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CONTENTS
Volume 36, Number 6, December20 2010
 

Abstract
In general means, the stress concentration problem of elastic plate with a rectangular hole can be investigated by numerical methods, and only approximative results are derived. This paper deduces an analytical study of the stress concentration due to a rectangular hole in an elastic plate under bending loads. Base on classical elasticity theory and FEM applying the U-transformation technique, the uncoupled governing equations with 3-DOF are established, and the analytical displacement solutions of the finite element equations are derived in series form or double integral form. Therefore, the stress concentration factor can then be discussed easily and conveniently. For the plate subjected to unidirectional bending loads, the non-conforming plate bending element with four nodes and 12-DOF is taken as examples to demonstrate the application of the proposed method. The inner force distribution is obtained. The solutions are adequate for the condition when the hole is far away from the edges and the thin plate subjected to any transverse loadings.

Key Words
U-transformation; stress concentration; rectangular hole; analytical solution; bending loads.

Address
Y. Yang: School of Civil Engineering and Transportation, South China University of Technology, Guangzhou, 510640, P.R. China
J.K. Liu: Department of Mechanics, Sun Yat-sen University, Guangzhou, 510275, P.R. China
C.W. Cai: Department of Mechanics, Sun Yat-sen University, Guangzhou, 510275, P.R. China

Abstract
In-plane vibrations of slightly curved beams having cracks are investigated numerically and experimentally. The curvature of the beam is circular and stays in the plane of vibration. Specimens made of steel with different lengths but with the same radius of curvature are used in the experiments. Cracks are opened using a hand saw having 0.4 mm thickness. Natural frequencies depending on location and depth of the cracks are determined using a Bruel & Kjaer 4366 type accelerometer. Then the beam is assumed as a Rayleigh type slightly curved beam in finite element method (FEM) including bending, extension and rotary inertia. A flexural rigidity equation given in literature for straight beams having a crack is used in the analysis. Frequencies are obtained numerically for different crack locations and depths. Experimental results are presented and compared with the numerical solutions. The natural frequencies are affected too much due to larger moments when the crack is around nodes. The effect can be neglected when it is at the location of maximum displacements. When the crack is close to the clamped end, the decrease in the frequencies in all modes is very high. The consistency of the results and validity of the equations are discussed.

Key Words
curved beam; crack; transverse vibration.

Address
H. Ridvan Oz: Department of Genetics and Bioengineering, Engineering Faculty, Fatih University, 34500, B.cekmece, Istanbul, Turkey

Abstract
This paper presents an improved version of the Hilbert-Huang transform (HHT) for the modal evaluation of structural systems or signals. In this improved HHT, a well-designed bandpass filter is used as preprocessing to separate and determine each mode of the signal for solving the inherent modemixing problem in HHT (i.e., empirical mode decomposition, EMD, associated with the Hilbert transform). A screening process is then applied to remove undesired intrinsic mode functions (IMFs) derived from the EMD of the signal\'s mode. A \"best\" IMF is selected in each screening process that utilizes the orthogonalization coefficient between the signal\'s mode and its IMFs. Through mode-by-mode signal filtering, parameters such as the modal frequency can be evaluated accurately when compared to the theoretical value. Time history of the identified modal frequency is available. Numerical results prove the efficiency of the proposed approach, showing relative errors 1.40%, 2.06%, and 1.46%, respectively, for the test cases of a benchmark structure in the lab, a simulated time-varying structural system, and of a linear superimposed cosine waves.

Key Words
bandpass filter; Hilbert-Huang transform; modal frequency; orthogonalization coefficient; signal filtering.

Address
Jeng-Wen Lin: Department of Civil Engineering, Feng Chia University, Taichung 40724, Taiwan

Abstract
An experimental investigation is conducted here to study the effects of applying frictional sliding fuses (FSF) in concrete infilled steel frames. Firstly, the influences of some parameters on the behavior of the sliding fuse are studied: Methods of adjusting the FSF for a certain sliding strength are explained and influences of time duration, welding and corrosion are investigated as well. Based on the results, time duration does not significantly affect the FSF, however influences of welding and corrosion of the constitutive plates are substantial. Then, the results of testing two 1/3 scale single-storey single-bay concrete infilled steel frames having FSF are presented. The specimens were similar, except for different regulations of their fuses, tested by displacement controlled cyclic loading. The results demonstrate that applying FSF improves infill behaviors in both perpendicular directions. The infilled frames with FSF have more appropriate hysteresis cycles, higher ductility, much lower deteriorations in strength and stiffness in comparison with regular ones. Consequently, the infills, provided with FSF, can be regarded as an engineered element, however, special consideration should be taken into the affecting parameters of their fuses.

