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CONTENTS
Volume 33, Number 1, September10 2009
 

Abstract
Hong Kong is now recognized as an area of moderate seismic hazard, but most of the buildings have been designed with no seismic provision. It is of great significance to develop effective and practical measures to retrofit existing buildings against moderate seismic attacks. Researches show that beam-column joints are critical structural elements to be retrofitted for seismic resistance for reinforced concrete frame structures. This paper explores the possibility of using a Hydraulic Displacement Amplification Damping System (HDADS), which can be easily installed at the exterior of beam-column joints, to prevent structural damage against moderate seismic attacks. A series of shaking table tests were carried out with a 1/3 prototype steel frame have been carried out to assess the performance of the HDADS. A Numerical model representing the HDADS is developed. It is also used in numerical simulation of the shaking table tests. The numerical model of the HDADS and the numerical simulation of the shaking table tests are verified by experimental results.

Key Words
viscous fluid damper; displacement amplification; retrofitting; beam-column joint; shaking table test.

Address
Tracy Sau-Kwai Chung and Eddie Siu-Shu Lam: Department of Civil and Structural Engineering, Hong Kong Polytechnic University, Hung Hum, Kowloon, Hong Kong
Bo Wu: Department of Civil Engineering, South China University of Technology, Guangzhou, China
You-Lin Xu:Department of Civil and Structural Engineering, Hong Kong Polytechnic University, Hung Hum, Kowloon, Hong Kong


Abstract
In this study, the nonlinear vibrations of stepped beams having different boundary conditions were investigated. The equations of motions were obtained by using Hamilton\'s principle and made non dimensional. The stretching effect induced non-linear terms to the equations. Natural frequencies are calculated for different boundary conditions, stepped ratios and stepped locations by Newton-Raphson Method. The corresponding nonlinear correction coefficients are also calculated for the fundamental mode. At the second part, an alternative method is produced for the analysis. The calculated natural frequencies and nonlinear corrections are used for training an artificial neural network (ANN) program which has a multi-layer, feed-forward, back-propagation algorithm. The results of the algorithm produce errors less than 2.5% for linear case and 10.12% for nonlinear case. The errors are much lower for most cases except clamped-clamped end condition. By employing the ANN algorithm, the natural frequencies and nonlinear corrections are easily calculated by little errors, and the computational time is drastically reduced compared with the conventional numerical techniques.

Key Words
stepped beam; nonlinear vibration; perturbation method; artificial neural networks.

Address
S. M. Ba datli and E. Ozkaya : Department of Mechanical Engineering, Celal Bayar University, 45140, Muradiye, Manisa, Turkey
H.A. Ozyi it : Department of Mechanical Engineering, Zonguldak Karaelmas University, 67100, Zonguldak, Turkey
A. Tekin : Celal Bayar University, 45100, Soma, Manisa, Turkey

Abstract
An anisotropic damage mechanics approach is introduced which models the static and dynamic behavior of mass concrete in 3D space. The introduced numerical approach is able to model non-uniform cracking within the cracked element due to cracking in Gaussian points of elements. The validity of the proposed model is considered using available experimental and theoretical results under the static and dynamic loads. No instability and stress locking is observed in the conducted analyses. The Morrow Point dam is analyzed including dam-reservoir interaction effects to consider the nonlinear seismic behavior of the dam. It is found that the resulting crack profiles are in good agreement with those obtained from the smeared crack approach. It is concluded that the proposed model can be used in nonlinear static and dynamic analysis of concrete dams in 3D space and enables engineers to define the damage level of these infrastructures. The performance level of the considered system is used to assess the static and seismic safety using the defined performance based criteria.

Key Words
concrete dams; dam-reservoir interaction; damage echanics; dynamic analysis; non-uniform cracking; performance level.

