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CONTENTS
Volume 39, Number 4, August25 2011
 

Abstract
A free vibration analysis is made of a moderately-thick toroidal shell based on a shear deformation (Timoshenko-Mindlin) shell theory. This work represents an extension of earlier work by the authors which was based on a thin (Kirchoff-Love) shell theory. The analysis uses a modal approach in the circumferential direction, and numerical results are found using the differential quadrature method (DQM). The analysis is first developed for a shell of revolution of arbitrary meridian, and then specialized to a complete circular toroidal shell. A second analysis, based on the three-dimensional theory of elasticity, is presented to cover thick shells. The shear deformation theory is validated by comparing calculated results with previously published results for fifteen cases, found using thin shell theory, moderately-thick shell theory, and the theory of elasticity. Consistent agreement is observed in the comparison of different results. New frequency results are then given for moderately-thick and thick toroidal shells, considered to be completely free. The results indicate the usefulness of the shear deformation theory in determining natural frequencies for toroidal shells.

Key Words
vibration; toroidal shells; shear deformation theory; theory of elasticity; differential quadrature method

Address
X.H. Wang: Department of Civil Engineering, Shantou University, 243 Da Xue Road, Shantou, P.R. China
D. Redekop: Department of Mechanical Engineering, University of Ottawa, Ottawa, Canada K1N 6N5

Abstract
Concrete structures are generally cracked in flexural tension at working loads. Concrete beams with asymmetric section details and crack patterns exhibit different flexural rigidity depending upon the sense of the applied flexural moment. In this paper, three different models, having the same natural period, of such SDOF bilinear dynamical systems have been proposed. The Model-I and Model-II have constant damping coefficient, but the latter is characterized by two stiffness coefficients depending upon the sense of vibration amplitude. The Model-III, additionally, has two damping coefficients as well. In this paper, the dynamical response of Model-III to sinusoidal loading has been investigated and compared with that of Model-II studied earlier. It has been found that Model-III exhibits regular and irregular subharmonics, jump phenomena and strong sensitivity to initial conditions, forcing frequency, system period as well as the sense of peak sinusoidal force. The constant sustained load has been found to affect the natural period of the dynamical system. The predictions of Model-I have been compared with those of the approximate linear model adopted in present practice. The behaviour exhibited by different models of the SDOF cracked elastic concrete structures under working loads and the theoretical and practical implications of the approach followed have been critically evaluated.

Key Words
bilinear dynamics; bilinearity ratio; cracked concrete structures; jump phenomena; sensitivity to system parameters; stability portrait; sub-harmonic resonance

Address
Umesh Kumar Pandey: Department of Civil Engineering, National Institute of Technology, Hamirpur (H.P.)-177005, India
Gurmail S. Benipal: Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India

Abstract
The effectiveness of a technique for the repair of reinforced concrete members in combination with a technique for the repair of masonry walls of infilled frames, damaged due to cyclic loading, is experimentally investigated. Three single - story, one - bay, 1/3 - scale frame specimens are tested under cyclic horizontal loading, up to a drift level of 4%. One bare frame and two infilled frames with weak and strong infills, respectively, have been tasted. Specimens have spirals as shear reinforcement. The applied repair technique is mainly based on the use of thin epoxy resin infused under pressure into the crack system of the damaged RC joint bodies, the use of a polymer modified cement mortar with or without a fiberglass reinforcing mesh for the damaged infill masonry walls and the use of CFRP plates to the surfaces of the damaged structural RC members, as external reinforcement. Specimens after repair, were retested in the same way. Conclusions concerning the effectiveness of the applied repair technique, based on maximum cycles load, loading stiffness, and hysteretic energy absorption capabilities of the tested specimens, are drawn and commented upon.

Key Words
infilled RC frames; masonry strength; repair technique; experimental results

Address
D.J. Kakaletsis and K.N. David: Technological Educational Institution of Serres, Serres 62124, Greece
C.G. Karayannis: Democritus University of Thrace, Xanthi 67100, Greece

Abstract
Jilin highway concrete bridge is located in the center of Jilin City, which is positioned in the middle part in Jilin Province in the east north of China. This bridge crosses the Songhua River and connects the north and the south of Jilin City. The main purpose of damages inspection of the bridge components is to ensure the safety of a bridge and to identify any maintenance, repair, or strengthening which that need to be carried out. The damages that occur in reinforced concrete bridges include different types of cracks, scalling and spalling of concrete, corrosion of steel reinforcement, deformation, excessive deflection, and stain. The main objectives of this study are to inspect the appearance of Jilin highway concrete bridge and describe all the damages in the bridge structural members, and to evaluate the structural performance of the bridge structure under dead and live loads. The tests adopted in this study are: (a) the depth of concrete carbonation test, (b) compressive strength of concrete test, (c) corrosion of steel test, (d) static load test, and (e) dynamic load test. According to the damages inspection of the bridge structure appearance, most components of the bridge are in good conditions with the exception arch waves, spandrel arch, deck pavement of new arch bridge, and corbel of simply supported bridge which suffer from serious damages. Load tests results show that the deflection, strain, and cracks development satisfy the requirements of the standards.

