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CONTENTS
Volume 4, Number 1, January 2008
 

Abstract
This study proposes a conceptual framework of in-situ vibration tests and analyses for quality appraisal of non-slender, cast-in-place piles with irregular cross-section configuration. It evaluates a frequency index from vibration recordings to a series of impulse loadings that is related to total soil-resistance forces around a pile, so as to assess if the pile achieves the design requirement in terms of bearing capacity. In particular, in-situ pile-vibration tests in sequential are carried out, in which dropping a weight from different heights generates series impulse loadings with low-to-high amplitudes. The high-amplitude impulse is designed in way that the load will generate equivalent static load that is equal to or larger than the designed bearing capacity of the pile. This study then uses empirical mode decomposition and Hilbert spectral analysis for processing the nonstationary, short-period recordings, so as to single out with accuracy the frequency index. Comparison of the frequency indices identified from the recordings to the series loadings with the design-based one would tell if the total soil resistance force remains linear or nonlinear and subsequently for the quality appraisal of the pile. As an example, this study investigates six data sets collected from the in-situ tests of two piles in Taipu water pump project, Jiangshu Province of China. It concludes that the two piles have the actual axial load capacity higher than the designed bearing capacity. The true bearing capacity of the piles under investigation can be estimated with accuracy if the amplitude of impact loadings is further increased and the analyses are calibrated with the static testing results.

Key Words
cast-in-place pile; in-situ vibration test; bearing capacity; soil-resistant force; nonstationary data process and analysis.

Address
Ray Ruichong Zhang; Division of Engineering, Colorado School of Mines, Golden, CO80401, USA

Abstract
Nowadays developments in the field of laminated composite structures with piezoelectric have attracted significant attention of researchers due to their wide range of applications in engineering such as sensors, actuators, vibration suppression, shape control, noise attenuation and precision positioning. Due to large number of parameters associated with its manufacturing and fabrication, composite structures with piezoelectric display a considerable amount of uncertainty in their material properties. The present work investigates the effect of the uncertainty on the free vibration response of piezoelectric laminated composite plate. The lamina material properties have been modeled as independent random variables for accurate prediction of the system behavior. System equations have been derived using higher order shear deformation theory. A finite element method in conjunction with Monte Carlo simulation is employed to obtain the secondorder statistics of the natural frequencies. Typical results are presented for all edges simply supported piezoelectric laminated composite plates to show the influence of scattering in material properties on the second order statistics of the natural frequencies. The results have been compared with those available in literature.

Key Words
free vibration; piezoelectric composite plates; random material properties; second-order statistics.

Address
B. N. Singh; Department of Aerospace Engineering, Indian Institute of Technology, Kharagpur- 721 302, India
Atul Umrao and K. K. Shukla; Department of Applied Mechanics, MN National Inst. of Technology, Allahabad-211004, India
N. Vyas; Department of Aerospace Engineering, IIT Kharagpur -721 302, India

Abstract
In this paper the authors address the problem of comparing two different smart damping techniques using the numerical modelling of the electro-mechanical impedance for plate structures partially treated with active constrained layer damping treatments. The paper summarizes the modelling procedures including a finite element formulation capable of accounting for the observed behaviour. The example used is a smart cantilever plate structure containing a viscoelastic material (VEM) layer sandwiched between a piezoelectric constrained layer and the host vibrating plate. Comparisons are made between active constrained layer and active damping only and based on the resonance frequency amplitudes of the electrical admittance numerically evaluated at the surface of the piezoelectric model of the vibrating structure.

Key Words
smart damping; ACDL; electomechanical impedance; FEM; piezoelectric actuators/sensors.

