Risk based structural safety methods in context

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.     

Generating design activities through sketches in multi-agent systems

This study describes a multi-agent system that acts as a mediator between the designer and the information environment. The system enables designers to locate and retrieve information from distributed resources. There are three types of agents in the proposed model. The ‘user agents’ consist of designers, engineers, and technicians. The ‘information agents’ include various knowledge domains as legislation, codes, previous cases, expert domains. The ‘communication agents’ that identify and match agents are based on the goals and agent’s interest. The communication agents working over the Web use sketches as a collaboration medium in the conceptual phase of the design process. The results of the empirical study showed that the design domain and variables; and design strategies and activities are not independent of each other. The quality of a project increases as the communication increases among collaborators during the conceptual design phase and the Internet provides a suitable medium for communication through sketches.     

Use of meteorological/constructional statistics to estimate building heat needs

Building heat needs over a month or a year are often estimated on the basis of the relevant degree day value, in which some crude account is taken of solar and other casual gains in the choice of the base temperature. A more realistic assessment of building heat needs including the effects of passive gain (through a window or glazed wall) can be made using the ‘empirical’ approach of Davies. In this article a statistical approach is developed in which use is made of degree day type data, and measures of days which are ‘disadvantageous’ and ‘advantageous’ from the point of view of saving back-up heating, together with the first four moments of the distribution of advantageous days (7 statistics in all). From five of these statistics a curve can be fitted to the distribution. After suitable integration of the fitted curves another estimate of building heat needs is obtained (the ‘curve fitting’ value). The heat needs as obtained empirically and by curve fitting agree closely. The 7 statistics are easily handled by a mini computer. They thus provide a convenient and accurate extension to degree day methods when local meteorological information has been processed in conjunction with passive solar collector characteristics. Window area, or glazed wall resistance, and assumptions about ventilation rate are only needed in the final stage of computing heat needs.     

Interrupted interface on the cybernetics of digital design process

From the viewpoint of Batesonian cybernetics, ‘conscious purpose’ and ‘artistic process’ are distinct ends of a spectrum of the functioning of ‘self’. The conceptual stage of the design process is essentially an artistic activity unencumbered with accuracy, dimensionality, scale, program or even tectonics, albeit all of these maybe tacitly present at the ‘back of a designer's mind’. Artistic activities involve broad mental processes that are beneath the stratum of consciousness. By definition, consciousness is selective awareness; it is linear in execution and limited in its capability to synthesize complex parameters. One of the central questions of this paper is “if artistic process requires one to abandon, or relinquish conscious purpose at the time of the generation of the work of art, and if the early stages of artistic process is a result of a vast number of ‘unconscious’ forces and impulses, then how can the computer, which demands (and thus propagates) geometric precision, focused operation and rational execution, be part of that process?” This paper will explore how, cybernetically, the computer can be ‘coupled’ with ‘self’ (via a visual interface) and the artistic process. Three specially devised conceptual design exercises—namely BlurrDesign, BlinDesign and BlitzDesign—and three corresponding “interruptive” computer interface modifications were deployed in an introduction to digital media course. The results of this study are now under consideration for their effectiveness in promoting conceptual design using the computer, and how the ‘self’ might form a cybernetic whole with the machine. The findings could have implications in design pedagogy, informatics and interface design.     

A computational intelligent fuzzy model approach for excavator cycle time simulation

The tracked hydraulic excavator is one of the most versatile and widely utilised piece of earthmoving equipment. In many instances, the ‘excavator’ represents the first choice of earthmoving plant for both construction managers and estimators, since when properly employed (i.e. with a competent operator and in an appropriate working environment), it offers high production rates at economical cost. Nonetheless, predicting machine production performance is difficult; given the typical multiple operational parameters (e.g. machine weight, machine configuration, ground conditions, operator ability) that can apply. Consequently, determination of accurate cost estimates and predicted contract durations are subject to considerable inaccuracy, especially where a significant amount of site work is needed.

To address this inadequacy, this paper presents a computational intelligent ‘fuzzy’ model with the ability to forecast excavator cycle time. In this context, a cycle is defined as one complete revolution, from ‘place empty bucket in dig material’ through ‘fill bucket’, ‘move charged bucket to target’, ‘empty charged bucket’ and ‘return bucket to dig material’. The developed model is based upon 70 separate cycle time observations obtained from four plant manufacturers. These data provide a representative spread of machine cycle times since they include a range on a continuum from optimum to adverse operational parameters. Tests on the derived model identified that its accuracy was acceptable; but the accuracy could be improved using larger samples and a more comprehensive and exhaustive range of variables to predict machine cycle time.     

