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CONTENTS
Volume 21, Number 5, November30 2005
 

Abstract
A neural network based model is developed for the structural analysis of masonry infilled steel frames, which can account for the non-linearities in the material properties and structural behaviour. Using the data available from the analytical methods, an ANN model with input parameters consisting of dimension of frame, size of infill, properties of steel and infill was developed. It was found to be acceptable in predicting the failure modes of infilled frames and corresponding failure load subject to limitations in the training data and the predicted results are tested using the available experimental results. The study shows the importance of validating the ANN models in simulating structural behaviour especially when the data are limited. The ANN model was also compared with the available experimental results and was found to perform well.

Key Words
neural network-model; infilled steel frames; failure modes; collapse load.

Address
K. Subramanian; Civil Engineering Dept., Coimbatore Institute of Technology, Coimbatore, India
K. M. Mini; Applied Mechanics Dept., Amrita Vishwa Vidyapeetham, Ettimadai, Coimbatore, India
S. Josephine Kelvina Florence; Civil Engineering Dept, Coimbatore Institute of Technology, Coimbatore, India

Abstract
In the shear-lag analysis of structures deterministic procedure is insufficient to provide complete information. Probabilistic analysis is a holistic approach for analyzing shear-lag effects considering uncertainties in structural parameters. This paper proposes an efficient and accurate algorithm to analyze shear-lag effects of structures with parameter uncertainties. The proposed algorithm integrated the advantages of the response surface method (RSM), finite element method (FEM) and Monte Carlo simulation (MCS). Uncertainties in the structural parameters can be taken into account in this algorithm. The algorithm is verified using independently generated finite element data. The proposed algorithm is then used to analyze the shear-lag effects of a simply supported beam with parameter uncertainties. The results show that the proposed algorithm based on the central composite design is the most promising one in view of its accuracy and efficiency. Finally, a parametric study was conducted to investigate the effect of each of the random variables on the statistical moment of structural stress response.

Key Words
probabilistic analysis; response surface method (RSM); finite element method (FEM); Monte Carlo simulation (MCS); shear-lag effect; box-section beam.

Address
Jin Cheng; Department of Bridge Engineering, Tongji University, Shanghai, 200092, China
C. S. Cai; Department of Civil and Environmental Engineering, 3510 CEBA, Louisiana State University,
Baton Rouge, LA, 70803, USA
Ru-cheng Xiao; Department of Bridge Engineering, Tongji University, Shanghai, 200092, China

Abstract
A new generalized Bernoulli/Timoshenko beam-column element on a two-parameter elastic foundation is presented herein. This element is based on the exact solution of the differential equation which describes the deflection of the axially loaded beam resting on a two-parameter elastic foundation, and can take into account shear deformations, semi – rigid connections, and rigid offsets. The equations of equilibrium are formulated for the deformed configuration, so as to account for axial force effects. Apart from the stiffness matrix, load vectors for uniform load and non-uniform temperature variation are also formulated. The efficiency and usefulness of the new element in reinforced concrete or steel structures analysis is demonstrated by two examples.

Key Words
finite element method; second order analysis; beam on elastic foundation; two-parameter elastic foundation; semi-rigid connections.

Address
Dept. of Civil Engineering, Division of Structural Engineering, Aristotle Univ. ofThessaloniki, 540 06 Thessaloniki, Greece

Abstract
Finite elements based on isoparametric formulation are known to suffer spurious stiffness properties and corresponding stress oscillations, even when care is taken to ensure that completeness and continuity requirements are enforced. This occurs frequently when the physics of the problem requires multiple strain components to be defined. This kind of error, commonly known as locking, can be circumvented by using reduced integration techniques to evaluate the element stiffness matrices instead of the full integration that is mathematically prescribed. However, the reduced integration technique itself can have a further drawback - rank deficiency, which physically implies that spurious energy modes (e.g., hourglass modes) are introduced because of reduced integration. Such instability in an existing stiffness matrix is generally detected by means of an eigenvalue test. In this paper we show that a knowledge of the dimension of the solution space spanned by the column vectors of the strain-displacement matrix can be used to identify the instabilities arising in an element due to reduced/selective integration techniques a priori, without having to complete the element stiffness matrix formulation and then test for zero eigenvalues.

