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CONTENTS
Volume 26, Number 5, July30 2007
 

Abstract
In case of considering the shear effect, the complete solutions are obtained for dynamic plastic response of a rigid, perfectly plastic hinged-free beam, of which one end is hinged and the other end free, subjected to a transverse strike by a travelling rigid mass at an arbitrary location along its span. Special attention is paid to new deformation mechanisms due to shear sliding on both sides of the rigid mass and the plastic energy dissipation. The dimensionless numerical results demonstrate that three parameters, i.e., mass ratio, impact position of mass, as well as the non-dimensional fully plastic shear force, have significant influence on the partitioning of dissipated energy and failure mode of the hingedfree beam. The shear effect can never be negligible when the mass ratio is comparatively small and the impact location of mass is close to the hinged end.

Key Words
hinged-free beam; impact; plastic dissipated energy; deformation mechanism; complete solution.

Address
Y. Zhang: School of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, P.O. Box 93, Beijing, 100029, P. R. China
J. L. Yang: Solid Mechanics Research Center, Beijing University of Aeronautics and Astronautics, Beijing, 100083, P. R. China

Abstract
An experimental method denoted as Impulse Method is proposed as a cost-effective nondestructive technique for the on-site evaluation of concrete elastic modulus in existing structures: on the basis of Hertz?s quasi-static theory of elastic impact and with the aid of a simple portable testing equipment, it makes it possible to collect series of local measurements of the elastic modulus in an easy way and in a very short time. A Hypothesis Testing procedure is developed in order to provide a statistical tool for processing the data collected by means of the Impulse Method and assessing the possible occurrence of significant variations in the elastic modulus without exceeding some prescribed error probabilities. It is based on a particular formulation of the renowned sequential probability ratio test and reveals to be optimal with respect to the error probabilities and the required number of observations, thus further improving the time-effectiveness of the Impulse Method. The results of an experimental investigation on different types of plain concrete prove the validity of the Impulse Method in estimating the unknown value of the elastic modulus and attest the effectiveness of the proposed Hypothesis Testing procedure in identifying significant variations in the elastic modulus.

Key Words
non-destruction testing; statistical data processing; hypothesis testing; concrete, elastic modulus.

Address
Paola Antonaci and Pietro G. Bocca: Dipartimento di Ingegneria Strutturale e Geotecnica, Politecnico di Torino, Corso Duca degli Abruzzi, 24-10129, Torino, Italy
Fabrizio Sellone: Dipartimento di Elettronica, Politecnico di Torino, Corso Duca degli Abruzzi, 24-10129, Torino, Italy

Abstract
This study shows a fuzzy tuning scheme to fuzzy sliding mode controller (FSMC) for seismic isolation of earthquake-excited structures. The sliding surface can rotate in the phase plane in such a direction that the seismic isolation can be improved. Since ideal sliding mode control requires very fast switch on the input, which can not be provided by real actuators, some modifications to the conventional sliding-mode controller have been proposed based on fuzzy logic. A superior control performance has been obtained with FSMC to deal with problems of uncertainty, imprecision and time delay. Furthermore, using the fuzzy moving sliding surface, the excellent system response is obtained if comparing with the conventional sliding mode controller (SMC), as well as reducing chattering effect. For simulation validation of the proposed seismic response control, 16-floor tall building has been considered. Simulations for six different seismic events, Elcentro (1940), Hyogoken (1995), Northridge (1994), Takochi-oki (1968), the east-west acceleration component of Duzce and Bolu records of 1999 Duzce-Bolu earthquake in Turkey, have been performed for assessing the effectiveness of the proposed control approach. Then, the simulations have been presented with figures and tables. As a result, the performance of the proposed controller has been quite remarkable, compared with that of conventional SMC.

Key Words
fuzzy; moving sliding mode; control; seismic isolation; structures.

