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CONTENTS
Volume 13, Number 4, April 2002
 

Abstract
In this paper, we address the numerical investigation on the effect of liquid compressibility onto the natural frequency of liquid-filled containers. Traditionally the liquid motion has been treated as an ideal fluid motion. However, from the numerical experiments for the axisymmetrical free-vibration of cylindrical liquid-storage tanks, we found that the relative difference in natural frequencies between ideal and compressible motions becomes remarkable, as the slenderness of tank or the relative liquid-fill height becomes larger. Therefore, in such cases of dynamic systems, the liquid compressibility becomes an important parameter, for the accurate vibration analysis. For the free-vibration analysis of compressible liquid-structure interaction we employed the coupled finite element formulation expressed in terms of the acoustic wave pressure and the structure deformation.

Key Words
axisymmetrical free vibration, liquid compressibility, acoustic wave, coupled liquid-structure formulation, relative difference, parametric variation

Address
Cho JR, Pusan Natl Univ, Sch Mech Engn, Pusan 609735, South Korea
Pusan Natl Univ, Sch Mech Engn, Pusan 609735, South Korea

Abstract
Ductility capacity is comprehensively studied for steel moment-resisting frames. Local, story and global ductility are being considered. An appropriate measure of global ductility is suggested. A time domain nonlinear seismic response algorithm is used to evaluate several definitions of ductility. It is observed that for one-story structures, resembling a single degree of freedom (SDOF) system, all definitions of global ductility seem to give reasonable values. However, for complex structures it may give unreasonable values. It indicates that using SDOF systems to estimate the ductility capacity may be a very crude approximation. For multi degree of freedom (MDOF) systems some definitions may not be appropriate, even though they are used in the profession. Results also indicate that the structural global ductility of 4, commonly used for moment-resisting steel frames, cannot be justified based on this study. The ductility of MDOF structural systems and the corresponding equivalent SDOF systems is studied. The global ductility values are very different for the two representations. The ductility reduction factor F-mu is also estimated. For a given frame, the values of the F-mu parameter significantly vary from one earthquake to another, even though the maximum deformation in terms of the interstory displacement is roughly the same for all earthquakes. This is because the F-mu values depend on the amount of dissipated energy, which in turn depends on the plastic mechanism, formed in the frames as well as on the loading, unloading and reloading process at plastic hinges. Based on the results of this study, the Newmark and Hall procedure to relate the ductility reduction factor and the ductility parameter cannot be justified. The reason for this is that SDOF systems were used to model real frames in these studies. Higher mode effects were neglected and energy dissipation was not explicitly considered. In addition, it is not possible to observe the formation of a collapse mechanism in the equivalent SDOF systems. Therefore, the ductility parameter and the force reduction factor should be estimated by using the MDOF representation.

Key Words
ductility capacity, ductility reduction factor, energy dissipation, global ductility, local ductility, story ductility, multiple degree of freedom systems, nonlinear seismic response, single degree of freedom systems, statistical analysis, strong motion

Address
Reyes-Salazar A, Fraccionamiento Loma Linda, Av Cerro Otates 3246, Culiacan 80180, Sinaloa, Mexico
Fraccionamiento Loma Linda, Culiacan 80180, Sinaloa, Mexico

Abstract
Formulation of an 8 nodes assumed strain shell element is presented for the analysis of shells. The stiffness matrix based on the Mindlin-Reissner theory is analytically integrated through the thickness. The element is free of membrane and shear locking behavior by using the assumed strain method such that the element performs very well in modeling of thin shell structures. The material is assumed to be isotropic and laminated composite. The element has six degrees of freedom per node and can model the stiffened plates and shells. A great number of numerical testing carried out for the validation of present 8 node shell element are in good agreement with references.

