Performance Assessment of Concrete Crack Repairing Materials using PZT Transducers

Department of Urban and Environmental Engineering (Urban Infrastructure Engineering)Concrete is a widely used material in construction of civil infrastructure engineerings such as dams, houses, bridges, and energy plants. Due to shrinkage, rapid dry of the concrete, and overload, cracks are usually generated on the concrete structures and can possibly cause durability-related issues and structural damages. Thus, the concrete crack is an important indicator of potential durability degradation and damage, and the crack should be monitored and repaired through regular maintenance. Indeed, identifying and repairing the concrete cracks using healing materials is important. While most research efforts to date have been devoted to investigation of crack locations and sizes and effective repair, few are evaluating the repairing performance. Therefore, to find an effective nondestructive evaluation (NDE) method for assessing the repairing performance of different healing materials is necessary. Meanwhile, the electro-mechanical impedance (EMI) employing the Piezoelectric Ceramic Lead Zirconate Titanate (PZT) is widely used in structural health monitoring (SHM) as an NDE method in the civil engineering field. The PZT-based EMI is usually applied to detect and locate structural damage in operation. This study used PZT EMI to extract the impedance, which was used as the damage indicator to evaluate the repairing performance of three different materials of the healing cement material from Intchem company, superabsorbent polymer (SAP), and epoxy. A comparison study on the different computation methods of damage index (the root-mean-square deviation (RMSD), the shift of resonance frequency (SRF) and the mean absolute percentage deviation (MAPD)) is also conducted. Results show that the increase of crack depth level and the completing process of repairing crack can be carried out by the change rates of the impedance (admittance) and the shifts of the resonance frequency of PZT sensor in the selected frequency range clearly. .ope

A Review of integrity constraint maintenance and view updating techniques

Two interrelated problems may arise when updating a database. On one hand, when an update is applied to the database, integrity constraints may become violated. In such case, the integrity constraint maintenance approach tries to obtain additional updates to keep integrity constraints satisfied. On the other hand, when updates of derived or view facts are requested, a view updating mechanism must be applied to translate the update request into correct updates of the underlying base facts. This survey reviews the research performed on integrity constraint maintenance and view updating. It is proposed a general framework to classify and to compare methods that tackle integrity constraint maintenance and/or view updating. Then, we analyze some of these methods in more detail to identify their actual contribution and the main limitations they may present.Postprint (published version

Alpha Entanglement Codes: Practical Erasure Codes to Archive Data in Unreliable Environments

Data centres that use consumer-grade disks drives and distributed peer-to-peer systems are unreliable environments to archive data without enough redundancy. Most redundancy schemes are not completely effective for providing high availability, durability and integrity in the long-term. We propose alpha entanglement codes, a mechanism that creates a virtual layer of highly interconnected storage devices to propagate redundant information across a large scale storage system. Our motivation is to design flexible and practical erasure codes with high fault-tolerance to improve data durability and availability even in catastrophic scenarios. By flexible and practical, we mean code settings that can be adapted to future requirements and practical implementations with reasonable trade-offs between security, resource usage and performance. The codes have three parameters. Alpha increases storage overhead linearly but increases the possible paths to recover data exponentially. Two other parameters increase fault-tolerance even further without the need of additional storage. As a result, an entangled storage system can provide high availability, durability and offer additional integrity: it is more difficult to modify data undetectably. We evaluate how several redundancy schemes perform in unreliable environments and show that alpha entanglement codes are flexible and practical codes. Remarkably, they excel at code locality, hence, they reduce repair costs and become less dependent on storage locations with poor availability. Our solution outperforms Reed-Solomon codes in many disaster recovery scenarios.Comment: The publication has 12 pages and 13 figures. This work was partially supported by Swiss National Science Foundation SNSF Doc.Mobility 162014, 2018 48th Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN

Privacy Vulnerabilities in the Practices of Repairing Broken Digital Artifacts in Bangladesh

This paper presents a study on the privacy concerns associated with the practice of repairing broken digital objects in Bangladesh. Historically, repair of old or broken technologies has received less attention in ICTD scholarship than design, development, or use. As a result, the potential privacy risks associated with repair practices have remained mostly unaddressed. This paper describes our three-month long ethnographic study that took place at ten major repair sites in Dhaka, Bangladesh. We show a variety of ways in which the privacy of an individual’s personal data may be compromised during the repair process. We also examine people’s perceptions around privacy in repair, and its connections with their broader social and cultural values. Finally, we discuss the challenges and opportunities for future research to strengthen the repair ecosystem in developing countries. Taken together, our findings contribute to the growing discourse around post-use cycles of technology

Development and implementation of preventive-maintenance practices in Nigerian industries.

A methodology for the development of PM using the modern approaches of FMEA, root-cause analysis, and fault-tree analysis is presented. Applying PM leads to a cost reduction in maintenance and less overall energy expenditure. Implementation of PM is preferable to the present reactive maintenance procedures (still prevalent in Nigeria

The Influence of Trust in Traditional Contracting: Investigating the "Lived Experience" of Stakeholders

The traditional procurement approach is ever-present within the construction industry. With fundamental design principles founded on definitive risk allocation, this transactional based approach fails to acknowledge or foster the cooperative relationships considered to be vital to the success of any project. Contractual design encourages stakeholders to defend their own individual interest to the likely detriment of project objectives. These failings are not disputed, however, given that trust is a fundamental requirement for human interaction the influence of trust is potentially important in terms of stakeholder relationships and ultimate project success. Trust is therefore examined within this context. A conceptual framework of trust is presented and subsequently used to code and analyse detailed, semi-structured interviews with multiple stakeholders from different projects. Using a phenomenological investigation of trust via the lived experiences of multiple practitioners, issues pertaining to the formation and maintenance of trust within traditionally procured construction projects are examined. Trust was found to be integral to the lived experiences of practitioners, with both good and bad relationships evident within the constructs of traditional procurement mechanisms. In this regard, individual personalities were considered significant, along with appropriate risk identification and management. Communication, particularly of an informal nature, was also highlighted. A greater emphasis on project team selection during the initial stages of a project would therefore be beneficial, as would careful consideration of the allocation of risk. Contract design would also be enhanced through prescriptive protocols for developing and maintaining trust, along with mandated mechanisms for informal communication, particularly when responding to negative events. A greater understanding regarding the consequences of lost trust and the intricacies of trust repair would also be of value. 

Structuring the process of integrity maintenance (extended version)

Two different approaches have been traditionally considered for dealing with the process of integrity constraints enforcement: integrity checking and integrity maintenance. However, while previous research in the first approach has mainly addressed efficiency issues, research in the second approach has been mainly concentrated in being able to generate all possible repairs that falsify an integrity constraint violation. In this paper we address efficiency issues during the process of integrity maintenance. In this sense, we propose a technique which improves efficiency of existing methods by defining the order in which maintenance of integrity constraints should be performed. Moreover, we use also this technique for being able to handle in an integrated way the integrity constraintsPostprint (published version

NASA space station automation: AI-based technology review. Executive summary

Research and Development projects in automation technology for the Space Station are described. Artificial Intelligence (AI) based technologies are planned to enhance crew safety through reduced need for EVA, increase crew productivity through the reduction of routine operations, increase space station autonomy, and augment space station capability through the use of teleoperation and robotics