Use of fuzzy risk assessment in FMEA of offshore engineering systems

This paper proposes a novel framework for analysing and synthesising engineering system risks on the basis of a generic Fuzzy Evidential Reasoning (FER) approach. The approach is developed to simplify the inference process and overcome the problems of traditional fuzzy rule based methods in risk analysis and decision making. The framework, together with the FER approach has been applied to model the safety of an offshore engineering system. The benchmarking between the new model and a well-established Rule based Inference Methodology using the Evidential Reasoning (RIMER) is conducted to demonstrate its reliability and unique characteristics. It will facilitate subjective risk assessment in different engineering systems where historical failure data is not available in their safety practice

LOG-IDEAH: LOGic trees for identification of damage due to earthquakes for architectural heritage.

In the framework of PERPETUATE, LOG-IDEAH: “LOGic trees for Identification of Damage due to Earthquakes for Architectural Heritage” has been developed as a post-earthquake assessment tool for the evaluation of the global seismic performance of architectural assets (AAs). LOG-IDEAH is an expert system which interprets the seismic damage collected on site by relying on the knowledge of engineers and architects in seismic vulnerability assessment. The present expert system has been set up on logic trees, implemented in answer set programming to encode the recognition process that surveyors proceed to investigate the causes of damage and to evaluate the failures occurring on an AA. LOG-IDEAH, available at (http://perpetuate.cs.bath.ac.uk/), allows sketching AAs, recording the state of damage, uploading GPS referenced images and comparing collapse mechanisms observed on site with collapse mechanisms identified by the system. The seismic damage, which is the minimum data required by LOG-IDEAH, is collected at the level of both structural elements and artistic assets (local level) and interpreted at the level of the AA (global level). The answer set programming applied for the construction of the machine-processable representation, once the input data has been recorded into the web-interface, provides all possible failure modes and related possibilities of occurrence by taking into consideration the reliability level of the collected data. Its capability has been validated by applying LOG-IDEAH to the historic centre of L’Aquila of the 2009 earthquake by pointing out that answer set programming is a valid alternative approach to the existing methods developed to identify the seismic performance of masonry AAs

Development of a decision support system for assessment of mobile bridges

The development of a prototype Decision Support System (DSS) for the condition assessment of the Armored Vehicle Launched Bridge (AVLB) has been demonstrated in the current work. AVLB is a mobile bridge that has been used by the US Army for tank and assault vehicle crossing. It is employed for spanning short gaps of 50 feet or less in the terrain. The condition assessment of such bridges, to ensure safety of personnel and tank, is of strategic importance. The methodology of the prototype DSS is based on a refined visual inspection procedure and a previously established vibration measurement technique.;Conforming to the design requirements, the DSS has been developed as an Internet based, interactive application, and is integrated with an automated vibration measurement system. The web-based DSS, which incorporates an expert system and a database system, can be run from a web-browser. The development of the system, as described in this thesis, involved: identification of important visual and vibration inspection parameters; development of an expert system for bridge condition assessment, based on these parameters; and design of a database for storing important inspection data and other vital bridge records. The prototype system has been validated through limited test runs. Discussion on further verification and validation issues has also been put forth in this work.;The unique feature of this DSS is its accessibility through the Internet, which is practical considering that the AVLB is deployed worldwide. With a central database, this system provides a useful research tool for further study of the AVLB behavior and damage mechanisms, and can be used to establish failure prediction model and remaining life assessment

