João Bento

An agent-based paradigm for building intelligent CAD systems

The present paper proposes a hybrid approach based on reactive agent technology as a post-object paradigm for building intelligent CAD systems. It represents an evolution of previous positions and articles by the authors motivated by a clear need to provide forms of active support for the design process rather than seeking full design automation purposes. Key concepts about agency and reactivity, as well as their usefulness in design systems, are presented. Also a basic tool called XLOG+, for developing agent-based systems, comprising logic and object oriented approaches, is discussed. Finally, the proposed hybrid agents are embedded in a new integrated CAD system architecture and an implemented prototype example in the area of solid modelling is briefly presented.

Distributed Agents Supporting Event-Driven Design Processes

In event-driven design processes, a digital mock-up is made of entities which are more than 3D, passive, virtual objects; they may be seen as part of a society of agents whose behavior emerges from their mutual interaction. This paper proposes the concept of Extended Constraint Graphs with bi-directional reactivity and one-way actions to represent reactivity and pro-activeness in a society of distributed design agents. Also, while the majority of CORBA applications in CAD systems uses static invocations, this paper presents an original approach to deal with the necessarily dynamic nature of event-driven design processes through the use of the interpreted language Lua with a CORBA binding called LuaOrb. Moreover, the use of ACIS as a Geometry Bus is presented in the context of the CORBA dynamic invocation interface.

Reactive Design Agents in Solid Modelling

This paper proposes a reactive agent architecture for the integration of solid modelling processes into more general design processes. The basic idea is to focus on reactivity rather than on symbolic representations of design knowledge. Also an Application Programming Interface is proposed to help developers writing intelligent CAD systems with links to any open architecture geometric modeller. In the proposed approach, solid modelling processes are formally immersed in the design process with the concept of modified CSG trees. Furthermore, solids are considered to be reactive design agents. A working system is also presented.

Long-term monitoring and assessment of a precast continuous viaduct

Precast girders have recently been widely employed in the construction of bridges and viaducts. The new bridge over the Tagus River in Portugal, the Lezíria Bridge, comprehends a 9160 m long south approach viaduct, which was built with precast girders made continuous in situ. Given the relevance of this construction, a long-term monitoring system was implemented and measurements were taken since the start of the construction. The observed parameters were concrete strains and temperatures, deck rotations, joint displacements, accelerations and also environment temperature and relative humidity. The work presents the precast structure, the monitoring system and the appraisal of a statistical procedure for the long-term assessment of the structural behaviour. This procedure is based on prediction models, which establish the normal correlation patterns between environmental and material parameters (such as concrete temperature and shrinkage strains), and the observed structural response in terms of strains, rotations and movements of expansion joints. The calculation of the normal correlation pattern comprehends the minimisation of a square error. By applying the prediction model to the structural response measured in the south approach viaduct of the Lezíria Bridge, it was found that this methodology is a feasible tool for real-time damage detection of bridges.

A logic-based environment for reactive agents in intelligent CAD systems

Abstract This paper is an evolution of a previous article by the authors [1] (Bento, J. P., Feijo, B., Lloyd-Smith, D., Computers and Structures, 1977, 63(5), 1015–1032) motivated by the need to provide computational support to an agent-based implementation of design processes. It presents a new programming environment to support the development of CAD systems based on a hybrid agent architecture in which the symbolic reasoning is carried out by first-order logic. The reactive behaviour of the agents can be achieved through a number of characteristics proposed for the object-oriented environment. This environment is also a general proposal for representing engineering design knowledge in which logic is integrated into an object-oriented paradigm.

Assessment and Management of Concrete Bridges Supported by Monitoring Data-Based Finite-Element Modeling

The long-term assessment of large and complex civil infrastructures, such as prestressed concrete bridges, based on finite-element (FE) modeling remains a challenging task. The construction process, the influence of erection methods, the characterization of concrete properties, geometric accuracy, and environmental conditions are key factors involved in the development of robust FE models. Data collected using permanently installed monitoring systems is the most reliable strategy to improve such assessments. The availability of monitoring data are increasingly being used in the validation of design assumptions, updating of FE models, and safety factors. In this work, the long-term behavior of a long segmental bridge built in Portugal (Leziria Bridge) is evaluated using FE model updating. The combination of several factors, including (1) the bridge’s scale, (2) the monitoring database, (3) the comprehensive scanning of important characteristics of the bridge, and (4) the FE modeling approach, makes this case study unique. Although the sensor trends are satisfactorily predicted, extrapolation of shrinkage and creep models, the influence of interior and exterior environments, and thickness variations of the structural elements are identified as areas for further research.

Assessment of traffic load events and structural effects on road bridges based on strain measurements

AbstractSeveral technical and scientific publications have been made available focussing on Bridge Weight-in-Motion (BWIM) concerning railway bridges. On the contrary, BWIM analysis on road bridges are more scarce and therefore, this work intends to provide a contribution by presenting the BWIM analysis performed on two major road bridges in Portugal – Leziria Bridge and Pinhao Bridge. These bridges are equipped with electric and optical strain gauges, acquisition systems with features that allow high sampling rates. Based on the collected data and focussing on the bridges’ lifetime, a probabilistic approach to quantify extreme traffic loads was implemented using extreme distribution functions. The bridges’ behaviour to these extreme traffic loads is numerically evaluated and a comparison with the alarm levels established by the bridge designers is performed. Although the bridges safety is not compromised, it was concluded that the representativeness of the observation period is a critical issue and the ...

Design support for viaducts

The paper deals with the development of a system for supporting the design of highway bridges. The adopted approach is considered to innovate in relation to previous approaches of design systems for viaducts, for making a pragmatic combined use of a number of AI techniques such as CBR, neural networks and notions of agency. An interesting feature of the proposal is related to the fact that, instead endorsing a complex, and usually rigid design model for the adaptation phase of CBR-based design, the authors provide a conceptual (and partly implemented) framework for designers to interactively adapt the retrieved solutions. This adaptation takes place by using a constrained graphical/drafting environment, i.e. a CAD environment where design entities may carry physical and functional constraints relating to them in isolation, or to themselves in relation to the surrounding ones. Such constraints may be posted prior to the adaptation phase or throughout that process.

Dam safety: Improving management

Dam engineering emerged as a structured branch of engineering in the earlier parts of this century. Because many large dams are now over 50 years old, special attention has been devoted to the issue of their efficient management. The act of managing large dams is very complex and requires the effort of multi-disciplinary teams involving highly specialised knowledge. In the case of dams, such knowledge is accumulated through a process of learning and understanding how each structure responds to the current and exceptional actions. Material properties may change during the course of their life, which means the structural responses to certain actions may change with time. Through the surveillance activity the changes in structural behaviour can be monitored and any anomalous situation should be identified by a thoroughly analysis. As old structures tend to deteriorate and request special attention from managers and as more structures are built every day, managers are faced with large amounts of information which need to be evaluated in order to highlight any anomalous situation which may endanger the structure serviceability or its safety, and trigger possible remedial actions. The present work has been dedicated to investigate how knowledge based system technology could help managers in the everyday duty of the dam safety control activity. The system is meant to support dam managers in the decision-making process but not to act as a replacement of sound human and engineering judgements.