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The stochastic finite element method is applied to study the effect of a spatially varying soil medium on the settlement of singlepile foundations. In this study, the soil medium is assumed to be linearelastic, and it is modeled as a homogeneous random field. The random field captures the uncertainty in the soil modulus by means of the coefficient of variation and the scales of fluctuation. Using a firstorder secondmoment technique, the mean and coefficient of variation of the pile head settlement are determined. It is found that the uncertainty of the pile head settlement is dependent on both deterministic and stochastic parameters. Reliability analysis is then performed to compute the reliability index and the corresponding probability of unserviceable behavior. In order to facilitate the probabilistic design of pile foundations, the results of the analysis are presented in the form of concise charts suitable for use by practicing engineers.

Torsional vibration control can be crucial for applications of smart materials and structures. In this paper, the problem of topology optimization of collocated piezoelectric sensor/actuator (S/A) pairs for torsional vibration control of a laminated composite plate is directly addressed. Both isotropic and anisotropic PZT S/A pairs are considered and it is highlighted that the torsional vibration can be more effectively damped out by employing the topological optimal design of the S/A pairs than by using the conventional designs. To implement this topology optimization, a genetic algorithm (GA) based on a bit-array representation method is presented and a finite element (FE) simulation model based on the first-order shear theory and an output feedback control law is adopted. Numerical experiments are used to verify the present algorithm and show that the present optimal topology design can achieve significantly better active damping effect than the one using a continuously distributed PZT S/A pair, which was often adopted by many other researchers. Together with the progress in laser cutting and micromachining techniques, topology optimization of piezoelectric sensors and/or actuators would be promising in active vibration control of smart structures.

In this paper, an extension of an earlier study (Tua et al 2004 Smart Mater. Struct. 13 643–60) for health monitoring of plate structures using time of flight of propagating Lamb waves is presented. First, the detection of micro-width cracks of size 330 and 220 µm on an aluminum plate is considered. Second, the ability of the technique to detect and locate cracks in-filled with impurities such as grease, araldite epoxy, metallic epoxy and spray paint is investigated. Third, the technique is applied to the case of welds where a notch is induced on an aluminum weld applied on a slot in an aluminum plate. Comparison of the results obtained for the weld with and without the notch is made. For all three cases, results showed that the technique of Tua et al (2004 Smart Mater. Struct. 13 643–60) using a piezoelectric (PZT) actuator and sensor pair can be successfully applied to detect and locate such cracks. The methodology to detect and locate cracks in homogenous cylinders and pipes based on the time-of-flight and strength analysis of propagating Lamb waves is proposed. By observing the attenuation in the strength of the direct wave incidence at the sensor, the presence of a crack can be determined. At least four actuation positions with two on each end of the pipe segment of interest are needed to exhaustively interrogate for the presence of cracks. The detailed procedure for locating and tracing the geometry of the crack(s) is described. It is shown experimentally that the detection using a circular PZT actuator and sensor, with dimensions of 5 mm diameter and 0.5 mm thickness, is possible for an aluminum pipe segment of up to at least 4 m in length. The proposed methodology is also explored for an aluminum pipe under more practical situations, such as burying it in sand with only the actuator and sensor positions exposed. Experimental results obtained showed the feasibility of detecting the ‘concealed’ crack on pipes buried in sand.

A one-way reinforced concrete (RC) slab was subjected to short-duration concentrated impact load and its dynamic characteristic for the virgin and damaged conditions were studied using two signal processing techniques. The recorded strain and acceleration signals were analyzed using the Fast Fourier Transform (FFT) and the Hilbert Huang Transform (HHT). From these analyses, the percentage reductions in the modal frequency for varying degrees of damage (or magnitude of applied load) were obtained. Based on the eigen-solution of a 3-element partitioned beam model, the frequency–damage relationship was also estimated using the observed initial flexural stiffness of the half-cycle hysteresis path associated with each stage of applied load. Both semi-empirical and experimental results showed close agreement and a 30% frequency reduction was observed between the virgin state and yield. Three quarters of the total frequency reduction from virgin-to-yield occurred within an applied load range of 30% of the yield load.

An analytical method is presented to model the excitation and propagation of Lamb waves by inter–digital transducers (IDTs). The acoustic field underneath the IDT (i.e. near field) excited by the IDT was obtained by modelling both the electromechanical coupling effect and the interaction between the IDT and the host plate. The amplitudes of the Lamb waves propagating in the far field were computed through a mode–expansion method based on the acoustic solution of the near field excited by the IDT. Experiments were carried out to excite Lamb waves in an aluminium plate. The ratio of amplitudes from experimental results agrees with that from the analytical solution. This analytical method may provide guidance on design of IDTs.