Address
C. P. Providakis; Department of Applied Sciences, Technical University of Crete, Chania, Greece
D.-P. N. Kontoni; Department of Civil Engineering, Technological Educational Institute of Patras, Patras, Greece
M. E. Voutetaki and M. E. Stavroulaki; Department of Applied Sciences, Technical University of Crete, Chania, Greece

Abstract
The present work utilizes system identification technique for health monitoring of shear building, wherein Parametric State Space modeling has been adopted. The method requires input excitation to the structure and also output acceleration responses of both undamaged and damaged structure obtained from numerically simulated model. Modal parameters like eigen frequencies and eigen vectors have been extracted from the State Space model after introducing appropriate transformation. Least square technique has been utilized for the evaluation of the stiffness matrix after having obtained the modal matrix for the entire structure. Highly accurate values of stiffness of the structure could be evaluated corresponding to both the undamaged as well as damaged state of a structure, while considering noise in the simulated output response analogous to real time scenario. The damaged floor could also be located very conveniently and accurately by this adopted strategy. This method of damage detection can be applied in case of output acceleration responses recorded by sensors from the actual structure. Further, in case of even limited availability of sensors along the height of a multi-storeyed building, the methodology could yield very accurate information related to structural stiffness.

Key Words
structural health monitoring; system identification; state space modeling; modal parameters; damage detection; earthquake ground acceleration.

Address
Manab Medhi, Anjan Dutta and S. K. Deb; Department of Civil Engineering, Indian Institute of Technology Guwahati 781039 India

Abstract
The present contribution is concerned with the static and dynamic stability of a piezo-laminated Bernoulli-Euler beam subjected to an axial compressive force. Recently, an inconsistent derivation of the equations of motions of such a smart structural system has been presented in the literature, where it has been claimed, that an axial piezoelectric actuation can be used to control its stability. The main scope of the present paper is to show that this unfortunately is impossible. We present a consistent theory for composite beams in plane bending. Using an exact description of the kinematics of the beam axis, together with the Bernoulli-Euler assumptions, we obtain a single-layer theory capable of taking into account the effects of piezoelectric actuation and buckling. The assumption of an inextensible beam axis, which is frequently used in the literature, is discussed afterwards. We show that the cited inconsistent beam model is due to inadmissible mixing of the assumptions of an inextensible beam axis and a vanishing axial displacement, leading to the erroneous result that the stability might be enhanced by an axial piezoelectric actuation. Our analytical formulations for simply supported Bernoulli-Euler type beams are verified by means of three-dimensional finite element computations performed with ABAQUS.

Key Words
smart beam; piezoelectric actuation; Bernoulli-Euler beam; buckling load; static stability; dynamic stability.

Address
C. Zehetner; Linz Center of Competence in Mechatronics (LCM), A-4040 Linz, Altenbergerstr.69, Austria
H. Irschik; Institute of Technical Mechanics, Johannes Kepler University of Linz, A-4040 Linz, Altenbergerstr.69, Austria

Abstract
In this paper, excitation systems using a linear mass shaker (LMS) and an active tuned mass damper (ATMD) are presented to simulate the wind induced responses of a building structure. The actuator force for the excitation systems is calculated by using the inverse transfer function of a target structural response to the actuator. Filter and envelop functions are used to prevent the actuator from exciting unexpected modal responses and an initial transient response and thus, to minimize the error between the wind and actuator induced responses. The analyses results from a 76-story benchmark building problem for which the wind load obtained by a wind tunnel test is given, indicate that the excitation system installed at a specific floor can approximately reproduce the structural responses induced by the wind load applied to each floor of the structure. The excitation system designed by the proposed method can be effectively used for evaluating the wind response characteristics of a practical building structure and for obtaining an accurate analytical model of the building under wind load.

Key Words
actuator; linear mass shaker; active tuned mass damper; wind-induced response.

Address
Eun Churn Park, Sang-Hyun Lee, Kyung-Won Min, Lan Chung, Sung-Kyung Lee and Seung-Ho Cho; Department of Architectural Engineering, Dankook University, Jukjeon-dong, San 44-1, Suji-Gu, Yongin-si, Gyeonggi-do, Korea
Eunjong Yu; Department of Architectural Engineering, Hanyang University, 17, Haengdang-dong, Seongdong-gu, Seoul, Korea
Kyung-Soo Kang; Department of Architectural Engineering, Tongmyong University, Pusan, Korea

Abstract
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Key Words
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Address
N. Lakshmanan, K. Muthumani, N. Gopalakrishnan and D. Basu; Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai 600113, India
B. K. Raghuprasad; Department of Civil Engineering, Indian Institute of Science, Bangalore 560012, India


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