6, Canada

Abstract
Using the continuous Hopfield network model as the basis to solve the general crisp and fuzzy constrained optimization problem is presented and examined. The model lies in its transformation to a parallel algorithm which distributes the work of numerical optimization to several simultaneously computing processors. The method is applied to different structural engineering design problems that demonstrate this usefulness, satisfaction or potential. The computing algorithm has been given and discussed for a designer who can program it without difficulty.

Key Words
Hopfield-Tank neural networks, Hopfield neuron based optimization, engineering optimization, structural optimization, fuzzy optimization, nonlinear programming

Address
Shih CJ, Tamkang Univ, Dept Engn Mech, Tamsui 25137, Taiwan
Tamkang Univ, Dept Engn Mech, Tamsui 25137, Taiwan

Abstract
Practicing a hole or an orifice through a plate or a slab constitutes a very frequent engineering situation due to operational reasons imposed on the structural system. From a designer\'s viewpoint it is important to know the effect of this modification of the mechanical system upon its elastodynamic characteristics. The present study deals with the determination of the lower natural frequencies of the structural element described in the title of the paper using a variational approach and expressing the displacement amplitude of the plate in terms of the double Fourier series which constitutes the classical, exact solution when the structure is simply supported at its four edges.

Key Words
simply supported, orthotropic, rectangular plates, cut-outs, elastically mounted mass, Rayleigh-Ritz, double Fourier series

Address
Avalos DR, Univ Mar del Plata, Sch Engn, Dept Phys, RA-7600 Mar Del Plata, Argentina
Univ Mar del Plata, Sch Engn, Dept Phys, RA-7600 Mar Del Plata, Argentina
Univ Nacl Sur, Dept Engn, RA-8000 Bahia Blanca, Argentina
CONICET, Inst Appl Mech, RA-8000 Bahia Blanca, Argentina

Abstract
This paper presents exact close form solutions of plastic limit loads of a clamped circular plate under uniformly distributed load with different loading radii. A unified yield criterion, which includes a family of piecewise linear yield criteria and the commonly adopted yield criteria such as the Tresca criterion and the maximum principal deviatoric stress criterion or the twin shear stress criterion that are its special cases, and the Mises criterion can be approximated by it, is employed in the analysis. The plastic limit loads, moment fields and velocity fields of the clamped circular plate are calculated based on the unified yield criterion. The influences of the yield criteria, the edge effects and the loading radius on the plastic limits of the clamped circular plate are investigated. Analytical results are calculated and compared. The exact close form solutions presented in this paper provide efficient approaches for obtaining plastic limit loads and the corresponding moments and velocities of the clamped circular plates. The previously derived solutions based on the Tresca and the Mises criteria are its special cases.

Key Words
plastic limit analysis, circular plate, yield criterion, moment fields, velocity fields

Address
Ma GW, Nanyang Technol Univ, Sch Civil & Struct Engn, Nanyang Ave, Singapore 639798, Singapore
Nanyang Technol Univ, Sch Civil & Struct Engn, Singapore 639798, Singapore
Iwate Univ, Dept Civil & Environm Engn, Morioka, Iwate 020, Japan


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