The main objective of the study is to formulate a numerical strategy suitable for structure member assessment in a quantifiable and objective way. Involving both numerical and experimental studies, the emphasis is on nondestructive damage detection of structural members with predominantly flexural deformations such as beams and columns. A time-domain system identification method, namely the extended Kalman Filter method, is adopted with some modifications. To reduce the identification system nonlinearity and hence improve the convergence performance, the method of stiffness-damping uncoupling is introduced. Flexural members with semirigid connections are modeled by the finite element method. Local damage is assumed to manifest itself as reduction in flexural rigidity. Numerical simulation study is carried out to illustrate the performance of the damage identification strategy, accounting for the effects of measurement noise. Dimensionless indicators are used to reveal the damage location and severity effectively. The problem of numerical leakage is reduced, by comparing average identification results before and after damage. Lastly, an experimental study for a reinforced concrete beam with controlled change in local stiffness further substantiates the feasibility of the proposed strategy.

This article reports the numerical and experimental studies of concrete damaged under impact loading. In the framework of continuum damage mechanics, a relatively simple damage model is developed by incorporating experimental relations to account for strain rate effects on concrete characteristics, such as tensile and compressive strengths and elastic moduli. The computational study is supplemented by an experimental investigation programme. A test rig with a spring ejector is designed to produce impact on concrete specimens. In conjunction, a thin load cell suitable for measurement of reaction force is specially developed. Comparison of numerical and experimental results show that the proposed model captures well the non-linear behaviour of concrete under impact compressive load.

A random process can be represented as a series expansion involving a complete set of deterministic functions with corresponding random coefficients. Karhunen–Loeve (K–L) series expansion is based on the eigen-decomposition of the covariance function. Its applicability as a simulation tool for both stationary and non-stationary Gaussian random processes is examined numerically in this paper. The study is based on five common covariance models. The convergence and accuracy of the K–L expansion are investigated by comparing the second-order statistics of the simulated random process with that of the target process. It is shown that the factors affecting convergence are: (a) ratio of the length of the process over correlation parameter, (b) form of the covariance function, and (c) method of solving for the eigen-solutions of the covariance function (namely, analytical or numerical). Comparison with the established and commonly used spectral representation method is made. K–L expansion has an edge over the spectral method for highly correlated processes. For long stationary processes, the spectral method is generally more efficient as the K–L expansion method requires substantial computational effort to solve the integral equation. The main advantage of the K–L expansion method is that it can be easily generalized to simulate non-stationary processes with little additional effort. Copyright © 2001 John Wiley & Sons, Ltd.

The moment redistribution behaviour of continuous cold-formed profiled steel deck and concrete composite slab was studied both experimentally and numerically. An experimental programme consisting of three two-span continuous composite slabs was performed. The experimental results indicated that the composite slabs have adequate ductility for redistributing moments, and the ultimate capacity of continuous composite slabs can be increased significantly. The short-term deflection at the increased service load satisfies the serviceability criteria. A numerical procedure to determine the negative to positive moment redistribution capacity and the corresponding deflection at serviceability for profiled steel–concrete composite slab was validated using the experimental results.

The effect of asymmetric imperfection on the limit-load response of pipelines buried in shallow trenches is investigated. The pipeline is modeled as a long beam resting on a rigid foundation and a small strain, large displacement formulation is used. Three different asymmetric imperfection shapes for the beam are considered and the corresponding limit loads are compared with that for a symmetric imperfection. It is found that the shape of initial imperfection plays an important role. The difference between limit loads based on a symmetric imperfection and a nonsymmetric imperfection can be quite significant.

The risk of collision in an expressway merging process is investigated using the traffic conflict technique. The severity of conflict in a merging event is quantified by a measure that is the inverse of the time measured to collision. To determine this measure, recordings of merging events were obtained at a merging area of an expressway in Singapore over eight periods, and the arrival times of vehicles at constantly spaced intervals were subsequently extracted in the laboratory. The errors in the data‐collection process were minimized by using two video cameras simultaneously in the recording process to increase the size of images and playing back the tapes at a lower speed during data extraction. The systematic errors in the data due to observers' bias were also estimated to facilitate data adjustment. Based on the adjusted data, the computed measure from about 200 merging events in each observation period was found to be best fitted by the mixed Weibull distribution. Using the tail end of the distribution, the probability of near‐accident per merge in each period was estimated.

