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CONTENTS
Volume 26, Number 4, July10 2007
 

Abstract
A FE-BE procedure is presented for dynamic analysis of concrete arch dams. In this technique, dam body is discretized by finite elements, while foundation rock is handled by three dimensional boundary element formulation. This would allow a rigorous inclusion of dam-foundation rock interaction, with no limitations imposed on geometry of canyon shape. Based on this method, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various ratios of foundation rock to dam concrete elastic moduli under an empty reservoir condition. Furthermore, the effects of canyon shape on response of dam, is also discussed.

Key Words
concrete arch dams; boundary element; dam-foundation rock interaction.

Address
Department of Civil Engineering, Amirkabir University of Technology, Tehran, Iran

Abstract
A discrete sliding mode control (SMC) method based on hybrid model of neural network and nominal model is proposed to reduce the vibration of flexible structures, which is a robust active controller developed by using a sliding manifold approach. Since the thick boundary layer will reduce the virtue of SMC, the multilayer feed-forward neural network is adopted to model the uncertainty part. The neural network is trained by Levenberg-Marquardt backpropagation. The design objective of the sliding mode surface is based on the quadratic optimal cost function. In course of running, the input signal of SMC come from the hybrid model of the nominal model and the neural network. The simulation shows that the proposed control scheme is very effective for large uncertainty systems.

Key Words
sliding mode control; neural network; flexible structure; hybrid model.

Address
Yong-an Huang: School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi?an, 710072, China
School of Mechanical Science & Engineering, Huazhong University of Science & Technology, Wuhan, 430074, China
Zi-chen Deng: School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi?an, 710072, China
State Key Laboratory of Structural Analysis of Industrial Equipment, Dalian University of Technology, Dalian, 116024, China
Wen-cheng Li: School of Science, Northwestern Polytechnical University, Xi?an, 710072, China

Abstract
The effects of material nonhomogeneity and nonisothermal conditions on the stress response of pressurized tubes are assessed by virtue of a computational model. The modulus of elasticity, the Poisson?s ratio, the yield strength, and the coefficient of thermal expansion, are assumed to vary nonlinearly in the tube. A logarithmic temperature distribution within the tube is proposed. Under these conditions, it is shown that the stress states and the magnitudes of response variables are affected significantly by both the material nonhomogeneity and the existence of the radial temperature gradient.

Key Words
pressure chamber; functionally graded material; stress analysis; von Mises?criterion.

Address
Ahmet N. Eraslan: Department of Engineering Sciences, Middle East Technical University, Ankara 06531, Turkey

Abstract
Following previous work carried out in Building Research Institute in Japan, finite element analyses of conceptual column designs are performed in this paper. The effectiveness of the numerical model is evaluated by experimental tests and parametric studies are conducted to determine influential factors in conceptual column designs. First, three different column designs are analysed: bonded, unbonded, and un-bonded with additional reinforcing bars. The load-displacement curves and cracking patterns in concrete are obtained and compared with experimental ones. The comparisons indicate that the finite element model is able to reflect the experimental results closely. Both numerical and experimental results show that, the introduction of un-bonded zones in a column end can reduce cracking strains, accordingly reduce the stiffness and strength as well; the addition of extra reinforcement in the un-bonded zones can offset the losses of the stiffness and strength. To decide the proper length of the un-bonded zones and the sufficient amount of the additional reinforcing bars, parametric studies are carried out on their influences. It has been found that the stiffness of un-bonded designs slightly decreases with increasing the length of the un-bonded zones and increases with the size of the additional reinforcing bars.

Key Words
column; concrete; reinforcement; cracking; bond-slip; finite element method; non-linear analysis.

