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CONTENTS
Volume 10, Number 4, October 2000
 

Abstract
The response of an embedded body to dynamic loads is greatly influenced by the reactions of the soil to the motion of the body. The properties of the soil surrounding embedded bodies (e.g., piles) may be different than those of the far-field for a variety of reasons. It may be weakened or strengthened according to the method of installation of piles, or altered due to applying one of the soil strengthening technique (e.g., electrokinetic treatment of soil, El Naggar ct al. 1998). In all these cases, the shear strength of the soils and its shear modulus vary gradually in the radial direction, resulting in a radially inhomogeneous soil layer. This paper describes an analysis to compute vertical and torsional dynamic soil reactions of a radially inhomogeneous soil layer with a circular hole. These soil reactions could then be used to model the soil resistance in the analysis of the pile vibration under dynamic loads. The soil layer is considered to have a piecewise, radial variation for the complex shear modulus. The model is developed for soil layers improved using the electrokinetic technique but can be used for other situations where the soil properties vary gradually in the radial direction (strengthened or weakened). The soil reactions (impedance functions) are evaluated over a wide range of parameters and compared with those obtained from other solutions. A parametric study was performed to examine the effect of different soil improvement parameters on vertical and torsional impedance functions of the soil. The effect of the increase in the shear modulus and the width of the improved zone is investigated.

Key Words
soil reactions, soil improvement, piles, dynamic analysis

Address
El Naggar MH, Univ Western Ontario, Geotech Res Ctr, London, ON N6A 5B9, Canada
Univ Western Ontario, Geotech Res Ctr, London, ON N6A 5B9, Canada

Abstract
The focus of this paper is on the development and implementation of a methodology for automated design of discrete structural systems. The research is aimed at utilizing Genetic Algorithms (GA) as an automated design tool. Several key enhancements are made to the simple GA in order to increase the efficiency, reliability and accuracy of the methodology for code-based design of structures. The AISC-ASD design code is used to illustrate the design methodology. Small as well as large-scale problems are solved. Simultaneous sizing, shape and topology optimal designs of structural framed systems subjected to static and dynamic loads are considered. Comparisons with results from prior publications and solution to new problems show that the enhancements made to the GA do indeed make the design system more efficient and robust.

Key Words
genetic algorithm, optimal design, AISC, frame design, design automation

Address
Chen SY, Honeywell Engines & Syst Inc, Phoenix, AZ USA
Arizona State Univ, Dept Civil Engn, Tempe, AZ 85287 USA

Abstract
Analytical formulations and solutions for the first time, to the stability analysis of a simply supported composite and sandwich plates based on a higher order refined theory, developed by the first author and already reported in the literature are presented. The theoretical model presented herein incorporates laminate deformations which account for the effects of transverse shear deformation, transverse normal strain/stress and a nonlinear variation of inplane displacements with respect to the thickness coordinate - thus modelling the warping of transverse cross sections more accurately and eliminating the need for shear correction coefficients. The equations of equilibrium are obtained using the Principle of Minimum Potential Energy (PMPE). The comparison of the results using this higher order refined theory with the available elasticity solutions and the results computed independently using the first order and the other higher order theories developed by other investigators and available in the literature shows that this refined theory predicts the critical buckling load more accurately than all other theories considered in this paper. New results for sandwich laminates are also presented which may serve as a benchmark for future investigations.

Key Words
higher order theory, analytical solutions, buckling, shear deformation, sandwich plates, laminated plates, Navier solutions

Address
Kant T, Indian Inst Technol, Dept Civil Engn, Bombay 400076, Maharashtra, India
Indian Inst Technol, Dept Civil Engn, Bombay 400076, Maharashtra, India

Abstract
Random loading identification has long been a difficult problem for Multi-Input-Multi-Output (MIMO) structure. In this paper, the Pseudo Excitation Method (PEM), which is an exact and efficient method for computing the structural random response, is extended inversely to identify the excitation power spectral densities (PSD). This identified method, named the Inverse Pseudo Excitation Method (IPEM), resembles the general dynamic loading identification in the frequency domain, and can be used to identify the definite or random excitations of complex structures in a similar way. Numerical simulations are used to reveal the the difficulties in such problems, and the results of some numerical analysis are discussed, which may be very useful in the setting up and processing of experimental data so as to obtain reasonable predictions of the input loading from the selected structural responses.

