3.7.3.5 Shell Sections
The 'Shell-Section'-component lets you determine forces, stresses and displacements of a shell along arbitrary poly-lines.
The "Shell Section"-component comes as a multi-component where the drop-down menu at the bottom selects between the different response properties: forces, stresses and displacements. These inputs form the basis for results retrieval:
"Model"
The input-plug 'Model' receives an evaluated, structural model.
"ShellIds"
List of identifiers to specify the shells for which to get results. If not provided all shells potentially contribute response data.
"LCase"
Specifies the load-case of interest - the first by default. Use "Expand ValueLists" from the context menu for selection via ValueList-component.
"IGeom"
The geometry used to find a cutting curve on shell elements. Valid geometries are: - Meshes: A mesh-mesh with the shell elements will be done. - Surfaces: An automatic meshing operation is done first and a mesh-mesh intersection hereafter.
- Polyline: The polyline will be projected on shell's elements. A projection direction must be supplied in this case.
"PDir"
The projection direction to be used just in case the intersection geometry supplied is a polyline.
Besides results specific to the evaluation type, the component provides these outputs (see Fig. 3.7.16.1):
"Model"
Same model as on the input-side for further processing.
"Cuts"
Poly-line of the section on the shell - one segment per mesh face.
"FInds"
The index of the mesh-face of each segment of the above poly-line.
"Meshes"
Meshes of the diagram which displays the result values along the shell section when the user selects the option "filled".
"Curves"
Line-segments that indicate the result amplitudes along the section.
Results
Depending on the result type, the output-plugs of this sub-menu give access to numerical results. In case of distributed forces and stresses there is one value per face. For displacements there results one value per face-edge.
Display Results
Use this sub-menu to specify and adapt the rendering of results in the Rhino viewport. By default the result diagrams consists of curves that connect the value points painted in the normal direction of the shell elements (see output-plug "Curve"). Distributed forces and stresses show as column diagrams with one column per face. Beatify these diagrams with the option 'Smooth': values then get interpolated at the element edges. The "Mesh" output-plug delivers the graphical outcome for further processing. If you want to see numbers at the result points enable them via the radio button "Numbers". The slider "Text height" can be used to scale their display size. Depending on the type of results, one or more sliders set the value to length factor for the result diagrams. A set of radio-buttons at the bottom of the sub-menu let's one select result components to be displayed. In case you wonder why nothing is displayed check whether at least on of those buttons has been enabled.
Display Axes
A shell section comes with its own local coordinate system. Enable its display in the sub-menu "Display axes" by clicking on the 'Local axes' button. The tangential direction (red) points in the direction of the cutting line and inherits its orientation from the poly-line used to define the section in the first place. The Z-direction (blue) points in the direction of the shell elements local Z-axis. Green arrows depict the section's normal-direction and forms with the section's Y- and Z-directions a right-handed coordinate system.
Shell Section Forces
The result type "forces" retrieves distributed normal-, shear-forces and bending moments. The force and bending moment components have two indices: the first one depicts the plane on which the force or moment causes stresses, the second index represents the direction of the stress vector. "t" stands for tangential direction, "n" for the normal direction of the section. The image in figure 3.7.16.2 displays the bending moments which cause normal stresses in tangential direction to the section.
In case of the transverse shear components the index indicates the plane in which the shear stresses get added up. In the above example the component Vt gives the customary, linear distribution of shear forces with the maxima at the supports.
Shell Section Stresses
The section stresses display works similar to the one for forces. Since stresses may change over the plate thickness, one needs to specify the layer-position where to retrieve results (see fig. 3.7.16.3). In case of reinforced concrete cross sections there may be several shell layeres with different stresses to be selected via the "LayerInd" input-plut. The figure below shows what happens if result smoothing is disabled: there is one result column for each face. Instead of one poly-line several line-segments show up at the "Curve" output. For the meaning of the "n" and "t" see the above paragraph.
Shell Section Displacements
This lets you retrieve displacements at the element edges in global X-, Y- or Z-direction. Additionally resultant displacement can be output via the "DispLen"-option.
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