Structural health monitoring : vibration-based damage detection and condition assessment of bridges

Structural health is a vital aspect of infrastructure sustainability. As a part of a vital infrastructure and transportation network, bridge structures must function safely at all times. However, due to heavier and faster moving vehicular loads and function adjustment, such as Busway accommodation, many bridges are now operating at an overload beyond their design capacity. Additionally, the huge renovation and replacement costs are a difficult burden for infrastructure owners. The structural health monitoring (SHM) systems proposed recently are incorporated with vibration-based damage detection techniques, statistical methods and signal processing techniques and have been regarded as efficient and economical ways to assess bridge condition and foresee probable costly failures. In this chapter, the recent developments in damage detection and condition assessment techniques based on vibration-based damage detection and statistical methods are reviewed. The vibration-based damage detection methods based on changes in natural frequencies, curvature or strain modes, modal strain energy, dynamic flexibility, artificial neural networks, before and after damage, and other signal processing methods such as Wavelet techniques, empirical mode decomposition and Hilbert spectrum methods are discussed in this chapter.

Labour rights as human rights : workers' safety at work in Australian-based supply chains

The increase of buyer-driven supply chains, outsourcing and other forms of non-traditional employment has resulted in challenges for labour market regulation. One business model which has created substantial regulatory challenges is supply chains. The supply chain model involves retailers purchasing products from brand corporations who then outsource the manufacturing of the work to traders who contract with factories or outworkers who actually manufacture the clothing and textiles. This business model results in time and cost pressures being pushed down the supply chain which has resulted in sweatshops where workers systematically have their labour rights violated. Literally millions of workers work in dangerous workplaces where thousands are killed or permanently disabled every year. This thesis has analysed possible regulatory responses to provide workers a right to safety and health in supply chains which provide products for Australian retailers. This thesis will use a human rights standard to determine whether Australia is discharging its human rights obligations in its approach to combating domestic and foreign labour abuses. It is beyond this thesis to analyse Occupational Health and Safety (OHS) laws in every jurisdiction. Accordingly, this thesis will focus upon Australian domestic laws and laws in one of Australia’s major trading partners, the Peoples’ Republic of China (China). It is hypothesised that Australia is currently breaching its human rights obligations through failing to adequately regulate employees’ safety at work in Australian-based supply chains. To prove this hypothesis, this thesis will adopt a three- phase approach to analysing Australia’s regulatory responses. Phase 1 will identify the standard by which Australia’s regulatory approach to employees’ health and safety in supply chains can be judged. This phase will focus on analysing how workers’ rights to safety as a human right imposes a moral obligation on Australia to take reasonablely practicable steps regulate Australian-based supply chains. This will form a human rights standard against which Australia’s conduct can be judged. Phase 2 focuses upon the current regulatory environment. If existing regulatory vehicles adequately protect the health and safety of employees, then Australia will have discharged its obligations through simply maintaining the status quo. Australia currently regulates OHS through a combination of ‘hard law’ and ‘soft law’ regulatory vehicles. The first part of phase 2 analyses the effectiveness of traditional OHS laws in Australia and in China. The final part of phase 2 then analyses the effectiveness of the major soft law vehicle ‘Corporate Social Responsibility’ (CSR). The fact that employees are working in unsafe working conditions does not mean Australia is breaching its human rights obligations. Australia is only required to take reasonably practicable steps to ensure human rights are realized. Phase 3 identifies four regulatory vehicles to determine whether they would assist Australia in discharging its human rights obligations. Phase 3 then analyses whether Australia could unilaterally introduce supply chain regulation to regulate domestic and extraterritorial supply chains. Phase 3 also analyses three public international law regulatory vehicles. This chapter considers the ability of the United Nations Global Compact, the ILO’s Better Factory Project and a bilateral agreement to improve the detection and enforcement of workers’ right to safety and health.

Reliability analysis of transform-based stereo matching techniques, and a new matching constraint

Stereo vision is a method of depth perception, in which depth information is inferred from two (or more) images of a scene, taken from different perspectives. Practical applications for stereo vision include aerial photogrammetry, autonomous vehicle guidance, robotics and industrial automation. The initial motivation behind this work was to produce a stereo vision sensor for mining automation applications. For such applications, the input stereo images would consist of close range scenes of rocks. A fundamental problem faced by matching algorithms is the matching or correspondence problem. This problem involves locating corresponding points or features in two images. For this application, speed, reliability, and the ability to produce a dense depth map are of foremost importance. This work implemented a number of areabased matching algorithms to assess their suitability for this application. Area-based techniques were investigated because of their potential to yield dense depth maps, their amenability to fast hardware implementation, and their suitability to textured scenes such as rocks. In addition, two non-parametric transforms, the rank and census, were also compared. Both the rank and the census transforms were found to result in improved reliability of matching in the presence of radiometric distortion - significant since radiometric distortion is a problem which commonly arises in practice. In addition, they have low computational complexity, making them amenable to fast hardware implementation. Therefore, it was decided that matching algorithms using these transforms would be the subject of the remainder of the thesis. An analytic expression for the process of matching using the rank transform was derived from first principles. This work resulted in a number of important contributions. Firstly, the derivation process resulted in one constraint which must be satisfied for a correct match. This was termed the rank constraint. The theoretical derivation of this constraint is in contrast to the existing matching constraints which have little theoretical basis. Experimental work with actual and contrived stereo pairs has shown that the new constraint is capable of resolving ambiguous matches, thereby improving match reliability. Secondly, a novel matching algorithm incorporating the rank constraint has been proposed. This algorithm was tested using a number of stereo pairs. In all cases, the modified algorithm consistently resulted in an increased proportion of correct matches. Finally, the rank constraint was used to devise a new method for identifying regions of an image where the rank transform, and hence matching, are more susceptible to noise. The rank constraint was also incorporated into a new hybrid matching algorithm, where it was combined a number of other ideas. These included the use of an image pyramid for match prediction, and a method of edge localisation to improve match accuracy in the vicinity of edges. Experimental results obtained from the new algorithm showed that the algorithm is able to remove a large proportion of invalid matches, and improve match accuracy.