Analytical approach to sensitivity analysis of flutter speed in bridges considering variable deck mass

Design techniques based upon sensitivity analysis are not usual in the current design of suspension bridges. However, sensitivity analysis has been proved to be a useful tool in the car and aircraft industries. Evaluation of sensitivity analysis is a mandatory step in the way towards an efficient automated optimum design process which would represent a huge jump in the conception of long span bridges. Some of the authors of this paper were pioneers in establishing a methodology for obtaining the sensitivity analysis of flutter speed in suspension bridges a few years ago. That approach was completely analytical and required the evaluation of many matrices related to the phenomenon. In those works the total mass of the deck was considered as constant and such a circumstance supposed a limitation of the method. In the present paper the complete analytical formulation of the sensitivity analysis problem in bridges considering variable deck mass is presented, as well as its application to the design problem of the Great Belt Bridge. Analytical evaluation of sensitivities is a time demanding task, and in order to avoid excessive computation times, distributed computing strategies have been implemented which can be considered as an additional benefit of this approach. For the application example, it has been found that deck cross-section area and torsional inertia are the structural properties with the greatest influence on the flutter performance.     

Multidisciplinary approach to aeroelastic studies of long-span bridges

This paper focuses on the design of long-span suspension bridges under aeroelastic constraints. Such challenging structures need to be protected against wind-induced instabilities as flutter. The authors envision that a set of scientific disciplines not currently used in bridge engineering may help along the design process and constitute a useful tool. First, the formulation of sensitivity analysis of flutter speed is described, indicating how this technique can be a guide for engineers making changes in the prototype; two examples of important bridges, as the Great Belt and Messina Strait, are used to demonstrate the capability of this approach. Then, the idea of producing computer animations to represent the aeroelastic deformation of bridges simulating virtual boundary layer wind tunnel testing is presented showing pictures of the Tacoma Narrows and Messina Bridges. Finally, the advantages of introducing distributed computing to make easier to implement the previously mentioned techniques are demonstrated. The authors have previously published papers related with sensitivity analysis in bridges or computer animations of the aeroelastic behaviour of suspension bridges. However, this is the first time that their comprehensive multidisciplinary approach is presented.     

Optimum design of Omnia reinforcement truss concrete plank

The omnia reinforcement truss concrete plank is a special concrete composite slab which has been used for the construction of bridges and buildings. Because of its complicated reinforcement layout, it is commonly analysed and designed by simplified methods which neglect the contributions of the reinforcement truss actions and the design is usually over-conservative. In this paper, a non-linear optimum design model considering the reinforcement truss action is proposed. Significant saving in reinforcement is achieved through such an optimum analysis.     

Architecture of a coupled expert system for optimum design of plate girder bridges

A prototype knowledge-based expert system has been developed for optimum design of steel plate girders used in highway bridges. This expert system, called PG-BRIDGE1, is a coupled system in which AI-based symbolic processing is combined with the traditional numerical processing. Plate girders can be unstiffened or stiffened with single- or doublesided transverse stiffeners. They can be homogeneous or hybrid, made of high-strength flange plates and low-strength web plate. A mathematical optimization algorithm has been developed for minimum weight design of plate girders using the generalized geometric programming technique. The basis of design is the American Association of State Highway and Transportation Officials (AASHTO) specifications. The plate girders are subjected to the live (moving) loads of the AASHTO specifications. The knowledge base and symbolic processing has been developed using the Expert System Development Environment (ESDE). Numerical processing for structural analysis, optimization algorithm and graphics interface have been developed in FORTRAN 77.     

