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CONTENTS
Volume 8, Number 3, September 1999
 

Abstract
In the present study, the elasto-plastic analysis of prismatic plate structures subjected to pure bending is carried out using the finite strip method. The end cross-sections of the structure are assumed to remain plane during deformation, and the compatibility along corner lines is ensured by choosing proper displacement functions. The effects of both the initial geometrical imperfections and residual stresses due to fabrication are included in the combined geometrically and materially nonlinear simulation. The von-Mises yield criterion and the Prandtl-Reuss flow theory of plasticity are applied in modelling the elasto-plastic behavior of material. Newton-Raphson iterations are carried out as the rotation of the end cross sections of the structure is increased step by step. The parameter representing the overall axial strain of structure is adjusted constantly during the iteration process in order to eliminate the resulting overall axial force on any cross-section of the structure in correspondence with the assumption of zero axial force in pure bending. Several numerical examples are presented to validate the present method and to investigate the effects of some material and geometrical parameters.

Key Words
finite strip, elasto-plastic analysis, thin walled structures, pure bending.

Address
Cheung MS, Univ Ottawa, Dept Civil Engn, Ottawa, ON K1N 9B4, Canada
Univ Ottawa, Dept Civil Engn, Ottawa, ON K1N 9B4, Canada
Royal Mil Coll Canada, Dept Civil Engn, Kingston, ON K7K 5L0, Canada
Carleton Univ, Dept Civil Engn, Ottawa, ON K1S 5B6, Canada

Abstract
Using appropriate transformations, the differential equation for flexural free vibration of a cantilever bar with variably distributed mass and stiffness is reduced to a Bessel\'s equation or an ordinary differential equation with constant coefficients by selecting suitable expressions, such as power functions and exponential functions, for the distributions of stiffness and mass. The general solutions for flexural free vibration of one-step bar with variable cross-section are derived and used to obtain the frequency equation of multi-step cantilever bars. The new exact approach is presented which combines the transfer matrix method and closed form solutions of one step bars. Two numerical examples demonstrate that the calculated natural frequencies and mode shapes of a 27-storey building and a television transmission tower are in good agreement with the corresponding experimental data. It is also shown through the numerical examples that the selected expressions are suitable for describing the distributions of stiffness and mass of typical tall buildings and high-rise structures.

Key Words
vibration, natural frequency, mode shape, tall building

Address
Li QS, City Univ Hong Kong, Dept Bldg & Construct, Tat Chee Ave, Hong Kong, Hong Kong
City Univ Hong Kong, Dept Bldg & Construct, Hong Kong, Hong Kong

Abstract
In this paper a simple finite element is proposed for analyzing out of plane vibration of thin walled curved beams, with both open and closed sections, considering shear flexibility. The present element is obtained from a variational formulation governing the dynamics of a three-dimensional elastic body in which the stress tensor as well as the displacements are variationally independent. The element has two nodes with four degrees of freedom in each. Numerical examples for the first six frequencies are performed in order to assess the accuracy of the finite element formulation and to show the influence of the shear flexibility on the dynamics of the member.

Key Words
beam, bridges, finite element, shear flexibility, thin walled, vibration

Address
Cortinez VH, Univ Technol Nacl, Mech Syst Anal Grp, 11 Abril 461, RA-8000 Bahia Blanca, Buenos Aires, Argentina
Univ Technol Nacl, Mech Syst Anal Grp, RA-8000 Bahia Blanca, Buenos Aires, Argentina
Univ Nacl Sur, Dept Engn, RA-8000 Bahia Blanca, Buenos Aires, Argentina

Abstract
Two physical experiments are performed to verify the effectiveness of beam-particle model for simulating the progressive failure of particulate composites such as sandstone and concrete. In the numerical model, the material is schematized at the meso-level as an assembly of discrete, interacting particles which are linked through a network of brittle breaking beams. The uniaxial compressive tests of cubic and parallelepipedal specimens made of carbon steel rod assembly which are glued together by a mixture are represented. The crack patterns and load-displacement response observed in the experiments are in good agreement with the numerical results. In the application respect of beam-particle model to the particulate composites, the influence of defects, particle arrangement and boundary conditions on crack propagation is approached, and the correlation existing between the cracking evolution and the level of loads imposed on the specimen is characterized by fractal dimensions.

Key Words
beam-particle model, particulate composites, progressive failure, meso-structure, fractal dimension

Address
Xing JB, Yantai Univ, Dept Civil Engn, Yamtai, Peoples R China
Yantai Univ, Dept Civil Engn, Yamtai, Peoples R China
Tsing Hua Univ, Dept Civil Engn, Beijing 100084, Peoples R China

Abstract
A method is presented to find the location and magnitude of damage in a structure using data from dynamic tests. The test data include a combination of natural frequency measurements, taken before and after the occurrence of damage, and response measurements taken after damage. An algorithm is developed to identify localized increases in the flexibility of the structural members. increases in flexibility are attributed to damage. The algorithm uses the sensitivity of the flexibility matrix to changes in the natural frequencies of the structure to identify the damage. A set of underdetermined equations is solved using an objective function which is derived from measurements of the system moments. Damage ranging from 10 to 60% increase in the flexibility of a member was successfully identified in a 50 d.o.f. structure, using a small number of natural frequency and velocity measurements.

Key Words
inverse identification, damage, dynamic measurement, system moments.

Address
Hassiotis S, Univ S Florida, Dept Civil & Environm Engn, Tampa, FL 33620 USA
Univ S Florida, Dept Civil & Environm Engn, Tampa, FL 33620 USA

Abstract
One problem with base isolators of the sliding type is that their dynamic responses are nonlinear, which cannot be solved in an easy manner, as distinction must be made between the sliding and non-sliding phases. The lack of a simple method for analyzing structures installed with base isolators is one of the obstacles encountered in application of these devices. As an initial effort toward simplification of the analysis procedure for base-isolated structures, an approach will be proposed in this paper for computing the equivalent damping for the resilient-friction base isolators (R-FBI), based on the condition that the sum of the least squares of errors of the linearized response with reference to the original nonlinear one is a minimum. With the aid of equivalent damping, the original nonlinear system can be replaced by a linear one, which can then be solved by methods readily available. in this paper, equivalent damping curves are established for all ranges of the parameters that characterize the R-FBI for some design spectra.

Key Words
base isolator, damping, equivalent damping, resilient-friction base isolator, sliding

Address
Yang YB, Natl Taiwan Univ, Dept Civil Engn, Taipei 10617, Taiwan
Natl Taiwan Univ, Dept Civil Engn, Taipei 10617, Taiwan


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