1,720,991 research outputs found
Initial postbuckling behavior of thin-walled frames under mode interaction
No full text"An L frame made up by beam and column having channel cross sections, has been analyzed in a previous. work by two of the authors [14]. Depending on the aspect ratio and the joint configuration, it has been. proved that the structure can exhibit two simultaneous buckling modes. Here using the asymptotic. theory of elastic bifurcation that takes into account mode interaction, the initial slope of the bifurcated. paths has been determined. Three cases of joint configurations, which are the more common used in. welded connections, have been considered. For each case three admissible bifurcated paths have been. found. Two of them show a slope having the same order of magnitude of the ones found in the absence of. mode interaction while the remaining exhibits a slope largely steepest. Selecting, for each joint case, the. bifurcated path with the higher slope and between them the smallest one, it is found that it is associated. to the path which bifurcates at the higher critical load. This means that the stiffer structure is also the less. imperfection sensitive. Finally for each one of the cases studied, the effect of initial imperfection has been. considered and the real load carrying capacity of the frames has been determined. Finally some results. have been compared with those obtained using the FE code ABAQUS.
Capturing the helical to spiral transitions in thin ribbons of nematic elastomers
No full textWe provide a quantitative description of the helicoid-to-spiral transition in thin ribbons of nematic elastomers using an elementary calculation based on a Koiter-type plate with incompatible reference configuration. Our calculation confirms that such transition is ruled by the competition between stretching energy and bending energy
A 1D nonlinear TWB model accounting for in plane cross-section deformation
No full textIn this paper a procedure for constructing a 1D continuum equivalent to a Koiter plate, is presented. The result is used to build-up a coarse model of a Thin Walled Beam. The model results to be a nonlinear hyperelastic 1D second gradient continuum, endowed with an internal microstructure described by seven scalar kinematic parameters. The kinematic parameters are able to describe, although in a rough way, the deformation of the TWB in the plane of its cross-section. The nonlinear behaviour of a simply supported strut has been analyzed and the results compared with those given by the commercial finite element code ABAQUS
The effects of warping on the postbuckling behaviour of thin-walled structures
No full textA direct 1D model able to describe the mechanical behaviour of thin-walled beams is used to analyse
the initial postbuckling of some sample frames. The model allows to take into account the boundary
conditions on warping in a very simple way and proves to be a very efficient tool for the analysis of
thin-walled frames. Making use of the FEM based COMSOL multiphysics software, numerical results for
a number of L frames are obtained and shown
Growth-induced compatible strains
No full textWe studied the time evolution problem driven by growth for a non-Euclidean ball which at its initial state is equipped with a non-compatible distortion field. The problem is set within the framework of non-linear elasticity with large growing dis- tortions. No bulk accretive forces are considered, and growth is only driven by the stress state. We showed that, when stress-driven growth is considered, distortions can evolve along different trajectories which share a common attracting manifold; moreover, they eventually attain a steady and compatible form, to which there corresponds a stress-free state of the ball
Microcracked materials as non-simple continua
Get PDFA non-simple continuum model is adopted to grossly describe the behaviour of elastic microcracked bodies. The constitutive relations, obtained using a multiscale modelling based on the hypotheses of the classical molecular theory of elasticity, allow taking into account the microscopic features of the material. Referring to a one-dimensional microcracked bar, the possibility of the continuum to reveal the presence of internal heterogeneities is investigated. © (2010) Trans Tech Publications
Revisiting the form finding techniques of Sergio Musmeci: the Bridge over the Basento River
No full textSergio Musmeci (1926‐1981), once an apprentice to Pier Luigi Nervi (1892‐1979) and Riccardo
Morandi (1902‐1989), is noteworthy for his ability to design and construct continuous shells
with unprecedented shapes well ahead of his time. He had the design goal of minimizing area
while maximizing structural function in shells. Musmeci’s Basento Viaduct in Potenza, Italy
was built from 1972‐75, and is a historical example of this structural efficiency. What is most
intriguing about Musmeci is his understanding and manipulation of physical, numerical and
analytical methods of form finding prior to achieve his design intent. This work investigates
Sergio Musmeci’s previous experience leading to the Basento Viaduct project, analyzes his
modeling and testing techniques of the time, and revisits and discusses the shape generation of
the three dimensional structural surface structure using contemporary numerical form finding
techniques. The final shape is then validated with the support of a FE model
R-Funicularity of form found shell structures
No full textThe study of new design methods targeted to minimize the use of materials is a theme of great relevance nowadays; structural designers pursue structural solutions characterized by efficiency, sustainability and optimization. Funicular systems adopt the ârightâ shape in accordance with the applied load and are ideally able to act without introducing bending. In this work an effective and easy-to-read method to study and quantify the funicularity is presented and applied to structural shells obtained using form finding, and analyzed under different static loads. In order to formulate the new method, the classical funicularity concept has been extended and the definition of Relaxed Funicularity (R-Funicularity) introduced. The parameter used to define the funicularity is the eccentricity and a structural shell is called R-Funicular when the eccentricity is included into an admissibility interval
About the funicularity of Velaroidal Shells
No full textWe present some preliminary results of a funicularity analysis of the so called Velaroidal surfaces, a class of analytical forms widely used between the'50s and the'70s to define de shape of thin reinforced concrete shells. After recalling the membrane theory of shells, we illustrate how mentioned analytical forms can be obtained as an approximate solution of the membrane equation. Additionally, the same equation is used to form find a shell by the finite difference scheme. The velaroidal surface and the finite difference solution are then compared by evaluating the generalized eccenticity in order to estimate the R-funicularity of the two solutions
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