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CONTENTS
Volume 31, Number 2, January30 2009
 

Abstract
The reflection and transmission of micropolar thermoelastic plane waves at the interface between an elastic solid and micropolar generalized thermoelastic solid is discussed. The interface boundary conditions obtained contain interface stiffness (normal stiffness and transverse stiffness). The expressions for the reflection and transmission coefficients which are the ratios of the amplitudes of reflected and transmitted waves to the amplitude of incident waves are obtained for normal force stiffness, transverse force stiffness and welded contact. Numerical calculations have been performed for amplitude ratios of various reflected and transmitted waves. The variations of amplitude ratios with angle of incident wave have been depicted graphically. It is found that the amplitude ratios of reflected and transmitted waves are affected by the stiffness, micropolarity and thermal distribution of the media.

Key Words
micropolar generalized thermoelastic solid; normal force stiffness; transverse force stiffness; welded contact; amplitude ratios.

Address
Rajneesh Kumar

Abstract
Mechanic behavior of Y-shape thin-walled box girder bridge structure is complex, so one can not exactly hold the mechanical behavior of the Y-shape thin-walled box girder bridge structure through general calculation theory and analytical method. To hold the mechanical behavior better, based on elementary beam theory, by increasing the degree of freedom analytical method, taking account of restrained torsiondistortion angledistortion warp and shearing lag effect at the same time, authors obtain a thin-walled box beam analytical element of 10 degrees of freedom of every node, derive stiffness matrix of the element, and code a finite element procedure. In addition, authors combine the obtained procedure with spatial grillage analytical method, meanwhile, they build a new analytical method that is the spatial thin-walled box girder element grillage analysis method. In order to validate the precision of the obtained analysis method, authors analyze a type Y-shape thin-walled box girder bridge structure according to the elementary beam theory analytical method, the shell theory analytical method and the spatial thin-walled box girder element grillage analysis method respectively. At last, authors test a type Y-shape thin-walled box girder bridge structure. Comparisons of the results of theory analysis with the experimental text show that the spatial thin-walled box girder element grillage analysis method is simple and exact. The research results are helpful for the knowledge of the mechanics property of these Y-shape thin-walled box girder bridge structures.

Key Words
structure of Y-shape bridge; increasing of freedom degree; stiffness matrix; space grillage analysis.

Address
Lu Peng-zhen; School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China
Zhang Jun-ping; School of Civil Engineering of Guangzhou University, Guangzhou 510006, China
Zhao Ren-da; School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China
Huang Hai-yun; School of Civil Engineering of Guangzhou University, Guangzhou 510006, China

Abstract
The reduction of the dynamic response of an offshore structure subjected to wind-generated random ocean waves is of extreme significance in the aspects of serviceability, fatigue life and safety of the structure. In this study, a new neuro-control scheme is applied to the vibration control of a fixed offshore platform under random wave loads to examine the applicability of the proposed method. It is called the Lattice Probabilistic Neural Network (LPNN), as it utilizes lattice pattern of state vectors as the training data of PNN. When control results of the LPNN are compared with those of the NN and PNN, LPNN showed better performance in effectively suppressing the structural responses in a shorter computational time.

Key Words
active control; probabilistic neural network; lattice; training pattern; wave load.

Address
Dong Hyawn Kim; Department of Ocean System Engineering, Kunsan National University, Kunsan, Jeonbuk 573-701, Korea
Dookie Kim

Abstract
In the design of tall reinforced concrete (R/C) buildings, the serviceability stiffness criteria in terms of maximum lateral displacement and inter-story drift must be satisfied to prevent large secondorder P-delta effects. To accurately assess the lateral deflection and stiffness of tall R/C structures, cracked members in these structures need to be identified and their effective member flexural stiffness determined. In addition, the implementation of the geometric nonlinearity in the analysis can be significant for an accurate prediction of lateral deflection of the structure, particularly in the case of tall R/C building under lateral loading. It can therefore be important to consider the cracking effect together with the geometric nonlinearity in the analysis in order to obtain more accurate results. In the present study, a computer program based on the iterative procedure has been developed for the three dimensional analysis of reinforced concrete frames with cracked beam and column elements. Probability-based effective stiffness model is used for the effective flexural stiffness of a cracked member. In the analysis, the geometric nonlinearity due to the interaction of axial force and bending moment and the displacements of joints are also taken into account. The analytical procedure has been demonstrated through the application of R/C frame examples in which its accuracy and efficiency in comparison with experimental and other analytical results are verified. The effectiveness of the analytical procedure is also illustrated through a practical four story R/C frame example. The iterative procedure provides equally good and consistent prediction of lateral deflection and effective flexural member stiffness. The proposed analytical procedure is efficient from the viewpoints of computational effort and convergence rate.

Key Words
three dimensional analysis; reinforced concrete frames; effective moment of inertia; deflections.

