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CONTENTS
Volume 8, Number 1, July 1999
 

Abstract
Procedures are investigated by which nonlinear finite element shell analysis algorithms can be simplified to provide more cost effective approximate analyses of orthogonally-reinforced concrete flat plate structures. Two alternative effective stiffness formulations, and an unbalanced force formulation, are described. These are then implemented into a nonlinear shell analysis algorithm. Nonlinear geometry, three-dimensional layered stress analyses, and other general formulations are bypassed to reduce the computational burden. In application to standard patch test problems, these simplified approximate analysis procedures are shown to provide reasonable accuracy while significantly reducing the computational effort. Corroboration studies using various simple and complex test specimens provide an indication of the relative accuracy of the constitutive models utilized. The studies also point to the limitations of the approximate formulations, and identify situations where one should revert back to full nonlinear shell analyses.

Key Words
analysis, deflection, finite elements, plates, reinforced concrete, slabs, stiffness, tests

Address
Vecchio FJ, Univ Toronto, Dept Civil Engn, Toronto, ON M5S 1A4, Canada
Univ Toronto, Dept Civil Engn, Toronto, ON M5S 1A4, Canada

Abstract
Superior performance of field consistent eight-node hexahedron element in static bending problems has already been demonstrated in literature. In this paper, its performance in free vibration is investigated. Free vibration frequencies of typical test problems have been computed using this element. The results establish its superior performance in free vibration, particularly in thin plate application and near incompressibility regimes, demonstrating that shear locking, Poisson\'s stiffening and volumetric locking have been eliminated.

Key Words
field consistent element, eight-node hexahedron element, free vibration, shear locking, bubble functions

Address
Rajendran S, Mat Technol Applicat Ctr, Singapore Prod & Stand Board, Sci Pk Dr, Singapore 118221, Singapore
Natl Aerosp Labs, Struct Div, Bangalore 560017, Karnataka, India

Abstract
Cables are used in many applications such as cable-stayed bridges, suspension bridges, transmission lines, telephone lines, etc. Generally, the linear relationship is inadequate to present the behavior of cable structure. In finite element analysis, cables have always been modeled as truss elements. For these types of model, the nonlinear behavior of cables has been always ignored. In order to investigate the importance of the nonlinear effect on the structural system, the effect of cable stiffness has been studied. The nonlinear behavior of cable is due to its sag. Therefore, the cable pretension provides a large portion of the inherent stiffness. Since a cable-stayed bridge has numerous degrees of freedom, analytical methods at present are not convenient to solve this type of structures but numerical methods may be feasible. It is necessary to provide a different and more representative analytical model in order to present the effect of cable stiffness on cable-stayed bridges in numerical analysis. The characteristics of cable deformation have also been well addressed. A formulation of modified modulus of elasticity has been proposed using a numerical parametric study. In order to investigate realistic bridges, a cable-stayed bridge having the geometry similar to that of Quincy Bayview Bridge is considered. The numerical results indicate that the characteristics of the cable stiffness are strongly nonlinear. It also significantly affects the structural behaviors of cable-stayed bridge systems.

Key Words
characteristics, cable stiffness, cable-stayed bridge

Address
Wang YC, Chinese Mil Acad, Dept Civil Engn, 1 Hwang Poo Rd, Feng Shan 83000, Thailand
Chinese Mil Acad, Dept Civil Engn, Feng Shan 83000, Thailand

Abstract
The dynamic response of buried pipelines has gained considerable importance because these pipelines perform vital role in conducting energy, water, communication and transportation. After realizing the magnitude of damage, and hence, the human uncomfort and the economical losses, researchers have paid sincere attention to this problem. A number of papers have appeared in the past which discuss the different aspects of the problem. This paper presents a theoretical analysis of nonaxisymmetric dynamic response of buried orthotropic cylindrical shell subjected to a moving load along the axis of the shell. The orthotropic shell has been buried in a homogeneous, isotropic and elastic medium of infinite extent. A thick shell theory including the effects of rotary inertia and shear deformation has been used. A perfect bond between the shell and the surrounding medium has been assumed. Results have been obtained for very hard (rocky), medium hard and soft soil surrounding the shell. The effects of shell orthotropy have been brought out by varying the non-dimensional orthotropic parameters over a long range. Under these conditions the shell response is studied in axisymmetric mode as well as in the flexural mode. It is observed that the shell response is significantly affected by change in orthotropic parameters and also due to change of response mode. It is observed that axial deformation is large in axisymmetric mode as compared to that in flexural mode.

