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CONTENTS
Volume 4, Number 2, March 1996
 

Abstract
New active \'\'intelligent\'\' structural systems with integrated self-sensing, diagnosis, and control capabilities can lead to a new design dimension for the next generation high-performance structures and mechanical systems. However, temperature effects to the piezoelectric transducers are not fully understood. This paper is concerned with a mathematical modeling and analysis of a laminated piezothermoelastic cylindrical shell composite exposed to mechanical, electric, and thermal fields. Generic shell equations and solution procedures are derived. Contributions of spatial and time components in the mechanical, electric, and temperature excitations are discussed and their analytical solutions derived. A laminated cylindrical shell composite with fully distributed piezoelectric layers is used in a case study; its multifield step and impulse responses are investigated. Analyses suggest that the fully distributed actuators are insensitive to even modes due to load averaging and cancellation. Accordingly, these even modes are filtered from the total response and only the modes that are combinations of m = 1, 3, 5, ... and n = 1, 3, 5, ... participating in dynamic response of the shell.

Key Words
piezoelectric transducers, smart structures, distributed control

Address
Tzou HS, UNIV KENTUCKY,CTR MFG SYST,DEPT MECH ENGN,LEXINGTON,KY 40506

Abstract
This paper deals with the application of certain active and passive control mechanisms to control the dynamic response of a steel jacket platform due to wave-induced forces. The forces are estimated using the nonlinear Morison equation which provides nonlinear self-excited hydrodynamic forces. The influence of these forces on the response of a structure without and with vibration control mechanisms is demonstrated using a steel jacket platform as a simple example.

Key Words
active control, control mechanisms, hydrodynamic forces, nonlinear dynamics, offshore structures, structural control

Address
AbdelRohman M, KUWAIT UNIV,DEPT CIVIL ENGN,POB 5969,SAFAT 13060,KUWAIT

Abstract
Vector algorithms and the relative importance of the four basic modules (computation of element stiffness matrices, assembly of the global stiffness matrix, solution of the system of linear simultaneous equations, and calculation of stresses and strains) of a finite element computer program for inelastic analysis of reinforced concrete shells are presented. Performance of the vector program is compared with a scalar program. For a cooling tower problem, the speedup factor from the scalar to the vector program is 34 for the element stiffness matrices calculation, 25.3 for the assembly of global stiffness matrix, 27.5 for the equation solver, and 37.8 for stresses, strains and nodal forces computations on a Gray Y-MP. The overall speedup factor is 30.9. When the equation solver alone is vectorized, which is computationally the most intensive part of a finite element program, a speedup factor of only 1.9 is achieved.

When the rest of the program is also vectorized, a large additional speedup factor of 15.9 is attained. Therefore, it is very important that all the modules in a nonlinear program are vectorized to gain the full potential of the supercomputers. The vector finite element computer program for inelastic analysis of RC shells with layered elements developed in the present study enabled us to perform mesh convergence studies. The vector program can be used for studying the ultimate behavior of RC shells and used as a design tool.


Key Words
inelastic, inelasticity, nonlinear, nonlinearity, vector computer, vector programming, vector algorithm, finite element method, finite element analysis, reinforced concrete shells

Address
Min CS, CHEJU NATL UNIV,DEPT OCEAN & CIVIL ENGN,CHEJU 690756,SOUTH KOREA
N CAROLINA STATE UNIV,CTR NUCL POWER PLANT STRUCT EQUIPMENT & PIPING,RALEIGH,NC 27695

Abstract
A postbuckling analysis is presented for a simply supported, moderately thick rectangular plate subjected to combined axial compression and uniform temperature loading and resting on a two-parameter elastic foundation. The two cases of thermal postbuckling of initially compressed plates and of compressive postbuckling of initially heated plates are considered. The initial geometrical imperfection of the plate is taken into account. The formulations are based on the Reissner-Mindlin plate theory considering the first order shear deformation effect, and including the plate-foundation interaction and thermal effect. The analysis uses a deflection-type perturbation technique to determine the buckling loads and postbuckling equilibrium paths. Numerical examples cover the performances of perfect and imperfect, moderately thick plates resting on Winkler or Pasternak-type elastic foundations. Typical results are presented in dimensionless graphical form.

Key Words
structural stability, thermomechanical postbuckling, moderately thick plate, Pasternak-type elastic foundation, perturbation method

Address
Shen HS, SHANGHAI JIAO TONG UNIV,DEPT CIVIL ENGN,SHANGHAI 200030,PEOPLES R CHINA

Abstract
The tension and compression buckling behaviour of a square plate with localized zones of damage and subjected to non-uniform loading is studied using a finite element analysis. The influence of parameters such as position of damage, extent of damage, size of damage and position of load on instability behaviour are discussed. The dynamic behaviour for certain load and damage parameters are also presented. It is observed that the presence of damage has a marked effect on the static buckling load and natural frequency of the plate.

Key Words
stability, plates, tension buckling, compression buckling, vibration, in-plane load

Address
Prabhakara DL, INDIAN INST TECHNOL,DEPT AEROSP ENGN,KHARAGPUR 721302,W BENGAL,INDIA

Abstract
A method to numerically evaluate the behaviour of single span beams, prestressed with external tendons and symmetrically loaded is presented. This algorithm, based on the Finite Difference Method, includes second order effects and large displacements in an attempt to more fully understand the behaviour of the beam up to collapse. The numerical technique discussed is particularly appropriate for the analysis of R.C. and P.C. beams rehabilitated or strengthened by means of external prestressing but it is reliable for the analysis of new beams as well.

Key Words
external prestressing, numerical method, simple span beams

Address
Pisani MA, POLITECN MILAN,DEPT STRUCT ENGN,PZZA L DA VINCI 32,I-20133 MILAN,ITALY

Abstract
This paper presents a construction of adaptive boundary element for the problem with mixed boundary conditions such as heat transfer between heated body surface and surrounding medium. The scheme is based on the sample point error analysis and on the extended error indicator, proposed earlier by the authors for the potential and elastostatic problems, and extended successfully to multidomain and thermoelastic analyses. Since the field variable is connected with its derivative on the boundary, their errors are also interconnected by the specified condition. The extended error indicator on each boundary element is modified to meet with the situation. Two numerical examples are shown to indicate the differences due to the prescribed boundary conditions.

Key Words
boundary element method, adaptive mesh, error analysis, h-version method, boundary conditions, mixed boundary conditions, potential problem, elastostatics

Address
Kamiya N, NAGOYA UNIV,SCH INFORMAT & SCI,DEPT INFORMAT & NAT SCI,NAGOYA,AICHI 46401,JAPAN
NAGOYA UNIV,GRAD SCH,NAGOYA,AICHI 46401,JAPAN
NIPPON HP CO,SUGINAMI KU,TOKYO 168,JAPAN


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