Adam Borkowski

Improved bounds for displacements at shakedown

Abstract A method is proposed for obtaining an upper bound for the displacement which can occur in a structure adapted to a given variable-repeated load. First, the exact formulation of the problem is presented which leads to a problem of optimal control. Then the differential constraints are neglected or replaced by algebraic conditions. The solution of the resulting linear programming problem supplies an upper bound to the exact elastic-plastic deflection. Further approximation can be introduced, if desired, which allows the decomposition of the problem into separate bounds to elastic and plastic parts of displacement. Numerical examples include a two-span continuous beam and a two-storey frame. The first was solved analytically, the second by means of a specially developed computer routine capable of evaluating the displacements at shakedown of arbitrary planar frames or trusses. The results obtained confirm the validity of the small displacement approach.

On a numerical approach to shakedown analysis of structures

Abstract Two alternative ways of performing the shakedown analysis of structures subjected to variable repeated loads are presented. The first one enables one to check whether the structure shakes down (i.e. responds elastically after a few elastoplastic cycles) or not. Such a check is done by reproducing incrementally a critical cyclic load which corresponds to a cyclic repetition of piecewise-proportional load path that contains all the vertices of the variable load domain. The second approach enables one to find a safety factor for the limit of shakedown capability. The problem is one of convex or linear programming, depending on the kind of yield condition used. Numerical results presented in the paper show that the general purpose software that performs incremental elastoplastic calculations can be successfully used for shakedown analysis.

Towards semantic navigation in mobile robotics

Nowadays mobile robots find application in many areas of production, public transport, security and defense, exploration of space, etc. In order to make further progress in this domain of engineering, a significant barrier has to be broken: robots must be able to understand the meaning of surrounding world. Until now, mobile robots have only perceived geometrical features of the environment. Rapid progress in sensory devices (video cameras, laser range finders, microwave radars) and sufficient computational power available on-board makes it possible to develop robot controllers that possess certain knowledge about the area of application and which are able to reason at a semantic level. The first part of the paper deals with mobile robots dedicated to operate inside buildings. A concept of the semantic navigation based upon hypergraphs is introduced. Then it is shown how semantic information, useful for mobile robots, can be extracted from the digital documentation of a building. In the second part of the paper we report the latest results on extracting semantic features from the raw data supplied by laser scanners. The aim of this research is to develop a system that will enable a mobile robot to operate in a building with ability to recognise and identify objects of certain classes. Data processing techniques involved in this system include a 3D-model of the environment updated on-line, rule-based and feature-based classifiers of objects, a path planner utilizing cellular networks and other advanced tools. Experiments carried out under real-life conditions validate the proposed solutions.

Assisting Creativity by Composite Representation

The paper presents a composite syntactic-semantic representation of objects that is particularly suited for creative design in engineering. This representation is to a great extent oriented towards visual evaluation. The role of emergence both in art and in engineering design is discussed firstly. It is shown on examples taken from Escher’s prints, Civil Engineering and Mechanical Engineering that the emergence can occur with respect to the shape of the object or to its internal structure or topology. The composite representation supports the search for alternative solutions in both domains. It has been implemented as a design tool including the editor of graph grammars, the generator of composition graphs, the library of primitives and the visualisation module.

GraCAD - Graph-Based Tool for Conceptual Design

This paper proposes a new methodology for computer-aided design of layouts of buildings. The presented methodology addresses the very early phase of designing that is called Conceptual Design. In this methodology the architect does not pay attention to layout details, but operates on functional requirements, constraints, and high-level architectural concepts such as functional areas and rooms. The GraCAD system realizes this methodology by adding a high-level design tool to the well-known commercial program ArchiCAD. This design tool has been realized using graph-based knowledge representation techniques and graph grammars as offered by the system PROGRES. Preliminary results show that the developed ArchiCAD add-on and the formalism of graph grammars seems to be useful in aiding architectural design.

Converting function into object

The aim of the present paper is to show how the multi-layered graph-based representation could stimulate creative thinking in design. The prototype software developed in this project allows the user to define functional requirements for the designed object and to transform them into the object itself. It is done in several phases and the representation scheme encourages the designer to look for alternatives, analogies and novel solutions at each level of abstraction. The proposed methodology is illustrated by simple example of designing the teapot but the same principles apply for each artefact.

Graph Visualization in ArchiCAD

This paper deals with computer aided design in architecture. A two-phase representation of objects is used that separates the definition of structure from the interpretation. It is shown how to integrate such a graph-based representation with the commercial ArchiCAD system used by many architects. Preliminary results reported in this paper indicate that it is possible to augment ArchiCAD by a graph grammar-based tool that would allow the designer to generate alternative solutions and to evaluate them.

Optimization of slab reinforcement by linear programming

Abstract A numerical procedure is developed to compute the minimum volume design for the reinforcement of concrete slabs. The optimum solution ensures a given safety factor against plastic collapse and meets technological requirements. A linear programming approach to the optimization of rigid-plastic structures is briefly outlined, and a dual discrete model of a slab is then introduced that uses finite elements. A linear function is chosen for the deflection rate, while the bending and twisting moments are kept constant throughout the element. The mesh lines are potential yield lines, and the admissibility of stresses is checked along these lines. As a result a kinematic estimate of the optimum reinforcement is obtained. Several examples illustrate the method.

Towards collaborative creative design

Abstract The paper presents a design support system for collaborative work based upon the composite knowledge representation. It addresses the main challenges of distributed environment: ensuring a convenient access to the common data by multiple users and maintaining consistency of such data. The main idea is to couple the design support system implemented in C/C++ with the knowledge database using the ODBC library developed by the Microsoft. The ability of the proposed system is demonstrated on several examples.

Generalized Inverses in Elastic-Plastic Analysis of Structures∗

Abstract This paper deals with elastic-plastic analysis of skeletal structures that are subjected to proportionally increasing loading. It is assumed that no local unloading occurs (holonomic behavior) and that yield conditions are piecewise linearized. A quadratic programming problem, which arises from the application of the minimum complementary energy principle for such structures, is shown to have an explicit form of solution. The matrix expression of this solution involves certain modifications of the Bott-Duffin generalized inverse. This inverse can be effectively calculated for a given structure and allows one to obtain a unique stress distribution under agiven load. Moreover, if the load is prescribed up to an unknown scalar factor, the ultimate value of this multiplier (collapse load) and the elastoplastic stress state at collapse can be found by the same method