Address
H. Mirzabozorg: Department of Civil Engineering, KN-Toosi University of Technology, Tehran, Iran
R. Kianoush : Department of Civil Engineering, Ryerson University, Toronto, Canada
B. Jalalzadeh : KN-Toosi University of Technology


Abstract
Radiation damping due to wave propagation in unbounded domains may cause a significant reduction of structural vibrations when excited near resonance. Here a novel matrix-valued algebraic Padelike stiffness formulation in the frequency-domain and a corresponding state equation in the time domain are elaborated for a soil-structure interaction problem with a layered soil excited in a transient manner by a flexible rotor during startup and shutdown. The contribution of radiation damping caused by a soil-layer upon a rigid bedrock is characterized by the corresponding amount of critical damping as it is used in structural dynamics.

Key Words
boundary element method; soil dynamics; frequency-to-time transformation; radiation damping; soil-structure interaction.

Address
Ediansjah Zulkifli and Peter Ruge : Lehrstuhl Dynamik der Tragwerke, Fakultat Bauingenieurwesen, Technische Universitat Dresden, D-01062 Dresden, Germany

Abstract
The soil response calculation is described, by which, threw the fictive path of stress, the stress-deformation diagrams are determined, considering the nonlinear soil behavior. The calculation are lead incrementally, by which is shown that in the presented soil model (modified Cam Clay), considering the influence of overconsolidated soil pressure OCR, the number of calculation steps may, but not necessarily, have a sufficient influence on the value of failure load and definite soil deformation. The simplicity and the practicalness of the procedure, the enables modeling the complex relations in soil.

Key Words
nonlinearity; average normal stress; deviation stress; plasticity; increment; calculation; volume and deviation deformation; modified Cam clay model.

Address
Krešo Ivandi and Božo Soldo: Faculty of Geotechnical Engineering, Varaždin, Hallerova Aleja 7, Croatia

Abstract
This paper investigates the possibility of controlling the response of typical portal frame structures to blast loading using a combination of semi-active and passive control devices. A one storey reinforced concrete portal frame is modelled using non-linear finite elements with each column discretised into multiple elements to capture the higher frequency modes of column vibration response that are typical features of blast responses. The model structure is subjected to blast loads of varying duration, magnitude and shape, and the critical aspects of the response are investigated over a range of structural periods in the form of blast load response spectra. It is found that the shape or length of the blast load is not a factor in the response, as long as the period is less than 25% of the fundamental structural period. Thus, blast load response can be expressed strictly as a function of the momentum applied to the structure by a blast load. The optimal device arrangements are found to be those that reduce the first peak of the structural displacement and also reduce the subsequent free vibration of the structure. Semi-active devices that do not increase base shear demands on the foundations in combination with a passive yielding tendon are found to provide the most effective control, particularly if base shear demand is an important consideration, as with older structures. The overall results are summarised as response spectra for eventual potential use within standard structural design paradigms.

Key Words
structural control; semi-active device; blast loading; momentum; free vibration; shear stress; peak displacement; permanent deflection.

Address
C.M. Ewing and C. Guillin : Department of Mechanical Engineering, University of Canterbury, Private Bag 4800,
Christchurch, New Zealand
R.P. Dhakal :Department of Civil Engineering, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
J.G. Chase : Department of Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch, New Zealand


Abstract
A method for vibration analysis of asymmetric shear wall and Thin walled open section structures is presented in this paper. The whole structure is idealized as an equivalent bending-warping torsion beam in this method. The governing differential equations of equivalent bending-warping torsion beam are formulated using continuum approach and posed in the form of simple storey transfer matrix. By using the storey transfer matrices and point transfer matrices which consider the inertial forces, system transfer matrix is obtained. Natural frequencies can be calculated by applying the boundary conditions. The structural properties of building may change in the proposed method. A numerical example has been solved at the end of study by a program written in MATLAB to verify the presented method. The results of this example display the agreement between the proposed method and the other valid method given in literature.

Key Words
vibration; asymmetric; wall; thin walled; transfer matrix.

Address
Kanat Burak Bozdogan and Duygu Ozturk : Civil Engineering Department, Ege University, Bornova, zmir, Turkey

Abstract


Key Words
material design; inverse homogenization; D-function; HS bound; negative poisson

Address
State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian, 116023, China


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