Address
G. Chen: Queensland University of Technology, QLD 4001, Australia
H. Fukuyama, M. Teshigawara, H. Etoh, K. Kusunoki and H. Suwada: Building Research Institute, 1 Tachihara, Tsukuba, Ibaraki 305-0802, Japan

Abstract
The exploitation of fibre reinforced polymer composites, as external reinforcement is an evergreen and well-known technique for improving the structural performance of reinforced concrete structures. The demand to use FRP composites in the civil engineering industry is mainly due to its high strength, light weight, and stiffness. This paper exemplifies the shear strength of partially precracked reinforced concrete rectangular beams repaired with externally bonded Bi-Directional Carbon Fibre Reinforced Polymer (CFRP) Fabrics strips. All specimens were cast in the laboratory environment without any internal shear reinforcement. The test parameters were longitudinal tensile reinforcement, shear span to effective depth ratio, spacing of CFRP strips, and orientation of CFRP reinforcement. It mainly focuses on the shear capacity and modes of failure of the CFRP strengthened shear beams. Results have shown that the CFRP repaired beams attained a shear enhancement of 32% and 107.64% greater than the control beams. This study underscores that the CFRP strip technique significantly enhanced the shear capacity of precracked reinforced concrete rectangular beams without any internal shear reinforcement.

Key Words
shear; CFRP; repair.

Address
J. Jayaprakash: Dept. of Civil Engineering, Universiti Putra Malaysia, Malaysia
Abdul Aziz Abdul Samad: Universiti Tun Hussein Onn Malaysia, Malaysia
Ashrabov Anvar Abbasovich: Tashkent Automobile and Road Construction Institute, Tashkent, Uzbekistan
Abang Abdullah Abang Ali: Housing Research Centre, Universiti Putra Malaysia, Malaysia

Abstract
A new numerical model based on the spline finite strip method is presented here for the analysis of buckling of built-up columns with and without end stay plates. The channels are modelled with spline finite strips while the connecting elements are represented by a 3D beam finite element, for which the stiffness matrix is modified in order to ensure complete compatibility with the strips. This numerical model has the advantage to give all possible failure modes of built-up columns for different boundary conditions. The end stay plates are also taken into account in this method. To validate the model a comparative study was carried out. First, a general procedure was chosen and adopted. For each numerical analysis, the lowest buckling loads and modes were calculated. The basic or ?pure? buckling modes were identified and their critical loads were compared with solutions obtained using analytical methods and/or other numerical methods. The results showed that the proposed numerical model can be used in practice to study the elastic buckling of built-up columns. This model is considered accurate and efficient for the local buckling of short columns and global buckling for slender columns.

Key Words
batten plates; built-up columns; elastic buckling; spline finite strip; stay plates.

Address
M. Djafour and A. Megnounif: Dept. of Civil Engineering, A. Belkaid University of Tlemcen, B.P. 230, Tlemcen, Algeria
D. Kerdal: Det. of Civil Engineering, Univ. of Sciences and Technology of Oran, Oran, Algeria
A. Belarbi: Dept. of Civil, Architectural, and Environmental Engineering, University of Missouri Rolla, Rolla, Missouri, USA

Abstract
A bi-directional tuned mass damper (BTMD) in which a mass connected by two translational springs and two viscous dampers in two orthogonal directions has been introduced to control coupled lateral and torsional vibrations of asymmetric building. An efficient control strategy has been presented in this context to control displacements as well as acceleration responses of asymmetric buildings having asymmetry in both plan and elevation. The building is idealized as a simplified 3D model with two translational and a rotational degrees of freedom for each floor. The principles of rigid body transformation have been incorporated to account for eccentricity between center of mass and center of rigidity. The effective and robust design of BTMD for controlling the vibrations in structures has been presented. The redundancy of optimum design has been checked. Non dominated sorting genetic algorithm (NSGA) has been used for tuning optimum stages and locations of BTMDs and its parameters for control of vibration of seismically excited buildings. The optimal locations have been observed to be reasonably compact and practically implementable.

Key Words
bi-directional tuned mass damper; genetic algorithm; Pareto optimization; passive control; asymmetric building; rigid body transformations.

Address
Nagendra Babu Desu , Anjan Dutta and S.K. Deb: Dept. of Civil Engineering, Indian Institute of Technology, Guwahati, India

Abstract
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Key Words
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Address
Qi-Lin Zhang, Li-Xin Chen and Xiao-Qun Luo: College of Civil Engineering, Tongji University, 1239 Sipin Road, Shanghai 200092, P. R. China
Zong-Lin Yang: Architectural Design and Research Institute, Tongji University, 1239 Sipin Road, Shanghai 200092, P. R. China


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