Charalampos Baniotopoulos

Analysis and design of the prototype of a steel 1-MW wind turbine tower

In the present paper, some basic features of the analysis and the design of the prototype of a steel 1 MW wind turbine tower are presented. The structure is 44,075 m high and has a tubular shape with variable cross section and variable thickness of the wall along its height. The steelwork has been manufactured by steel quality S355J2G3. For the simulation of its structural response, two different finite element models have been developed. Based on the results of the latter analyses, the design of the steel tower for gravity, seismic and wind loadings has been performed according to the relevant Eurocodes. In particular, regarding seismic loading, a dynamic phasmatic analysis of the tower has been carried out according to the Greek Antiseismic Code (EAK 2000). The structure has been also checked against fatigue by applying the respective Eurocodes methodology. In the last part of the paper, some points that concern the previous analysis and the respective design procedure are discussed in detail.

Design and robust optimal control of smart beams with application on vibrations suppression

This paper presents the design of a vibration control mechanism for a beam with bonded piezoelectric sensors and actuators and an application of the arising smart structure for vibrations suppression. The mechanical modeling of the structure and the subsequent finite element approximation are based on Hamiltons principle and classical engineering theory for bending of beams in connection with simplified modeling of piezoelectric sensors and actuators. Two control schemes LQR and H2 are considered. The latter robust controller takes into account uncertainties of the dynamical system and moreover incompleteness of the measured information, it therefore leads to applicable design of smart structures. The numerical simulation shows that sufficient vibration suppression can be achieved by means of the proposed general methods.

Steel T-Stub connections under static loading: an effective 2-D numerical model

Abstract The proposed numerical model concerns the simulation of the structural behaviour of steel bolted T-stub connections in the case where the development of zones of plastification, as well as unilateral contact effects on the interfaces between connection members and bolts, are taken into account. Within such a framework, an effective two-dimensional finite element model capable of describing plasticity, large displacement and unilateral contact effects is proposed. The model constitutes an easy-to-use and accurate numerical model for the analysis of steel connections subjected to tensile loading, and is a simplification of a respective three-dimensional one and aims to reduce in a reliable way the huge computational effort required for the analysis of fine meshes of discretized steel bolted connections. The validity of the assumptions that led to the proposed 2-D model is demonstrated by comparing the numerical results with those obtained by laboratory tests.

A hemivariational inequality and substationarity approach to the interface problem: Theory and prospects of applications

Abstract In the present paper a new type of variational principles in the form of hemivariational inequalities is derived for the interface problem. The interface action is described by appropriately defined non-convex superpotentials leading to substationarity principles for the potential and complementary energy of the structure. The proposed variational theory is applied to the investigation of the problem of the concrete confinement in tied columns and to the tension stiffening effect in reinforced concrete. Further hemivariational inequalities describing the cracking and crushing of the concrete are derived. For the numerical treatment a regularisation procedure and is applied to the calculation of an interface problem.

Steel column-to-column connections under combined load: A quadratic programming approach

Abstract The aim of this paper is the investigation of the mechanical behaviour of bolted steel column-to-column connections under moment and axial loads by means of a method that takes into account the possibility of the appearance of detachment phenomena between the splice plates. As is well known, regions of detachment (called nonactive contact regions below), due to the appearance of the prying-action phenomenon, do appear on the adjacent fronts of such steel splice plates, greatly affecting the mechanical response of steel connections of this type. The significance of the problem under investigation arises from the fact that column-to-column splices are extensively applied in any possible combination to the design and construction of steel structures. It is therefore obvious that, since local failure phenomena on such connections due to undesirable—and not a priori defined—detachment between the splice plates (as consequence of the development of the prying-action phenomenon) may cause a total destruction of the whole steel structure. For this reason, it is important for such a behaviour to be accurately predicted and the previously mentioned nonactive contact regions on the splice plates to be defined. In this sense, such an investigation leads to an amelioration of the design principles for bolted steel column-to-column splices and to a refinement of the respective steel construction standards.

Sea bed-structure interaction for submarine cables

Abstract In this study, the dynamic behaviour of a submarine cable constrained by a frictionless rigid sea profile is studied. After a suitable local and time discretization, the arising unilateral contact-impact problem is formulated as a sequence of variational inequality problems which lead equivalently to a sequence of quadratic programming problems. The solution method is based on some propositions which constitute the mechanical “interpretation” of some theorems of quadratic programming and combines the advantages of the optimization algorithms with the advantages of the “trial and error” methods. Finally the applicability of the proposed method is illustrated by means of a numerical example.

PARAMETRIC ANALYSIS OF THE STRUCTURAL RESPONSE OF STEEL BASE PLATE CONNECTIONS

Abstract The present paper aims to contribute to the parametric analysis of semirigid steel base plate connections. The method is based on the theoretical results of nonsmooth mechanics, which is a relatively new branch of mechanics initiated three decades ago and deals with problems from mechanics and/or structural analysis that involve generalizations of the gradient. The numerical modelling of the structural response of a steel column base plate under static loading where unilateral contact with friction and yielding phenomena are taken into account, could be considered as a typical problem that can be very effectively treated within such a theoretical framework. In particular, the respective stress states of the steel connection under static loading are calculated by taking into account the development of plastification zones and the unilateral contact and friction effects on the interfaces between connection members. An effective two-dimensional finite element model, capable of describing the previously mentioned phenomena is constructed. The aforementioned model is a simplification of the respective three-dimensional one and aims to reduce in a reliable way the huge computational effort required for the analysis of three-dimensional fine meshes of discretized steel connections. A numerical application demonstrates the effectiveness and the applicability of the method altering two parameters, the base plate thickness and the axial load of the model.

Sea-bed-structure interaction in the presence of frictional effects for submarine pipelines

Abstract In this paper, the static behaviour of a submarine pipeline, constrained by a rigid sea-floor and subjected to Coulomb friction, is studied. An approximation method is proposed, solving iteratively, by means of the appropriate use of linear solvers, the two following quadratic programming (Q.P.) problems: the Unilateral Contact Problem of the pipeline with constant friction forces and the Friction Problem with constant reaction forces. As a result the sliding and nonsliding friction regions are accurately determined, together with the contact and noncontact regions, as well as the respective reactions.

A contribution to the sensitivity analysis of the sea-bed-structure interaction problem for underwater pipelines

Abstract The sensitivity analysis problem for a pipeline freely resting on a frictionless sea-bed profile is considered. First, the sensitivity problem is formulated for the discrete structure having taken into account the unilateral contact phenomenon, i.e. the possibility, for certain regions of the pipeline to be in contact with the underlying sea-bed profile, whereas the rest to lie above it. The sensitivity problem is thus formulated as a quadratic programming problem with inequality constraints which can be solved by means of the suitable application of the Theil-van de Panne method that transforms the initial sensitivity problem into a sequence of linear problems. The solution of the latter problem leads to the solution of the sensitivity analysis problem under consideration. The applicability of the proposed method is illustrated by means of two numerical examples.

Environmental wind engineering and design of wind energy structures

T. Stathopoulos: Introduction to environmental aerodynamics.- T. Stathopoulos: Applications of environmental aerodynamics.- B. Blocken: Computational wind engineering. Theory and applications.- A. Zasso, P. Schito: Aero-servo-elastic design of wind turbines: numerical and wind tunnel modeling contribution.- P. Schaumann et al.: Support structures of wind energy converters.- C. C. Baniotopoulos et al.: Topics of the design of tubular steel wind turbine towers.- C. Borri, P. Biagnini, E. Marion: Large wind turbines in earthquake areas: structural analyses, design/construction and in-situ testing.