Cilmar Basaglia

Buckling Analysis of Thin-Walled Steel Structural Systems Using Generalized Beam Theory (GBT)

This paper deals with the application of beam finite element models based on generalized beam theory (GBT) to analyze the buckling behavior of four thin-walled steel structural systems, namely (i) beams belonging to storage rack systems, (ii) pitched-roof industrial frames, (iii) portal frames built from cold-formed rectangular hollow section (RHS) profiles and (iv) roof-supporting trusses, exhibiting different support conditions and subjected to various loadings. In particular, taking advantage of the GBT unique and structurally clarifying modal features, it is possible to assess how different geometries and/or bracing arrangements affect (improve) the local, distortional and/or global buckling behavior of the above structural systems. The accuracy of the GBT-based buckling results is assessed through the comparison with values yielded by rigorous shell finite element analyzes carried out in the code ANSYS. In spite of the disparity between the numbers of degrees of freedom involved, which are orders of magnitude apart, there is a virtual coincidence between the critical loads and mode shapes provided by the GBT (beam) and ANSYS (shell) finite element analyzes.

Buckling, Postbuckling, Strength, and DSM Design of Cold-Formed Steel Continuous Lipped Channel Beams

The work reported in this paper is part of an ongoing numerical investigation aimed at (1) assessing the buckling, postbuckling, strength, and collapse behavior of cold-formed steel continuous beams and simple frames and (2) developing an efficient methodology, based on the direct strength method (DSM) approach, to design such structural systems. The results available at this stage concern two- and three-span lipped channel beams subjected to nonuniform bending, and they include the assessment of how accurately the beam ultimate strengths can be predicted by the current DSM design curves. The numerical results presented and discussed are obtained through analyses based on generalized beam theory (elastic buckling analyses) and shell finite-element models (all the remaining analyses). Ultimate strength values yielded by geometrically and materially nonlinear shell finite-element analyses are compared with estimates provided by the DSM equations, and on the basis of this comparison, it is possible to identify some features that must be included in a DSM approach applicable to continuous cold-formed steel beams.

Formulation of a GBT-Based Finite Element to Analyse the Global Buckling Behaviour of Plane and Spatial Thin-Walled Frames

This paper deals with the use of Generalised Beam Theory (GBT) to analyse the global buckling behaviour of plane and spatial thin-walled frames. After a brief presentation of the main concepts and procedures involved in the performance of a GBT buckling analysis, one presents in detail the formulation and numerical implementation of a GBT-based beam finite element that includes only the four rigid-body deformation modes namely, one describes the determination of the elementary and frame linear and geometric stiffness matrices (the latter incorporate the influence of the frame joints and boundary conditions). Particular attention is paid to issues concerning (i) the quantification of the warping transmission at the frame joints, (ii) effects stemming from the non-coincidence of the member centroidal and shear centre axes (cross-sections without double symmetry), and (iii) the definition of joint elements that relate the connected member GBT degrees of freedom to the joint generalised displacements. Next, one addresses kinematical models to simulate the warping transmission at frame joints connecting two or more non-aligned U and I-section members and exhibiting two different configurations (diagonal-stiffened and box-stiffened). Finally, in order to illustrate the application and capabilities of the proposed GBT-based finite element formulation, one presents and discusses numerical results concerning the global buckling behaviour of (i) an “L-shaped” frame (see Fig. 1), (ii) a pitched-roof plane frame (in-plane and spatial behaviours) and (iii) a three-bar simple spatial frame, acted by loadings that cause only member compression. Both diagonal-stiffened and box-stiffened joints are considered and, for validation purposes, most of the GBT-based results are compared with values yielded by beam finite element analyses carried out in the commercial code ANSYS. An excellent correlation, involving both the frame critical buckling loads and mode shapes, was found in all cases. Open image in new window Figure 1 “L-shaped” plane frame global buckling: deformed configurations of the member mid-span cross-sections.

Analysis of Fiber Reinforced Laminated Timber Beams

The necessity to restore the design specifications of a determined structure, combined with cost, weight and environmental impact reduction makes the use of high performance composite systems, involving, either synthetic or natural materials, interesting. By applying a layer of fiber reinforcement bonded with the glued laminated timber beam (Glulam) with an appropriate adhesive, a high performance composite system is obtained, resulting on a significant increase of strength and bending stiffness of the structural element that each isolated material did not have before. This paper carried out an analysis of the feasibility of use synthetic and natural fibers as alternative to structural reinforcement to laminated timber beams, made of the reforestation wood species Pinus caribea and Eucalyptus grandis that represent respectively two resistance classes of monocotyledon and dicotyledonous, exposing, through an analytical model. The numerical results obtained from the analysis of the Glulam beams reinforced with glass, carbon, Vectran® and natural fibers such as sisal fibers, are compared among each other considering cost, weight and gain of resistance and stiffness. It is observed that for small lengths (and therefore, small cross sections), the use of Vectran® fiber is not the best option, since an equivalent resistance gain can be obtained by applying a thicker layer of glass fiber, once it possesses a lower cost and a non-significant impact on the final structures weight. For all the other considered cases, the choice of the Vectran® fiber is very interesting, since on these situations a thicker layer of glass fiber does not provide much cost reduction and is not enough to achieve the desired strength without increasing the structures weight significantly. Regarding the sisal fiber, it is a material that is easy to find and with a low cost in Brazil, its utilization is interesting when working with low resistance wood species. Although the gain of resistance provided by this fiber as a reinforcement material is fairly low, the desired result can be obtained by increasing the thickness of the reinforcement layer, which still keeps the cost and weight of the reinforced element much smaller than those resulting from the implementation of a thinner layer of glass fiber.