Key Words
steel frame; fibrous concrete; cyclic loads; ductility; retrofitting; damping; frictional sliding fuse; engineered infill.

Address
M. Mohammadi-Gh: Structural Research Center, International Institute of Earthquake Engineering and Seismology, IIEES, Arghavan Gharbi, Dibaji Shomali, Tehran, Islamic Republic of Iran
V. Akrami: Student of Sharif University, Civil Engineering Department, Sharif University, Azadi Ave., Tehran, Islamic Republic of Iran

Abstract
There is world wide concern for safety of nuclear power installations after the terrorist attack on World Trade Center in 2001 and several other civilian structures in the last decade. The nuclear containment structure in many countries is a double shell structure (outer shell a RCC and inner a prestressed concrete). The outer reinforced concrete shell protects the inner shell and is designed for external loading like impact and blast. A comparative study of non-linear response of reinforced concrete nuclear containment cylindrical shell subjected to impact of an aircraft (Phantom) and explosion of different amounts of blast charges have been presented here. A material model which takes into account the strain rate sensitivity in dynamic loading situations, plastic and visco-plastic behavior in three dimensional stress state and cracking in tension has been developed earlier and implemented into a finite element code which has been validated with published literature. The analysis has been made using the developed software. Significant conclusions have been drawn for dissimilarity in response (deflections, stresses, cracks etc.) of the shell for impact and blast loading.

Key Words
impulsive; dynamic; blast charge; yielding; visco-plastic; tensile cracking.

Address
A.K. Pandey: Central Building Research Institute, Roorkee (CSIR), 247667, Uttarakhand, India

Abstract
12 typical laminated composite reinforced concrete (RC) walls with different concrete ages and 3 cast-in-place RC walls subjected to low frequency cyclic load were carried out in this study. The failure mode, force-deformation response and energy dissipation capacity of these specimens were investigated. Differences of structural behaviours between composite RC walls and common cast-in-place RC walls were emphasized in the analysis. The compatibility of the composite specimens with different concrete ages was discussed based on the experiment. Test results indicated that the differences between the lateral bearing capacity and the displacement ductility of the composite walls and the common walls were not so obvious. Some of the composite specimen even has higher bearing capacity under the experiment loading situation. Besides, the two parts of the laminated composite specimens demonstrates incompatibility at the later loading sequence on failure mode and strain response when it is in tension. Finally, this laminated composite shear walls are suggested to be applied in rapid reconstruction structures which is not very high.

Key Words
different concrete ages; prefabricated wall; cast-in-place; laminated composite wall; cyclic loading test; compatibility.

Address
Hongmei Zhang: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China
Xilin Lua: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China
Jianbao Li: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China
Lin Liang: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China

Abstract
In this paper, compressive strength of carbon fiber reinforced polymer (CFRP) confined concrete cylinders is formulated using a hybrid method coupling genetic programming (GP) and simulated annealing (SA), called GP/SA, and a robust variant of GP, namely multi expression programming (MEP). Straightforward GP/SA and MEP-based prediction equations are derived for the compressive strength of CFRP-wrapped concrete cylinders. The models are constructed using two sets of predictor variables. The first set comprises diameter of concrete cylinder, unconfined concrete strength, tensile strength of CFRP laminate, and total thickness of CFRP layer. The most widely used parameters of unconfined concrete strength and ultimate confinement pressure are included in the second set. The models are developed based on the experimental results obtained from the literature. To verify the applicability of the proposed models, they are employed to estimate the compressive strength of parts of test results that were not included in the modeling process. A sensitivity analysis is carried out to determine the contributions of the parameters affecting the compressive strength. For more verification, a parametric study is carried out and the trends of the results are confirmed via some previous studies. The GP/SA and MEP models are able to predict the ultimate compressive strength with an acceptable level of accuracy. The proposed models perform superior than several CFRP confinement models found in the literature. The derived models are particularly valuable for pre-design purposes.

Key Words
CFRP-confined concrete; compressive strength; genetic programming; simulated annealing; multi expression programming; formulation.

Address
S.M. Mousavi: Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
A.H. Alavi: School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran
A.H. Gandomi: College of Civil Engineering, Tafresh University, Tafresh, Iran
M. Arab Esmaeili: Department of Civil Engineering, Islamic Azad University, Shahrood Branch, Shahrood, Iran
M. Gandomi: School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran


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