Thermal response of sprinklers part II. Characteristics and test methods

This paper presents an introduction to the measurement of the thermal response characteristics of sprinklers and aspects of testing which are relevant to performance requirements for specific applications, e.g., for life safety and for protecting high-rack storage. Comparisons are made between test results and ranking orders derived from two methods; the ‘rate-of-rise’ test developed in the U.K. and the ‘plunge’ test as developed in the U.S.A. This paper describes the background to both tests and presents explanations for the differences in the results obtained from each method. The rate-of-rise test is suggested for sprinkler classification; the plunge test for measuring consistency in operation.     

Understanding imperfection-sensitivity in the buckling of thin-walled shells

The buckling of thin-walled shell structures under load is still imperfectly understood, in spite of much research over the past 50 years. In this paper the author traces the history of the ideas which have been deployed in order to shed light on what is often referred to as ‘imperfection-sensitive’ buckling behaviour of shells. The ideas, which recur in various combinations, involve interaction of competing buckling modes, nonlinear behaviour, the growth of initial geometric imperfections under load and the alteration of the distribution of membrane stress as imperfections grow. The author claims that there are strong grounds for supposing that ‘locked in’ initial stresses on account of imperfect initial geometry and the static indeterminacy of boundary conditions of real shells have a pronounced effect on the buckling performance. This effect has been ignored in the past, and is the subject of a current experimental study.     

The reconstruction of the Cathedral of Noto

The Cathedral of Noto, one of the most important baroque monuments that has given notoriety to the town of Noto, collapsed in the 13th of March 1996, approximately 5 years after the earthquake of ‘Santa Lucia’ that took place in December 13th 1990. The collapse has pointed out serious deficiencies in constructive materials of pilasters, even in their capacity to support vertical loads. That is why the earthquake of 1990 has acted as ‘the last blow’, coming after a long period of fatigue. Instead, the geometry of the church results to be ‘good’, and for this reason the reconstruction design consists merely in new pilasters, well made with local material, the well known ‘pietra di Noto’ and the replacement is going to take place both on the right, in the place of the collapsed pilasters, and on the left, in substitution of the old pilasters, really not adaptive for restoration. In this way, and with few other interventions, the ‘new’ church should result capable to resist to earthquakes similar to the one that occurred in 1693.     

A review of the emission of VOCs from polymeric materials used in buildings

Building and furnishing materials and consumers products are important sources of formaldehyde and other volatile organic compounds (VOCs) in the indoor environment. The emission from materials is usually continuous and may last for many years in a building. The available evidence indicates that VOCs can cause adverse health effects to the building occupants and may contribute to symptoms of ‘Sick Building Syndrome’.

Control of VOC emission should increasingly become an important consideration for the design and manufacture of polymeric materials used in buildings. The EC Construction Products Directive ‘Essential Requirements’ set a framework for limiting the use of materials that could pose a health risk to building occupants. Furthermore, the on-going development of voluntary labelling schemes and data bases of material emissions that could be used by building designers, should further strengthen the demand for ‘low VOC emitting’ products.

This paper reviews available information about the emission of VOCs from polymeric building materials, the level of emissions in the indoor environment and the requirements for testing of the materials.     

A review of the methods of calculation of added resistance for ships in a seaway

Most recent studies of performance and assessment of auxillary wind powered ships have been based primarily upon the calm water resistance of the ships hull. This resistance is then used as a first estimate of the power required to drive the ship in a seaway. Some allowance has been made to this estimate for weather and seaway via a ‘weather margin’. For many years theoreticians have produced methods for the calculation of this weather margin of a ship in a random seaway due to the induced rigid body motions. This paper sets out to review the present day methods that are used to calculate ‘added resistance’ as it is often termed. This will allow, hopefully, designers and practitioners of wind powered vessels to discriminate between the different methods that are now available.     

Aesthetics of thin-walled structures

Thin-walled structures are assumed to include all ‘surface-acting’ structures. This is a brief review of the factors generally considered to influence our emotional and intellectual response to built forms. General problems arising from the strong forms and large plain surfaces of thin-walled structures are considered. A number of specific types are then treated under the headings of ‘bridges’, ‘shells’, ‘silos’, ‘tents’ and ‘air-supported structures’.     

Addition of communication paths to diagrammatic layouts

Most work on layout planning has stopped at the stage at which a layout showing the ‘ideal’ relationships of spaces in diagrammatic form has been produced. This paper presents a method by which the next, usually empirical, step of adding the best communication paths to the layout, may be tackled in a logical fashion.     

Loading arrangement and structures, as one system—temporary instability of elements and structure

The paper deals with some special questions of experimental research being important when frames are tested and the load carrying capacity of the structure is lost because of any instability phenomena. Computer simulation results are presented:

• -to illustrat the difference between the real and ‘virtual’ structural behaviour, which is dependent on the character of loading, and

• -to show that in certain conditions a structure, which became unstable because of the instability of one of its elements, is able to turn to a stable state and to carry increasing loads before complete loss of its load carrying capacity.

