Techno Press


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CONTENTS
Volume 33, Number 4, November10 2009
 

Abstract
Viscoelastic materials store as well as dissipate energy to the thermal domain under deformation. Two efficient modelling techniques reported in literature use coupled (thermo-mechanical) ATF (Augmenting Thermodynamic Fields) displacements and ADF (Anelastic Displacement Fields) displacements, to represent the constitutive relationship in time domain by using certain viscoelastic parameters. Viscoelastic parameters are first extracted from the storage modulus and loss factor normally reported in hand books with the help of Genetic Algorithm and then constitutive relationships are used to obtain the equations of motion of the continuum after discretizing it with finite beam elements. The equations of motion are solved to get the frequency response function and modal damping ratio. The process may be applied to study the dynamic behaviour of composite beams and rotors comprising of several viscoelastic layers. Dynamic behaviour of a composite beam, formed by concentric layers of steel and aluminium is studied as an example.

Key Words
viscoelastic beam; augmenting thermodynamic field; anelastic displacement field; viscoelastic model parameters; modal damping ratio; composite beam.

Address
H. Roy: Dept. of Mechanical Engineering, National Institute of Technology, Rourkela-769008, Orissa, India
J.K. Dutt: Dept. of Mechanical Engineering, Indian Institute of Technology, Delhi, Hauz Khas, 110016, New Delhi, India
P.K. Datta: Dept. of Aerospace Engineering, Indian Institute of Technology, Kharagpur-721302, West Bengal, India

Abstract
The effects of the uniform and spatially varying ground motions on the stochastic response of fluid-structure interaction system during an earthquake are investigated by using the displacement based fluid finite elements in this paper. For this purpose, variable-number-nodes two-dimensional fluid finite elements based on the Lagrangian approach is programmed in FORTRAN language and incorporated into a general-purpose computer program SVEM, which is used for stochastic dynamic analysis of solid systems under spatially varying earthquake ground motion. The spatially varying earthquake ground motion model includes wave-passage, incoherence and site-response effects. The effect of the wavepassage is considered by using various wave velocities. The incoherence effect is examined by considering the Harichandran-Vanmarcke and Luco-Wong coherency models. Homogeneous medium and firm soil types are selected for considering the site-response effect where the foundation supports are constructed. A concrete gravity dam is selected for numerical example. The S16E component recorded at Pacoima dam during the San Fernando Earthquake in 1971 is used as a ground motion. Three different analysis cases are considered for spatially varying ground motion. Displacements, stresses and hydrodynamic pressures occurring on the upstream face of the dam are calculated for each case and compare with those of uniform ground motion. It is concluded that spatially varying earthquake ground motions have important effects on the stochastic response of fluid-structure interaction systems.

Key Words
spatially varying earthquake motion; stochastic analysis; Lagrangian approach; fluid finite element, fluid-structure interaction.

Address
Yasemin Bilici, Alemdar Bayraktar and Suleyman Adanur:
Karadeniz Technical University, Department of Civil Engineering, 61080, Trabzon, Turkey

Abstract
Three-scale homogenization procedure is proposed in this paper to provide estimates of the effective thermal conductivities of porous carbon-carbon textile composites. On each scale - the level of fiber tow (micro-scale), the level of yarns (meso-scale) and the level of laminate (macro-scale) - a two step homogenization procedure based on the Mori-Tanaka averaging scheme is adopted. This involves evaluation of the effective properties first in the absence of pores. In the next step, an ellipsoidal pore is introduced into a new, generally orthotropic, matrix to make provision for the presence of crimp voids and transverse and delamination cracks resulting from the thermal transformation of a polymeric precursor into the carbon matrix. Other sources of imperfections also attributed to the manufacturing processes, including non-uniform texture of the reinforcements, are taken into consideration through the histograms of inclination angles measured along the fiber tow path together with a particular shape of the equivalent ellipsoidal inclusion proposed already in Sko ek (1998). The analysis shows that a reasonable agreement of the numerical predictions with experimental measurements can be achieved.

Key Words
carbon-carbon composites; multi-scale analysis; Mori-Tanaka method; optimization; porous materials.