Key Words
random, loading, identification, simulation, vibration

Address
Zhi H, No Jiaotong Univ, Dept Mech Engn, Beijing 100044, Peoples R China
No Jiaotong Univ, Dept Mech Engn, Beijing 100044, Peoples R China
Dalian Univ Technol, Dept Mech, Dalian 116032, Peoples R China

Abstract
Application of \"advanced analysis\" methods suitable for non-linear analysis and design of steel frame structures permits direct and accurate determination of ultimate system strengths, without resort to simplified elastic methods of analysis and semi-empirical specification equations. However, the application of advanced analysis methods has previously been restricted to steel frames comprising only compact sections that are not influenced by the effects of local buckling. A concentrated plasticity method suitable for practical advanced analysis of steel frame structures comprising non-compact sections is presented in this paper. The pseudo plastic zone method implicitly accounts for the effects of gradual cross-sectional yielding, longitudinal spread of plasticity, initial geometric imperfections, residual stresses, and local buckling. The accuracy and precision of the method for the analysis of steel frames comprising non-compact sections is established by comparison with a comprehensive range of analytical benchmark frame solutions. The pseudo plastic zone method is shown to be more accurate and precise than the conventional individual member design methods based on elastic analysis and specification equations.

Key Words
pseudo plastic analysis, steel frame structures, advanced analysis, local buckling

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

Abstract
Linear stress analysis without body force can be easily solved by means of the boundary element method. Some cases of linear stress analysis with body force can also be solved without a domain integral. However, domain integrals are generally necessary to solve the linear stress problem with arbitrary body forces. This paper shows that the linear stress problem with arbitrary body forces can be solved approximately without a domain integral by the triple-reciprocity boundary element method. In this method, the distribution of arbitrary body forces can be interpolated by the integral equation. A new computer program is developed and applied to several problems.

Key Words
elasticity, body force, boundary element method, computational mechanics, numerical analysis

Address
Ochiai Y, Kinki Univ, Dept Mech Engn, 3-4-1 Kowakae, Higashiosaka, Osaka 577, Japan
Kinki Univ, Dept Mech Engn, Higashiosaka, Osaka 577, Japan
Res Inst Sci Invest Kyoto Pref, Kamigyo Ku, Kyoto 602, Japan

Abstract
Two approximate methods based on mechanism analysis suitable for seismic assessment/design of structural concrete are reviewed. The methods involve use of equal energy concept or equal displacement concept along with appropriate patterns of inelastic deformations to relate structure\'s maximum lateral displacement to member and plastic deformations. One of these methods (Clough\'s method), defined here as a ductility-based approach, is examined in detail and a modification for its improvement is suggested. The modification is based on estimation of maximum inelastic displacement using inelastic design response spectra (IDRS) as an alternative to using equal energy concept. The IDRS for demand displacement ductilities are developed for a single degree of freedom model subjected to several accelerograms as functions of response modification factor (R), damping ratios, and strain hardening. The suggested revised methodology involves estimation of R as the ratio of elastic strength demand to code level demand, and determination of design base shear using R-design less than or equal to R and maximum displacement, determination of plastic displacement using IDRS and subsequent local plastic deformations. The methodology is demonstrated for the case of a 10-story precast wall panel building.

Key Words
precast concrete, seismic design, inelastic response spectra

Address
Astarlioglu S, Penn State Univ, Dept Civil & Environm Engn, University Pk, PA 16802 USA
Penn State Univ, Dept Civil & Environm Engn, University Pk, PA 16802 USA
Penn State Univ, Dept Architectural Engn, University Pk, PA 16802 USA


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