Key Words
buried pipelines, cylindrical shell, dynamic response, moving load, non-axisymmetric response

Address
Singh VP, Banaras Hindu Univ, Inst Technol, Dept Mech Engn, Varanasi 221005, Uttar Pradesh, India
Banaras Hindu Univ, Inst Technol, Dept Mech Engn, Varanasi 221005, Uttar Pradesh, India

Abstract
The most important features of linear soil-foundation-structure interaction are reviewed, using stochastic modeling and considering kinematic interaction, inertial interaction, and structural distortion as three separate stages of the dynamic response to the free-field motion. The way in which each of the three dynamic stages modifies the spectral density of the motion is studied, with the emphasis being on interpretation of these results, rather than on the development of new analysis techniques. Structural distortion and inertial interaction analysis are shown to be precisely modeled as linear filtering operations. Kinematic interaction, though, is more complicated, even though it has a filter-like effect on the frequency content of the motion.

Key Words
filtering, seismic, soil-structure interaction, stochastic models, transfer functions

Address
Sarkani S, George Washington Univ, Sch Engn & Appl Sci, Washington, DC 20052 USA
George Washington Univ, Sch Engn & Appl Sci, Washington, DC 20052 USA
Texas A&M Univ, Dept Civil Engn, College Stn, TX 77843 USA
Haynes Whaley Associates Inc, Houston, TX USA

Abstract
This paper is concerned with shape optimization problems by the boundary element method (BEM) emphasizing the use of a reduced basis reanalysis technique proposed recently by the author. Problems of this class are conventionally carried out iteratively through an optimizer; a sequential quadratic programming-based optimizer is used in this study. The iterative process produces a succession of intermediate designs. Repeated analyses for the systems associated with these intermediate designs using an exact approach such as the LU decomposition method are time consuming if the order of the systems is large. The newly developed reanalysis technique devised for boundary element systems is utilized to enhance the computational efficiency in the repeated system solvings. Presented numerical examples on optimal shape design problems in electric potential distribution and elasticity show that the new reanalysis technique is capable of speeding up the design process without sacrificing the accuracy of the optimal solutions.

Key Words
shape optimization, boundary element method, reduced basis, reanalysis

Address
Leu LJ, Natl Taiwan Univ, Dept Civil Engn, Taipei 106, Taiwan
Natl Taiwan Univ, Dept Civil Engn, Taipei 106, Taiwan

Abstract
With the advent of computer, the finite element method has become a most powerful numerical method for structural analysis. However, bridge designers are reluctant to use it in their designs because of its complex nature and its being time consuming in the preparation of the input data and analyzing the results. This paper describes the development of a computer based finite element model using the idea of eccentric beam elements for the analysis of slab-on-girder bridges. The proposed method is supported by a laboratory test using a reinforced concrete bridge model. Other bridge analytical schemes are also introduced and compared with the proposed method. The main aim of the comparison is to prove the effectiveness of the shell and eccentric beam modelling in the studies of lateral load distribution of slab-on-girder bridges. It is concluded that the proposed finite element method gives a closer to real idealization and its developed computer program, SHECAN, is also very simple to use. It is highly recommended to use it as an analytical tool for the design of slab-on-girder bridges.

Key Words
bridge deck analysis, eccentric beam model, finite element methods, grillage analogy method, lateral load distribution, rigid link element, semi-continuum method, slab-on-girder bridge

Address
Chan THT, Hong Kong Polytech Univ, Dept Civil & Struct Engn, Kowloon, Hong Kong
Hong Kong Polytech Univ, Dept Civil & Struct Engn, Kowloon, Hong Kong

Abstract
The structural integrity of the reactor pressure vessel under pressurized thermal shock (PTS) is evaluated in this study. For given material properties and transient histories such as temperature and pressure, the stress distribution is found and stress intensity factors are obtained for a wide range of crack sizes. The stress intensity factors are compared with the fracture toughness to check if cracking is expected to occur during the transient. A round robin problem of the PTS during a small break loss of coolant transient has been analyzed as a part of the international comparative assessment study, and the evaluation results are discussed. The maximum allowable nil-ductility transition temperatures are determined for various crack sizes.

Key Words
reactor vessel, pressurized thermal shock, stress intensity factor, fracture toughness, crack initiation, nil-ductility transition temperature

Address
Jhung MJ, Korea Inst Nucl Safety, Yusong Gu, 19 Kusong Dong, Taejon 305338, South Korea
Korea Inst Nucl Safety, Yusong Gu, Taejon 305338, South Korea


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