Key Words
damages; inspection; Jilin bridge; static load; dynamic load; tests; deflection; strain; cracks; spalling

Address
Ali Fadhil Naser and Wang Zonglin: School of Transportation Science and Engineering, Bridge and Tunnel Engineering,
Harbin Institute of Technology, Harbin-150090, Heilongiang, China

Abstract
This paper presents an analysis of stochastic eigenvalue problem of plane bar structures. Particular attention is paid to the effect of spatial variations of the flexural properties of the structure on the first four eigenvalues. The problem of spatial variations of the structure properties and their effect on the first four eigenvalues is analyzed in detail. The stochastic eigenvalue problem was solved independently by stochastic finite element method (stochastic FEM) and Monte Carlo techniques. It was revealed that the spatial variations of the structural parameters along the structure may substantially affect the eigenvalues with quite wide gap between the two extreme cases of zero- and full-correlation. This is particularly evident for the multi-segment structures for which technology may dictate natural bounds of zero- and full-correlation cases.

Key Words
eigenvalue problem; bar structure; spatial stiffness variation; stochastic finite element method; Monte Carlo method; random field; midpoint method

Address
B. Rozycki: Voivodeship Roads Administration in Opole, Opole, Poland
Z. Zembaty: Faculty of Civil Engineering, The Opole University of Technology, Opole, Poland

Abstract
In regions of high seismic risk, high-strength concrete (HSC) columns of tall buildings are designed to be fully ductile during earthquake attack by providing substantial amount of confining steel within the critical region. However, in areas of low to moderate seismic risk, the same provision of confining steel is too conservative because of the reduced seismic demand. More critically, it causes problematic steel congestion in the beam-column joints and column critical region. This will eventually affect the quality of concrete placing owing to blockage. To relieve the problem, the confining steel in the critical region of HSC columns located in low to moderate seismicity regions can be suitably reduced, while maintaining a limited ductility level. Despite the advantage, there are still no guidelines developed for designing limited ductility HSC columns. In this paper, a formula for designing limited ductility HSC columns is presented. The validity of the formula was verified by testing half-scale HSC columns subjected to combined high-axial load and flexure, in which the confining steel was provided as per the proposed formula. From the test results, it is evident that the curvature ductility factors obtained for all these columns were about 10, which is the generally accepted level of limited ductility.

Key Words
axial load; columns; confinement; flexural strength; high-strength concrete; limited ductility; reinforced concrete

Address
Johnny Ching Ming Ho: Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R.C.

Abstract
The present work mainly reports a significant development of a novel efficient meshfree method for vibration and buckling analysis of orthotropic plates. The plate theory with orthotropic materials is followed the Kirchhoff\'s assumption in which the only deflection is field variable and approximated by the moving Kriging interpolation approach, a new technique used for constructing the shape functions. The moving Kriging technique holds the Kronecker delta property, thus it makes the method efficiently in imposing the essential boundary conditions and no special techniques are required. Assessment of numerical results is to accurately illustrate the applicability and the effectiveness of the proposed method in the class of eigenvalue problems.

Key Words
vibration; meshfree; moving Kriging interpolation; orthotropic plate; buckling

Address
Tinh Quoc Bui: Chair of Structural Mechanics, Department of Civil Engineering, University of Siegen, Paul-Bonatz-Strasse 9-11, D-57076, Siegen, Germany
Minh Ngoc Nguyen: Department of Civil Engineering, Ruhr University Bochum, Germany

Abstract
The investigation on possible causes of failures related to documented collapses is a complicated issue, primarily due to the scarcity and inadequacy of information available. Although several studies have tried to understand which are the inherent structural deficiencies or circumstances associated to failure of the main structural elements in a reinforced concrete frame, to the authors knowledge a uniform approach for the evaluation building static vulnerability, does not exist yet. This paper investigates, by means of a detailed case study, the potential failure mechanisms of an existing reinforced concrete building. The linear elastic analysis for the three-dimensional building model gives an insight on the working conditions of the structural elements, demonstrating the relevance of a number of structural faults that could sensibly lower the structure\'s safety margin. Next, the building\'s bearing capacity is studied by means of parametric nonlinear analysis performed at the element\'s level. It is seen that, depending on material properties, concrete strength and steel yield stress, the failure hierarchy could be dominated by either brittle or ductile mechanisms.

Key Words
static vulnerability; case study; failure mechanisms; reinforced concrete frames; elastic analysis; non-linear analysis; load multiplier

Address
Polese Maria, Verderame Gerardo M. and Manfredi Gaetano: Department of Structural Engineering, University of Naples \"Federico II\", Via Claudio 21, 80125 – Naples, Italy


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