196,077 research outputs found
The shear strain influence on the dynamics of thin-walled beams
No full textThe influence of middle-surface shear strains on the dynamics of thin-walled beams is analyzed. By means of a suitable choice of the axial displacement field, shear lag effects in bending and torsion are taken into account for open and closed cross-sections. The equations of motion are obtained via Hamilton's principle. The flexural-torsional natural frequencies in the presence of warping which varies along the beam axis are compared with those given by Timoshenko-Vlasov models. The solution to the problem is pursued by means of the most natural choice, i.e. the classical trigonometric series expansion. A suitable algorithm is developed to solve the resulting eigenvalue problem which turns out to be strongly ill-conditioned
Shear strain effects in flexure and torsion of thin-walled beams with open or closed cross-section
No full textIn this study a unified approach is presented for the analysis of the shear strain effects in thin-walled beams subjected to both non-uniform bending and torsion. Middle surface shear strains are taken into account for open as well as closed cross-sections. A suitable axial displacement field is introduced by making the basic choice that the solution to the St. Venant problems is to be reproduced for v = 0. By making use of a variational formulation, a system of differential equations is derived which rules the behaviour of a thin-walled beam with any cross-section. Hence the influence of the shear strains on the stress state as well as on the global deformation of the beam is shown through some significant examples
Cathleen M. Giustino, Tearing Down Prague’s Jewish Town Ghetto Clearance and the Legacy of Middle-Class Ethnic Politics around 1900. New York: Columbia University Press, 2003
No full textA generalization of the timoshenko beam model for coupled vibration analysis of thin‐walled beams
No full textA generalization of the Timoshenko beam model is presented which accounts for the influence of the shear strains, due to non-uniform bending and torsion, on the flexural-torsional vibrations of thin-walled cores with open or closed cross-section. The axial displacement field incorporates the torsion secondary warping as well as the warping terms depending on the shear resultants. It is shown that exact solutions for the interior domain problem can be obtained under proper load conditions. Moreover, a discrete model for the free-vibration analysis is derived by adopting a linear interpolation of the unknown functions and a reduced integration in order to avoid locking phenomena. Various applications are developed, including the case of the coupled vibrations of a shear-core-steel-frame building
A refined model for laminated beams. Part I:A new high-order approach
No full textThis paper presents a new displacement-based one-dimensional model for the analysis of multilayered composite beams. The kinematic restriction of cross sections rigid in their own planes is introduced. The axial displacements over the cross sections are represented in terms of explicitly defined piecewise polynomial warping functions with discontinuous derivatives at the interlaminae, whereas the amplitude of the displacements along the beam axis is established by means of a variational formulation. It is proved that the proposed representation of the axial displacements yields the exact solution of the interior domain problem for a beam subjected to a transverse load varying according to a polynomial law. It is shown that two or three coordinate functions are sufficient to yield continuous distributions of equilibrated stresses except for small neighborhoods of the constrained cross sections, where a higher number of warping functions could be used in order to obtain a better accuracy. The numerical results show excellent agreement with plane stress finite element and plane strain exact solutions
Continuum model for analysis of multiply connected perforated cores
No full textAs is known, when a shear core presents rows of regular openings along the height, the stiffness properties of the connecting beams can be smeared over the height by making use of concepts of statics or energy equivalence. Hence, by virtue of the constraining action of the floor slabs, the shear core can be seen as a nonhomogeneous thin-walled beam, with open or closed (possibly multicell) cross section, constituted by an assemblage of interconnected prismatic curtains having different elastic properties. This paper presents a one-dimensional model for the flexural-torsional analysis of such “nonhomogeneous” thin-walled beam with any given cross section, allowing for shear deformations due to nonuniform bending and torsion. The axial displacement field is represented by separating the cross sectional and axial variables, and the governing equations for the coupled flexural-torsional behavior are given. Some examples are solved of beams with one or two planes of symmetry, showing excellent agreement with experimental and finite-element method (FEM) results
A refined model for laminated beams. Part II: An iterative variational approach
No full textThis paper presents a displacement-based one-dimensional model for the analysis of laminated composite beams, based on the assumption of cross sections rigid in their own planes. The proposed model is mainly focused on the boundary layer analysis. The representation of the axial displacements is given as products between line functions and warping modes of the cross section. Both the sets of unknown functions are determined by means of a variational formulation in order to obtain the ‘best choice’ for the thickness coordinate functions. The minimization of the total potential energy functional is reduced to a sequence of linear problems by means of a gradient technique. Various examples referring to simply supported and cantilever beams, subjected to distributed or concentrated loads, are solved. The results for stress distributions are found to be in excellent agreement with exact plane strain and finite element plane stress solutions even at very low distances from the end sections
A Timoshenko-like beam model for dynamic analysis of thin-walled beams
No full textA generalization of the Timoshenko beam model is presented which accounts for the influence of the shear strains, due to non uniform bending and torsion, on the flexural-torsional vibrations of thin-walled cores with open or closed cross-section. Moreover, a discrete model is derived and two applications are developed concerning torsional and coupled vibrations of open profiles
An iterative procedure for collapse analysis of reinforced concrete plates
No full textAn iterative procedure is proposed for evaluating the ultimate load of a laterally loaded plate discretized by finite elements. The procedure regards reinforced concrete plates, but it can be extended to metallic plates without any conceptual change. The stress and displacement fields are approximated by means of a finite element model with constant stress and linear displacement fields. Consequently, any load distribution is represented by the equivalent system of nodal forces for a given mesh. In the set of mechanisms compatible with the assumed discretization the best upper bound to the collapse multiplier of the actual load is obtained via linear programming. By dualization a sequence of linear programming problems is obtained which allows an evaluation of a lower bound of the collapse multiplier for the equivalent load system. When the mesh gets finer and finer, the value obtained does not change substantially anymore. This value can be regarded as an estimate of the collapse multiplier for the original load system. Some numerical examples of plates subjected to uniform pressure confirm the reliability of this approximate multiplier
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