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Volume 27, Number 5, November30 2007

The modal controller of single-input system cannot stabilize the defective system with positive real part of repeated eigenvalues, because some of the generalized modes are uncontrollable. In order to stabilize the uncontrollable modes with positive real part of eigenvalues, the multi-input system should be introduced. This paper presents a recursive procedure for designing the feedback controller of the multi-input system with defective repeated eigenvalues. For a nearly defective system, we first transform it into a defective one, and apply the same method to manage. The proposed methods are based on the modal coordinate equations, to avoid the tedious mathematic manipulation. As an application of the presented procedure, two numerical examples are given at end of the paper.

Key Words
design of the feedback controller; multiple-input systems; recursive design procedure; defective systems; nearly defective systems.

Department of Mechanics, Jilin University, Nanling Campus Changchun, 130025, China

A simplified yet effective design procedure for viscous dampers was presented based on
improved capacity spectrum method in the context of performance-based seismic design. The amount of
added viscous damping required to meet a given performance objective was evaluated from the difference
between the total demand for effective damping and inherent damping plus equivalent damping resulting
from hysteretic deformation of system. Application of the method is illustrated by means of two
examples, using Chinese design response spectrum and mean response spectrum. Nonlinear dynamic
analysis results indicate that the maximum displacements of structures installed with supplemental
dampers designed in accordance with the proposed method agree well with the given target displacements.
The advantage of the presented procedure over the conventional iterative design method is also

Key Words
viscous dampers; equivalent damping; improved capacity spectrum method; nonlinear dynamic analysis; performance-based seismic design.

Bo Li; College of Civil Engineering, Chang?an University, Xi?an 710061, China
Xing-wen Liang; College of Civil Engineering, Xi?an University of Architecture and Technology, Yanta Road 13#, Xi?an, postalcode: 710055, China

Static response of an elastic beam on a two-parameter tensionless foundation is investigated by assuming that the beam is symmetrically subjected to a uniformly distributed load and concentrated edge loads. Governing equations of the problem are obtained and solved by pointing out that a concentrated edge foundation reaction in addition to a continuous foundation reaction along the beam axis in the case of complete contact and a discontinuity in the foundation reactions in the case of partial contact come into being as a direct result of the two-parameter foundation model. The numerical solution of the complete contact problem is straightforward. However, it is shown that the problem displays a highly non-linear character when the beam lifts off from the foundation. Numerical treatment of the governing equations is accomplished by adopting an iterative process to establish the contact length. Results are presented in figures to demonstrate the linear and non-linear behavior of the beam-foundation system for various values of the parameters of the problem comparatively.

Key Words
elastic beam; two-parameter foundation; lift-off.

Z. Celep; Dept. of Structural and Earthquake Engineering, Faculty of Civil Engineering, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
F. Demir; Dept. of Civil Engineering, Faculty of Engineering, Suleyman Demirel University, 3260 Isparta, Turkey

In this paper, two algorithms are presented for the optimum design of geometrically nonlinear
steel space frames using tabu search. The first algorithm utilizes the features of short-term memory
(tabu list) facility and aspiration criteria and the other has long-term memory (back-tracking) facility in
addition to the aforementioned features. The design algorithms obtain minimum weight frames by
selecting suitable sections from a standard set of steel sections such as American Institute of Steel
Construction (AISC) wide-flange (W) shapes. Stress constraints of AISC Allowable stress design (ASD)
specification, maximum drift (lateral displacement) and interstorey drift constraints were imposed on the
frames. The algorithms were applied to the optimum design of three space frame structures. The designs
obtained using the two algorithms were compared to each other. The comparisons showed that the second
algorithm resulted in lighter frames.

Key Words
optimum design; tabu search; steel space frames; non-linear analysis; allowable stress design.

S. O. Degertekin and M. S. Hayalioglu; Department of Civil Engineering, Dicle University, 21280, iyarbakir, Turkey
M. Ulker; Department of Civil Engineering, Firat University, 23119, Elazig, Turkey

Two series of tests were conducted to investigate the behavior of local thin jacketing for the retrofitting of reinforced concrete (RC) columns. In the first series, four full-scale RC columns with a height of 400 cm and a 30 cm square cross-section were tested under constant axial load and reversed cyclic lateral displacements. The heavily damaged columns were retrofitted with local thin jacketing. Selfcompacting concrete (SCC) was used in the production of 7.5 cm thick, four-sided jacketing. The height of the jacketing was 100 cm for one specimen and 200 cm for all others. In the second series, the retrofitted columns were retested with the same axial load and displacement history. The effectiveness of local thin jacketing in the retrofitting of RC columns was examined with respect to lateral strength, stiffness, inelastic load-deformation behavior and energy dissipation.

Key Words
reinforced concrete column; precast column; retrofitting; jacketing; self-compacting concrete.

Structural and Earthquake Engineering Laboratory, Faculty of Civil Engineering, Istanbul Technical University, 34469, Maslak-Istanbul, Turkey

The problem of a semi-infinite magneto-electro-elastically impermeable mode-III crack in a magneto-electro-elastic material is considered under the action of impact loads. For the case when a pair of concentrated anti-plane shear impacts, electric displacement and magnetic induction impacts are exerted symmetrically on the upper and lower surfaces of the crack, the magneto-electro-elastic field ahead of the crack tip is determined in explicit form. The dynamic intensity factors and dynamic energy density factor are obtained. The method adopted is to reduce the mixed initial-boundary value problem, by using the Laplace and Fourier transforms, into three simultaneous dual integral equations, one of which is converted into an Abel?s integral equation and the others into a singular integral equation with Cauchy kernel. Based on the obtained fundamental solutions of point impact loads, the solutions of two kinds of different loading cases are evaluated

Key Words
dynamic response; crack; magneto-electro-elastic field; intensity factor; dynamic energy
density factor; magneto-electrically impermeable.

Department of Mechanics and Engineering Science, Shijiazhuang Railway Institute, Shijiazhuang 050043, P. R. China

The damage detection process may appear difficult to be implemented for truss structures because not all degrees of freedom in the numerical model can be experimentally measured. In this context, the damage locating vector (DLV) method, introduced by Bernal (2002), is a useful approach because it is effective when operating with an arbitrary number of sensors, a truncated modal basis and multiple damage scenarios, while keeping the calculation in a low level. In addition, the present paper also evaluates the noise influence on the accuracy of the DLV method. In order to verify the DLV behavior under different damages intensities and, mainly, in presence of measurement noise, a parametric study had been carried out. Different excitations as well as damage scenarios are numerically tested in a continuous Warren truss structure subjected to five noise levels with a set of limited measurement sensors. Besides this, it is proposed another way to determine the damage locating vectors in the DLV procedure. The idea is to contribute with an alternative option to solve the problem with a more widespread algebraic method. The original formulation via singular value decomposition (SVD) is replaced by a common solution of an eigenvector-eigenvalue problem. The final results show that the DLV method, enhanced with the alternative solution proposed in this paper, was able to correctly locate the damaged bars, using an output-only system identification procedure, even considering small intensities of damage and moderate noise levels.

Key Words
structural health monitoring; flexibility based technique; damage locating vector; noise.

Leandro Fleck Fadel Miguel; Department of Civil Engineering, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil
Leticia Fleck Fadel Miguel; Department of Mechanical Engineering, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil
Jorge Daniel Riera and Ruy Carlos Ramos de Menezes; Department of Civil Engineering, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil

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