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CONTENTS
Volume 8, Number 4, October 2011
 

Abstract
Structural system identification (SSI) is an inverse problem of difficult solution. Currently, difficulties lie in the development of algorithms which can cater to large size problems. In this paper, a parameter estimation technique based on evolutionary strategy is presented to overcome some of the difficulties encountered in using the traditional system identification methods in terms of convergence. In this paper, a non-traditional form of system identification technique employing evolutionary algorithms is proposed. In order to improve the convergence characteristics, it is proposed to employ immune algorithms which are proved to be built with superior diversification mechanism than the conventional evolutionary algorithms and are being used for several practical complex optimisation problems. In order to reduce the number of design variables, domain decomposition methods are used, where the identification process of the entire structure is carried out in multiple stages rather than in single step. The domain decomposition based methods also help in limiting the number of sensors to be employed during dynamic testing of the structure to be identified, as the process of system identification is carried out in multiple stages. A fifteen storey framed structure, truss bridge and 40 m tall microwave tower are considered as a numerical examples to demonstrate the effectiveness of the domain decomposition based structural system identification technique using immune algorithm.

Key Words
system identification; domain decomposition; evolutionary algorithm; immune algorithm; measurement noise; Nelder Mead algorithm.

Address
A. Rama Mohan Rao and K. Lakshmi : CSIR-Structural Engineering Research Centre, Council of Scientific and Industrial Research, Chennai, 600113, India

Abstract
This paper presents the design and experimental evaluation of fast output sampling feedback controller to minimize structural vibration of a cantilever beam using Shape Memory Alloy (SMA) wires as control actuators and piezoceramics as sensor and disturbance actuator. Linear dynamic models of the smart cantilever beam are obtained using online recursive least square parameter estimation. A digital control system that consists of Simulink modeling software and dSPACE DS1104 controller board is used for identification and control. The effectiveness of the controller is shown through simulation and experimentation by exciting the structure at resonance.

Key Words
shape memory alloy actuator; smart structure; system identification; active vibration control; fast output sampling feedback control.

Address
K. Dhanalakshmi, M. Umapathy and D. Ezhilarasi : Department of Instrumentation and Control Engineering, National Institute of Technology,Tiruchirappalli - 620 015, India
B. Bandyopadhyay : Systems and Control Engineering, Indian Institute of Technology Bombay, Mumbai - 400076, India

Abstract
This paper discusses the applicability of Acoustic Emission (AE) to assess the damage in reinforced concrete (RC) structures subjected to complex dynamic loadings such as those induced by earthquakes. The AE signals recorded during this type of event can be complicated due to the arbitrary and random nature of seismicity and the fact that the signals are highly contaminated by many spurious sources of noise. This paper demonstrates that by properly filtering the AE signals, a very good correlation can be found between AE and damage on the RC structure. The basic experimental data used for this research are the results of fourteen seismic simulations conducted with a shake table on an RC slab supported on four steel columns. The AE signals were recorded by several low-frequency piezoelectric sensors located on the bottom surface of the slab. The evolution of damage under increasing values of peak acceleration applied to the shake table was monitored in terms of AE and dissipated plastic strain energy. A strong correlation was found between the energy dissipated by the concrete through plastic deformations and the AE energy calculated after properly filtering the signals. For this reason, a procedure is proposed to analyze the AE measured in a RC structure during a seismic event so that it can be used for damage assessment.

Key Words
acoustic emission; damage evaluation; reinforced concrete; slab; seismic loads.

Address
Antolino Gallego and Cristobal Infantes : Department of Applied Physics, University of Granada, 18071 Granada, Spain
Amadeo Benavent-Climent : Department of Mechanics of Structures, University of Granada, 18071 Granada, Spain

Abstract
This study compares the performance of two smart isolation systems that utilize superelastic shape memory alloys (SMAs) for seismic protection of bridges using energy balance concepts. The first isolation system is a SMA/rubber-based isolation system (SRB-IS) and consists of a laminated rubber bearing that decouples the superstructure from the bridge piers and a SMA device that provides additional energy dissipation and re-centering capacity. The second isolation system, named as superelastic-friction base isolator (S-FBI), combines the superelastic SMAs with a flat steel-Teflon bearing rather than a laminated rubber bearing. Seismic energy equations of a bridge structure with SMA-based isolation systems are established by absolute and relative energy balance formulations. Nonlinear time history analyses are performed in order to assess the effectiveness of the isolation systems and to compare their performance. The program RSPMatch 2005 is employed to generate spectrum compatible ground motions that are used in time history analyses of the isolated bridge. Results indicate that SRB-IS produces higher seismic input energy, recoverable energy and base shears as compared to the S-FBI system. Also, it is shown that combining superelastic SMAs with a sliding bearing rather than rubber bearing significantly reduce the amount of the required SMA material.

Key Words
shape memory alloy; superelasticity; energy balance; seismic isolation; bridges.

Address
O.E. Ozbulut and S. Hurlebaus : Zachry Department of Civil Engineering, Texas A&M University, College Station, TX, USA

Abstract
Under the external shearing stress, the external radial stress and the electric potential simultaneously, the piezoelectric hollow cylinder transducer is studied. With the Airy stress function method, the analytical solutions of this transducer are obtained based on the theory of piezo-elasticity. The solutions are compared with the finite element results of Ansys and a good agreement is found. Inherent properties of this piezoelectric cylinder transducer are presented and discussed. It is very helpful for the design of the bearing controllers.

Key Words
piezoelectric material; transducer; cylinder; multi-layer; shearing stress; radial stress.

Address
Zhang Taotao : School of Transportation Science and Engineering, Beihang University, Beijing, 100191, P. R. China
Shi Zhifei : School of Civil Engineering, Beijing Jiaotong University, Beijing, 100044, P. R. China


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