Search

ABSTRACT This paper presents a series of investigative studies, mainly parametric and numerical, into various issues related to the practical application of the wave propagation (WP) technique in monitoring of [...]

ABSTRACT Electromechanical impedance (EMI) technique has been proven effective in strength development monitoring of early age cementitious materials with the aid of statistical tools. The critical limitation of this technique [...]

ABSTRACT Smart piezoelectric material, namely, the Lead Zirconate Titanate (PZT) has recently found its application in concrete curing and strength development monitoring using the wave propagation (WP) technique. Real-life application [...]

We aimed to examine the prevalence of poor sleep quality and short sleep and their associated factors in a working population in Singapore.

Fatigue cracks often initiate at the weld toes of welded steel connections. Usually, these cracks cannot be identified by the naked eyes. Existing identification methods like dye-penetration test and alternating current potential drop (ACPD) may be useful for detecting fatigue cracks at the weld toes. To apply these non-destructive evaluation (NDE) techniques, the potential sites have to be accessible during inspection. Therefore, there is a need to explore other detection and monitoring techniques for fatigue cracks especially when their locations are inaccessible or cost of access is uneconomical. Electro-mechanical Impedance (EMI) and Lamb wave techniques are two fast growing techniques in the Structural Health Monitoring (SHM) community. These techniques use piezoelectric ceramics (PZT) for actuation and sensing. Since the monitoring site is only needed to be accessed once for the instrumentation of the transducers, remote monitoring is made possible. The permanent locations of these transducers also translate to having consistent measurement for monitoring. The main focus of this study is to conduct a comparative investigation on the effectiveness and efficiency of the EMI technique and the Lamb wave technique for successful fatigue crack identification and monitoring of welded steel connections using piezoelectric transducers. A laboratory-sized non-load carrying fillet weld specimen is used in this study. The specimen is subjected to cyclic tensile load and data for both techniques are acquired at stipulated intervals. It can be concluded that the EMI technique is sensitive to the crack initiation phase while the Lamb wave technique correlates well with the crack propagation phase.

In cylindrical structures such as pipelines and pressure vessels, cracks are most likely to occur along the longitudinal (axial) direction and they can be fatal to the serviceability of the structures. Unfortunately, the conventional ultrasonic crack detection techniques, which usually use longitudinal wave, are not very sensitive to this type of cracks. This paper focuses on the detection and monitoring of axial cracks in cylindrical structures using torsional wave generated by piezoelectric macro-fiber composite (MFC). The first order torsional wave is a kind of non-dispersive pure shear wave which propagates at a fixed wave speed. Torsional wave is utilized in this work because, intuitively, it is more sensitive to axial cracks than the family of longitudinal waves. Numerical simulation has been performed using ANSYS to show the effectiveness of torsional wave in detecting and monitoring axial cracks. The time of flight (TOF) of the waves is used to determine the crack position, while the crack propagation is monitored by measuring the variation in the crack induced disturbances. Experiments have also been conducted to investigate the feasibility of the proposed method. MFC transducers oriented at 45° against the axis of the specimen are used to generate and receive torsional waves. The experimental results demonstrated that the crack position can be indentified and its growth can be well monitored with the presented approach using torsional wave.

In cylindrical structures such as pipelines, cracks are more likely to occur along the longitudinal (axial) direction and they are usually fatal to the serviceability of the structures. Unfortunately, the conventional ultrasonic crack detection methods are not very sensitive to this type of cracks. This paper focuses on using piezoelectric macro-fiber composite (MFC) to generate torsional wave for health monitoring of cylindrical structures. Numerical simulations are performed using ANSYS. Nodal release method is used to model the crack. Experimental verifications are also presented. Four pieces of MFC oriented at 45° against the axis of the specimen are used to generate both longitudinal wave and torsional wave. The numerical results and the experimental results show that the axial-direction crack propagation in cylindrical structures can be well monitored using the presented wave propagation approach.