This Paper reports the application of a data analysis procedure proposed by Lee (1981) to three series of constant rate of strain (CRS) consolidation tests on undisturbed and reconstituted Singapore marine clay samples. These tests were carried out to large deformations: the final compression of the samples was typically 40% of their initial thickness. The proposed data analysis procedure produced three compression curves and two sets of coefficient of consolidation Cv for different parts of the sample. It was proposed that a successful CRS test would be one for which the compression curves and the Cv values agreed; this was confirmed by the favourable comparison between the results of successful CRS tests and standard oedometer tests. Further analysis of the successful CRS tests showed that their dimensionless strain rate β was generally below the theoretical threshold value of 0-1. This theoretical threshold value provided the basis for a proposed test rate selection procedure.L'article présente l'application de la procédure d'analyse des données, proposée par Lee (1981) à trois séries d'essais de consolidation à vitesse de déformation constante (CRS), réalisés sur des échantillons intacts ou reconstitués d'argile marine de Singapour. Ces essais ont été réalisés de façon à obtenir de grandes déformations: la compression finale des échantillons est typiquement égale à 40% de leur hauteur initiale. La procédure d'analyse des données utilisée permet d'obtenir trois courbes de compression et deux jeux de coefficients de consolidation Cv associés à différentes parties de l'échantillon. Un essai CRS sera supposé réussi si les courbes de compression et les valeurs de Cy sont en accord; ceci a été confirmé par la bonne adéquation entre les résultats obtenus lors d'essais CRS réussis et lors d'essais oedométriques standards. Une analyse plus poussée des essais CRS réussis montre que le coefficient de déformation adimensionnel β est généralement inférieur à la valeur théorique de seuil égale à 0,1 qui est à la base de la procédure de sélection de la vitesse de déformation à utiliser.This Paper reports the application of a data analysis procedure proposed by Lee (1981) to three series of constant rate of strain (CRS) consolidation tests on undisturbed and reconstituted Singapore marine clay samples. These tests were carried out to large deformations: the final compression of the samples was typically 40% of their initial thickness. The proposed data analysis procedure produced three compression curves and two sets of coefficient of consolidation Cv for different parts of the sample. It was proposed that a successful CRS test would be one for which the compression curves and the Cv values agreed; this was confirmed by the favourable comparison between the results of successful CRS tests and standard oedometer tests. Further analysis of the successful CRS tests showed that their dimensionless strain rate β was generally below the theoretical threshold value of 0-1. This theoretical threshold value provided the basis for a proposed test rate selection procedure.L'article présente l'application de la procédure d'analyse des données, proposée par Lee (1981) à trois séries d'essais de consolidation à vitesse de déformation constante (CRS), réalisés sur des échantillons intacts ou reconstitués d'argile marine de Singapour. Ces essais ont été réalisés de façon à obtenir de grandes déformations: la compression finale des échantillons est typiquement égale à 40% de leur hauteur initiale. La procédure d'analyse des données utilisée permet d'obtenir trois courbes de compression et deux jeux de coefficients de consolidation Cv associés à différentes parties de l'échantillon. Un essai CRS sera supposé réussi si les courbes de compression et les valeurs de Cy sont en accord; ceci a été confirmé par la bonne adéquation entre les résultats obtenus lors d'essais CRS réussis et lors d'essais oedométriques standards. Une analyse plus poussée des essais CRS réussis montre que le coefficient de déformation adimensionnel β est généralement inférieur à la valeur théorique de seuil égale à 0,1 qui est à la base de la procédure de sélection de la vitesse de déformation à utiliser.This Paper reports the application of a data analysis procedure proposed by Lee (1981) to three series of constant rate of strain (CRS) consolidation tests on undisturbed and reconstituted Singapore marine clay samples. These tests were carried out to large deformations: the final compression of the samples was typically 40% of their initial thickness. The proposed data analysis procedure produced three compression curves and two sets of coefficient of consolidation Cv for different parts of the sample. It was proposed that a successful CRS test would be one for which the compression curves and the Cv values agreed; this was confirmed by the favourable comparison between the results of successful CRS tests and standard oedometer tests. Further analysis of the successful CRS tests showed that their dimensionless strain rate β was generally below the theoretical threshold value of 0-1. This theoretical threshold value provided the basis for a proposed test rate selection procedure. L'article présente l'application de la procédure d'analyse des données, proposée par Lee (1981) à trois séries d'essais de consolidation à vitesse de déformation constante (CRS), réalisés sur des échantillons intacts ou reconstitués d'argile marine de Singapour. Ces essais ont été réalisés de façon à obtenir de grandes déformations: la compression finale des échantillons est typiquement égale à 40% de leur hauteur initiale. La procédure d'analyse des données utilisée permet d'obtenir trois courbes de compression et deux jeux de coefficients de consolidation Cv associés à différentes parties de l'échantillon. Un essai CRS sera supposé réussi si les courbes de compression et les valeurs de Cy sont en accord; ceci a été confirmé par la bonne adéquation entre les résultats obtenus lors d'essais CRS réussis et lors d'essais oedométriques standards. Une analyse plus poussée des essais CRS réussis montre que le coefficient de déformation adimensionnel β est généralement inférieur à la valeur théorique de seuil égale à 0,1 qui est à la base de la procédure de sélection de la vitesse de déformation à utiliser.