Optimum weight analysis of steel grid bridges

Bridges include different types, mainly, the truss, the plate girder, the box, the cabled systems, and the grid type. In this research work the main objective will be to analyze the grid type bridges consisting of main girders and cross girders. Optimization techniques have been utilized in order to determine the minimum weight of the steel grid bridges. The purpose of this research work is to accomplish the following: (1) To determine the ideal number of main girders supporting a reinforced concrete slab for the same geometrical dimensioning, the same conditions of live loads, the same number of cross girders, and the same type of steel. (2) To determine for the previous ideal number of main girders, whether or not the spacing between cross girders is changing, the optimum situation. (3) To determine the optimum type of steel. Three different types of steel, 37, 44, and 52, are used for both main girders and cross girders. (4) To determine to what extent the model of optimization is influenced by the restrictions of side constraints.The problem here is to find the optimum weight of steel grid bridges. Different grid bridges having two, three, four, and five main girders have been analyzed. The objective function is given by the weight of the structure and the design variables are the dimensions of the cross section. The design and side constraints are respected. The unconstrained formulation using the interior penalty function technique is selected. Powell's algorithm is chosen for the generation of the search vector and the quadratic interpolation technique is chosen for the determination of the step size.The conclusions are (1) The optimum solution for the different cases of steel types 37, 44, and 52 was the use of three main girders. (2) The use of steel type 52 with the cases of two, three, four, and five main girders would provide a saving in steel weight amounting to 20% and 25% relative to steel types 44 and 37, respectively. (3) Practically speaking, steel type 52 is more expensive than steel types 44 and 37. Nevertheless, this factor being considered, there would be a saving of 18.8% and 22% if steel type 52 is used instead of steel types 44 and 37, respectively. (4) When three main girders are used with steel types 52, 44, and 37, the weight of cross girders amounted to 10.7%, 7.1%, and 10.8%, respectively.     

Reliability-based optimum design of cable-stayed bridges

This paper presents a procedure for finding the reliability-based optimum design of cable-stayed bridges. The minimisation problem is stated as the minimisation of stresses, displacements, reliability and bridge cost. A finite-element approach is used for structural analysis. It includes a direct analytic sensitivity analysis module, which provides the structural behaviour responses to changes in the design variables. An equivalent multicriteria approach is used to solve the non-differentiable, non-linear optimisation problem, turning the original problem into the sequential minimisation of unconstrained convex scalar functions, from which a Pareto optimum is obtained. Examples are given illustrating the procedure.     

Formal models for user interface design artefacts

There are many different ways of building software applications and of tackling the problems of understanding the system to be built, designing that system and finally implementing the design. One approach is to use formal methods, which we can generalise as meaning we follow a process which uses some formal language to specify the behaviour of the intended system, techniques such as theorem proving or model-checking to ensure the specification is valid (i.e., meets the requirements and has been shown, perhaps by proof or other means of inspection, to have the properties the client requires of it) and a refinement process to transform the specification into an implementation. Conversely, the approach we take may be less structured and rely on informal techniques. The design stage may involve jotting down ideas on paper, brainstorming with users etc. We may use prototyping to transform these ideas into working software and get users to test the implementation to find problems. Formal methods have been shown to be beneficial in describing the functionality of systems, what we may call application logic, and underlying system behaviour. Informal techniques, however, have also been shown to be useful in the design of the user interface to systems. Given that both styles of development are beneficial to different parts of the system we would like to be able to use both approaches in one integrated software development process. Their differences, however, make this a challenging objective. In this paper we describe models and techniques which allow us to incorporate informal design artefacts into a formal software development process.     

Case-based reasoning in steel bridge engineering

The current inventory of the Ohio Department of Transportation (ODOT) contains about 12000 bridges. The great majority of the bridges rated by ODOT engineers are based on the working stress design (WSD) method. The new Federal Highway Administration guidelines require that all bridge ratings be done using the load factor design (LFD) method. Consequently, thousands of bridges have to be re-rated according to the LFD code. The WSD-based data files for existing bridges do not contain the detailed information about steel sections and cross frames needed for the LFD-based rating. In this research a case-based reasoning (CBR) system has been developed to assist the bridge engineer in converting the WSD-based ratings for existing bridges to new LFD-based ratings. A domain model has been created to represent the ODOT standard design cases of bridges.     

Advances in the analysis of short span railway bridges for high-speed lines

The physical model based on moving constant loads is widely used for the analysis of railway bridges. Nevertheless, the moving loads model is not well suited for the study of short bridges (L⩽20–25 m) since the results it produces (displacements and accelerations) are much greater than those obtained from more sophisticated ones. In this paper two factors are analysed which are believed to have an influence in the dynamic behaviour of short bridges. These two factors are not accounted for by the moving loads model and are the following: the distribution of the loads due to the presence of the sleepers and ballast layer, and the train–bridge interaction. In order to decide on their influence several numerical simulations have been performed. The results are presented and discussed herein.     

