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CONTENTS
Volume 15, Number 3, March 2003
 

Abstract
This paper reports a series of component tests on a lightweight floor system and a method to predict the natural frequency of the floor using a frame analysis program. Full-scale floor tests are also briefly described. DuraGal steel Rectangular Hollow Sections (in-line galvanised RHS) are used as joists, bearers and piers in DuraGal lightweight floor systems. A structural grade particleboard is used as decking. Connection stiffness between different components (bearer, joist, pier and floor decking) was determined. A 40% composite action was achieved between the RHS joist and the particleboard. Both 2D and 3D models were developed to study the effect of connection stiffness on predicting the natural frequency of DuraGal lightweight floor systems. It has been found that the degree of shear connection between the bearer and the joist has a significant influence on the floor natural frequency. The predicted natural frequencies are compared with measured values from full scale floor testing.

Key Words
floor system; steel hollow sections; rotational stiffness; natural frequency.

Address
Department of Civil Engineering, Monash University, Clayton, VIC 3168, Australia

Abstract
Complementing recent advances made in the field of structural health monitoring and damage detection, the concept of a wireless sensing network with distributed computational power is proposed. The fundamental building block of the proposed sensing network is a wireless sensing unit capable of acquiring measurement data, interrogating the data and transmitting the data in real time. The computational core of a prototype wireless sensing unit can potentially be utilized for execution of embedded engineering analyses such as damage detection and system identification. To illustrate the computational capabilities of the proposed wireless sensing unit, the fast Fourier transform and auto-regressive time-series modeling are locally executed by the unit. Fast Fourier transforms and auto-regressive models are two important techniques that have been previously used for the identification of damage in structural systems. Their embedment illustrates the computational capabilities of the prototype wireless sensing unit and suggests strong potential for unit installation in automated structural health monitoring systems.

Key Words
structural health monitoring; damage detection; time-series analysis; wireless monitoring; wireless sensing unit; structural monitoring; auto-regressive modeling.

Address
The John A. Blume Earthquake Engineering Center, Stanford University, Stanford, CA 94305, USA

Abstract
This investigation presents an efficient method for identifying modal characteristics from the measured displacement, velocity and acceleration signals of multiple channels on structural systems. A Vector Backward Auto-Regressive model (VBAR) that describes the relationship between the output information in different time steps is used to establish a backward state equation. Generally, the accuracy of the identified dynamic characteristics can be improved by increasing the order of the Auto-Regressive model (AR) in cases of measurement of data under noisy circumstances. However, a higher-order AR model also induces more numerical modes, only some of which are the system modes. The proposed VBAR model provides a clear characteristic boundary to separate the system modes from the spurious modes. A numerical example of a lumped-mass model with three DOFs was established to verify the applicability and effectiveness of the proposed method. Finally, an offshore platform model was experimentally employed as an application case to confirm the proposed VBAR method can be applied to real-world structures.

Key Words
vector backward auto-regressive model (VBAR); modal identification; offshore platform model; finite element method; experimental dynamics.

Address
Department of Engineering Science and Ocean Engineering, National Taiwan University, Taipei, 106, Taiwan


Abstract
As shear occurs along a soil-structure interface, a localized zone with a thickness of several grain diameters will develop in soil along the interface, forming an interfacial layer. In this paper, the behaviour of a soil-structure interface is studied numerically by modelling the plane shear of a granular layer bounded by rigid plates. The mechanical behaviour of the granular material is described with a micro-polar hypoplastic continuum model. Numerical results are presented to show the development of shear localization along the interface for shearing under conditions of constant normal pressure and constant volume, respectively. Evolution of the resistance on the surface of the bounding plate is considered with respect to the influences of grain rotation.

Key Words
soil-structure interface; shear localization; Cosserat continuum; hypoplasticity.

Address
Discipline of Civil, Surveying & Environmental Engineering, School of Engineering,
The University of Newcastle, NSW 2308, Australia
Institute of General Mechanics, Graz University of Technology, A-8010, Graz, Austria
Discipline of Civil, Surveying & Environmental Engineering, School of Engineering, The University of Newcastle, NSW 2308, Australia

Abstract
The plane contact problem for two infinite elastic layers whose elastic constants and heights are different is considered. The layers lying on a Winkler foundation are acted upon by symmetrical distributed loads whose lengths are 2a applied to the upper layer and uniform vertical body forces due to the effect of gravity in the layers. It is assumed that the contact between two elastic layers is frictionless and that only compressive normal tractions can be transmitted through the interface. The contact along the interface will be continuous if the value of the load factor, l, is less than a critical value. However, interface separation takes place if it exceeds this critical value. First, the problem of continuous contact is solved and the value of the critical load factor, lcr , is determined. Then, the discontinuous contact problem is formulated in terms of a singular integral equation. Numerical solutions for contact stress distribution, the size of the separation areas, critical load factor andseparation distance, and vertical displacement in the separation zone are given for various dimensionless quantities and distributed loads.

Key Words
continuous contact; discontinuous contact; separation integral equation; elastic layer; Winkler foundation; elasticity.

Address
Karadeniz Technical University, Civil Engineering Department, 61080, Trabzon, Turkey

Abstract
The adoption of fibre reinforced polymer (FRP) rebars (whose behaviour is elastic-brittle) in reinforced concrete (RC) cross sections requires the assessment of the influence of time-dependent behaviour of concrete on the load-carrying capacity of these sections. This paper presents a method of computing the load-carrying capacity of sections that are at first submitted to a constant long-term service load and then overloaded up to ultimate load. The method solves first a non-linear visco-elastic problem, and then a non-linear instantaneous analysis up to ultimate load that takes into account the self-equilibrated stress distribution previously computed. This method is then adopted to perform a parametric analysis that shows that creep and shrinkage of concrete increase the load-carrying capacity of the cross section reinforced with FRP and allows for the suggestion of simple design rules.

Key Words
RC; compact cross-sections; long-term loading; load-carrying capacity; FRP reinforcement.

Address
Politecnico di Milano, Department of Structural Engineering, Piazza Leonardo da Vinci 32, 20133 Milan, Italy

Abstract
The magnitude of the plastic zone around the crack tip of DENT (Double Edge Notched Tension) specimen and the crack growth length under cyclic loading were measured by ESPI (Electronic Speckle Pattern Interferometry) system. The measured magnitude of plastic zone was compared with the proposed by Irwin and calculated by a nonlinear static method of MSC/NASTRAN. The measured crack growth length by ESPI system was also compared with the obtained data by the image analysis system. From the study, it is confirmed that the plastic zone and crack growth length can be measured accurately with the high-tech equipment (ESPI System).


Key Words
electronic speckle pattern interferometry system; plastic zone size; strain distribution; crack growth length; crack growth rate.

Address
Department of Naval Architecture and Ocean Engineering, Inha University, Incheon 402-751, Korea


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