Rack element type - rack

This element is a 3D beam element with thin-walled, open, cross-sections. The element is characterized by seven degrees of freedom per node, so as to correctly estimate both the displacements and the internal stresses, including warping displacements and bi-moment stresses, and to correctly predict the flexural-torsional and lateral-torsional buckling, derived by the coupling between flexure and torsion. Furthermore, the model accounts for the eccentricity of the shear centre from section centroid, and it considers all the Wagner coefficients, which makes it suitable for use with non-symmetric cross-sections.

As a result, the formulation is ideal for the modelling of steel storage pallet racks, as well as scaffolding structures, which are generally composed by uprights which have mono-symmetric lipped channel cross-sections.

The rack element can be fully defined, if the (elastic) material properties (modulus of elasticity and Poisson ratio) and the section configuration are provided. The former are given on the main dialog box of the rack element class.

The section geometry can be defined in a dialog box. Any thin-walled open section configuration can be modelled, and different thicknesses may be assigned at the different parts of the section. After the user defines the coordinates of the corner points of the section, and clicks on the Create Section button, the section is shown on the screen and the elastic section properties, the Wagner coefficients and the position of the shear centre are automatically calculated.

In this element's dialog box it is also possible to define an element-specific damping, as opposed to the global damping described in here. To do so, users need simply to press the Damping button and then select the type of damping that better suits the element in question (users should refer to the Damping menu for a discussion on the different types of damping available and hints on which might the better options). Users are reminded also that damping defined at element level takes precedence over global damping, that is, the "globally-computed" damping matrix coefficients that are associated to the degrees-of-freedom of a given element will be replaced by coefficients that will have been calculated through the multiplication of the mass matrix of the element by a mass-proportional parameter, or through the multiplication of the element stiffness matrix by a stiffness-proportional parameter, or through the calculation of an element damping Rayleigh matrix.

Note: If Rayleigh damping is defined at element level, using varied coefficients from one element to the other, or with respect to those employed in the global damping settings, then non-classical Rayleigh damping is being modelled, classing Rayleigh damping requires uniform damping definition.

Local Axes and Output Notation