The development of "DISDECO", the Delft Interactive Shell DEsign COde is described. The purpose of this project is to make the accumulated theoretical, numerical and practical knowledge of the last 25 years or so readily accessible to users interested in the analysis of buckling sensitive structures. With this open ended, hierarchical, interactive computer code the user can access from his workstation successively programs of increasing complexity. The computational modules currently operational in DISDECO provide the prospective user with facilities to calculate the critical buckling loads of stiffened anisotropic shells under combined loading, to investigate the effects the various types of boundary conditions will have on the critical load, and to get a complete picture of the degrading effects the different shapes of possible initial imperfections might cause, all in one interactive session. Once a design is finalized, its collapse load can be verified by running a large refined model remotely from behind the workstation with one of the current generation 2-dimensional codes, with advanced capabilities to handle both geometric and material nonlinearities.

Numerical simulations of the mechanical behaviour of structures composed of cohesive-frictional materials such as soils, concrete and rocks, still suffer from a lack of robustness. Too often an inability to continue the computation beyond a certain level of loading is encountered. Also, predictions of the structural behaviour can be quite inaccurate, with errors amounting up to 100%. Some typical causes for these observations are discussed and some remedies are suggested.

This paper presents an algorithm for parallel computers, which is suitable for the global (arbitrary displacements) computation of elastic bar structures subject to quasi-static loads. Our method is also capable to determine equilibria which are not connected to the initial, trivial configuration. The paper discusses the gains and the disadventages of the method, comparing it with other techniques.

In this paper two domain decomposition formulations are presented in conjunction with the preconditioned conjugate gradient method (PCG) for the solution of large-scale problems in solid and structural mechanics. In the first approach the PCG method is applied to the global coefficient matrix, while in the second approach it is applied to the interface problem after eliminating the internal d.o.f. For both implementations a Subdomain-by-Subdomain (SBS) polynomial preconditioner is employed based on local information of each subdomain. The approximate inverse of the global coefficient matrix or the Schur complement matrix, which acts as the preconditioner, is expressed by a truncated Neumann series resulting in an additive type local preconditioner. Block type preconditioning, where full elimination is performed inside each block, is also studied and compared with the proposed polynomial preconditioning.

Despite the long history of the theory of stability of deformable system, many basic notions, statements and theorems are applied, unfortunately, not rarely incorrectly. This situation is a result of the fineness, complexity, and diversity of the phenomena connected with diverse aspects of the loss of stability of equilibrium states of nonlinear deformable systems. The first part of the article is devoted to the attempt of elucidation of the use of a number of basic statements as the exchange of stabilities at singular points, or the effect of disappearance of bifurcation phenomena as result of geometrical imperfection of the system, and others. The second part of the present work deals with the method of investigation of the global picture of stability of nonlinear deformable systems subjected to multiparametrical loading. This method worked of by the author is based on the so-called ``deformation map'' which contains the whole information of the behaviour of the system subjected to three-parametrical loading. As a basic example taken the stability of geometrically nonlinear spherical shells subjected to transient pressure, contour external forces and temperature field. A number of new effects was revealed. The map can be applied for any nonlinear system (even non elastic) which is described by means of differential equations.

Walsh series and wavelets are nowadays widely applied in digital processes. Their use as approximation functions in a hybrid-mixed finite element formulation for elastic-plastic structural analysis is presented. This formulation is based on the direct approximation of the stress, displacement and plastic multiplier fields in the domain of the finite elements. The displacements on the boundary of the elements are also approximated independently. The essential characteristics and properties of the Walsh and wavelet approximation functions are reviewed. The performances achieved in the different solution phases of elastic and elastoplastic problems are illustrated with numerical applications.