In this paper, the feasibility of damage detection and characterization using the EMI technique on high cycles fatigue induced damage is investigated. Cyclic tensile load is applied on a lab sized aluminium beam up to failure. Piezo-impedance transducer in the form of PZT patch (lead zirconate titanate) is surface bonded on the specimen for crack detection. Progressive shift in admittance signatures measured by the PZT patch corresponding to increase of loading cycles reflects effectiveness of the EMI technique in tracing the process of fatigue damage progression.

This paper presents a new approach for the non-destructive evaluation of concrete, covering both strength prediction and damage assessment, using the electro-mechanical impedance technique. A new empirical method is proposed to determine in situ concrete strength non-destructively using admittance signatures of surface-bonded piezo-impedance transducers. This is followed by the ‘identification’ of appropriate impedance parameters for concrete. The identified parameters are found to be sensitive to structural damages as well as to concrete strength gain during curing. Comprehensive tests were conducted on concrete specimens up to failure to empirically calibrate the ‘identified’ system parameters with damage severity. An empirical fuzzy probabilistic damage model is proposed to quantitatively predict damage severity in concrete based on variation in the identified equivalent stiffness.

Proc. Instn Ciu. Engrs Ciu. Engng, 1993, 93,Nov., 156-162 An integrated intelligent system for scheduling construction projects Chee-Kiong Soh,BEng, SM, PhD, Kok- Wai Phang, BSc, MSC, and Woon-Ping wong,BSc, MEng, MBA Existing project planning tools for construction programmes have many inherent limitations, such s the need for manual inputof data, constant a training in planning skills and the lack means to accumulate expertise. of An ` intelligent' construction scheduling advisor, CICONSA, has been conceived and developed to take advantage state-of-the-art expert system of techniques, a popular relational database management system, dBase 111, and an established project management system, Hornet...

Stress analysis reinforced tubular of joints subjected to different load types Ai-Kah Soh, BEna. PhD. Chee-Kiona Soh, BEng, MSc, PhD, and Kay-Hiang Hoon, BSc, PhD I EngrsI Structs & ROC.s h Civ. n Bldgs, 1994, 104, Aug..257-266 Structural and Building Board Structures Panel Paper I0426 W The reinforcing o tubular joints using f doubler plates has been a common industrial practice as a last minute solution to resolve punching shear problems due to a x i a l compression...

As knowledge-based systems become more widely used in engineering companies, it is increasingly clear that such systems need to integrate well with the existing numerical processing environments, such as database management and project management systems. This paper describes an implemented system, CICONSA, to illustrate the applicability of another approach to the integration problem via: (1) the direct integration of knowledge-bases and databases to form what we will call knowledge-embedded database systems, and (2) the coupling of knowledge-bases and the existing numerical computing packages to create a hybrid symbolic-numeric computing environment. The focus of this approach is on the enhancement of the widely used dBase III database management system for the embedding of knowledge in a database system, as well as for the coupling of the knowledge-embedded database system to existing programs for numerical analysis. At the end, we demonstrate its practical application with a worked example.

The focus of the present paper is on the data‐knowledge integration problem, whereby data and knowledge can be made radically more useful within the same framework. Most tools for developing knowledge‐based systems do not integrate well with data bases. This lack of integration is usually hampered by slow data base queries or by overly limited data base interfaces. On the other hand, since data base management systems are already well developed, leveraging knowledge‐based systems with data base management systems would provide significant advantages like speed, security, and portability across data formats (e.g. easy conversion between dBase and ASCII formats). In the present paper, we describe a novel approach to the data‐knowledge integration problem. This approach entails the simple but powerful extension of a data base system to increase its ability to represent and manipulate knowledge. We describe Kbase, an environment for developing knowledge‐based systems using facilities and extended constructs of the familiar dBase III data base programming environment. At the end, we use an implemented example, IPDOS, to support our hypothesis.

The useof precedent cases in computer-aided designof offshore structures Chee-Kiong Soh,BE, SM,PhD, and Ai-Kah Soh,BE, PhD The use of precedent cases for referenceis probably a very common practice in industry even for experts because each previously completedcase, whether a success or failure, constitutes a wealth of experience and expertise which is too invaluable to ignore. In addition, making use of precedentcases for references can cut down the time required forcompleting the new design, thereby increasingthe productivity andthe competitive edge of the designers. With this observation in mind, the approach of this study is to develop an integrated knowledge-based system which is capable of making use of both the precedent cases and the earned expertise...