Key Words
rank deficiency; zero energy mode; eigen value; function space; basis vectors; locking; reduced integration.

Address
K. Sangeeta; CSIR Centre for Mathematical Modelling and Computer Simulation (C-MMACS), Bangalore 560 037, India
Somenath Mukherjee; Structures Division, National Aerospace Laboratories, Bangalore 560 017, India
Gangan Prathap; CSIR Centre for Mathematical Modelling and Computer Simulation (C-MMACS), Bangalore 560 037, India

Abstract
Dynamic and static analyses of existing structures are very important to obtain reliable information relating to actual structural properties. For this purpose a series of material test, dynamic test and static collapse test of the existing two brick chimneys, in Tokoname, are carried out. From the material tests, Young? modulus and compressive strength of the brick used for these chimneys are estimated to be 3200 MPa and 7.5 MPa, respectively. The results of static collapse test of the existing two brick chimneys are discussed in this paper and composed with the results from FEA (Finite Element analysis). From the results of dynamic tests, the fundamental frequencies of Howa and Iwata brick chimneys are estimated to be about 2.69 Hz and 2.93 Hz, respectively. Their natural modes are identified by ARMAV (Autoregressive Moving Average Vectors) model. On the basis of the static and dynamic experimental tests, a numerical model has been prepared. According to the European code (Eurocode n. 8: ?esign of structures for earthquake resistance? non-linear static (Pushover) analysis of the two chimneys is carried out and they seem to be vulnerable to earthquakes with 0.25 to 0.35 g.

Key Words
brick chimney; dynamic test; static collapse test; identification; ARMAV; non-linear analysis; pushover analysis.

Address
T. Aoki; Graduate School of Design and Architecture, Nagoya City University, Kitachikusa 2-1-10, Chikusa-ku, 464-0083 Nagoya, Japan
D. Sabia; Department of Structural and Geotechnical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Turin, Italy

Abstract
An 8 node assumed stress hexahedral element with rotational degrees of freedom is proposed for static and free vibration analyses. The element formulation is based directly on an 8-node element. This direct formulation requires fewer computations than a similar element that is derived from an internal 20-node element in which the midside degrees of freedom are eliminated by expressing them in terms of displacements and rotations at corner nodes. The formulation is based on Hellinger-Reissner variational principle. Numerical examples are presented to show the validity and efficiency of the present element for static and free vibration analysis.

Key Words
solid element; 8-node hexahedral element; hybrid finite element; static analysis; free vibration.

Address
Department of Civil Engineering, Istanbul Technical University 34469, Maslak, Istanbul, Turkey

Abstract
A general analytical model for thin-walled composite beams with an arbitrary open/(or/and) closed cross section and arbitrary laminate stacking sequence i.e., symmetric, anti-symmetric as well as un-symmetric with respect to the mid plane of the laminate, is developed in the first paper. All the mechanical properties, mechanical centre of gravity and mechanical shear centre of the cross section are defined in the function of the geometry and the material properties of the section. A program ?ungen?and ?lprop?are developed in Fortran to compute all the mechanical properties and tested for various isotropic sections first and compared with the available results. The locations of mechanical centre of gravity and mechanical shear centre are given with respect to the fibre angle variation in composite beams. Variations of bending and torsional stiffness are shown to vary with respect to the fibre angle orientations.

Key Words
FRP (Fibre reinforced plastics); thin-walled composite; open section; mechanical centre of gravity; mechanical shear centre.

Address
PSG College of Technology, Coimbatore, 641004, Tamilnadu, India


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