Pedro Borges Dinis

GBT-based Structural Analysis of Thin-walled members: Overview, Recent Progress and Future Developments

This paper provides an overview of the Generalised Beam Theory (GBT) fundamentals and reports on the novel formulations and applications recently developed at the TU Lisbon: the use of conventional GBT to derive analytical distortional buckling formulae and extensions to cover (i) the buckling behaviour of members with (i1) branched, closed and closed/branched cross-sections and (i2) made of orthotropic and elastic-plastic materials, and (ii) the vibration and post-buckling behaviours of elastic isotropic/orthotropic members. In order to illustrate the usefulness and potential of the new GBT formulations, a few numerical results are presented and briefly discussed. Finally, some (near) future developments are briefly mentioned.

On the Use of Shell Finite Element Analysis to Assess the Local Buckling and Post-Buckling Behaviour of Cold-Formed Steel Thin-Walled Members

This paper deals with the use of shell finite element analyses to assess the (i) elastic bifurcation and (ii) elastic and elastic-plastic local-plate and distortional post-buckling behaviours of cold-formed steel thin-walled members (mostly columns, i.e., uniformly compressed members) all the geometrically and physically non-linear analyses are performed using the code ABAQUS and adopting 4-node isoparametric shell elements to discretise the members. First, one addresses several relevant issues concerning (i) the member discretisation (shell element type and mesh refinement), (ii) the simulation of the member end support conditions (a key aspect in numerical structural analysis), (iii) the modelling of the applied loading and material behaviour, (iv) the incorporation of member initial geometrical imperfections and residual stresses, (v) the assessment of buckling mode interaction effects and (v) the methods employed to solve either the eigenvalue problem or the system of non-linear algebraic equilibrium equations. Then, in order to illustrate the concepts and issues mentioned above and, at the same time, illustrate the power and versatility of the shell finite element analyses, one presents and thoroughly discusses a fairly large number of numerical results concerning the buckling and post-buckling behaviour of lipped channel (mostly), Zed-section and Rack-section cold-formed steel members some of the post-buckling analyses include interaction effects between local-plate and distortional buckling modes. These results consist of (i) buckling curves providing the variation of the critical stress with the member length (see Fig. 1(a)), (ii) elastic and elastic-plastic non-linear (post-buckling) equilibrium paths (see Figs. 1(b)-(c)), (iii) figures providing the evolution, along those equilibrium paths, of the elastic and elastic-plastic member deformed configurations, and (iv) figures showing the spread of plasticity along the members up to failure (see Fig. 1(d)) and conveying relevant information about the nature of their collapse mechanisms. Open image in new window Figure 1 Lipped channel simply supported columns: (a) elastic buckling, (b) elastic distortional post-buckling and (c) elastic-plastic distortional post-buckling results, and (d) distortional post-buckling plastic strain evolution.

Developments on the Design of Cold-Formed Steel Angles

AbstractThis paper presents procedures for the design of fixed- and pin-ended equal-leg angle columns with short-to-intermediate lengths. First, some remarks concerning the buckling and postbuckling behavior of the angle columns are presented that (1) illustrate the main differences between the fixed- and pin-ended column responses and (2) demonstrate the need for specific design procedures. Then, the paper reports an in-depth investigation aimed at gathering a large column ultimate strength data bank that includes (1) experimental values collected from the literature and (2) numerical values obtained from shell finite-element analyses carried out in the code ABAQUS. The set of experimental results is comprised of 41 fixed-ended columns and 37 pin-ended columns and the numerical results obtained include 89 fixed-ended columns and 28 pin-ended columns; various cross-section dimensions, lengths, and yield stresses are considered. Finally, the paper closes with the proposal of new design procedures for fixed...

Direct strength method—a general approach for the design of cold-formed steel structures

Abstract This chapter presents a state-of-the-art report on the direct strength method (DSM), which may be viewed as the most modern and universally accepted approach for the development of methodologies to design a wide variety of thin-walled structural systems, namely cold-formed steel structures. The introductory section describes the basic concepts and procedures of the method, and provides a historical perspective of its development in the last two decades. Then the chapter addresses the development, validation, and application of the currently codified DSM design expressions (strength curves), making a distinction between “first generation” and “second generation”: the former are those originally codified 12 years ago, concerning members under compression (columns) or bending (beams), and the latter correspond to subsequent developments that have reached codification, concerning members under shear (including bending–shear interaction) and perforated columns and beams. The last section is devoted to recent advances and future developments of the DSM. It reports on ongoing research activity concerning structural problems/failures for which DSM-based design expressions are currently being sought, and includes topics that constitute possible/promising extensions of the DSM domain of application. The chapter has an extensive list of references covering the various aspects addressed and making it easy for the reader to acquire additional information on specific topics.

Cracking Analysis in Concrete Dams using Isotropic Damage Models. Objectivity of Numerical Solutions

The numerical simulation of cracking in large concrete structures can be made, in many cases, adopting the smeared cracking approach and using constitutive laws of continuous damage (with softening), in order to simulate the material tension ruptures.

INTERACÇÃO DISTORCIONAL/GLOBAL EM COLUNAS DE AÇO ENFORMADAS A FRIO COM SECÇÃO EM C

Apresentam-se e discutem-se os resultados de um estudo sobre o comportamento de pos-encurvadura, em regime elastico e elasto-plastico, de perfis de aco enformados a frio com seccao em C e afectados por interaccao entre modos de instabilidade distorcional e global (flexao-torcao). As analises geometrica e fisicamente nao lineares sao efectuadas atraves do metodo dos elementos finitos, utilizando o programa ABAQUS e adoptando discretizacoes das colunas em elementos de casca com 4 nos. As colunas analisadas (i) sao simplemente apoiadas (seccoes extremas articuladas e com empenamento livre), (ii) tem seccoes com dimensoes que asseguram tensoes criticas distorcional e global (flexao-torcao) identicas e (iii) contem imperfeicoes geometricas com varias configuracoes (combinacoes lineares dos modos distorcional e global) e a mesma amplitude. Apos abordar as caracteristicas dos comportamentos de pos-encurvadura “puros” distorcionais e globais, apresentam-se e discutem-se resultados numericos relativos ao comportamento de pos-encurvadura de colunas identicas, altamente susceptiveis a interaccao distorcional/global e diferindo apenas na configuracao das imperfeicoes iniciais. Esses resultados numericos consistem em (i) trajectorias de pos-encurvadura elasticas e elasto-plasticas, (ii) curvas ou figuras com a evolucao da deformada na pos-encurvadura e, no caso das colunas elasto-plasticas, (iii) resistencias ultimas e figuras que mostram (iii1) a localizacao e o espalhamento das deformacao plasticas e (iii2) as caracteristicas dos modos de colapso detectados.