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CONTENTS
Volume 8, Number 2, August 1999
 

Abstract
The failure load of a continuous prestressed concrete beam depends partially on the amount of redistribution of moment that occurs prior to failure. Results from a parametric study, carried out using a nonlinear finite element computer program, are presented to demonstrate the influences of various factors on redistribution of moment in two-span, continuous bonded prestressed concrete beams. Trends in the data from the numerical studies are compared with those from a theoretical expression for percentage of redistribution, and it is shown that the redistribution of moment occurring in a continuous prestressed concrete beam is a function of number of parameters.

Key Words
redistribution of moment, continuous beam, prestressed concrete, nonlinear analysis, secondary moment, parametric study, bonded post-tensioned beams

Address
Kodur VKR, Natl Res Council Canada, Inst Res Construct, Ottawa, ON K1A 0R6, Canada
Natl Res Council Canada, Inst Res Construct, Ottawa, ON K1A 0R6, Canada

Abstract
This paper presents a numerical study on the flat plates in deep basements, subjected to floor load and in-plane compressive load due to soil and hydraulic lateral pressure. For nonlinear finite element analysis, a computer program addressing material and geometric nonlinearities is developed. The validity of the numerical model is established by comparison with existing experiments performed on plates simply supported on four edges. The flat plates to be studied are designed according to the Direct Design Method in ACI 318-95. Through numerical study on the effects of different load combinations and loading sequence, the load condition that governs the strength of the flat plates is determined. For plates under the governing load condition, parametric studies are performed to investigate the strength variations with reinforcement ratio, aspect ratio, concrete strength, and slenderness ratio. Based on the numerical results, the floor load magnification factor is proposed.

Key Words
axial compression, finite element analysis, flat plate, reinforced concrete, slenderness, two-way slab

Address
Park H, Seoul Natl Univ, Dept Architecture, San 56-1, Seoul 151742, South Korea
Seoul Natl Univ, Dept Architecture, Seoul 151742, South Korea

Abstract
The large deflection theory of the Mindlin plate and Galerkin\'s method are employed to examine the static responses of a plate produced by the weight of the plate, and the dynamic responses of the plate caused by the coupling effect of these static responses with a set of moving forces. Results obtained by the large deflection theory are compared with those by the small deflection theory. The results indicate that the effect of weight of the plate increases the modal frequencies of the structure. The deviations of dynamic transverse deflection and of dynamic bending moment produced by a moving concentrated force between the two theories are significant for a thin plate with a large area. Both dynamic transverse deflection and dynamic bending moment obtained by the Mindlin plate theory are greater than those by the classical plate.

Key Words
large deflection theory, Mindlin plate, weight, moving force

Address
Wang RT, Natl Cheng Kung Univ, Dept Engn Sci, Tainan 70101, Taiwan
Natl Cheng Kung Univ, Dept Engn Sci, Tainan 70101, Taiwan

Abstract
The cost effectiveness of using steel roof systems fur residential buildings is becoming increasingly apparent with the decrease in manufacturing cost of steel components, reliability and efficiency in construction practices, and the economic and environmental concerns. While steel has been one of the primary materials for structural systems, it is only recently that its use for residential buildings is being explored. A comprehensive system for the design of residential steel roof truss systems is presented. In the first stage of the research the design curves obtained from the AISI-LRFD code for the manufactured cross-sections were verified experimentally. Components of the truss systems were tested in order to determine their member properties when subjected to axial force and bending moments. In addition, the experiments were simulated using finite element analysis to provide an additional source of verification. The second stage of the research involved the development of an integrated design approach that would automatically design a lowest cost roof truss given minimal input. A modified genetic algorithm was used to handle sizing, shape and topology variables in the design problem. The developed methodology was implemented in a software system for the purpose of designing the lowest cost truss that would meet the AISI code provisions and construction requirements given the input parameters. The third stage of the research involved full-scale testing of a typical residential steel roof designed using the developed software system. The full scale testing established the factor of safety while validating the analysis and design procedures. Evaluation of the test results indicates that designs using the present approach provide a structure with enough reserve strength to perform as predicted and are very economical.

Key Words
steel roof truss, full-scale testing, design curves, finite element analysis, optimal design

Address
Rajan SD, Arizona State Univ, Dept Civil & Environm Engn, Tempe, AZ 85287 USA
Arizona State Univ, Dept Civil & Environm Engn, Tempe, AZ 85287 USA

Abstract
This paper presents an investigation of the mode localization and frequency loci veering phenomena in an aircraft with disordered external stores. Two theoretical analyses are carried out to study the occurring mechanism of the two phenomena: condensation technique in the subspace spanned by modes of interest and geometric mapping theory in the complex plane. Two simple criteria for predicting the occurrence of the mode localization and frequency loci veering are put forward. The prediction of the phenomena by our theoretically proposed criteria is in good agreement with that obtained through numerical calculations of characteristic solutions of the disordered system.

Key Words
structural dynamics, aircraft, external stores, disorder, mode localization, frequency loci veering, geometric theory, complex plane mapping, condensation, subspace, eigenvalue problem

Address
Liu JK, Zhongshan Univ, Dept Mech, Guangzhou, Peoples R China
Zhongshan Univ, Dept Mech, Guangzhou, Peoples R China
Univ Hong Kong, Dept Civil Engn, Hong Kong, Hong Kong

Abstract
A formulation for the dynamic stability analysis of cylindrical shells resting on elastic foundations is presented. In this previously not studied problem, a normal-mode expansion of the partial differential equations of motion, which includes the effects of the foundation as well as a harmonic axial loading, yields a system of Mathieu-Hill equations the stability of which is analyzed using Bolotin\'s method. The present study examines the effects of the elastic foundation on the instability regions of the cylindrical shell for the transverse, longitudinal and circumferential modes.

Key Words
dynamic stability, elastic foundation, cylindrical shell

Address
Ng TY, Natl Univ Singapore, Inst High Performance Comp, 89B Sci Pk Dr,01-05-08, Singapore 118261, Singapore
Natl Univ Singapore, Inst High Performance Comp, Singapore 118261, Singapore

Abstract
A versatile 4-node shell element which is useful for the analysis of arbitrary shell structures is presented. The element is developed by flat shell approach, i.e., by combining a membrane element with a Mindlin plate element. The proposed element has six degrees of freedom per node and permits an easy connection to other types of finite elements. Tn the plate bending part, an improved Mindlin plate has been established by the combined use of the addition of non-conforming displacement modes (N) and the substitute shear strain fields (S). Tn the membrane part, the nonconforming displacement modes are also added to the displacement fields to improve the behavior of membrane element with drilling degrees of freedom and the modified numerical integration (M) is used to overcome the membrane locking problem. Thus the element is designated as NMS-4F. The rigid link correction technique is adopted to consider the effect of out-of-plane warping. The shell element proposed herein passes the patch tests, does not show any spurious mechanism and does not produce shear and membrane locking phenomena. It is shown that the element produces reliable solutions even for the distorted meshes through the analysis of benchmark problems.

Key Words
shell element, non-conforming mode, plate element, membrane element, drilling degree of freedom, substitute shear strain, modified integration, rigid link correction

Address
Choi CK, Korea Adv Inst Sci & Technol, Dept Civil Engn, Taejon 305701, South Korea
Korea Adv Inst Sci & Technol, Dept Civil Engn, Taejon 305701, South Korea
Res Inst Ind Sci & Technol, Steel Str Tech Div, Kyungkido 445810, South Korea


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