Result Evaluation
The primary results in the Beam interface are the section forces: axial force, shear forces, bending moment, and twisting moment. The shear forces and bending moments are oriented along the principal directions as described in the Section Orientation node.
The formulation of the beam element is such that the variation of axial force, bending moments, and twisting moment is linear along the element, whereas the shear forces are constant within each element. This means that the solution is exact with any discretization as long as there are no distributed transverse loads.
When looking at line plots or line graphs of section forces, it is important consider the type of averaging that is used between elements. In a frame structure, axial forces and shear forces are continuous as long as two adjacent beams have the same direction. If two beams, for example, meet a right angle, the shear force in one of them will be the axial force in the other. In this case, an averaging of section forces at the common point clearly would be wrong. Similarly, a twisting moment in one of the beams will be a bending moment in the next.
In the Quality section of the plot, you can control the level of averaging by changing the Smoothing method.
For details about the settings in the Quality section, see Entering Quality Settings for Plot Settings Windows.
The default method is Inside material domains. In the Beam interface, two adjacent edges are considered as part of the same material domain only if they share both material and cross-section data. In many cases this gives an optimal level of smoothing since beams that meet at nonzero angles often have different cross sections.
You may however want to use Inside geometry domains instead as smoothing method. This means that there will be no smoothing at points where a connection may occur.
Since the stresses are functions of the section forces, the same reasoning applies to stress plots.
Evaluation of stresses in beam elements required special consideration since the stress field produced by various section forces have different distributions over the cross section. All that is known in the beam formulation is the peak value of each stress contribution. Details about how stresses are combined are given in the section Stress Evaluation. In general, the different contributions to the total stress are combined in a conservative manner. If you need to study the stress distribution over the cross section in detail, this can be done using the Beam Cross Section interface.