Carlos Rebelo

Resistance of cold-formed high strength steel circular and polygonal sections - Part 2: Numerical investigations

Abstract This paper is the second part of the study on the cold-formed high strength steel circular and polygonal sections intended to be used in tubular wind towers. Results from 32 numerical finite element analysis (FEA) models were compared with and calibrated against results of the tests on 32 corresponding specimens. The FEA results agreed well with the experimental results in terms of resistances and load-displacement curves. Further investigations on the numerical models were performed. Yield stress used in the FEA significantly affected the resistances of the numerical models. Using 0.2% proof stress leaded to higher resistance than the experimental results. Corners significantly influenced buckling behaviour in the polygonal section models. Analyses of an oval opening in the tubular specimens showed that peak stresses around the opening were considerably higher in the polygonal section models than in the circular section models. Finally, investigation of sensitivity to geometrical imperfections indicated that failure modes of numerical models with geometrical imperfections according to EC3 significantly differed from those of tested specimens and numerical models with geometrical imperfections obtained from the 3D scans.

Wind turbine tower design, erection and maintenance

: Higher towers for wind turbines are the main trend to achieve better effectiveness in the conversion of wind energy to electrical energy. This leads to an increasing contribution of the tower costs to the total investment costs. Optimization of the structural design by improving the design of connections in the tower is an important issue for the competitiveness of the wind energy sector. The basis of the design model of the flange connection and the possibilities of retrofitting are shown. A short overview of the main structural solutions for towers and the most common criteria for the design are provided in the text.

Numerical Validation of the Eurocode 3 Design Rules for Lateral-Torsional Buckling of I-Beams

This work presents a numerical study of the behaviour of steel I-beams subjected to lateral torsional buckling. The results obtained are compared with the beam stability design curves from Eurocode 3.

Numerical analysis of a double shear standard bolted connection considering monotonic loadings

The behaviour of standard bolted steel connections submitted to monotonic loads, through the use of numerical models, is presented in the current paper. The bolted connections allow speed up constructive processes in an increasingly competitive and globalized world in which the costs are a decisive factor in the development of a project. The use of computational tools in the analysis of bolted connections becomes determinant, mainly for new solutions or solutions less explored in terms of design codes. Throughout the years, bolted connections have been suffering transformations resulting from research activities performed by many authors. Rivets have been replaced by bolts, the main achievement being the pre-stressed bolts. Methodologies based on finite element analyses were proposed for double shear bolted connection. The non-linear behaviour of these connections is investigated and their performances are compared. In the numerical modelling of the bolted connection, linear elastic and elastoplastic analyzes reveal that there are two slip levels associated with local non-linearities caused by the contact pairs, which vary with clamping stresses.

Cyclic performance of single and group micropiles on loose sand

An increase in the height of new generation of wind towers is foreseen in order to improve their performance. This will imply larger shallow foundations, which represent a substantial percentage of the overall budget. Consequently, it is of interest to develop alternative foundation solutions, with a smaller environmental impact, in particular in terms of the required volume of excavation and reinforced concrete. The proposed improvement consists in the use of micropiles placed along the foundation perimeter as a way to increase the overturning resistance of the system as well as the foundation behavior. The main focus of this paper is the characterization of the behavior of single and groups of micropiles, tested under controlled conditions. An extensive set of experimental tests were conducted on single and 2x2 groups of micropiles under monotonic or cyclic loading installed in loose sand. The effect of the cyclic loading on the behavior of the micropiles was assessed as well as the effect of the grouting on the improvement of the micropile resistance and stiffness and also on the improvement of the soil mechanical properties. The assembly and procedure of the tests are described and the corresponding resistance and stiffness are presented and compared.

RESISTANCE OF DOOR OPENINGS IN TOWERS FOR WIND TURBINES

In this paper, a study of resistance of a lower part of a wind tower including a door opening is presented. Nonlinear 3-D shell element models with real geometry of lower tower segment have been us ...

High-strength tower in steel for wind turbines (Histwin) : Final report

Innovative solutions for assembling joints of a tubular tower for wind turbines were studied and the project provides a background for design. This solution is simpler to produce and 80 % less expe ...

Statistical Evaluation of the Eurocode 3 Design Rules for Lateral-Torsional Buckling of I-Beams

This work reports the statistical evaluation of resistance design models for lateral-torsional buckling of I-beams according to the EN1993(eurocode 3) [3] and EN1990(eurocode 0) [2].

Fatigue resistance curves for single and double shear riveted joints from old portuguese metallic bridges

Abstract The maintenance and safety of ancient bridges is a major concern of governmental authorities. In particular, the safety of old riveted bridges fabricated and placed into service at the end of the 19th century deserves particular attention. These structures are susceptible to exhibit high fatigue damage levels due to their long operational period with increasing traffic intensity associated to an original design not covering the fatigue phenomenon. This paper reviews recent fatigue behaviour investigations on single and double shear riveted joints performed by Universities of Porto (Portugal), Tras-os-Montes e Alto Douro (Portugal), and Wroclaw (Poland), in particular concerning the fatigue characterization of riveted joints extracted from representative Portuguese riveted bridges, namely the Eiffel, Luiz I, Fao, Pinhao and Trezoi bridges. In order to overcome the influence of scatter and establish a reliable assessment for the obtained experimental data, two statistical approaches were used: implement linearized boundaries following the recommendation in ASTM E739 standard and defining probabilistic S N fields using the Castillo & Fernandez-Canteli model. This statistical analysis allows to propose design S N curves for single and double riveted joints and evaluate the applicability (safety) of using the design curves suggested in Eurocode 3 as well as design curves proposed by Taras and Greiner.

Behaviour of Square Tubular Columns in Connection to I Beams with Welded Reverse Channel under Experimental Tests

This article presents some results of the experimental monotonic bending tests on the behaviour of the tubular columns and the reverse channel, effected based on a parametric variation of the most significant characteristics of the tubular profiles. The parameters considered are the thicknesses and the widths of the tubular columns faces, the filling with concrete and the axial load. The experimental tests program, included in the framework of the Doctoral Program Thesis in the scientific domain of the Steel Composite Structures, were performed on a test layout, corresponds to a framed structure, in the Structural Mechanic Laboratory of the Department of Civil Engineering of the University of Coimbra. The objective is to determine the characteristics of the nonlinear cyclic behaviour of the principal components of the tubular columns and the reverse channel, in this shape of joints. These components are related to the tubular columns walls, and to the web and flanges of the reverse channel yielding, crushing or instability, when submitted to bending, shear, compression and tension. The results of this experimental tests allow correlate the parameters considered with the structural behaviour of the connection, defined by the resistance, the stiffness, and the rotation capability.