3.7.1.8 Utilization of Elements
Last updated
Last updated
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. The output of the component has this structure: element, sub-element (shells only), load-case result. The branch index of element results corresponds to the element indexes.
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 inputs are element identifiers and elements themselves. By default, the component returns results for all elements. The “LCase”-input selects the load-case result options to be used for calculating the utilization. With no value given the model's default result selection applies. Minimum and Maximum options (see Min/Max selection in Fig. 3.7.1.8.1) apply to the "Util"-output, the other results accompany "Util".
Fig. 3.7.1.8.1 shows the utilization component for beams. The meaning of the input-plugs “nSamples”, “Elast”, “gammaM0”, “gammaM1” and "SwayFrame" exactly corresponds to that of the “Optimize Cross Section” (see section 3.6.8). 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 and lateral torsional buckling.
The output-plugs “sig-max”, “sig-min” and “tau-max” return the minimum and maximum normal and shear 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].
The output at "LCInd" returns the index of the load-case within the load-case combination to which the result-values belong. In combination with a "Disassemble LCC"-component (see fig. 3.7.1.8.1 left) details regarding the governing load-case for an element-utilization can be retrieved.
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 sub-element of the shell in the same order as the mesh-faces are listed in the mesh which underlies the shell geometry. The branch index corresponds to the face index. The second left-most branch index is the shell element index.
At the "LCInd"-output one gets the load-case indexes within the considered load-case-combination of the "Util"-values.
In Fig. 3.7.1.8.2 three alternative load-cases exist and in the result-selection component both "Min"- and "Max"-options are enabled. The minimum and maximum utilization occurs for the point-loads of size 45kN at the top and bottom layer. Therefore, the displaced geometry of the minimum and maximum case are identical.