Optimal design of truss structures using parallel computing

Parallel design optimization of large structural systems calls for a multilevel approach to the optimization problem. The general optimization problem is decomposed into a number of non-interacting suboptimization problems on the first level. They are controlled from the second level through coordination variables. Thus, the solutions of the independent first-level subsystems are directed towards the overall system optimum. In the present paper, optimal design of truss structures using parallel computing technique is described. In this method, optimization of a large truss structure has been carried out by decomposing the structure into sub-domains and suboptimization tasks. Each sub-domain has independent design variables and a small number of behaviour constraints. The two-level sub-domain optimum design approach is summarized by several numerical examples with speedups and efficiencies of algorithms on message passing systems. It has been noticed that the efficiency of the algorithm for design optimization increases with the size of the structure.     

Object-oriented modelling and simulation for broadband network design

Various broadband networks have been planned and installed in recent years due to the increasing demand for new media applications and services. Since a nation-wide broadband network or national backbone as information superhighway requires an astronomical amount of investment, optimum design of the broadband network is very important. The design of the broadband network is very complicated and one has to consider network topology, resource capacities, routing schemes, and call admission control schemes as well as various traffic types.In this paper, an object-oriented (OO) approach is proposed for modelling and simulation of broadband networks for the purpose of analysis and design. An OO model which represents object and behaviour is presented with the broadband bursty traffics being modeled at the burst and call levels. The proposed OO modelling approach is applied to a backbone network design problem in Korea for demonstrating its validity and usefulness.     

A general purpose real-world structural design optimization computing platform

Structural optimization has matured from a narrow academic discipline, where researchers focused on optimum design of small idealized structural components and systems, to become the basis in modern design of complex structural systems. Some software applications in recent years have made these tools accessible to professional engineers, decision-makers and students outside the structural optimization research community. These software applications, mainly focused on aerospace, aeronautical, mechanical and naval structural systems, have incorporated the optimization component as an additional feature of the finite element software package. On the other hand though there is not a holistic optimization approach in terms of final design stage for real-world civil engineering structures such as buildings, bridges or more complex civil engineering structures. The optimization computing platform presented in this study is a generic real-world optimum design computing platform for civil structural systems and it is implemented within an innovative computing framework, founded on the current state of the art in topics like metaheuristic optimization, structural analysis and parallel computing. For demonstration purposes the application of the optimization computing platform in five real-world design projects is presented.     

Agent-Based Simulation of Animal Behaviour

In the biological literature on animal behaviour, in addition to real experiments and field studies, also simulation experiments are a useful source of progress. Often specific mathematical modelling techniques are adopted and directly implemented in a programming language. Modelling more complex agent behaviours is less adequate using the usually adopted mathematical modelling techniques. The literature on AI and Agent Technology offers more specific methods to design and implement (also more complex) intelligent agents and agent societies on a conceptual level. One of these methods is the compositional multi-agent system design method DESIRE. In this paper it is shown how (depending on the complexity of the required behaviour) a simulation model for animal behaviour can be designed at a conceptual level in an agent-based manner. Different models are shown for different types of behaviour, varying from purely reactive behaviour to pro-active, social and adaptive behaviour. The compositional design method for multi-agent systems DESIRE and its software environment supports the conceptual and detailed design, and execution of these models. A number of experiments reported in the literature on animal behaviour have been simulated for different agent models.     

Differential Evolution Training Algorithm for Feed-Forward Neural Networks

An evolutionary optimization method over continuous search spaces, differential evolution, has recently been successfully applied to real world and artificial optimization problems and proposed also for neural network training. However, differential evolution has not been comprehensively studied in the context of training neural network weights, i.e., how useful is differential evolution in finding the global optimum for expense of convergence speed. In this study, differential evolution has been analyzed as a candidate global optimization method for feed-forward neural networks. In comparison to gradient based methods, differential evolution seems not to provide any distinct advantage in terms of learning rate or solution quality. Differential evolution can rather be used in validation of reached optima and in the development of regularization terms and non-conventional transfer functions that do not necessarily provide gradient information. This revised version was published online in June 2006 with corrections to the Cover Date.     