K TUBULAR TOINTS of Energy Guidance Notes." Rosette gauges were placed in pairs around the whole brace/chord intersection, oneon the brace and the other on the chord.However, the two brace/chord intersection regions of the joint had different densityof strain gauges. For the brace attached to the actuators (hereafter called brace A) and its intersection region with the chord (hereafter called chord region A), the strain rosette pairs were attachedat 22.5" intervals over 180" of brace/chord intersection starting from the crown, which wasat the gap between the two braces, to the opposite crown...

This paper describes the framework of the proposed intelligent structural design system, ISTRUDS, currently under development, and an implemented example, IPDOJS, intended for the preliminary design of fixed‐steel offshore jacket structures. The framework comprises of a knowledge‐based system development tool, a conventional structural analysis and design package, and an interfacing automatic data generator cum interactive graphic editor. Function of the latter is essentially to couple the first two tools into an integrated system so that the expertise knowledge in the implemented expert system can be used to guide the numerical procedures embedded in the analysis and design package. An interactive graphic editor has also been provided to facilitate visual modification of the pre‐ and postprocessed structural model. The objective of the example is to illustrate an approach to the development of an intelligent structural design system for the design of offshore and/or onshore structures.

The conventional finite‐element method shows its weakness in determining the stress distributions along free‐ and interboundaries for plate (facet shell) analysis. This is because the chosen element displacement and rotation functions do not implicitly satisfy the conditions that prevail at the boundaries. A procedure has been proposed to modify the conventional finite‐element method so as to allow the elastic stresses along the free‐ and interboundaries of plates to be determined with improved accuracy. The results obtained by this modified method are compared with both an experimental and a traditional finite‐element solution. The comparison shows that the modified solution is in better agreement with the experimental test data as compared with the traditional solution. The computation time required to perform the additional calculations for determining free‐ and interboundary stresses with improved accuracy is only a small fraction of that required for the complete finite‐element analysis.

In this work, a novel 2 degree-of-freedom (DOF) vibration energy harvester is proposed. The harvester comprises one main cantilever beam and one secondary cantilever beam cut out within the main beam. By varying the proof masses, the first two resonances can be tuned close to each other, while maintaining significant magnitudes, thus providing a useful wide bandwidth for energy harvesting. Unlike previous 2-DOF harvesters, the proposed harvester is compact and utilizes the beam more efficiently by generating energy from both the main and secondary cantilevers. Therefore, the proposed harvester is more adaptive and functional in practical random or frequency-variant vibrational circumstances.

DISCUSSION building if additional amenities are required. The French terminal site has space for further development. If a delaywere to occur, depending on the nature and location of the incident, vehicles would be parked nosebtail on platforms, overbridges, allocation areas, c r parks and access roads. At all a major intersections in the system there are releaseheject routes into the emergency traffic roads and exits to the M20 and MO. It has been calculated that 3 h of traffic flow could be stored on site in an emergency at the UK terminal and significantly more at the French terminal...

Fatigue is a progressive and localised damage that occurs when a material is subjected to cyclic loading. Historical cases have shown that undetected fatigue cracks often lead to catastrophic failure, including loss of lives and assets. It is therefore important to have a robust Structural Health Monitoring (SHM) technique to detect and monitor these cracks. The Lamb Wave technique for SHM is promising due to its ability to interrogate a large area of the structure from only a few locations. The feasibility of fatigue crack detection in wide specimens, where the effect of boundary reflections is not significant in the signal processing and damage quantification process, have been investigated by other researchers7-9. However, in a narrow structural component, the boundary reflection has a significant role in the sensor signal and the damage quantifier from available literatures cannot be applied readily. The main focus of this study is to investigate the feasibility of monitoring fatigue crack growth in a narrow structural component using the Lamb Wave technique. Experimental study conducted on lab-sized aluminum beam finds that as crack propagates amplitude of the sensor signal decreases. A damage index is proposed, and a linear relationship between the damage index and the crack length is identified. With the proposed damage index, a crack length can be estimated from the acquired sensor signals through a correlation factor.