Address
Jan Vorel: Dept. of Mechanics, Faculty of Civil Engineering, Czech Technical University in Prague,
Thakurova 7, 166 29 Prague 6, Czech Republic
Michal Sejnoha: Dept. of Mechanics, Faculty of Civil Engineering, Czech Technical University in Prague,
Thakurova 7, 166 29 Prague 6, Czech Republic
Centre for Integrated Design of Advances Structures, Thakurova 7, 166 29 Prague 6, Czech Republic

Abstract
The spatially coupled buckling, in-plane, and lateral bucking analyses of thin-walled Timoshenko curved beam with non-symmetric, double-, and mono-symmetric cross-sections resting on elastic foundation are performed based on series solutions. The stiffness matrices are derived rigorously using the homogeneous form of the simultaneous ordinary differential equations. The present beam formulation includes the mechanical characteristics such as the non-symmetric cross-section, the thicknesscurvature effect, the shear effects due to bending and restrained warping, the second-order terms of semitangential rotation, the Wagner effect, and the foundation effects. The equilibrium equations and forcedeformation relationships are derived from the energy principle and expressions for displacement parameters are derived based on power series expansions of displacement components. Finally the element stiffness matrix is determined using force-deformation relationships. In order to verify the accuracy and validity of this study, the numerical solutions by the proposed method are presented and compared with the finite element solutions using the classical isoparametric curved beam elements and other researchers

Key Words
buckling analysis; curved beam; thin-walled; shear deformation; elastic foundation.

Address
Nam-Il Kim: Dept. of Civil and Environmental Engineering, Myongji University, San 38-2, Nam-Dong, Yongin, Kyonggi-Do, 449-728, Korea

Abstract
A new 8-node serendipity quadrilateral plate bending element (MQP8) based on the Mindlin-Reissner theory for the analysis of thin and moderately thick plate bending problems using Integrated Force Method is presented in this paper. The performance of this new element (MQP8) is studied for accuracy and convergence by analyzing many standard benchmark plate bending problems. This new element MQP8 performs excellent in both thin and moderately thick plate bending situations. And also this element is free from spurious/zero energy modes and free from shear locking problem.

Key Words
Mindlin-Reissner theory; plate bending element; integrated force method; displacement fields; stress-resultant fields.

Address
H.R. Dhananjaya: Dept. of Civil Engineering, Manipal Institute of Technology, Manipal-576 104, India
(Visiting faculty to Malaya University, Malaysia)
P.C. Pandey: Dept. of Civil Engineering, Indian Institute of Science, Bangalore-560012, India
J. Nagabhushanam: Dept. of Aerospace Engineering, Indian Institute of Science, Bangalore-560012, India

Abstract
This paper presents experimental results on the behaviour and ultimate load of fifteen pipes and six roof panels made of ferrocement. Additional results from three roof panels, carried out by others, are also compared with this research results. OPC cement, natural sand and galvanised iron wire mesh were used for the construction of 20 mm thick specimens. The pipe length was 2 m and roof panel length was 2.1 m. The main variables studied were the number of wire mesh layers which were 1, 2, 3, 4 and 6 layers, the inner pipe diameter which were 105, 210 and 315 mm, cross sectional shape of the panel which were channel and box sections and the depth of the edge beam which were 95 mm and 50 mm. All specimens were simply supported and tested for pure bending with test span of 600 mm at mid-span. Tests revealed that increasing the number of wire mesh layers increases the flexural strength and stiffness. Increasing the pipe diameter or depth of edge beam of the panel increases the cracking and ultimate moments. The change in the pipe diameter led to larger effect on ultimate moment than the effect of change in the number of wire mesh layers. The box section showed behaviour and strength similar to that of the channel with same depth and number of wire mesh layers.

Key Words
ferrocement; fibre reinforcement; ferrocement pipes; ferrocement panels; bending.

Address
Alnuaimi A.S., Hago A.W., Al-Jabri K.S. and Al-Saidy A.H.:
Civil and Architectural Engineering Department, College of Engineering, Sultan Qaboos University, Sultanate of Oman

Abstract
A key parameter in the design of a laterally loaded pile is the determination of its performance level. Performance level of a pile is usually expressed as the maximum head deflection and bending moment. In general, uncertainties in the performance of a pile originates from many factors such as inherent variability of soil properties, inadequate soil exploration programs, errors taking place in the determination of soil parameters, limited calculation models as well as uncertainties in loads. This makes it difficult for practicing engineers to decide for the reliability of laterally loaded piles both in cohesive and cohesionless soils. In this paper, limit state functions and consequent performance functions are obtained for single concrete piles to predict the maximum bending moment, a widely accepted design criterion along with the permissible pile head displacement. Analyses were made utilizing three dimensional finite element method and soil-structure-interaction (SSI) effects were accounted for.

Key Words
laterally loaded pile; clay; maximum bending moment; pile head displacement; response surface method; performance function; soil-structure-interaction.

Address
Gokhan Imancli, M. Rifat Kahyaoglu, Gurkan Ozden and Arif S. Kayalar: Dokuz Eylul University, Department of Civil Engineering, Kaynaklar Yerleskesi, Buca-Izmir 35160, Turkey

Abstract
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Key Words
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Address
Zhu Zeng-qing and Chen Jian-jun: School of Electromechanical Engineering, Xidian University, Xi


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