3.7.7: Utilization of Elements 🔷
Use the “Utilization of Elements”-component in order to get the level of utilization for each element. It comes as a multi-component where the drop-down list on the bottom decides whether the utilization of shell of beam elements shall be returned. With beam-utilization selected, the utilization output of shell patches will be output as zero - and vice versa. This serves to maintain the one to one relationship between elements and results. The sequence of element results corresponds to the sequence of elements.
The input-plug “Model” expects an analyzed model. With “Elems|Ids” it is possible to limit the range of elements which shall be considered. Accepted input are element identifiers or elements themselves. By default the component returns results for all elements. The “LCase”-input selects the load-case to be used for calculating the utilization. By default it is set to “-1” which means that the maximum utilization of all load-cases will be returned.
Fig. 3.7.7.1: Beam under two load-cases: Utilization of the cross sections
Fig. 3.7.7.1 shows the utilization component for beams. In case of shells, the utilization output value is zero. The meaning of the input-plugs “nSamples”, “Elast”, “gammaM0”, “gammaM1” and "SwayFrame" exactly corresponds to that of the “Optimize Cross Section” (see section 3.5.8). The algorithm for determining an element's utilization is the same as that underlying the cross section optimization procedure. Set the input-plug “Details?” to “True” in order to get intermediate values of the utilization calculation at the output-plug “Details”. For large structures the generation of the detailed output may take some time.
Utilization numbers for beams rendered by this component (output-plug “Util”) and the “ModelView” show differences – especially for compressive axial forces: The “ModelView”-component returns the ratio of stress to strength as the level of utilization, whereas the “Utilization of Elements”-component also includes buckling. See for example the two utilization entries on the in fig. 3.7.7.1: The second load case (i.e. number “1”) is made up of an axial load acting in the middle of the beam. As both ends are axially fixed, one beam is in tension, one in compression. The absolute value of the normal force in both elements is the same. Yet the beam under compression has a utilization of 0.26, the one under tension only 0.05. “1” means 100 %.
The output-plugs “sig-max” and “sig-min” return the minimum and maximum stress in each beam.
In order to diagnose the reason why a specific beam shows over-utilization the output-plugs “Util-N”, “Util-Vy”, “Util-Vz”, “Util-Mt”, “Util-My” and “Util-Mz” return the contribution of each cross section force component to the overall utilization. When enabled via “Details?” the output-plug “Details” renders a detailed account of intermediate values used for the calculation of the element’s utilization according to EN 1993-1-1 [5].
Fig. 3.7.6.2: Utilization of a shell consisting of two elements
The utilization calculated for shells (see fig. 3.7.6.2) is the ratio between the tensile or compressive strength and the material's comparative stress in each face of the shell. The strength criteria applied for evaluating the comparative stress can be 'VonMises', 'Tresca', 'Rankine' and for orthotropic materials 'TsaiWu' (see section 3.5.1). The sign of the comparative stress is determined by the sign or the principal stress with the largest absolute value. In case of different strength values for the tensile and compressive regime, the Von Mises stress gets calculate from the scaled principal stresses: tensile principal stresses get divided by the tensile strength, compressive tensile stresses by the compressive strength. The same procedure applies to the TsaiWu-comparative stress.
The output-plug “Util” lists the utilization of each element of the shell in the same order as the mesh-faces are listed in the mesh which underlies the shell geometry. In case of beams or trusses, 0 is output as utilization.
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