Key Words
8-node shell, assumed strain, laminated composite

Address
Kim KD, Asian Inst Technol, Sch Civil Engn, POB 4 Klongluang, Pathum Thani 12120, Thailand
Asian Inst Technol, Sch Civil Engn, Pathum Thani 12120, Thailand
Hanyang Univ, Dept Civil & Environm Engn, Seoul 133791, South Korea

Abstract
The B-spline finite strip method is developed for the prediction of the buckling of rectangular composite laminated plates under the combined action of applied uniaxial mechanical stress and increasing temperature. The analysis is conducted in two stages, namely an in-plane stress analysis in the pre-buckling stage to determine the pre-buckling stresses, followed by a buckling analysis using these determined stresses. The buckling analysis is based on the use of first-order shear deformation plate theory. The permitted lay-up of the laminates is quite general, within the constraint that the plate remains flat prior to buckling, and a wide range of boundary conditions can be accommodated. A number of applications is described and comparison of the results generated using the finite strip method is made with the results of previous studies.

Key Words
buckling, thermomechanical, plates, laminates, shear deformation, finite strip

Address
Univ Birmingham, Dept Civil Engn, Birmingham B15 2TT, W Midlands, England

Abstract
The current work presents an analysis algorithm for the modal analysis for the dynamic behaviors of offshore structures with concepts of mass perturbation influence term. The mass perturbation concept by using the term, presented in this paper offers an efficient solution procedure for dynamical response problems of offshore structures. The basis of the proposed method is the mass perturbation influence concepts associated with natural frequencies and mode shapes and mass properties of the given structure. The mathematical formulation of the mass perturbation influence method is described. New solution procedures for dynamics analysis are developed, followed by illustrative example problems, which deal with the effectiveness of the new solution procedures for the dynamic analysis of offshore structures. The solution procedures presented herein is compact and computationally simple.

Key Words
dynamic response, offshore structure, mass perturbation, modal analysis

Address
Cho KN, Hongik Univ, Jochiwon, Chungnam, South Korea
Hongik Univ, Jochiwon, Chungnam, South Korea

Abstract
In this paper, dynamic stiffness and flexibility for circular membranes are analytically derived using an efficient mixed-part dual boundary element method (BEM). We employ three approaches, the complex-valued BEM, the real-part and imaginary-part BEM, to determine the dynamic stiffness and flexibility. In the analytical formulation, the continuous system for a circular membrane is transformed into a discrete system with a circulant matrix. Based on the properties of the circulant, the analytical solutions for the dynamic stiffness and flexibility are derived. In deriving the stiffness and flexibility, the spurious resonance is cancelled out. Numerical aspects are discussed and emphasized. The problem of numerical instability due to division by zero is avoided by choosing additional constraints from the information of real and imaginary parts in the dual formulation. For the overdetermined system, the least squares method is considered to deterinine the dynamic stiffness and flexibility. A general purpose program has been developed to test several examples including circular and square cases.

Key Words
dynamic stiffness and flexibility, an efficient mixed-part dual BEM, overdetermined system

Address
Chen JT, Natl Taiwan Ocean Univ, Dept Harbor & River Engn, Chilung, Taiwan
Natl Taiwan Ocean Univ, Dept Harbor & River Engn, Chilung, Taiwan

Abstract
There is a growing demand to assess the remaining strength and endurance of existing composite steel and concrete bridge beams due to the aging infrastructure, increases in permissible vehicle weights and increases in their frequencies. As codes are generally dedicated to the design of new structures, new procedures are required to aid in the assessment of existing bridges to ensure that they are utilised to the full. In this paper, simple expressions are presented to perform partial-interaction analyses directly from full-interaction analyses, so that the beneficial effect of partial-interaction on the shear forces on the shear connectors can be utilised in assessment to extend the fatigue life of simply supported bridge beams and to determine the effect of remedial work if necessary. Use of the assessment technique is described by way of an illustrative example.

Key Words
steel-concrete beams, partial-interaction, fatigue assessment, longitudinal shear forces

Address
Seracino R, Univ Adelaide, Dept Civil & Environm Engn, Adelaide, SA 5005, Australia
Univ Adelaide, Dept Civil & Environm Engn, Adelaide, SA 5005, Australia


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