Address
Ilker Fatih Kara; Department of Civil Engineering, Nigde University, 51245, Nigde, Turkey
Cengiz Dundar; Department of Civil Engineering, Cukurova University, 01330, Adana, Turkey

Abstract
This paper presents the theoretical developments of an exact finite strip for the buckling and initial post-buckling analyses of isotropic flat plates. The so-called exact finite strip is assumed to be simply supported out-of-plane at the loaded ends. The strip is developed based on the concept that it is effectively a plate. The present method, which is designated by the name Full-analytical Finite Strip Method in this paper, provides an efficient and extremely accurate buckling solution. In the development process, the Von-Karman\'s equilibrium equation is solved exactly to obtain the buckling loads and the corresponding form of out-of-plane buckling deflection modes. The investigation of thin flat plate buckling behavior is then extended to an initial post-buckling study with the assumption that the deflected form immediately after the buckling is the same as that obtained for the buckling. It is noted that in the present method, only one of the calculated out-of-plane buckling deflection modes, corresponding to the lowest buckling load, i.e., the first mode is used for the initial post-buckling study. Thus, the post buckling study is effectively a single-term analysis, which is attempted by utilizing the so-called semienergy method. In this method, the Von-Karman\'s compatibility equation governing the behavior of isotropic flat plates is used together with a consideration of the total strain energy of the plate. Through the solution of the compatibility equation, the in-plane displacement functions which are themselves related to the Airy stress function are developed in terms of the unknown coefficient in the assumed outof-plane deflection function. These in-plane and out-of-plane deflected functions are then substituted in the total strain energy expressions and the theorem of minimum total potential energy is applied to solve for the unknown coefficient. The developed method is subsequently applied to analyze the initial postbuckling behavior of some representative thin flat plates for which the results are also obtained through the application of a semi-analytical finite strip method. Through the comparison of the results and the appropriate discussion, the knowledge of the level of capability of the developed method is significantly promoted.

Key Words
exact strip; relative stiffness; initial post-buckling stage; von-karman

Address
H. R. Ovesy; Aerospace Engineering Department and Centre of Excellence in Computational Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran
S. A. M. Ghannadpour; Space Engineering Department, Faculty of New Technologies and Energy Engineering, Shahid Beheshti University, G.C., Evin, 1983963113, Tehran, Iran

Abstract
Transient response analysis can be conducted either in the time domain, or via the frequency domain. Sometimes a frequency domain method (FDM) has advantages over a time domain method. A practical issue in the FDM is to find out an appropriate extended period, which may be affected by several factors, such as the excitation duration, the system damping, the artificial damping, the period of interest, etc. In this report, the extended period of the FDM based on the Duhamel\'s integral is investigated. This Duhamel\'s integral based FDM does not involve the unit impulse response function (UIRF) beyond the period of interest. Due to this fact, the ever-lasting UIRF can be simply set as zero beyond the period of interest to shorten the extended period. As a result, the preferred extended period is the summation of the period of interest and the excitation duration. This conclusion is validated by numerical examples. If the extended period is too short, then the front portion of the period of interest is more prone to errors than the rear portion, but the free vibration segment is free of the wraparound error.

Key Words
transient response; frequency domain method; fast fourier transform (FFT); laplace transform; Duhamel

Address
Kui Fu Chen; College of Sciences, China Agricultural University, Beijing 100083, P.R. China
Qiang Zhang; Architecture Engineering School, Shanghai Normal University, Shanghai 201418, P.R. China
Sen Wen Zhang; The Institute of Applied Mechanics, Jinan University, Guangzhou 510632, P.R. China


Abstract
The present paper reviews the shear design (of reinforced concrete beam) provisions of four different national codes and proposes a new but simplified shear strength empirical expression, incorporating variables such as compressive strength of concrete, percentage of longitudinal and vertical steel/s, depth of beam in terms of shear span-to-depth ratio, for reinforced concrete (RC) beams without shear reinforcement. The expression is based on the experimental vestigation on RC beams without shear reinforcement. Further, the comparisons of shear design provisions of four National codes viz.: (i) IS 456-2000, (iii) BS 8110-1997, (iv) ACI 318-2002 (v) EuroCode-2-2002 and the proposed expression for the prediction of shear capacity of normal beam/s, have been made by solving a numerical example. The results of the numerical example worked out suggest that there is need for revision in the shear design procedure of different codes. Also, the proposed expression is less conservative among the IS, BS & Eurocode.

Key Words
shear strength of concrete; compressive strength of concrete; percentage of longitudinal and vertical steel/s; depth of beam in terms of shear span-to-depth ratio; code provisions.

Address
R. S. Londhe; Applied Mechanics Department, Government College of Engineering Aurangabad, Maharashtra State, 431 005, India

Abstract


Key Words


Address
Pradip Sarkar; Bechtel India Pvt. Ltd., 249A Udyog Vihar Phase ? IV, Gurgaon, India
Maidhily Govind; Samsung Engineering Co., Ltd., 467-14, Dogok-2dong, Gangnam Gu, Seoul 135-856, Korea
Devdas Menon; Structural Engineering Division, Department of Civil Engineering, Indian Institute of Technology Madras, Chennai 600 036, India


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