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CONTENTS
Volume 9, Number 2, February 2000
 

Abstract
Truss type structures are attractive to a variety of engineering applications on earth as well as in space due to their high stiffness to mass ratios and ease of construction and fabrication. During the service life, an individual member of a truss structure may lose load carrying capacity due to many reasons, which may lead to collapse of the structure. An analytical and computational procedure has been developed to study the response of truss structures subject to member failure under static and dynamic loadings. Emphasis is given to the dynamic effects of member failure and the propagation of local damage to other parts of the structure. The methodology developed is based on nonlinear finite element analysis technique and considers elasto-plastic material nonlinearity, postbuckling of members, and large deformation geometric nonlinearity. The pseudo force approach is used to represent the member failure. Results obtained for a planar nine-bay indeterminate truss undergoing sequential member failure show that failure of one member can initiate failure of several members in the structure.

Key Words
truss structures, progressive failure, dynamic member failure, dynamic nonlinear analysis, buckling, post-buckling response, member failure propagation

Address
Malla RB, Univ Connecticut, Dept Civil & Environm Engn, Storrs, CT 06269 USA
Univ Connecticut, Dept Civil & Environm Engn, Storrs, CT 06269 USA
GM Corp, Electromot Div, Lagrange, IL 60525 USA

Abstract
The isoparametric element method is used for a plate on non-homogenous foundation. The surface displacement due to a point force acting on the non-homogeneous foundation is the fundamental solution. Based on this analysis, the interaction between the foundation and plate can be determined and the reaction of the foundation can be treated as the external force to the plate. Therefore, only the plate needs to be divided into some elements. The method presented in this paper can be used in cases such as thin or thick plate, different plate shapes, various loading, homogenous and non-homogenous foundations. The examples in this paper show that this method is versatile, efficient and highly accurate.

Key Words
plate on foundation, elastic half-space, non-homogeneous elastic half-space, fundamental solution

Address
Wang YH, Huazhong Univ Sci & Technol, Dept Civil Engn, Wuhan 430074, Peoples R China
Huazhong Univ Sci & Technol, Dept Civil Engn, Wuhan 430074, Peoples R China
Univ Hong Kong, Dept Civil Engn, Hong Kong, Hong Kong

Abstract
Based on the discussion about some empirical coherency models resulted from earthquake-induced ground motion recordings at the SMART-1 array in Taiwan, and a heuristic model of the coherency function from elementary notions of stationary random process theory and a few simplifying assumptions regarding the propagation of seismic waves, a practical coherency model for spatially varying ground motions, which can be applied in aseismic analysis and design, is proposed, and the regressive coefficients are obtained using least-square fitting technique from the above recordings.

Key Words
coherency function, practical model, strong ground motion, spatial variability

Address
Yang QS, No Jiaotong Univ, Dept Civil Engn, Beijing 100044, Peoples R China
No Jiaotong Univ, Dept Civil Engn, Beijing 100044, Peoples R China

Abstract
This paper presents four incompatible but convergent Rational quadrilateral elements, two four-node elements (RQ4Z and RQ4B) and two five-node elements (RQ5Z and RQ5B). The difference between the so-called Rational Finite Element (Zhong and Zeng 1996) and the Free Formulation (Bergan and Nygard 1984) are discussed and compared. The importance of the mode completeness in these formulations is emphasized. Numerical results for several benchmark problems show the good performance of these elements. The two five-nodes elements RQ5Z and RQ5B, which can be viewed as complete quadratic mode elements (with seven stress modes), always give better results than the four nodes elements RQ4Z and RQ4B.


Key Words
finite elements, quadrilateral, patch-tests, basic solutions of elasticity, rational elements

Address
Batoz JL, Univ Technol Compiegne, Lab Genie Mecan Mat & Struct, CNRS, UPRESA 6066, BP 20529, F-60205 Compiegne, France
Univ Technol Compiegne, Lab Genie Mecan Mat & Struct, CNRS, UPRESA 6066, F-60205 Compiegne, France

Abstract
An optimization procedure has been prescribed for the minimum weight design of symmetrical parabolic arches subjected to arbitrary loading. The cross section is assumed to be a symmetrical box section with variable depth and flange areas. The webs are unstiffened and have constant thickness. The proposed sequential, iterative search technique determines the optimum geometrical configuration of the parabolic arch which includes the optimum depth profile and the optimum lengths and areas of the required flange plates corresponding to the prescribed number of curtailments. The study shows that the optimum value of rise to span ratio (h/L) of a parabolic arch is maximum at 0.41 for uniformly distributed loading over the entire span. For any other loading, the optimum value of h/L is less than 0.41.

Key Words
optimization, arches, structural design, steel, constraints, minimum weight

Address
Azad AK, King Fahd Univ Petr & Minerals, Dept Civil Engn, Dhahran 31261, Saudi Arabia
King Fahd Univ Petr & Minerals, Dept Civil Engn, Dhahran 31261, Saudi Arabia

Abstract
The objective of this research is to propose a new global damage detection parameter, termed as the static defect energy (SDE). This candidate parameter possesses the ability to detect, locate and quantify structural damage. To have a full understanding about this parameter and its applications, the scope of work can be divided into several tasks: theory and formulation, numerical simulation studies, experimental verification and feasibility studies. This paper only deals with the first part of the task. Brief introduction will be given to the dynamic defect energy (DDE) after systematically reviewing the previous works. Process of applying the perturbation method to the oscillatory system to obtain a static expression will be followed. Two implementation methods can be used to obtain SDE equations and the diagrams. Both results are equally good for damage detection.

Key Words
damage assessment, static defect energy, global method, perturbation method

Address
Tseng SS, Natl Kaohsiung Inst Technol, Dept Civil Engn, 415 Cheng Kung Rd, Kaohsiung 807, Taiwan
Natl Kaohsiung Inst Technol, Dept Civil Engn, Kaohsiung 807, Taiwan

Abstract
To confirm the theory and static defect energy (SDE) equations proposed in the first part, extensive numerical simulation studies are performed in this portion. Stiffness method is applied to calculate the components of the stresses and strains from which the energy components and finally, the SDE are obtained. Examples are designed to cover almost all kinds of possibilities. Variables include structural type, material, cross-section, support constraint, loading type, magnitude and position. The SDE diagram is unique in the way of presenting damage information: two different energy constants are separated by a sharp vertical drop right at the damage location. Simulation results are successfully implemented for both methods in all the cases.

Key Words
damage assessment, static defect energy, stiffness method

Address
Tseng SS, Natl Kaohsiung Inst Technol, Dept Civil Engn, 415 Cheng Kung Rd, Kaohsiung 807, Taiwan
Natl Kaohsiung Inst Technol, Dept Civil Engn, Kaohsiung 807, Taiwan

Abstract
The main purpose of this paper is to develop the results introduced in Artan (1996) and to find a general nonlocal linear elastic solution for Boussinesq problem. The general nonlocal solution given Artan (1996) is valid only when the distance to the boundary is greater than one atomic measure. The nonlocal stress field presented in this paper is valid for the whole half plane.

Key Words
nonlocal elasticity, Boussinesq problem, half plane

Address
Artan R, Ruhr Univ Bochum, Inst Stat & Dynam, D-44780 Bochum, Germany
Ruhr Univ Bochum, Inst Stat & Dynam, D-44780 Bochum, Germany


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