David Blockley

Vulnerability of structural systems

Abstract A structure is vulnerable if relatively small damage leads to disproportionately large consequences. A structure which is unacceptably vulnerable in any one way is not acceptably robust. A theory of structural vulnerability has been previously reported by the authors. The purpose of the theory is to identify particular failure scenarios by analysing the connectivity of the structural form. In this paper vulnerability theory is applied to three-dimensional frames and, in a preliminary way, to structural dynamics which is crucially important in assessing impact damage in for example progressive collapse. The concepts are illustrated through examples. The vulnerable failure scenarios may then be examined by conventional response analysis and/or by systems reliability theory and risk assessment. The theory is also applicable to structural damage assessment or for assessing structures under unforeseen terrorist attack.

The use of grounded theory for conceptual analysis in knowledge elicitation

In many practical knowledge engineering contexts, interview data is the commonest form in which information is obtained from domain experts. Having obtained interview data the knowledge engineer is then faced with the difficult task of analysing what is initially relatively unstructured and complex material. It is argued that the knowledge engineers task of analysing interview data conceptually as part of the knowledge elicitation process is similar to that of the social scientist analysing qualitative data. One implication of this is that a range of methods originally developed by social scientists for the analysis of unstructured and semi-structured qualitative material will be of assistance to the knowledge engineer. The background philosophical issues linking qualitative social science research and knowledge elicitation are outlined; both are characterized as fundamentally creative, interpretative processes. “Grounded Theory”, a social science methodology for the systematic generation of conceptual models from qualitative data, is described in detail. An example is presented of the use of Grounded Theory for the analysis of expert interview transcripts, drawn from a knowledge engineering project in civil engineering. The discussion focuses upon the processes used to move from an initial unstructured interview transcript to a core set of interrelated concepts, memos and models that fully describe the data.

Interval Probability Theory for Evidential Support

An interval theory of probability is presented for use as a measure of evidential support in knowledge‐based systems. an interval number is used to capture, in a relatively simple manner, features of fuzziness and incompleteness. the vertex method is used for the interval analysis. A new parameter (also an interval number), p, called the degree of dependence is introduced. the relationship of this interval probability with the theories of Dempster‐Shafer, fuzzy sets, and Baldwins support logic are discussed. the advantage of the theory is that it is based on a development of the axioms of probability, but allows that evidential support for a conjecture be separated from evidential support for the negation of the conjecture.

UNCERTAIN INFERENCE USING INTERVAL PROBABILITY THEORY

Abstract The use of interval probability theory (IPT) for uncertain inference is demonstrated. The general inference rule adopted is the theorem of total probability. This enables information on the relevance of the elements of the power set of evidence to be combined with the measures of the support for and dependence between each item of evidence. The approach recognises the importance of the structure of inference problems and yet is an open world theory in which the domain need not be completely specified in order to obtain meaningful inferences. IPT is used to manipulate conflicting evidence and to merge evidence on the dependability of a process with the data handled by that process. Uncertain inference using IPT is compared with Bayesian inference.

Vulnerability of 3-dimensional trusses

Abstract A system is robust if it can withstand arbitrary damage. There are many practical ways to design in robustness but there is yet no accepted theory of robustness. One insight into the lack of robustness is gained if it were possible to identify how a system is vulnerable. This insight is in the form of ‘a theory of structural vulnerability’ developed at the University of Bristol for 2-dimensional structures [Lu Z, Yu Y, Woodman NJ, Blockley DI. A theory of structural vulnerability. The structural engineer 1999:77(18):17–24]. It is a theory of form and connectivity the purpose of which is to identify weak links within a structure. In this paper further development of the theory and its application to 3-dimensional structures is presented. Algorithms for implementing the theory are described and illustrated through three examples.

The importance of being process

The purpose of the paper is to outline the particular interpretation of systems thinking developed at the University of Bristol over the last 30 years. The importance of process and uncertainty are central themes. Put at its simplest, systems thinking is joined-up thinking. It is getting the right information (what) to the right people (who) at the right time (when) for the right purpose (why) in the right form (where) and in the right way (how). The three ideas at the heart of delivering systems thinking are thinking in layers, thinking in connected loops and thinking about new processes. Everything has life cycle and hence is a process – but one that is set in the context of a system containing other connected processes – some at higher and some at lower levels of definition. All processes have attributes that are characterised using why, how, who, what, where, when. There is a need to integrate hard and soft systems. This requires us to be very clear about the meaning and usage of the terms subjective and objective when we argue that engineering judgement is both valid and important. It is argued that truth is to knowledge as the inverse of risk is to action. The three attributes of uncertainty are stated as FIR – fuzziness, incompleteness and randomness. Robustness and its inverse, vulnerability, are crucial, though often ignored. Systems thinking is not simply an engineering approach; rather it is a philosophy for solving many practical problems such as joined-up government, social work, dealing with climate change and terrorism. Finally it is argued that our journey to 2030 requires us to adopt an evolutionary observational approach using systems thinking.

Engineering from reflective practice

Some ideas for a new epistemology, encompassing practical action, based on the concept of reflective practice, are presented. The term reflective practitioner was first suggested by Schon (1983) in an analysis of the need to define the nature of practical competence. The prevailing culture of technical rationality, which depends on science for it rigor, is compared with that of the “wise engineer” promoted by Elms (1989). Worldview, quality, systems thinking, and responsibility are discussed as preliminaries to an analysis of reflective practice. The model is based on the passing of hierarchically structured sets of message patterns from perception to reflection to action. Intelligence is defined as an ability to construct, evaluate, and act on alternative scenarios of the future in the reflective phase. Design involves the construction of scenarios where imagined artifacts operate to achieve predefined needs for some defined person(s). Rigor for the reflective practitioner stems from the achieving of appropriate objectives. The similarities and differences between science and engineering become apparent when both are viewed as examples of reflective practice.

The risk of vulnerable failure

There is, as yet, no generally accepted theory of structural robustness or of its corollary, structural vulnerability. The theory of structural vulnerability developed at the University of Bristol is a theory of form that seeks to identify failure scenarios where small damage can lead to disproportionate consequences. In this paper the previously reported theory is combined with a standard response analysis to produce a measure of structural risk which includes the chance of a vulnerable loss of functionality. A simple example of a pin jointed structure is presented.

Risk based structural safety methods in context

Abstract Structural reliability calculations are now recognised by many as only one part of the assessment of structural safety. They provide partial evidence about the total problem which has to be integrated with other evidence to support decision making. It is proposed that a ‘holistic’ systems view based on a clear understanding of process is required. The model consists of interacting processes arranged in a hierarchy of differing levels of precision of definition and scope. The various attributes of each process are outlined under the generic headings of ‘who, what, why, where, when and how’. The ‘how’ attributes of a process which are important in the control of a process are hazard and risk. It is suggested that Interval Probability Theory is a suitable measure of the evidence that a process is being and will be managed to a successful conclusion. This can be combined with structural reliability predictions to give bounds on the evidence about the success of the total process which covers all foreseeable aspects of the uncertainty.

VULNERABILITY OF SYSTEMS

Abstract A system is vulnerable if any damage from any source produces consequences that are disproportionately large in comparison with that damage. Conversely a system is not robust if it cannot withstand arbitrary damage. Reliability theory is not sufficient for robust safety. In this paper, we propose a contribution to a general theory of vulnerability that is a theory of form and connectivity. The purpose is to identify weak links. This preliminary theory can be applied to a wide range of systems including structures, water pipe works, traffic flows and organisations and is potentially of use for safety management and to reduce the risk of overlooking vulnerable failure scenarios.