Address
Hasan Alli and Oguz Yakut: Firat University, Department of Mechanical Engineering, Elazi , Turkey

Abstract
In this paper, a hybrid boundary element technique is implemented to analyze nonlinear transient pile soil interaction in Gibson type nonhomeogenous soil. Inelastic modeling of soil media is presented by introducing a rational approximation to the continuum with nonlinear interface springs along the piles. Modified Ozdemir?s nonlinear model is implemented and systems of equations are coupled at interfaces for piles and pile groups. Linear beam column finite elements are used to model the piles and the resulting governing equations are solved using an implicit integration scheme. By enforcing displacement equilibrium conditions at each time step, a system of equations is generated which yields the solution. A numerical example is performed to investigate the effects of nonlinearity on the pile soil interaction.

Key Words
pile-soil interaction; inelastic behavior; pile dynamics; transient response of piles.

Address
S. Kucukarslan: Dept. of Engineering Sciences, Istanbul Technical University, Maslak, 34469, Istanbul, Turkey
P. K. Banerjee: Dept. of Civil Engineering, State University of New York at Buffalo,14260, NY, USA

Abstract
The elastic T-stress is increasingly being recognized as an important second parameter to the stress intensity factor for fracture and fatigue assessments. In this paper, the mutual or M-contour integral approach is employed in conjunction with the Boundary Element Method (BEM) to determine the numerical T-stress solutions for cracks in plates with multiple holes. The problems investigated include plates of infinite width with multiple holes at which single or double, symmetric cracks have grown from. Comparisons of these results are also made with the corresponding solutions of finite plates with a single hole. For completeness, stress intensity factor solutions for the cracked geometries analyzed are presented as well. These results will be useful for failure assessments using the two-parameter linear elastic fracture mechanics approach.

Key Words
T-stress; crack-tip constraint; BEM; plate with multiple holes; M-contour integral.

Address
Jackie Yu, Xin Wang and Choon-Lai Tan: Dept. of Mechanical and Aerospace Engineering, Carleton University Ottawa, Ontario, K1S 5B6, Canada

Abstract
This paper presents an analytical model for RC beam-column connections that takes into account bond deterioration between reinforcing steel and concrete. The model is based on the Lumped Damage Mechanics (LDM) theory which allows for the characterization of cracking, degradation and yielding, and is extended in this paper by the inclusion of the slip effect as observed in those connections. Slip is assumed to be lumped at inelastic hinges. Thus, the concept of ?slip hinge?, based on the Coulomb friction plasticity theory, is formulated. The influence of cracking on the slip behavior is taken into account by using two concepts of LDM: the effective moment on an inelastic hinge and the strain equivalence hypothesis. The model is particularly suitable for wide beam-column connections for which bond deterioration dominates the hysteretic response. The model was evaluated by the numerical simulation of five tests reported in the literature. It is found that the model reproduces closely the observed behavior.

Key Words
R/C wide beam-column connection; bond deterioration; reinforcement slip; pinching in behavior loops; bond strengths; lumped damage mechanics; inelastic hinges; slip hinge.

Address
Ricardo Picon-Rodriguez: Dept. of Structural Engineering, Lisandro Alvarado University, Barquisimeto, Venezuela
Carlos Quintero-Febres and Julio Florez-Lopez: Dept. of Structural Engineering, University of Los Andes, Merida, Venezuela

Abstract
An improvement is introduced to solve the plane problems of linear elasticity by reciprocal theorem for orthotropic materials. This method gives an integral equation with complex kernels which will be solved numerically. An artificial boundary is defined to eliminate the singularities and also an algorithm is introduced to calculate multi-valued complex functions which belonged to the kernels of the integral equation. The chosen sample problem is a plate, having a circular or elliptical hole, stretched by the forces parallel to one of the principal directions of the material. Results are compatible with the solutions given by Lekhnitskii for an infinite plane. Five different orthotropic materials are considered. Stress distributions have been calculated inside and on the boundary. There is no boundary layer effect. For comparison, some sample problems are also solved by finite element method and to check the accuracy of the presented method, two sample problems are also solved for infinite plate.

Key Words
elasticity; orthotropy; finite plates having elliptical and circular holes; multi-valued function; boundary element; reciprocity theorem; singularity.

Address
N. Kadioglu and S. Ataoglu: Division of Mechanics, Civil Engineering Department, Faculty of Civil Engineering, Istanbul Technical University, Maslak 34469 Istanbul, Turkey


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