This paper is a modified (slightly extended) version of that which was presented during the ‘First International Conference on Coupled Instabilities in Metal Structures’. Reflections of participants initiated some modification.     

Coupled dynamics of tensioned buoyant platforms and mooring tethers

A mathematical model is presented of the coupled dynamics of a tensioned buoyant surface platform and the lateral dynamics of its taut mooring tethers. A finite element model of the lateral mooring tether dynamics is extended to take account of nonlinear square law fluid damping by a simple global ‘whole tether’ linearization and an alternative computationally more expensive ‘element-by-element’ linearization scheme. The resultant finite element model is combined with the surface platform dynamic analysis and the coupled dynamic model is used to investigate the effects of water depth, surface platform mass and tether mass per unit length on the tether displacements and bending stresses as well as the resultant surface platform displacements. The results show that the bending stresses induced in the tethers due to their dynamic motions are quite small and that the tether dynamics only affect the motion response of the platform appreciably if the tethers are long (1500 m or more), have a large mass per unit length and have a relatively low tension; or if the platform mass is relatively small. It was also found that the additional computing time required for the local ‘element-by-element’ equivalent linearization was not matched by the small improvement in accuracy obtained over the global ‘whole tether’ technique.     

Ramsey pricing: Its uses and limits

Since 1980, the idea of ‘Ramsey pricing’ has attained a marked vogue in the literature on utility pricing and deregulation in the USA. It seems to offer a simple rule - the ‘inverseelasticity’ rule -for reaching efficient price structures in multi-product firms. It has been applied particularly to utility firms in the electric and telecommunications industries, as well as to pipelines, railroads, airlines and other deregulated industries. Despite its proponents' great enthusiasm for the idea, there are a number of serious limits and problems. I will review these in this paper, trying to draw a balanced judgment about this economic tool. It is a flawed tool, and some of its defects appear to be crippling if not fatal.     

Environmental risk mapping of pollutants: State of the art and communication aspects

Risk maps help risk analysts and scientists to explore the spatial nature of the effects of environmental stressors such as pollutants. The development of Geographic Information Systems over the past few decades has greatly improved spatial representation and analysis of environmental information and data. Maps also constitute a powerful tool to communicate the outcome of complex environmental risk assessment to stakeholders such as the general public and policy makers. With appropriate cartography one can improve communication and thus bridge the gap between experts and users. Appropriate risk communication is pivotal to risk management, decision making and implementation and may prevent unnecessary concern about environmental pollutants. However, at present few risk maps are specifically tailored to meet the demands of such defined uses.This paper presents an overview of the most important types of risk maps that can be distinguished using examples from the scientific literature: contamination maps, exposure maps, hazard maps, vulnerability maps and ‘true’ risk maps. It also discusses, in a general way, the most important issues that need to be addressed when making risk maps for communication purposes: risk perception, target audience, scale and spatial aggregation and visualisation such as use of colours and symbols. Finally, some general rules of thumb are given for making environmental risk maps for communication purposes.     

Long-term performance of geocomposites used as highway edge drains

Prefabricated highway edge drains have been widely used in the USA since 1985. Laboratory testing and initial on-site evaluations have been generally positive, however long-term performance is an unknown. The major areas of concern are ‘blinding’ of the filter fabric that would prevent water from entering into the geocomposite and the ‘clogging’ of the core with fines. This paper presents the results of 72 randomly selected sites that were excavated in 3 states representing a total of 900 000 m (3 000 000 ft) of installed geocomposite edge drain.     

On the upward movement of smoke and related shopping mall problems

The data of Morgan and his co-workers for the movement of smoke in 1/10 scale shopping malls are re-examined. This has been done to see how far a simple theoretical treatment based on plume theory and virtual sources (a basis for many calculation methods) can be exploited instead of the more complicated theory of sources of finite sizes. The work follows and extends the work of Law.

A number of theoretical relationships are used to correlate data and, in particular, they confirm Law's view that the data can be used to give plausible values for the positions of the virtual sources. Some of the complexities of the theory for finite strip sources may be bypassed if experiments are used for estimating the position of effective virtual sources. Experiments to locate the effective virtual source and the limiting asymptotic form of the theory (appropriate to line sources) can correlate and scale data to an accuracy satisfactory for fire engineering purposes. Various aspects of theory are discussed including the method of allowing for the ‘ends’ of finite strip sources, and the use of the theory of weak plumes for strong plumes.

There remains however a problem in reconciling the ‘near’ field of the plume rising around the balcony edge to the ‘far field’, but it is shown that the introduction of an exceptionally high local entrainment could — for these data — be avoided if: (a) the mass at any level in the plume is about 45% larger than expected from other laboratory experiments on plumes; or (b) there is extra entrainment due to the deflection and consequent disturbance as the plume strikes the ceiling; or (c) there is extra upward flow owing to radiation heating up the lower walls and floor as suggested by recent investigations. These matters await further investigation.