Design ethnography in information systems

Until recently, most ethnographic research in information systems has been based on the traditional anthropological model of ethnography. In this traditional model of ethnography, one of the most important data‐gathering techniques is participant observation. The ethnographer observes and participates but does not actively seek to change the situation. In recent years, however, a new type of ethnographic research has emerged – one that can be called design ethnography. Design ethnography is where the researcher goes beyond observation and actively engages with people in the field. Our view is that design ethnography has much potential for research in information systems. It is a new form of engaged scholarship that bridges the gap between ethnographic research and design science research.     

Protocol modelling: A modelling approach that supports reusable behavioural abstractions

We describe a behavioural modelling approach based on the concept of a “Protocol Machine”, a machine whose behaviour is governed by rules that determine whether it accepts or refuses events that are presented to it. We show how these machines can be composed in the manner of mixins to model object behaviour and show how the approach provides a basis for defining reusable fine-grained behavioural abstractions. We suggest that this approach provides better encapsulation of object behaviour than traditional object modelling techniques when modelling transactional business systems. We relate the approach to work going on in model driven approaches, specifically the Model Driven Architecture initiative sponsored by the Object Management Group. Communicated by August-Wilhelm Scheer Ashley McNeile is a practitioner with over 25 years of experience in systems development and IT related management consultancy. His main areas of interest are requirements analysis techniques and model execution and in 2001 he founded Metamaxim Ltd. to pioneer new techniques in these areas. He has published and presented widely on object oriented development methodology and systems architecture. Nicholas Simons has been working with formal methods of system specification since their introduction, and has over 20 years experience in building tools for system design, code generation and reverse engineering. In addition, he lectures on systems analysis and design, Web programming and project planning. He is a co-founder and director of Metamaxim Ltd.     

Structural shape optimization integrated with CAD environment

The research work presented here is based on the concept of the integration of optimization techniques and numerical analysis with the finite element method (FEM) and computer-aided design (CAD). A microcomputer aided optimum design system, MCADS, has been developed for general structures. Certain techniques to be discussed in the paper, e.g. the semi-analytical method for design sensitivity analysis, optimization analysis modelling for shape design, application oriented user interfaces and the coupling of automated optimization and user intervention have rendered MCADS pratical and versatile in applications for engineering structures. The above techniques and an application are presented in this paper.     

Trading off usability and security in user interface design through mental models

The aim of this paper is to establish the foundations for developing a mental model that bridges the gap between usability and security in user-centred designs. To this purpose, a meta-model has been developed to align design features with the users’ requirements through tacit knowledge elicitation. The meta-model describes the combinatorial relationships of Security, Usability and Mental (SUM) and how these components can be used to design a usable and secure system. The SUM meta-model led to the conclusion that there is no antagonism between usability and security. However, the degree of usable security depends on the ability of the designer to capture and implement the user’s tacit knowledge. In fact, the SUM meta-model seeks the dilution of the trading-off effects between security and usability through compensating synergism of the tacit knowledge. A usability security cognitive map has been developed for the major constituents of usability and security to clarify the interactions and their influences on the meta-model stipulations. The three intersecting areas of the three components’ relationships are manipulated to expand the Optimal Equilibrium Solution (OES) (δ) expanse. To put the SUM meta-model into practice, knowledge management principles have been proposed for implementing user-centred security and user-centred design. This is accomplished by using collaborative brainpower from various knowledge constellations to design a system within the user’s current and future perception boundaries. Therefore, different knowledge groups, processes, techniques, tactics and practices have been proposed for knowledge transfer and transformation during the mental model development.     

Performance evaluation of metaheuristic search techniques in the optimum design of real size pin jointed structures

In recent years a number of metaheuristic search techniques have been widely used in developing structural optimization algorithms. Amongst these techniques are genetic algorithms, simulated annealing, evolution strategies, particle swarm optimizer, tabu search, ant colony optimization and harmony search. The primary goal of this paper is to objectively evaluate the performance of abovementioned seven techniques in optimum design of pin jointed structures. First, a verification of the algorithms used to implement the techniques is carried out using a benchmark problem from the literature. Next, the techniques compiled in an unbiased coding platform are evaluated and compared in terms of their solution accuracies as well as convergence rates and reliabilities using four real size design examples formulated according to the design limitations imposed by ASD-AISC (Allowable Stress Design Code of American Institute of Steel Institution). The results reveal that simulated annealing and evolution strategies are the most powerful techniques, and harmony search and simple genetic algorithm methods can be characterized by slow convergence rates and unreliable search performance in large-scale problems.