The treatment of uncertainty in construction price modelling

The purpose of this thesis was to acquaint the reader on the nature of the uncertainty present in construction price forecasting and to introduce an environment that has the ability to integrate these uncertainties with greater consistency than that possessed by available price models. The objective of this thesis was to establish that uncertainty can be explicitly treated in price forecasting models. This would have two benefits to concerned parties. Firstly, the effectiveness of price forecasts could be improved as provision could be made for any uncertain variable. This will be of great benefit to the client, as a more accurate assessment of the building process could be established at an earlier stage of the design process. Secondly, the price forecast will be more useful to quantity surveyors, architects and clients, as it would 'quantify' the extent of the uncertainty which could be provided for in a more meaningful manner. In order to establish that existing price models do not deal with the uncertainty present at the time of forecasting, the price models used by practitioners were evaluated against the different types of uncertainty found at the different stages of the price forecasting process. Once this had been established, eight techniques that have the ability to treat various forms of uncertainty, were presented. After analysing the techniques abilities to cope with the uncertainties associated with price forecasting, it was established that certain of these techniques do have the ability, and are suitable, to be incorporated into the price forecasting process. From the results of a questionnaire survey conducted on quantity surveying offices in South Africa, it was found that the price models used by practitioners do not take uncertainty into account, and have in fact, the potential for uncertainty inducement. Some of the uncertainty found to be present in the preparation of a construction price forecast include the lack or incompleteness of design information, the uncertainty in the communication of design information, the variability in the data used by quantity surveyors and, the uncertainty in the choice of price model during the different stages of the design process. As a possible solution to the problem of uncertainty, an expert system environment, utilising a three-dimensional classification of uncertainty, has been proposed. It has been proved that this environment has the ability to cater for the uncertainty associated with the price forecasting process, as well as having the attribute of providing the user with the reasoning behind the logic that the expert system has followed, a characteristic not possible with the traditional forms of price models. From the findings of this thesis, it can be concluded that the methods of price modelling used by quantity surveying practitioners, are unable to take uncertainty into account effectively. It can also be concluded that an expert system environment has the ability to handle the different forms of uncertainty found at the various stages of construction design. The proposed model is conceptual in nature and has not been tested in practice. It is therefore recommended that further research be carried out in this field, with the aim of producing a construction price forecasting expert system which utilises the proposed three-dimensional classification of uncertainty

Hierarchical risk assessment of water supply systems

Water supply systems are usually designed, constructed, operated, and managed in an open environment, thus they are inevitably exposed to varied uncertain threats and conditions. In order to evaluate the reliability of water supply systems under threatened conditions, risk assessment has been recognised as a useful tool to identify threats, analyse vulnerabilities and risks, and select proper mitigation measures. However, due to the complexity and uncertainty of water supply systems and risks, consistent and effective assessments are hard to accomplish by using available risk techniques. With respect to this, the current study develops a new method to assess the risks in complex water supply systems by reconsidering the organisation of risk information and risk mechanism based on the concepts of object-oriented approach. Then hierarchical assessments are conducted to evaluate the risks of components and the water supply system. The current study firstly adopts object-oriented approach, a natural and straightforward mechanism of organising information of the real world systems, to represent the water supply system at both component and system levels. At the component level, components of a water supply system are viewed as different and functional objects. Associated with each object, there are states transition diagrams that explicitly describe the risk relationships between hazards/threats, possible failure states, and negative consequences. At the system level, the water supply system is viewed as a network composed of interconnected objects. Objectoriented structures of the system represent the whole/part relationships and interconnections between components. Then based on the object states transition diagrams and object-oriented structures, this study develops two types of frameworks for risk assessment, i.e., framework of aggregative risk assessment and framework of fault tree analysis. Aggregative risk assessment is to evaluate the risk levels of components, subsystems, and the overall water supply system. While fault trees are to represent the cause-effect relationships for a specific risk in the system. Assessments of these two frameworks can help decision makers to prioritise their maintenance and management strategies in water supply systems. In order to quantitatively evaluate the framework of aggregative risk, this thesis uses a fuzzy evidential reasoning method to determine the risk levels associated with components, subsystems, and the overall water supply system. Fuzzy sets theory is used to evaluate the likelihood, severity, and risk levels associated with each hazard. Dempster-Shafer theory, a typical evidential reasoning method, is adopted to aggregate the risk levels of multiple hazards along the hierarchy of aggregative risk assessment to generate risk levels of components, subsystems, and the overall water supply system. Although fuzzy sets theory and Dempster-Shafer theory have been extensively applied to various problems, their potential of conducting aggregative risk assessments is originally explored in this thesis. Finally, in order to quantitatively evaluate the cause-effect relationships in a water supply system, fuzzy fault tree analysis is adopted in this study. Results of this analysis are likelihood of the occurrence for a specific event and importance measures of the possible contributing events. These results can help risk analysts to plan their mitigation measures to effectively control risks in the water supply system.EThOS - Electronic Theses Online ServiceGBUnited Kingdo